Simon Skouboe - Academia.edu (original) (raw)
Papers by Simon Skouboe
Medical Physics
Background: Hypofractionation in prostate radiotherapy is of increasing interest. Steep dose grad... more Background: Hypofractionation in prostate radiotherapy is of increasing interest. Steep dose gradients and a large weight on each individual fraction emphasize the need for motion management. Real-time motion management techniques such as multileaf collimator (MLC) tracking or couch tracking typically adjust for translational motion while rotations remain uncompensated with unknown dosimetric impact. Purpose: The purpose of this study is to demonstrate and validate dynamic real-time rotation-including dose reconstruction during radiotherapy experiments with and without MLC and couch tracking. Methods: Real-time dose reconstruction was performed using the in-house developed software DoseTracker. DoseTracker receives streamed target positions and accelerator parameters during treatment delivery and uses a pencil beam algorithm with water density assumption to reconstruct the dose in a moving target. DoseTracker's ability to reconstruct motion-induced dose errors in a dynamically rotating and translating target was investigated during three different scenarios: (1) no motion compensation and translational motion correction with (2) MLC tracking and (3) couch tracking. In each scenario, dose reconstruction was performed online and in real time during delivery of two dual-arc volumetric-modulated arc therapy prostate plans with a prescribed fraction dose of 7 Gy to the prostate and simultaneous intraprostatic lesion boosts with doses of at least 8 Gy, but up to 10 Gy as long as the organs at risk dose constraints were fulfilled. The plans were delivered to a pelvis phantom that replicated three patient-measured motion traces using a rotational insert with 21 layers of EBT3 film spaced 2.5 mm apart. Dose-Tracker repeatedly calculated the actual motion-including dose increment and the planned static dose increment since the last calculation in 84 500 points in the film stack. The experiments were performed with a TrueBeam accelerator with MLC and couch tracking based on electromagnetic transponders embedded in the film stack. The motion-induced dose error was quantified as the difference between the final cumulative dose with motion and without motion using the 2D 2%/2 mm γ-failure rate and the difference in dose to 95% of the clinical target volume (CTV ΔD 95%) and the gross target volume (GTV ΔD 95%) as well as the This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Radiotherapy and Oncology, 2021
PURPOSE The outcome of radiotherapy is a direct consequence of the dose delivered to the patient.... more PURPOSE The outcome of radiotherapy is a direct consequence of the dose delivered to the patient. Yet image-guidance and motion management to date focus on geometrical considerations as a practical surrogate for dose. Here, we propose real-time dose-guidance realized through continuous motion-including dose reconstructions and demonstrate this new concept in simulated liver stereotactic body radiotherapy (SBRT) delivery. MATERIALS AND METHODS During simulated liver SBRT delivery, in-house developed software performed real-time motion-including reconstruction of the tumor dose delivered so far and continuously predicted the remaining fraction tumor dose. The total fraction dose was estimated as the sum of the delivered and predicted doses, both with and without the emulated couch correction that maximized the predicted final CTV D95% (minimum dose to 95% of the clinical target volume). Dose-guided treatments were simulated for 15 liver SBRT patients previously treated with tumor motion monitoring, using both sinusoidal tumor motion and the actual patient-measured motion. A dose-guided couch correction was triggered if it improved the predicted final CTV D95% with 3, 4 or 5 %-points. The final CTV D95% of the dose-guidance strategy was compared with simulated treatments using geometry guided couch corrections (Wilcoxon signed-rank test). RESULTS Compared to geometry guidance, dose-guided couch corrections improved the median CTV D95% with 0.5-1.5%-points (p<0.01) for sinusoidal motions and with 0.9%-points (p<0.01, 3% trigger threshold), 0.5%-points (p=0.03, 4% threshold) and 1.2%-points (p=0.09, 5% threshold) for patient-measured tumor motion. CONCLUSION Real-time dose-guidance was proposed and demonstrated to be superior to geometrical adaptation in liver SBRT simulations.
Radiotherapy and Oncology, 2021
Bullet points: Intrafraction prostate rotations reduces target coverage and increases OAR dose.... more Bullet points: Intrafraction prostate rotations reduces target coverage and increases OAR dose. Gating, MLC tracking and couch tracking improved the dosimetric accuracy. Residual motion-related dose errors remained due to the lack of rotation correction.
![Research paper thumbnail of [OA011] DoseTracker: In-house developed software program for real-time reconstruction of motion-induced dose errors during radiotherapy](https://attachments.academia-assets.com/102076616/thumbnails/1.jpg)
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Medical Physics, 2019
In radiotherapy, tumor motion may deteriorate the planned dose distribution. However, the dosimet... more In radiotherapy, tumor motion may deteriorate the planned dose distribution. However, the dosimetric consequences of the motion are normally unknown for individual treatments. We here present a method for real-time motion-including tumor dose reconstruction and demonstrate its use for simulated stereotactic body radiotherapy (SBRT) of patients with liver cancer previously treated with Calypso-guided gating. Methods: Real-time motion-including dose reconstruction was performed using in-house developed software, DoseTracker, on offline replays of previous clinical treatments. The patient cohort consisted of fifteen patients previously treated in our clinic with three-fraction SBRT to the liver using conformal or IMRT plans. The tumor motion at treatment was monitored with implanted electromagnetic transponders. The dose reconstruction was performed for both the actual gated treatments and simulated nongated treatments using a 21 Hz data stream containing accelerator parameters and the recorded motion. The dose was reconstructed in the same calculation points within the planning target volume (PTV) as used by the treatment planning system (TPS). The reconstructed doses were compared with calculations performed in the TPS, in which the motion was modeled as a series of isocenter shifts. The comparison included point doses as a function of treatment time and the dose volume histogram (DVH) for the clinical target volume (CTV). The motion-induced reduction in the dose to 95% of the CTV, DD 95% , and in the mean CTV dose, DD Mean , was compared between DoseTracker and the TPS for each simulated fraction. DoseTracker currently assumes water density within the patient contour, so for comparison, the TPS calculations were performed with both CT density and water density. The calculation times were additionally analyzed. Results: Dose reconstruction was carried out for ninety SBRT sessions with calculation volumes ranging from 9.9 to 366.4 cm 3 and median calculation times of 55-155 ms (equivalent to 18.2-6.5 Hz). Time-resolved trends of doses to a single calculation point in the patient were well replicated and dose differences between actual and planned calculations matched well. DD Mean had a range of À0.1%-30.7%-points and was estimated by DoseTracker with a root-mean-square deviation (RMSD) to the TPS calculations of 0.43%-points (water density) and 0.79%-points (CT density). Similarly, DD 95% had a range of 0.0%-35.2%-points and was estimated by Dose-Tracker with an RMSD of 0.80%-points (water density) and 1.33%-points (CT density). Dose-Tracker predicted losses in tumor dose coverage above 5%-points with high sensitivity (91.7%) and specificity (97.6%). Conclusions: Real-time dose reconstruction to moving tumors was demonstrated on offline replays of previous clinical treatments. DVHs of actually delivered dose are made available immediately after the end of treatment fractions. It shows promising results for liver SBRT with accurate estimation of Med. Phys.
Radiotherapy and Oncology, 2019
To clinically implement and characterize real-time motion-including tumor dose reconstruction dur... more To clinically implement and characterize real-time motion-including tumor dose reconstruction during radiotherapy delivery. Methods: Seven patients with 2-3 fiducial markers implanted near liver tumors received stereotactic body radiotherapy on a conventional linear accelerator. The 3D marker motion during a setup CBCT scan was determined online from the CBCT projections and used to generate a correlation model between tumor and external marker block motion. During treatment, the correlation model was updated by kV imaging every three seconds and used for real-time tumor localization. Using streamed accelerator parameters and tumor positions, in-house developed software, DoseTracker, calculated the dose to the moving tumor in real-time assuming water density in the patient. Post-treatment, the real-time tumor localization was validated by comparison with independent marker segmentations and 3D motion estimations. Dose reconstruction was validated by comparison with treatment planning system (TPS) calculations that modeled motion as isocenter shifts and used both actual CT densities and water densities. Results: The real-time estimated tumor position had a mean 3D root-mean-square error of 1.7 mm (range: 0.9-2.6 mm). The motion-induced reduction in the minimum dose to 95% of the clinical target volume (CTV D95) per fraction was up to 12.3%-points. It was estimated in real-time by DoseTracker during patient treatment with a root-mean-square difference relative to the TPS of 1.3%-points (TPS CT) and 1.0%-points (TPS water). Conclusions: The world's first clinical real-time motion-including tumor dose reconstruction during radiotherapy was demonstrated. This marks an important milestone for real-time in-treatment quality assurance and paves the way for real-time dose-guided treatment adaptation.
Medical Physics, 2018
Purpose In radiotherapy, dose deficits caused by tumor motion often far outweigh the discrepancie... more Purpose In radiotherapy, dose deficits caused by tumor motion often far outweigh the discrepancies typically allowed in plan-specific quality assurance (QA). Yet, tumor motion is not usually included in present QA. We here present a novel method for online treatment verification by real-time motion-including 4D dose reconstruction and dose evaluation and demonstrate its use during stereotactic body radiotherapy (SBRT) delivery with and without MLC tracking. Methods Five volumetric modulated arc therapy (VMAT) plans were delivered with and without MLC tracking to a motion stage carrying a Delta4 dosimeter. The VMAT plans have previously been used for (nontracking) liver SBRT with intra-treatment tumor motion recorded by kilovoltage intrafraction monitoring (KIM). The motion stage reproduced the KIM-measured tumor motions in 3D while optical monitoring guided the MLC tracking. Linac parameters and the target position were streamed to an in-house developed software program (DoseTracker) that performed real-time 4D dose reconstructions and 3%/3mm γ-evaluations of the reconstructed cumulative dose using a concurrently reconstructed planned dose without target motion as reference. Offline, the real-time reconstructed doses and γ-evaluations were validated against 4D dosimeter measurements performed during the experiments. Results In total, 181,120 dose reconstructions and 5,237 γ-evaluations were performed online and in real time with median computation times of 30 ms and 1.2 s, respectively. The mean (standard deviation) Accepted Article This article is protected by copyright. All rights reserved. difference between reconstructed and measured doses was-1.2% (4.9%) for transient doses and-1.5% (3.9%) for cumulative doses. The root-mean-square deviation between reconstructed and measured motion-induced γ-fail rates was 2.0%-point. The mean (standard deviation) sensitivity and specificity of DoseTracker to predict γ-fail rates above a given threshold was 96.8% (3.5%) and 99.2% (0.4%), respectively, for clinically relevant thresholds between 1% and 30% γ-fail rate. Conclusions Real-time delivery-specific QA during radiotherapy of moving targets was demonstrated for the first time. It allows supervision of treatment accuracy and action on treatment discrepancy within two seconds with high sensitivity and specificity.
Physics in Medicine & Biology, 2018
This study validates a method of fast motion-including dose reconstruction for proton pencil beam... more This study validates a method of fast motion-including dose reconstruction for proton pencil beam scanning in the liver. The method utilizes a commercial treatment planning system (TPS) and calculates the delivered dose for any translational 3D target motion. Data from ten liver patients previously treated with photon radiotherapy with intrafraction tumour motion monitoring were used. The dose reconstruction method utilises an in-house developed program to incorporate beam's-eye-view tumour motion by shifting each spot in the opposite direction of the tumour and in-depth motion as beam energy changes for each spot. The doses are then calculated on a single CT phase in the TPS. Two aspects of the dose reconstruction were assessed: 1) The accuracy of reconstruction, by comparing dose reconstructions created using 4DCT motion with ground truth doses obtained by calculating phase specific doses in all 4DCT phases and summing up these partial doses. 2) The error caused by assuming 4DCT motion, by comparing reconstructions with 4DCT motion and actual tumour motion. The CTV homogeneity index (HI) and the root-mean-square (rms) dose error for all dose points receiving >70%, >80% and >90% of the prescribed dose were calculated. The dose reconstruction resulted in mean (range) absolute CTV HI errors of 1.0% (0.0-3.0)% and rms dose errors of 2.5% (1.0-5.3%), 2.1% (0.9-4.5%), and 1.8% (0.7-3.7%) for >70%, >80% and >90% doses, respectively, when compared with the ground truth. The assumption of 4DCT motion resulted in mean (range) absolute CTV HI errors of 5.9% (0.0-15.0)% and rms dose errors of 6.3% (3.9-12.6%), 5.9% (3.4-12.5%), and 5.4% (2.6-12.1%) for >70%, >80% and >90% doses, respectively. The investigated method allows tumour dose reconstruction with the actual tumour motion and results in significantly smaller dose errors than those caused by assuming that motion at treatment is identical to the 4DCT motion.
Medical Physics
Intrafractional motion during radiotherapy delivery can deteriorate the delivered dose. Dynamic r... more Intrafractional motion during radiotherapy delivery can deteriorate the delivered dose. Dynamic rotational motion of up to 38 degrees has been reported during prostate cancer radiotherapy, but methods to determine the dosimetric consequences of such rotations are lacking. Here, we create and experimentally validate a dose reconstruction method that accounts for dynamic rotations and translations in a commercial treatment planning system (TPS). Interplay effects are quantified by comparing dose reconstructions with dynamic and constant rotations. Methods: The dose reconstruction accumulates the dose in points of interest while the points are moved in six degrees of freedom (6DoF) in a precalculated time-resolved four-dimensional (4D) dose matrix to emulate dynamic motion in a patient. The required 4D dose matrix was generated by splitting the original treatment plan into multiple sub-beams, each representing 0.4 s dose delivery, and recalculating the dose of the split plan in the TPS (Eclipse). The dose accumulation was performed via TPS scripting by querying the dose of each sub-beam in dynamically moving points, allowing dose reconstruction with any dynamic motion. The dose reconstruction was validated with film dosimetry for two prostate dual arc VMAT plans with intra-prostatic lesion boosts. The plans were delivered to a pelvis phantom with internal dynamic rotational motion of a film stack (21 films with 2.5 mm separation). Each plan was delivered without motion and with three prostate motion traces. Motion-including dose reconstruction was performed for each motion experiment using the actual dynamic rotation as well as a constant rotation equal to the mean rotation during the experiment. For each experiment, the 3%/2 mm γ failure rate of the TPS dose reconstruction was calculated with the film measurement being the reference. For each motion experiment, the motion-induced 3%/2 mm γ failure rate was calculated using the static delivery as the reference and compared between film measurements and TPS dose reconstruction. DVH metrics for RT structures fully contained in the film volume were also compared between film and TPS. Results: The mean γ failure rate of the TPS dose reconstructions when compared to film doses was 0.8% (two static experiments) and 1.7% (six dynamic experiments). The mean (range) of the motioninduced γ failure rate in film measurements was 35.4% (21.3-59.2%). The TPS dose reconstruction agreed with these experimental γ failure rates with root-mean-square errors of 2.1% (dynamic rotation dose reconstruction) and 17.1% (dose reconstruction assuming constant rotation).
Medical Physics
Background: Hypofractionation in prostate radiotherapy is of increasing interest. Steep dose grad... more Background: Hypofractionation in prostate radiotherapy is of increasing interest. Steep dose gradients and a large weight on each individual fraction emphasize the need for motion management. Real-time motion management techniques such as multileaf collimator (MLC) tracking or couch tracking typically adjust for translational motion while rotations remain uncompensated with unknown dosimetric impact. Purpose: The purpose of this study is to demonstrate and validate dynamic real-time rotation-including dose reconstruction during radiotherapy experiments with and without MLC and couch tracking. Methods: Real-time dose reconstruction was performed using the in-house developed software DoseTracker. DoseTracker receives streamed target positions and accelerator parameters during treatment delivery and uses a pencil beam algorithm with water density assumption to reconstruct the dose in a moving target. DoseTracker's ability to reconstruct motion-induced dose errors in a dynamically rotating and translating target was investigated during three different scenarios: (1) no motion compensation and translational motion correction with (2) MLC tracking and (3) couch tracking. In each scenario, dose reconstruction was performed online and in real time during delivery of two dual-arc volumetric-modulated arc therapy prostate plans with a prescribed fraction dose of 7 Gy to the prostate and simultaneous intraprostatic lesion boosts with doses of at least 8 Gy, but up to 10 Gy as long as the organs at risk dose constraints were fulfilled. The plans were delivered to a pelvis phantom that replicated three patient-measured motion traces using a rotational insert with 21 layers of EBT3 film spaced 2.5 mm apart. Dose-Tracker repeatedly calculated the actual motion-including dose increment and the planned static dose increment since the last calculation in 84 500 points in the film stack. The experiments were performed with a TrueBeam accelerator with MLC and couch tracking based on electromagnetic transponders embedded in the film stack. The motion-induced dose error was quantified as the difference between the final cumulative dose with motion and without motion using the 2D 2%/2 mm γ-failure rate and the difference in dose to 95% of the clinical target volume (CTV ΔD 95%) and the gross target volume (GTV ΔD 95%) as well as the This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Radiotherapy and Oncology, 2021
PURPOSE The outcome of radiotherapy is a direct consequence of the dose delivered to the patient.... more PURPOSE The outcome of radiotherapy is a direct consequence of the dose delivered to the patient. Yet image-guidance and motion management to date focus on geometrical considerations as a practical surrogate for dose. Here, we propose real-time dose-guidance realized through continuous motion-including dose reconstructions and demonstrate this new concept in simulated liver stereotactic body radiotherapy (SBRT) delivery. MATERIALS AND METHODS During simulated liver SBRT delivery, in-house developed software performed real-time motion-including reconstruction of the tumor dose delivered so far and continuously predicted the remaining fraction tumor dose. The total fraction dose was estimated as the sum of the delivered and predicted doses, both with and without the emulated couch correction that maximized the predicted final CTV D95% (minimum dose to 95% of the clinical target volume). Dose-guided treatments were simulated for 15 liver SBRT patients previously treated with tumor motion monitoring, using both sinusoidal tumor motion and the actual patient-measured motion. A dose-guided couch correction was triggered if it improved the predicted final CTV D95% with 3, 4 or 5 %-points. The final CTV D95% of the dose-guidance strategy was compared with simulated treatments using geometry guided couch corrections (Wilcoxon signed-rank test). RESULTS Compared to geometry guidance, dose-guided couch corrections improved the median CTV D95% with 0.5-1.5%-points (p<0.01) for sinusoidal motions and with 0.9%-points (p<0.01, 3% trigger threshold), 0.5%-points (p=0.03, 4% threshold) and 1.2%-points (p=0.09, 5% threshold) for patient-measured tumor motion. CONCLUSION Real-time dose-guidance was proposed and demonstrated to be superior to geometrical adaptation in liver SBRT simulations.
Radiotherapy and Oncology, 2021
Bullet points: Intrafraction prostate rotations reduces target coverage and increases OAR dose.... more Bullet points: Intrafraction prostate rotations reduces target coverage and increases OAR dose. Gating, MLC tracking and couch tracking improved the dosimetric accuracy. Residual motion-related dose errors remained due to the lack of rotation correction.
Medical Physics, 2019
In radiotherapy, tumor motion may deteriorate the planned dose distribution. However, the dosimet... more In radiotherapy, tumor motion may deteriorate the planned dose distribution. However, the dosimetric consequences of the motion are normally unknown for individual treatments. We here present a method for real-time motion-including tumor dose reconstruction and demonstrate its use for simulated stereotactic body radiotherapy (SBRT) of patients with liver cancer previously treated with Calypso-guided gating. Methods: Real-time motion-including dose reconstruction was performed using in-house developed software, DoseTracker, on offline replays of previous clinical treatments. The patient cohort consisted of fifteen patients previously treated in our clinic with three-fraction SBRT to the liver using conformal or IMRT plans. The tumor motion at treatment was monitored with implanted electromagnetic transponders. The dose reconstruction was performed for both the actual gated treatments and simulated nongated treatments using a 21 Hz data stream containing accelerator parameters and the recorded motion. The dose was reconstructed in the same calculation points within the planning target volume (PTV) as used by the treatment planning system (TPS). The reconstructed doses were compared with calculations performed in the TPS, in which the motion was modeled as a series of isocenter shifts. The comparison included point doses as a function of treatment time and the dose volume histogram (DVH) for the clinical target volume (CTV). The motion-induced reduction in the dose to 95% of the CTV, DD 95% , and in the mean CTV dose, DD Mean , was compared between DoseTracker and the TPS for each simulated fraction. DoseTracker currently assumes water density within the patient contour, so for comparison, the TPS calculations were performed with both CT density and water density. The calculation times were additionally analyzed. Results: Dose reconstruction was carried out for ninety SBRT sessions with calculation volumes ranging from 9.9 to 366.4 cm 3 and median calculation times of 55-155 ms (equivalent to 18.2-6.5 Hz). Time-resolved trends of doses to a single calculation point in the patient were well replicated and dose differences between actual and planned calculations matched well. DD Mean had a range of À0.1%-30.7%-points and was estimated by DoseTracker with a root-mean-square deviation (RMSD) to the TPS calculations of 0.43%-points (water density) and 0.79%-points (CT density). Similarly, DD 95% had a range of 0.0%-35.2%-points and was estimated by Dose-Tracker with an RMSD of 0.80%-points (water density) and 1.33%-points (CT density). Dose-Tracker predicted losses in tumor dose coverage above 5%-points with high sensitivity (91.7%) and specificity (97.6%). Conclusions: Real-time dose reconstruction to moving tumors was demonstrated on offline replays of previous clinical treatments. DVHs of actually delivered dose are made available immediately after the end of treatment fractions. It shows promising results for liver SBRT with accurate estimation of Med. Phys.
Radiotherapy and Oncology, 2019
To clinically implement and characterize real-time motion-including tumor dose reconstruction dur... more To clinically implement and characterize real-time motion-including tumor dose reconstruction during radiotherapy delivery. Methods: Seven patients with 2-3 fiducial markers implanted near liver tumors received stereotactic body radiotherapy on a conventional linear accelerator. The 3D marker motion during a setup CBCT scan was determined online from the CBCT projections and used to generate a correlation model between tumor and external marker block motion. During treatment, the correlation model was updated by kV imaging every three seconds and used for real-time tumor localization. Using streamed accelerator parameters and tumor positions, in-house developed software, DoseTracker, calculated the dose to the moving tumor in real-time assuming water density in the patient. Post-treatment, the real-time tumor localization was validated by comparison with independent marker segmentations and 3D motion estimations. Dose reconstruction was validated by comparison with treatment planning system (TPS) calculations that modeled motion as isocenter shifts and used both actual CT densities and water densities. Results: The real-time estimated tumor position had a mean 3D root-mean-square error of 1.7 mm (range: 0.9-2.6 mm). The motion-induced reduction in the minimum dose to 95% of the clinical target volume (CTV D95) per fraction was up to 12.3%-points. It was estimated in real-time by DoseTracker during patient treatment with a root-mean-square difference relative to the TPS of 1.3%-points (TPS CT) and 1.0%-points (TPS water). Conclusions: The world's first clinical real-time motion-including tumor dose reconstruction during radiotherapy was demonstrated. This marks an important milestone for real-time in-treatment quality assurance and paves the way for real-time dose-guided treatment adaptation.
Medical Physics, 2018
Purpose In radiotherapy, dose deficits caused by tumor motion often far outweigh the discrepancie... more Purpose In radiotherapy, dose deficits caused by tumor motion often far outweigh the discrepancies typically allowed in plan-specific quality assurance (QA). Yet, tumor motion is not usually included in present QA. We here present a novel method for online treatment verification by real-time motion-including 4D dose reconstruction and dose evaluation and demonstrate its use during stereotactic body radiotherapy (SBRT) delivery with and without MLC tracking. Methods Five volumetric modulated arc therapy (VMAT) plans were delivered with and without MLC tracking to a motion stage carrying a Delta4 dosimeter. The VMAT plans have previously been used for (nontracking) liver SBRT with intra-treatment tumor motion recorded by kilovoltage intrafraction monitoring (KIM). The motion stage reproduced the KIM-measured tumor motions in 3D while optical monitoring guided the MLC tracking. Linac parameters and the target position were streamed to an in-house developed software program (DoseTracker) that performed real-time 4D dose reconstructions and 3%/3mm γ-evaluations of the reconstructed cumulative dose using a concurrently reconstructed planned dose without target motion as reference. Offline, the real-time reconstructed doses and γ-evaluations were validated against 4D dosimeter measurements performed during the experiments. Results In total, 181,120 dose reconstructions and 5,237 γ-evaluations were performed online and in real time with median computation times of 30 ms and 1.2 s, respectively. The mean (standard deviation) Accepted Article This article is protected by copyright. All rights reserved. difference between reconstructed and measured doses was-1.2% (4.9%) for transient doses and-1.5% (3.9%) for cumulative doses. The root-mean-square deviation between reconstructed and measured motion-induced γ-fail rates was 2.0%-point. The mean (standard deviation) sensitivity and specificity of DoseTracker to predict γ-fail rates above a given threshold was 96.8% (3.5%) and 99.2% (0.4%), respectively, for clinically relevant thresholds between 1% and 30% γ-fail rate. Conclusions Real-time delivery-specific QA during radiotherapy of moving targets was demonstrated for the first time. It allows supervision of treatment accuracy and action on treatment discrepancy within two seconds with high sensitivity and specificity.
Physics in Medicine & Biology, 2018
This study validates a method of fast motion-including dose reconstruction for proton pencil beam... more This study validates a method of fast motion-including dose reconstruction for proton pencil beam scanning in the liver. The method utilizes a commercial treatment planning system (TPS) and calculates the delivered dose for any translational 3D target motion. Data from ten liver patients previously treated with photon radiotherapy with intrafraction tumour motion monitoring were used. The dose reconstruction method utilises an in-house developed program to incorporate beam's-eye-view tumour motion by shifting each spot in the opposite direction of the tumour and in-depth motion as beam energy changes for each spot. The doses are then calculated on a single CT phase in the TPS. Two aspects of the dose reconstruction were assessed: 1) The accuracy of reconstruction, by comparing dose reconstructions created using 4DCT motion with ground truth doses obtained by calculating phase specific doses in all 4DCT phases and summing up these partial doses. 2) The error caused by assuming 4DCT motion, by comparing reconstructions with 4DCT motion and actual tumour motion. The CTV homogeneity index (HI) and the root-mean-square (rms) dose error for all dose points receiving >70%, >80% and >90% of the prescribed dose were calculated. The dose reconstruction resulted in mean (range) absolute CTV HI errors of 1.0% (0.0-3.0)% and rms dose errors of 2.5% (1.0-5.3%), 2.1% (0.9-4.5%), and 1.8% (0.7-3.7%) for >70%, >80% and >90% doses, respectively, when compared with the ground truth. The assumption of 4DCT motion resulted in mean (range) absolute CTV HI errors of 5.9% (0.0-15.0)% and rms dose errors of 6.3% (3.9-12.6%), 5.9% (3.4-12.5%), and 5.4% (2.6-12.1%) for >70%, >80% and >90% doses, respectively. The investigated method allows tumour dose reconstruction with the actual tumour motion and results in significantly smaller dose errors than those caused by assuming that motion at treatment is identical to the 4DCT motion.
Medical Physics
Intrafractional motion during radiotherapy delivery can deteriorate the delivered dose. Dynamic r... more Intrafractional motion during radiotherapy delivery can deteriorate the delivered dose. Dynamic rotational motion of up to 38 degrees has been reported during prostate cancer radiotherapy, but methods to determine the dosimetric consequences of such rotations are lacking. Here, we create and experimentally validate a dose reconstruction method that accounts for dynamic rotations and translations in a commercial treatment planning system (TPS). Interplay effects are quantified by comparing dose reconstructions with dynamic and constant rotations. Methods: The dose reconstruction accumulates the dose in points of interest while the points are moved in six degrees of freedom (6DoF) in a precalculated time-resolved four-dimensional (4D) dose matrix to emulate dynamic motion in a patient. The required 4D dose matrix was generated by splitting the original treatment plan into multiple sub-beams, each representing 0.4 s dose delivery, and recalculating the dose of the split plan in the TPS (Eclipse). The dose accumulation was performed via TPS scripting by querying the dose of each sub-beam in dynamically moving points, allowing dose reconstruction with any dynamic motion. The dose reconstruction was validated with film dosimetry for two prostate dual arc VMAT plans with intra-prostatic lesion boosts. The plans were delivered to a pelvis phantom with internal dynamic rotational motion of a film stack (21 films with 2.5 mm separation). Each plan was delivered without motion and with three prostate motion traces. Motion-including dose reconstruction was performed for each motion experiment using the actual dynamic rotation as well as a constant rotation equal to the mean rotation during the experiment. For each experiment, the 3%/2 mm γ failure rate of the TPS dose reconstruction was calculated with the film measurement being the reference. For each motion experiment, the motion-induced 3%/2 mm γ failure rate was calculated using the static delivery as the reference and compared between film measurements and TPS dose reconstruction. DVH metrics for RT structures fully contained in the film volume were also compared between film and TPS. Results: The mean γ failure rate of the TPS dose reconstructions when compared to film doses was 0.8% (two static experiments) and 1.7% (six dynamic experiments). The mean (range) of the motioninduced γ failure rate in film measurements was 35.4% (21.3-59.2%). The TPS dose reconstruction agreed with these experimental γ failure rates with root-mean-square errors of 2.1% (dynamic rotation dose reconstruction) and 17.1% (dose reconstruction assuming constant rotation).