Niek van Wieringen - Academia.edu (original) (raw)

Papers by Niek van Wieringen

Research paper thumbnail of PO-0877: First experience with the use of gold markers for image guidance in esophageal cancer radiotherapy

Radiotherapy and Oncology, 2014

Research paper thumbnail of SU-E-T-569: Potential Benefit of Dose-Guided Radiotherapy with On-Line Dose Evaluation for SBRT for Lung Tumors

Medical Physics, 2011

Purpose: Stereotactic body radiotherapy(SBRT) is associated with a high biological dose delivered... more Purpose: Stereotactic body radiotherapy(SBRT) is associated with a high biological dose delivered in a small number of fractions. Before treatment the position of the tumor is verified on cone‐beam CT(CBCT) and on‐line position correction is applied. A correction is always verified by a second CBCT. As only translational errors in the tumor position can be corrected, it is hard to determine the effect of anatomical changes of the patient or dose changes in the organs at risk (OARs). The goal of this study was to evaluate the actual dose distribution in stereotactic lungcancer patients to determine whether on‐line dose evaluation could improve the decision making. Methods: The actual dose distributions were determined by recalculating the original treatment plans on CBCT. 108 CBCTs of 10 patients were analyzed retrospectively (54 before and 54 after correction). The actual dose distribution was compared to the original plan. We analyzed the relative change in volume of the internal target volume (ITV) receiving the prescribed dose, dV100%, where a negative value indicates an underdosage with respect to the plan, and we evaluated the volume that exceeded the constraints of the OARs.Results: Before applying position correction dV100% was in the range −2% − 0 in 69% of the cases. In 7% the deterioration before correction was more than 30% with respect to the original plan. The average dV100% was −6.4% (range −75.9 to 0) before correction. After correction the largest error with respect to the plan was − 0.07%. The OARs never exceeded their constraints, neither before nor after correction. Conclusions: Compared to image‐guidedradiotherapy(IGRT),dose‐guidedradiotherapy (DGRT) may prevent the execution of unnecessary position correction and with that, treatment time can be reduced. Moreover, DGRT enables verification of the dose in the ITV and OARs in case of anatomical changes. This work was partially supported by a grant from Elekta.

Research paper thumbnail of Density override in treatment planning to mitigate the dosimetric effect induced by gastrointestinal gas in esophageal cancer radiation therapy

Acta Oncologica, 2018

Purpose: To investigate the dosimetric effect of variable gas volume in esophageal cancer radiati... more Purpose: To investigate the dosimetric effect of variable gas volume in esophageal cancer radiation therapy (RT) and whether a density override (DO) in treatment planning can effectively mitigate this dosimetric effect. Material and methods: Nine patients with gastrointestinal gas pockets in the planning computed tomography (pCT) were retrospectively included. Per patient, the intensity-modulated RT (IMRT) and volumetric-modulated arc therapy (VMAT) plans associated with no DO, DO ¼ 0.5, and DO ¼ 1 in the gas pockets were made. Initial and follow-up gas volumes were assessed from the pCTs and conebeam CTs (CBCTs), respectively. Fractional CTs were created based on the pCT and CBCTs to calculate the fractional doses using all six plans. We then investigated for all six plans the correlation between the gas volume difference (relative to initial gas volume) and the dose difference (relative to planned dose). We also calculated and compared the accumulated dose by summing the fractional doses using two strategies: single-plan strategy (i.e. using each of the six plans separately) and plan-selection strategy (i.e. selecting one of the three plans depending on the fractional gas volume for IMRT and VMAT planning separately). Results: The dose difference was approximately linearly correlated to the gas volume difference. Underdoses of >3.5% and overdoses of >7% were found for gas volume decreases >160 mL/330 mL and increases >260 mL/370 mL for IMRT/VMAT planning, respectively. Moreover, for most patients, the single-plan strategy with the use of DO ¼ 0.5 resulted in neither undesired underdose nor much overdose. The plan-selection strategy, however, can always ensure sufficient target coverage and minimize high dose regions to the most extent. Conclusions: The variation in gas volume during the treatment course can result in clinically undesired underdose or overdose. The DO-based plan-selection strategy can effectively mitigate the gas-induced underdose and minimize the overdose for esophageal cancer RT.

Research paper thumbnail of Improved tumour control probability with MRI-based prostate brachytherapy treatment planning

Acta Oncologica, 2013

Background: Due to improved visibility on MRI, contouring of the prostate is improved compared to... more Background: Due to improved visibility on MRI, contouring of the prostate is improved compared to CT. The aim of this study was to quantify the benefits of using MRI for treatment planning as compared to CT-based planning for temporary implant prostate brachytherapy. Methods: CT and MRI image data of 13 patients were used to delineate the prostate and organs at risk (OARs) and to reconstruct the implanted catheters (typically 12). An experienced treatment planner created plans on the CT-based structure sets (CT-plan) and on the MRI-based structure sets (MRI-plan). Then, active dwell-positions and weights of the CT-plans were transferred to the MRI-based structure sets (CT-plan MRI-contours) and resulting dosimetric parameters and tumour control probabilities (TCPs) were studied. Results: For the CT-plan MRI-contours a statistically significant lower target coverage was detected: mean V 100 was 95.1% as opposed to 98.3% for the original plans (p < 0.01). Planning on CT caused cold-spots that influence the TCP. MRI-based planning improved the TCPs by 6-10%, depending on the parameters of the radiobiological model used for TCP calculation. Basing the treatment plan on either CT-or MRI-delineations does not influence plan quality. Conclusions: Evaluation of CT-based treatment planning by transferring the plan to MRI reveals underdosage of the prostate, especially at the base side. Planning on MRI can prevent cold-spots in the tumour and improves the TCP.

Research paper thumbnail of Evaluation of bi-objective treatment planning for high-dose-rate prostate brachytherapy—A retrospective observer study

Brachytherapy, 2019

The purpose of this study is to improve upon a recently introduced bi-objective treatment plannin... more The purpose of this study is to improve upon a recently introduced bi-objective treatment planning method for prostate high-dose-rate (HDR) brachytherapy (BT), both in terms of resulting plan quality and runtime requirements, to the extent that its execution time is clinically acceptable. Methods: Bi-objective treatment planning is done using a state-of-the-art multiobjective evolutionary algorithm, which produces a large number of potential treatment plans with different trade-offs between coverage of the target volumes and sparing organs at risk. A graphics processing unit (GPU) is used for large-scale parallelization of dose calculations and the calculation of the dose-volume (DV) indices of potential treatment plans. Moreover, the objectives of the previously used bi-objective optimization model are modified to produce better results. Results: We applied the GPU-accelerated bi-objective treatment planning method to a set of 18 patients, resulting in a set containing a few hundred potential treatment plans with different trade-offs for each of these patients. Due to accelerations introduced in this article, results previously achieved after 1 hour are now achieved within 30 seconds of optimization. We found plans satisfying the clinical protocol for 15 of 18 patients, whereas this was the case for only 4 of 18 clinical plans. Higher quality treatment plans are obtained when the accuracy of DV index calculation is increased using more dose calculation points, requiring still no more than 3 minutes of optimization for 100 000 points. Conclusions: Large sets of high-quality treatment plans that trade-off coverage and sparing are now achievable within 30 seconds, due to the GPU-acceleration of a previously introduced bi-objective treatment planning method for prostate HDR brachytherapy. Higher quality plans can be achieved when optimizing for 3 minutes, which we still consider to be clinically acceptable. This allows for more insightful treatment plan selection in a clinical setting.

Research paper thumbnail of Feasibility of Conebeam CT-based online adaptive radiotherapy for neoadjuvant treatment of rectal cancer

Background Online adaptive radiotherapy has the potential to reduce toxicity for patients treated... more Background Online adaptive radiotherapy has the potential to reduce toxicity for patients treated for rectal cancer because smaller planning target volumes (PTV) margins around the entire clinical target volume (CTV) are required. The aim of this study is to describe the first clinical experience of a Conebeam CT (CBCT)-based online adaptive workflow for rectal cancer, evaluating timing of different steps in the workflow, plan quality, target coverage and patient compliance. Methods Twelve consecutive patients eligible for 5 × 5 Gy pre-operative radiotherapy were treated on a ring-based linear accelerator with a multidisciplinary team present at the treatment machine for each fraction. The accelerator is operated using an integrated software platform for both treatment planning and delivery. In all directions for all CTVs a PTV margin of 5 mm was used, except for the cranial/caudal borders of the total CTV where a margin of 8 mm was applied. A reference plan was generated based on a...

Research paper thumbnail of Automatic bi-objective parameter tuning for inverse planning of high-dose-rate prostate brachytherapy

Physics in Medicine & Biology

We present an automatic bi-objective parameter-tuning approach for inverse planning methods for h... more We present an automatic bi-objective parameter-tuning approach for inverse planning methods for high-dose-rate prostate brachytherapy, which aims to overcome the difficult and time-consuming manual parameter tuning that is currently required to obtain patient-specific high-quality treatment plans. We modelled treatment planning as a bi-objective optimization problem, in which dose-volume-based planning criteria related to target coverage are explicitly separated from organ-sparing criteria. When this model is optimized, a large set of high-quality plans with different trade-offs can be obtained. This set can be visualized as an insightful patient-specific trade-off curve. In our parameter-tuning approach, the parameters of inverse planning methods are automatically tuned, aimed to maximize the two objectives of the bi-objective planning model. By generating trade-off curves for different inverse planning methods, their maximally achievable plan quality can be insightfully compared. Automatic parameter tuning furthermore allows to construct standard parameter sets (class solutions) representing different trade-offs in a principled way, which can be directly used in current clinical practice. In this work, we considered the inverse planning methods IPSA and HIPO. Thirty-nine previously treated prostate cancer patients were included. We compared automatic parameter tuning, random parameter sampling, and the maximally achievable plan quality obtained by directly optimizing the bi-objective planning model with the state-of-the-art optimization software GOMEA. We showed that for each patient, a set of plans with a wide range of trade-offs could be obtained using automatic parameter tuning for both IPSA and HIPO. By tuning HIPO, better trade-offs were obtained than by tuning IPSA. For most patients, automatic tuning of HIPO resulted in plans close to the maximally achievable plan quality obtained by optimizing the bi-objective planning model directly. Automatic parameter tuning was shown to improve plan quality significantly compared to random parameter sampling. Finally, from the automatically-tuned plans, three class solutions were successfully constructed representing different trade-offs.

Research paper thumbnail of Tailoring four-dimensional cone-beam CT acquisition settings for fiducial marker-based image guidance in radiation therapy

Abstract. Use of four-dimensional cone-beam CT (4D-CBCT) and fiducial markers for image guidance ... more Abstract. Use of four-dimensional cone-beam CT (4D-CBCT) and fiducial markers for image guidance during radiation therapy (RT) of mobile tumors is challenging due to the trade-off among image quality, imaging dose, and scanning time. This study aimed to investigate different 4D-CBCT acquisition settings for good visibility of fiducial markers in 4D-CBCT. Using these 4D-CBCTs, the feasibility of marker-based 4D registration for RT setup verification and manual respiration-induced motion quantification was investigated. For this, we applied a dynamic phantom with three different breathing motion amplitudes and included two patients with implanted markers. Irrespective of the motion amplitude, for a medium field of view (FOV), marker visibility was improved by reducing the imaging dose per projection and increasing the number of projection images; however, the scanning time was 4 to 8 min. For a small FOV, the total imaging dose and the scanning time were reduced (62.5% of the dose usi...

Research paper thumbnail of Bi‐objective optimization of catheter positions for high‐dose‐rate prostate brachytherapy

Medical Physics

Bi-objective simultaneous optimization of catheter positions and dwell times for highdose-rate (H... more Bi-objective simultaneous optimization of catheter positions and dwell times for highdose-rate (HDR) prostate brachytherapy, based directly on dose-volume indices, has shown promising results. However, optimization with the state-of-the-art evolutionary algorithm MO-RV-GOMEA so far required several hours of runtime, and resulting catheter positions were not always clinically feasible. The aim of this study is to extend the optimization model and apply GPU parallelization to achieve clinically acceptable computation times. The resulting optimization procedure is compared with a previously introduced method based solely on geometric criteria, the adapted Centroidal Voronoi Tessellations (CVT) algorithm. Methods: Bi-objective simultaneous optimization was performed with a GPU-parallelized version of MO-RV-GOMEA. This optimization of catheter positions and dwell times was retrospectively applied to the data of 26 patients previously treated with HDR prostate brachytherapy for 8-16 catheters (steps of 2). Optimization of catheter positions using CVT was performed in seconds, after which optimization of only the dwell times using MO-RV-GOMEA was performed in 1 min. Results: Simultaneous optimization of catheter positions and dwell times using MO-RV-GOMEA was performed in 5 min. For 16 down to 8 catheters (steps of 2), MO-RV-GOMEA found plans satisfying the planning-aims for 20, 20, 18, 14, and 11 out of the 26 patients, respectively. CVT achieved this for 19, 17, 13, 9, and 2 patients, respectively. The P-value for the difference between MO-RV-GOMEA and CVT was 0.023 for 16 catheters, 0.005 for 14 catheters, and <0.001 for 12, 10, and 8 catheters. Conclusions: With bi-objective simultaneous optimization on a GPU, high-quality catheter positions can now be obtained within 5 min, which is clinically acceptable, but slower than CVT. For 16 catheters, the difference between MO-RV-GOMEA and CVT is clinically irrelevant. For 14 catheters and less, MO-RV-GOMEA outperforms CVT in finding plans satisfying all planning-aims.

Research paper thumbnail of Dosimetric Benefits of Midposition Compared With Internal Target Volume Strategy for Esophageal Cancer Radiation Therapy

International Journal of Radiation Oncology*Biology*Physics

PURPOSE Both midposition (MidP) and internal target volume (ITV) strategies can take the respirat... more PURPOSE Both midposition (MidP) and internal target volume (ITV) strategies can take the respiration-induced target motion into account. This study aimed to compare these 2 strategies in terms of clinical target volume (CTV) coverage and dose to organs at risk (OARs) for esophageal cancer radiation therapy (RT). METHODS AND MATERIALS Fifteen patients with esophageal cancer were included retrospectively for neoadjuvant RT planning. Per patient, a 10-phase, 4-dimensional (4D) computed tomography (CT) scan (4D-CT) was acquired with CTV and OARs delineated on the 20% phase. The MidP-CT scan was reconstructed based on deformable image registration between the 20% phase and the other 9 phases; thereby, the CTV and OARs delineations were propagated and an ITV was constructed. Both MidP and ITV strategies were used for treatment planning, yielding the planned dose. Next, these plans were applied to the 10-phase 4D-CT to calculate the dose distribution for each phase of the 4D-CT. On the basis of the deformable image registration, these calculated dose distributions were warped and averaged to yield the accumulated 4D dose. Subsequently, we compared, in terms of CTV coverage and dose to OARs, the planned dose with the accumulated 4D dose and the MidP strategy with the ITV strategy. RESULTS The differences between the planned dose and the accumulated 4D dose were limited and clinically irrelevant. In 14 patients, both MidP and ITV strategies showed V95% > 98% for the CTV. Compared with the ITV strategy, the MidP strategy showed a significant reduction of approximately 10% in the dose-volume histogram parameters for the lungs, heart, and liver (P < .001, Wilcoxon signed-rank test). CONCLUSIONS Compared with the ITV strategy, the MidP strategy in treatment planning can lead to a reduction of approximately 10% in the dose to OARs, with an adequate CTV coverage for esophageal cancer RT.

Research paper thumbnail of Metalen staafjes voor de thermische behandeling van tumoren

Research paper thumbnail of EP-1675: Dose calculation on CBCT: A simple approach accounting for the dependency of grey values on cone beam scan parameters

Radiotherapy and Oncology, 2014

Research paper thumbnail of 328 oral INTERFRACTION DISPLACEMENT OF PELVIC LYMPH NODES DURING RADIOTHERAPY FOR BLADDER CANCER

Research paper thumbnail of Validation of a Novel User-Friendly Approach to Inverse Optimization for Stepping Source Prostate Brachytherapy Treatment Planning

Research paper thumbnail of PO-205 Potential Benefit of Adaptive Treatment Planning for PDR Prostate Brachytherapy

Radiotherapy and Oncology, 2012

Research paper thumbnail of Modelling tissue heating with ferromagnetic seeds

Physics in Medicine and Biology, 1998

Interstitial hyperthermia using ferromagnetic seeds demands accurate treatment planning: the seed... more Interstitial hyperthermia using ferromagnetic seeds demands accurate treatment planning: the seed characteristics and implant geometry must be determined prior to the treatment. A new, finite difference based, seed modelling method is presented. The seed, together with all its surrounding (non-tissue) layers is described as one unit, independent of the tissue grid. The calculation of the seed-tissue interaction is based on the local seed temperature and several tissue temperature samples in the direct vicinity. All the layers between the seed and the surrounding tissue are taken into account in this interaction calculation. The presented implementation describes the analytical solution of the modelled steady-state configurations very accurately. The separation between tissue and seed allows easy assessment of the resulting seed temperature profile which is essential to the optimization of the seed characteristics in treatment planning. The thermal effect due to blood flow in the modelled tissue volume surrounding the seed can be accounted for by inclusion of a heat sink term as well as by inclusion of realistic discrete vasculature.

Research paper thumbnail of Reduction in Cardiac Volume During Chemoradiation Therapy for Patients With Esophageal Cancer: Magnitude and Possible Implications for Adaptive Radiation Therapy

International Journal of Radiation Oncology*Biology*Physics, 2013

Research paper thumbnail of Power absorption and temperature control of multi-filament palladium - nickel thermoseeds for interstitial hyperthermia

Physics in Medicine and Biology, 1996

In interstitial hyperthermia using ferromagnetic seeds, multi-filament seeds have gained interest... more In interstitial hyperthermia using ferromagnetic seeds, multi-filament seeds have gained interest because of a more effective power absorption than solid seeds. Palladium-nickel (PdNi) seeds composed of filaments with diameters in the range from 0.1 to 1.0 mm (maximally 90 filaments) have been investigated to find the conditions for optimal power absorption and temperature control. Magnetic and calorimetric experiments have shown that a decreasing filament radius results in a more effective power absorption. The power absorption approaches a common asymptote for high field intensities at all filament diameters. This asymptotic behaviour can be understood as a consequence of the approach of saturation magnetization of PdNi. The sharpness of the transition at the Curie temperature, which is a measure for the quality of temperature control, improves as the magnetic field strength increases, but it is limited by the asymptote of the power absorption. When the asymptote has been reached the quality of temperature regulation of a seed can only be improved by increasing the amount of PdNi, e.g. by increasing the number of filaments. Calculations of the power absorption, using the generally applied theory based on a linear relation between the magnetization of PdNi and the magnetic field strength, do not correspond quantitatively with experimental results for seeds having an induction number smaller than the &amp;amp;#39;optimal value&amp;amp;#39; of 2.5. For these seeds the measured heat production is larger than the calculated one.

Research paper thumbnail of Dose warping uncertainties for the accumulated rectal wall dose in cervical cancer brachytherapy

Research paper thumbnail of The TRENDY multi-center randomized trial on hepatocellular carcinoma – Trial QA including automated treatment planning and benchmark-case results

Radiotherapy and Oncology

Background and purpose: The TRENDY trial is an international multi-center phase-II study, randomi... more Background and purpose: The TRENDY trial is an international multi-center phase-II study, randomizing hepatocellular carcinoma (HCC) patients between transarterial chemoembolization (TACE) and stereotactic body radiation therapy (SBRT) with a target dose of 48-54 Gy in six fractions. The radiotherapy quality assurance (QA) program, including prospective plan feedback based on automated treatment planning, is described and results are reported. Materials and methods: Scans of a single patient were used as a benchmark case. Contours submitted by nine participating centers were compared with reference contours. The subsequent planning round was based on a single set of contours. A total of 20 plans from participating centers, including 12 from the benchmark case, 5 from a clinical pilot and 3 from the first study patients, were compared to automatically generated VMAT plans. Results: For the submitted liver contours, Dice Similarity Coefficients (DSC) with the reference delineation ranged from 0.925 to 0.954. For the GTV, the DSC varied between 0.721 and 0.876. For the 12 plans on the benchmark case, healthy liver normal-tissue complication probabilities (NTCPs) ranged from 0.2% to 22.2% with little correlation between NCTP and PTV-D95% (R 2 < 0.3). Four protocol deviations were detected in the set of 20 treatment plans. Comparison with co-planar autoVMAT QA plans revealed these were due to too high target dose and suboptimal planning. Overall, autoVMAT resulted in an average liver NTCP reduction of 2.2 percent point (range: 16.2 percent point to À1.8 percent point, p = 0.03), and lower doses to the healthy liver (p < 0.01) and gastrointestinal organs at risk (p < 0.001). Conclusions: Delineation variation resulted in feedback to participating centers. Automated treatment planning can play an important role in clinical trials for prospective plan QA as suboptimal plans were detected. Ó 2017 Elsevier B.V. All rights reserved. Radiotherapy and Oncology 125 (2017) 507-513 Quality assurance (QA) is essential to clinical trials involving radiation therapy, as protocol violations may seriously impact trial outcome [1-7]. This holds for all trial aspects, including delineation [8-11] and planning [12-14]. The TRENDY trial (registered as NCT02470533 on clinicaltrials.gov) is an international multi-center clinical trial in which patients with hepatocellular carcinoma (HCC) are randomized between transarterial chemoembolization (TACE) with drug

Research paper thumbnail of PO-0877: First experience with the use of gold markers for image guidance in esophageal cancer radiotherapy

Radiotherapy and Oncology, 2014

Research paper thumbnail of SU-E-T-569: Potential Benefit of Dose-Guided Radiotherapy with On-Line Dose Evaluation for SBRT for Lung Tumors

Medical Physics, 2011

Purpose: Stereotactic body radiotherapy(SBRT) is associated with a high biological dose delivered... more Purpose: Stereotactic body radiotherapy(SBRT) is associated with a high biological dose delivered in a small number of fractions. Before treatment the position of the tumor is verified on cone‐beam CT(CBCT) and on‐line position correction is applied. A correction is always verified by a second CBCT. As only translational errors in the tumor position can be corrected, it is hard to determine the effect of anatomical changes of the patient or dose changes in the organs at risk (OARs). The goal of this study was to evaluate the actual dose distribution in stereotactic lungcancer patients to determine whether on‐line dose evaluation could improve the decision making. Methods: The actual dose distributions were determined by recalculating the original treatment plans on CBCT. 108 CBCTs of 10 patients were analyzed retrospectively (54 before and 54 after correction). The actual dose distribution was compared to the original plan. We analyzed the relative change in volume of the internal target volume (ITV) receiving the prescribed dose, dV100%, where a negative value indicates an underdosage with respect to the plan, and we evaluated the volume that exceeded the constraints of the OARs.Results: Before applying position correction dV100% was in the range −2% − 0 in 69% of the cases. In 7% the deterioration before correction was more than 30% with respect to the original plan. The average dV100% was −6.4% (range −75.9 to 0) before correction. After correction the largest error with respect to the plan was − 0.07%. The OARs never exceeded their constraints, neither before nor after correction. Conclusions: Compared to image‐guidedradiotherapy(IGRT),dose‐guidedradiotherapy (DGRT) may prevent the execution of unnecessary position correction and with that, treatment time can be reduced. Moreover, DGRT enables verification of the dose in the ITV and OARs in case of anatomical changes. This work was partially supported by a grant from Elekta.

Research paper thumbnail of Density override in treatment planning to mitigate the dosimetric effect induced by gastrointestinal gas in esophageal cancer radiation therapy

Acta Oncologica, 2018

Purpose: To investigate the dosimetric effect of variable gas volume in esophageal cancer radiati... more Purpose: To investigate the dosimetric effect of variable gas volume in esophageal cancer radiation therapy (RT) and whether a density override (DO) in treatment planning can effectively mitigate this dosimetric effect. Material and methods: Nine patients with gastrointestinal gas pockets in the planning computed tomography (pCT) were retrospectively included. Per patient, the intensity-modulated RT (IMRT) and volumetric-modulated arc therapy (VMAT) plans associated with no DO, DO ¼ 0.5, and DO ¼ 1 in the gas pockets were made. Initial and follow-up gas volumes were assessed from the pCTs and conebeam CTs (CBCTs), respectively. Fractional CTs were created based on the pCT and CBCTs to calculate the fractional doses using all six plans. We then investigated for all six plans the correlation between the gas volume difference (relative to initial gas volume) and the dose difference (relative to planned dose). We also calculated and compared the accumulated dose by summing the fractional doses using two strategies: single-plan strategy (i.e. using each of the six plans separately) and plan-selection strategy (i.e. selecting one of the three plans depending on the fractional gas volume for IMRT and VMAT planning separately). Results: The dose difference was approximately linearly correlated to the gas volume difference. Underdoses of >3.5% and overdoses of >7% were found for gas volume decreases >160 mL/330 mL and increases >260 mL/370 mL for IMRT/VMAT planning, respectively. Moreover, for most patients, the single-plan strategy with the use of DO ¼ 0.5 resulted in neither undesired underdose nor much overdose. The plan-selection strategy, however, can always ensure sufficient target coverage and minimize high dose regions to the most extent. Conclusions: The variation in gas volume during the treatment course can result in clinically undesired underdose or overdose. The DO-based plan-selection strategy can effectively mitigate the gas-induced underdose and minimize the overdose for esophageal cancer RT.

Research paper thumbnail of Improved tumour control probability with MRI-based prostate brachytherapy treatment planning

Acta Oncologica, 2013

Background: Due to improved visibility on MRI, contouring of the prostate is improved compared to... more Background: Due to improved visibility on MRI, contouring of the prostate is improved compared to CT. The aim of this study was to quantify the benefits of using MRI for treatment planning as compared to CT-based planning for temporary implant prostate brachytherapy. Methods: CT and MRI image data of 13 patients were used to delineate the prostate and organs at risk (OARs) and to reconstruct the implanted catheters (typically 12). An experienced treatment planner created plans on the CT-based structure sets (CT-plan) and on the MRI-based structure sets (MRI-plan). Then, active dwell-positions and weights of the CT-plans were transferred to the MRI-based structure sets (CT-plan MRI-contours) and resulting dosimetric parameters and tumour control probabilities (TCPs) were studied. Results: For the CT-plan MRI-contours a statistically significant lower target coverage was detected: mean V 100 was 95.1% as opposed to 98.3% for the original plans (p < 0.01). Planning on CT caused cold-spots that influence the TCP. MRI-based planning improved the TCPs by 6-10%, depending on the parameters of the radiobiological model used for TCP calculation. Basing the treatment plan on either CT-or MRI-delineations does not influence plan quality. Conclusions: Evaluation of CT-based treatment planning by transferring the plan to MRI reveals underdosage of the prostate, especially at the base side. Planning on MRI can prevent cold-spots in the tumour and improves the TCP.

Research paper thumbnail of Evaluation of bi-objective treatment planning for high-dose-rate prostate brachytherapy—A retrospective observer study

Brachytherapy, 2019

The purpose of this study is to improve upon a recently introduced bi-objective treatment plannin... more The purpose of this study is to improve upon a recently introduced bi-objective treatment planning method for prostate high-dose-rate (HDR) brachytherapy (BT), both in terms of resulting plan quality and runtime requirements, to the extent that its execution time is clinically acceptable. Methods: Bi-objective treatment planning is done using a state-of-the-art multiobjective evolutionary algorithm, which produces a large number of potential treatment plans with different trade-offs between coverage of the target volumes and sparing organs at risk. A graphics processing unit (GPU) is used for large-scale parallelization of dose calculations and the calculation of the dose-volume (DV) indices of potential treatment plans. Moreover, the objectives of the previously used bi-objective optimization model are modified to produce better results. Results: We applied the GPU-accelerated bi-objective treatment planning method to a set of 18 patients, resulting in a set containing a few hundred potential treatment plans with different trade-offs for each of these patients. Due to accelerations introduced in this article, results previously achieved after 1 hour are now achieved within 30 seconds of optimization. We found plans satisfying the clinical protocol for 15 of 18 patients, whereas this was the case for only 4 of 18 clinical plans. Higher quality treatment plans are obtained when the accuracy of DV index calculation is increased using more dose calculation points, requiring still no more than 3 minutes of optimization for 100 000 points. Conclusions: Large sets of high-quality treatment plans that trade-off coverage and sparing are now achievable within 30 seconds, due to the GPU-acceleration of a previously introduced bi-objective treatment planning method for prostate HDR brachytherapy. Higher quality plans can be achieved when optimizing for 3 minutes, which we still consider to be clinically acceptable. This allows for more insightful treatment plan selection in a clinical setting.

Research paper thumbnail of Feasibility of Conebeam CT-based online adaptive radiotherapy for neoadjuvant treatment of rectal cancer

Background Online adaptive radiotherapy has the potential to reduce toxicity for patients treated... more Background Online adaptive radiotherapy has the potential to reduce toxicity for patients treated for rectal cancer because smaller planning target volumes (PTV) margins around the entire clinical target volume (CTV) are required. The aim of this study is to describe the first clinical experience of a Conebeam CT (CBCT)-based online adaptive workflow for rectal cancer, evaluating timing of different steps in the workflow, plan quality, target coverage and patient compliance. Methods Twelve consecutive patients eligible for 5 × 5 Gy pre-operative radiotherapy were treated on a ring-based linear accelerator with a multidisciplinary team present at the treatment machine for each fraction. The accelerator is operated using an integrated software platform for both treatment planning and delivery. In all directions for all CTVs a PTV margin of 5 mm was used, except for the cranial/caudal borders of the total CTV where a margin of 8 mm was applied. A reference plan was generated based on a...

Research paper thumbnail of Automatic bi-objective parameter tuning for inverse planning of high-dose-rate prostate brachytherapy

Physics in Medicine & Biology

We present an automatic bi-objective parameter-tuning approach for inverse planning methods for h... more We present an automatic bi-objective parameter-tuning approach for inverse planning methods for high-dose-rate prostate brachytherapy, which aims to overcome the difficult and time-consuming manual parameter tuning that is currently required to obtain patient-specific high-quality treatment plans. We modelled treatment planning as a bi-objective optimization problem, in which dose-volume-based planning criteria related to target coverage are explicitly separated from organ-sparing criteria. When this model is optimized, a large set of high-quality plans with different trade-offs can be obtained. This set can be visualized as an insightful patient-specific trade-off curve. In our parameter-tuning approach, the parameters of inverse planning methods are automatically tuned, aimed to maximize the two objectives of the bi-objective planning model. By generating trade-off curves for different inverse planning methods, their maximally achievable plan quality can be insightfully compared. Automatic parameter tuning furthermore allows to construct standard parameter sets (class solutions) representing different trade-offs in a principled way, which can be directly used in current clinical practice. In this work, we considered the inverse planning methods IPSA and HIPO. Thirty-nine previously treated prostate cancer patients were included. We compared automatic parameter tuning, random parameter sampling, and the maximally achievable plan quality obtained by directly optimizing the bi-objective planning model with the state-of-the-art optimization software GOMEA. We showed that for each patient, a set of plans with a wide range of trade-offs could be obtained using automatic parameter tuning for both IPSA and HIPO. By tuning HIPO, better trade-offs were obtained than by tuning IPSA. For most patients, automatic tuning of HIPO resulted in plans close to the maximally achievable plan quality obtained by optimizing the bi-objective planning model directly. Automatic parameter tuning was shown to improve plan quality significantly compared to random parameter sampling. Finally, from the automatically-tuned plans, three class solutions were successfully constructed representing different trade-offs.

Research paper thumbnail of Tailoring four-dimensional cone-beam CT acquisition settings for fiducial marker-based image guidance in radiation therapy

Abstract. Use of four-dimensional cone-beam CT (4D-CBCT) and fiducial markers for image guidance ... more Abstract. Use of four-dimensional cone-beam CT (4D-CBCT) and fiducial markers for image guidance during radiation therapy (RT) of mobile tumors is challenging due to the trade-off among image quality, imaging dose, and scanning time. This study aimed to investigate different 4D-CBCT acquisition settings for good visibility of fiducial markers in 4D-CBCT. Using these 4D-CBCTs, the feasibility of marker-based 4D registration for RT setup verification and manual respiration-induced motion quantification was investigated. For this, we applied a dynamic phantom with three different breathing motion amplitudes and included two patients with implanted markers. Irrespective of the motion amplitude, for a medium field of view (FOV), marker visibility was improved by reducing the imaging dose per projection and increasing the number of projection images; however, the scanning time was 4 to 8 min. For a small FOV, the total imaging dose and the scanning time were reduced (62.5% of the dose usi...

Research paper thumbnail of Bi‐objective optimization of catheter positions for high‐dose‐rate prostate brachytherapy

Medical Physics

Bi-objective simultaneous optimization of catheter positions and dwell times for highdose-rate (H... more Bi-objective simultaneous optimization of catheter positions and dwell times for highdose-rate (HDR) prostate brachytherapy, based directly on dose-volume indices, has shown promising results. However, optimization with the state-of-the-art evolutionary algorithm MO-RV-GOMEA so far required several hours of runtime, and resulting catheter positions were not always clinically feasible. The aim of this study is to extend the optimization model and apply GPU parallelization to achieve clinically acceptable computation times. The resulting optimization procedure is compared with a previously introduced method based solely on geometric criteria, the adapted Centroidal Voronoi Tessellations (CVT) algorithm. Methods: Bi-objective simultaneous optimization was performed with a GPU-parallelized version of MO-RV-GOMEA. This optimization of catheter positions and dwell times was retrospectively applied to the data of 26 patients previously treated with HDR prostate brachytherapy for 8-16 catheters (steps of 2). Optimization of catheter positions using CVT was performed in seconds, after which optimization of only the dwell times using MO-RV-GOMEA was performed in 1 min. Results: Simultaneous optimization of catheter positions and dwell times using MO-RV-GOMEA was performed in 5 min. For 16 down to 8 catheters (steps of 2), MO-RV-GOMEA found plans satisfying the planning-aims for 20, 20, 18, 14, and 11 out of the 26 patients, respectively. CVT achieved this for 19, 17, 13, 9, and 2 patients, respectively. The P-value for the difference between MO-RV-GOMEA and CVT was 0.023 for 16 catheters, 0.005 for 14 catheters, and <0.001 for 12, 10, and 8 catheters. Conclusions: With bi-objective simultaneous optimization on a GPU, high-quality catheter positions can now be obtained within 5 min, which is clinically acceptable, but slower than CVT. For 16 catheters, the difference between MO-RV-GOMEA and CVT is clinically irrelevant. For 14 catheters and less, MO-RV-GOMEA outperforms CVT in finding plans satisfying all planning-aims.

Research paper thumbnail of Dosimetric Benefits of Midposition Compared With Internal Target Volume Strategy for Esophageal Cancer Radiation Therapy

International Journal of Radiation Oncology*Biology*Physics

PURPOSE Both midposition (MidP) and internal target volume (ITV) strategies can take the respirat... more PURPOSE Both midposition (MidP) and internal target volume (ITV) strategies can take the respiration-induced target motion into account. This study aimed to compare these 2 strategies in terms of clinical target volume (CTV) coverage and dose to organs at risk (OARs) for esophageal cancer radiation therapy (RT). METHODS AND MATERIALS Fifteen patients with esophageal cancer were included retrospectively for neoadjuvant RT planning. Per patient, a 10-phase, 4-dimensional (4D) computed tomography (CT) scan (4D-CT) was acquired with CTV and OARs delineated on the 20% phase. The MidP-CT scan was reconstructed based on deformable image registration between the 20% phase and the other 9 phases; thereby, the CTV and OARs delineations were propagated and an ITV was constructed. Both MidP and ITV strategies were used for treatment planning, yielding the planned dose. Next, these plans were applied to the 10-phase 4D-CT to calculate the dose distribution for each phase of the 4D-CT. On the basis of the deformable image registration, these calculated dose distributions were warped and averaged to yield the accumulated 4D dose. Subsequently, we compared, in terms of CTV coverage and dose to OARs, the planned dose with the accumulated 4D dose and the MidP strategy with the ITV strategy. RESULTS The differences between the planned dose and the accumulated 4D dose were limited and clinically irrelevant. In 14 patients, both MidP and ITV strategies showed V95% > 98% for the CTV. Compared with the ITV strategy, the MidP strategy showed a significant reduction of approximately 10% in the dose-volume histogram parameters for the lungs, heart, and liver (P < .001, Wilcoxon signed-rank test). CONCLUSIONS Compared with the ITV strategy, the MidP strategy in treatment planning can lead to a reduction of approximately 10% in the dose to OARs, with an adequate CTV coverage for esophageal cancer RT.

Research paper thumbnail of Metalen staafjes voor de thermische behandeling van tumoren

Research paper thumbnail of EP-1675: Dose calculation on CBCT: A simple approach accounting for the dependency of grey values on cone beam scan parameters

Radiotherapy and Oncology, 2014

Research paper thumbnail of 328 oral INTERFRACTION DISPLACEMENT OF PELVIC LYMPH NODES DURING RADIOTHERAPY FOR BLADDER CANCER

Research paper thumbnail of Validation of a Novel User-Friendly Approach to Inverse Optimization for Stepping Source Prostate Brachytherapy Treatment Planning

Research paper thumbnail of PO-205 Potential Benefit of Adaptive Treatment Planning for PDR Prostate Brachytherapy

Radiotherapy and Oncology, 2012

Research paper thumbnail of Modelling tissue heating with ferromagnetic seeds

Physics in Medicine and Biology, 1998

Interstitial hyperthermia using ferromagnetic seeds demands accurate treatment planning: the seed... more Interstitial hyperthermia using ferromagnetic seeds demands accurate treatment planning: the seed characteristics and implant geometry must be determined prior to the treatment. A new, finite difference based, seed modelling method is presented. The seed, together with all its surrounding (non-tissue) layers is described as one unit, independent of the tissue grid. The calculation of the seed-tissue interaction is based on the local seed temperature and several tissue temperature samples in the direct vicinity. All the layers between the seed and the surrounding tissue are taken into account in this interaction calculation. The presented implementation describes the analytical solution of the modelled steady-state configurations very accurately. The separation between tissue and seed allows easy assessment of the resulting seed temperature profile which is essential to the optimization of the seed characteristics in treatment planning. The thermal effect due to blood flow in the modelled tissue volume surrounding the seed can be accounted for by inclusion of a heat sink term as well as by inclusion of realistic discrete vasculature.

Research paper thumbnail of Reduction in Cardiac Volume During Chemoradiation Therapy for Patients With Esophageal Cancer: Magnitude and Possible Implications for Adaptive Radiation Therapy

International Journal of Radiation Oncology*Biology*Physics, 2013

Research paper thumbnail of Power absorption and temperature control of multi-filament palladium - nickel thermoseeds for interstitial hyperthermia

Physics in Medicine and Biology, 1996

In interstitial hyperthermia using ferromagnetic seeds, multi-filament seeds have gained interest... more In interstitial hyperthermia using ferromagnetic seeds, multi-filament seeds have gained interest because of a more effective power absorption than solid seeds. Palladium-nickel (PdNi) seeds composed of filaments with diameters in the range from 0.1 to 1.0 mm (maximally 90 filaments) have been investigated to find the conditions for optimal power absorption and temperature control. Magnetic and calorimetric experiments have shown that a decreasing filament radius results in a more effective power absorption. The power absorption approaches a common asymptote for high field intensities at all filament diameters. This asymptotic behaviour can be understood as a consequence of the approach of saturation magnetization of PdNi. The sharpness of the transition at the Curie temperature, which is a measure for the quality of temperature control, improves as the magnetic field strength increases, but it is limited by the asymptote of the power absorption. When the asymptote has been reached the quality of temperature regulation of a seed can only be improved by increasing the amount of PdNi, e.g. by increasing the number of filaments. Calculations of the power absorption, using the generally applied theory based on a linear relation between the magnetization of PdNi and the magnetic field strength, do not correspond quantitatively with experimental results for seeds having an induction number smaller than the &amp;amp;#39;optimal value&amp;amp;#39; of 2.5. For these seeds the measured heat production is larger than the calculated one.

Research paper thumbnail of Dose warping uncertainties for the accumulated rectal wall dose in cervical cancer brachytherapy

Research paper thumbnail of The TRENDY multi-center randomized trial on hepatocellular carcinoma – Trial QA including automated treatment planning and benchmark-case results

Radiotherapy and Oncology

Background and purpose: The TRENDY trial is an international multi-center phase-II study, randomi... more Background and purpose: The TRENDY trial is an international multi-center phase-II study, randomizing hepatocellular carcinoma (HCC) patients between transarterial chemoembolization (TACE) and stereotactic body radiation therapy (SBRT) with a target dose of 48-54 Gy in six fractions. The radiotherapy quality assurance (QA) program, including prospective plan feedback based on automated treatment planning, is described and results are reported. Materials and methods: Scans of a single patient were used as a benchmark case. Contours submitted by nine participating centers were compared with reference contours. The subsequent planning round was based on a single set of contours. A total of 20 plans from participating centers, including 12 from the benchmark case, 5 from a clinical pilot and 3 from the first study patients, were compared to automatically generated VMAT plans. Results: For the submitted liver contours, Dice Similarity Coefficients (DSC) with the reference delineation ranged from 0.925 to 0.954. For the GTV, the DSC varied between 0.721 and 0.876. For the 12 plans on the benchmark case, healthy liver normal-tissue complication probabilities (NTCPs) ranged from 0.2% to 22.2% with little correlation between NCTP and PTV-D95% (R 2 < 0.3). Four protocol deviations were detected in the set of 20 treatment plans. Comparison with co-planar autoVMAT QA plans revealed these were due to too high target dose and suboptimal planning. Overall, autoVMAT resulted in an average liver NTCP reduction of 2.2 percent point (range: 16.2 percent point to À1.8 percent point, p = 0.03), and lower doses to the healthy liver (p < 0.01) and gastrointestinal organs at risk (p < 0.001). Conclusions: Delineation variation resulted in feedback to participating centers. Automated treatment planning can play an important role in clinical trials for prospective plan QA as suboptimal plans were detected. Ó 2017 Elsevier B.V. All rights reserved. Radiotherapy and Oncology 125 (2017) 507-513 Quality assurance (QA) is essential to clinical trials involving radiation therapy, as protocol violations may seriously impact trial outcome [1-7]. This holds for all trial aspects, including delineation [8-11] and planning [12-14]. The TRENDY trial (registered as NCT02470533 on clinicaltrials.gov) is an international multi-center clinical trial in which patients with hepatocellular carcinoma (HCC) are randomized between transarterial chemoembolization (TACE) with drug