Implanted dosimeters identify radiation overdoses during IMRT for prostate cancer (original) (raw)
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International Journal of Radiation Oncology*Biology*Physics, 2009
Purpose: High geometrical and dosimetrical accuracies are required for radiotherapy treatments where IMRT is applied in combination with narrow treatment margins in order to minimize dose delivery to normal tissues. As an overall check, we implemented a method for reconstruction of the actually delivered 3D dose distribution to the patient during a treatment fraction, i.e., the 'dose of the day'. In this article results on the clinical evaluation of this concept for a group of IMRT prostate cancer patients are presented. Materials and methods: The actual IMRT fluence maps delivered to a patient were derived from measured EPID-images acquired during treatment using a previously described iterative method. In addition, the patient geometry was obtained from in-room acquired cone-beam CT images. For dose calculation, a mapping of the Hounsfield Units from the planning CT was applied. With the fluence maps and the modified cone-beam CT the 'dose of the day' was calculated. The method was validated using phantom measurements and evaluated clinically for 10 prostate cancer patients in 4 or 5 fractions. Results: The phantom measurements showed that the delivered dose could be reconstructed within 3%/ 3 mm accuracy. For prostate cancer patients, the isocenter dose agreed within À0.4 ± 1.0% (1 SD) with the planned value, while for on average 98.1% of the pixels within the 50% isodose surface the actually delivered dose agreed within 3% or 3 mm with the planned dose. For most fractions, the dose coverage of the prostate volume was slightly deteriorated which was caused by small prostate rotations and small inaccuracies in fluence delivery. The dose that was delivered to the rectum remained within the constraints used during planning. However, for two patients a large degrading of the dose delivery was observed in two fractions. For one patient this was related to changes in rectum filling with respect to the planning CT and for the other to large intra-fraction motion during treatment delivery, resulting in mean underdosages of 16% in the prostate volume. Conclusions: A method to accurately assess the 'dose of the day' was evaluated for prostate cancer patients treated with IMRT. To correct for observed dose deviations off-line dose-adaptive strategies will be developed.
Image-guided in vivo dosimetry for quality assurance of IMRT treatment for prostate cancer
International Journal of Radiation Oncology*Biology*Physics, 2007
Purpose: In external beam radiotherapy (EBRT) and especially in intensity-modulated radiotherapy (IMRT), the accuracy of the dose distribution in the patient is of utmost importance. It was investigated whether image guided in vivo dosimetry in the rectum is a reliable method for online dose verification. Methods and Materials: Twenty-one dose measurements were performed with an ionization chamber in the rectum of 7 patients undergoing IMRT for prostate cancer. The position of the probe was determined with cone beam computed tomography (CBCT). The point of measurement was determined relative to the isocenter and relative to an anatomic reference point. The dose deviations relative to the corresponding doses in the treatment plan were calculated. With an offline CT soft-tissue match, patient positioning after ultrasound was verified. Results: The mean magnitude ؎ standard deviation (SD) of patient positioning errors was 3.0 ؎ 2.5 mm, 5.1 ؎ 4.9 mm, and 4.3 ؎ 2.4 mm in the left-right, anteroposterior and craniocaudal direction. The dose deviations in points at corresponding positions relative to the isocenter were ؊1.4 ؎ 4.9% (mean ؎ SD). The mean dose deviation at corresponding anatomic positions was 6.5 ؎ 21.6%. In the rare event of insufficient patient positioning, dose deviations could be >30% because of the close proximity of the probe and the posterior dose gradient. Conclusions: Image-guided dosimetry in the rectum during IMRT of the prostate is a feasible and reliable direct method for dose verification when probe position is effectively controlled. © 2007 Elsevier Inc.
Medical Physics, 2007
The purpose of this study was to check the setup and dose delivered to the patients during intraoperative electron beam radiation therapy ͑IORT͒ for prostate cancer. Twenty eight patients underwent IORT after radical prostatectomy for prostate cancer by means of a dedicated mobile accelerator, Novac7 ͑by Hitesys, SpA, Italy͒. A 9 MeV electron beam at high dose per pulse was used. Eighteen patients received IORT at escalating doses of 16, 18, and 20 Gy at 85% isodose, six patients for each dose level. Further, ten patients received 20 Gy at 85% isodose. The electron applicator position was checked in all cases by means of two orthogonal images obtained with brilliance intensifier. Target and organ at risk doses were measured in vivo by a MOSFETs dosimetry system. MOSFETs and microMOSFET dosimeters were inserted into sterile catheters and directly positioned into the rectal lumen, for ten patients, and into the bladder to urethra anastomosis, in the last 14 cases. Verification at 0°led to very few adjustments of setup while verifications at 90°often suggested to bring the applicator closer to the target. In vivo dosimetry showed an absorbed dose into the rectum wall Յ1% of the total dose. The average dose value inside the anastomosis, for the 12 patients analyzed, was 23.7 Gy with a standard deviation of ±7.6%, when the prescription was 20 Gy at 85% isodose. Using a C-arm mobile image intensifier, it is possible to assess if the positioning is correct and safe. Radio-opaque clips and liquid were necessary to obtain good visible images. In vivo MOSFETs dosimetry is feasible and reliable. A satisfactory agreement between measured and expected doses was found.
Physica Medica, 2014
Introduction: To investigate the dosimetric impact of daily on-line repositioning during a full course of IMRT for prostate cancer. Materials and methods: Twenty patients were treated with image-guided IMRT. Each pre-treatment plan (Plan A) was compared with a post-treatment plan sum (Plan B) based on couch shifts measured. The delivered dose to the prostate without a daily repositioning was inferred by considering each daily couch shift during the whole course of image-guided IMRT (i.e. plan B). Dose metrics were compared for prostate CTV (P-CTV) and PTV (P-PTV) and for organs at risk. Ten patients were treated with a 5 mm margin and 10 patients with a 10 mm margin. Results: For plan A vs plan B: the average D95, D98, D50, D mean and EUD were: 76.4 Gy vs 73.9 Gy (p ¼ 0.0007), 75.4 Gy vs 72.3 Gy (p ¼ 0.001), 78.9 Gy vs 78.4 Gy (p ¼ 0.014), 78.7 Gy vs 77.8 Gy (p ¼ 0.003) and 78.1 Gy vs 75.9 Gy (p ¼ 0.002), respectively for P-CTV, and 73.2 Gy vs 69.3 Gy (p ¼ 0.0006), 70.7 Gy vs 66.0 Gy (p ¼ 0.0008), 78.3 Gy vs 77.5 Gy (p ¼ 0.001), 77.8 Gy vs 76.4 Gy (p ¼ 0.0002) and 74.4 Gy vs 69.2 Gy (p ¼ 0.003), respectively for P-PTV.
Dose verification in clinical imrt prostate incidents
International Journal of Radiation Oncology Biology Physics, 2004
Purpose: In view of the need for dose-validation procedures on each individual intensity-modulated radiation therapy (IMRT) plan, dose-verification measurements by film, by ionization chamber, and by polymer gel-MRI dosimetry were performed for a prostate-treatment plan configuration. Treatment planning system (TPS) calculations were evaluated against dose measurements.
Acta Clinica Croatica
Intensity modulated radiotherapy (IMRT) has become widely used as a standard radiation therapy technique for the treatment of localized prostate cancer. The transition from conformal radiotherapy (3D CRT) to a more complex IMRT technique triggered the need for more thorough verification of the accuracy in the dose delivery. In this work we present the clinical workflow and the results of patient specific quality assurance (PSQA) procedures for 40 prostate cancer patients who have been treated with step and shot IMRT ever since its implementation in our routine clinical practice. PSQA procedures include dosimetric verification of each treatment plan with dedicated rotational phantom and high-resolution matrix detector system Octavius 4D (PTW Freiburg) that allows three-dimensional comparison of the calculated and delivered radiation dose distribution. Our results proved the compliance with the universal tolerance limits recommended for those procedures (1), assuring the safety of the treatment and providing the possibility for the adoption of more stringent constraints in the future.
Iranian Journal of Radiation Research, 2017
Background: To correct pa ent posi oning errors (setup errors) during prostate cancer treatment using EPID and fiducial gold markers, to improve the accuracy of the dose delivery in these pa ents. Materials and Methods: Fi"een pa ents with localized prostate carcinoma a"er implanta on of fiducial gold markers in their prostate gland underwent the five-field IMRT planning technique. The plan was prepared in accordance with ICRU 50 guidance (PTV to receive 95-107% dose). The so"ware program reconstructed the three-dimensional posi on of the markers from the different Beams Eye Views (BEV). The discrepancies of the seeds’ posi ons (prostate surrogate) between plan and daily images were calculated three dimensionally. Then, necessary correc ons were applied to match the prostate fiducial markers in the portal image with the BEV image in the planned one by moving the couch in the X, Y and Z direc ons. Results: Data from 15 pa ents and 469 frac ons of radiotherapy were anal...
Radiation Oncology, 2017
Background: The cumulative dose was compared with the planned dose among fourteen patients undergoing image-guided, intensity-modulated radiotherapy of the prostate bed. Moreover, we investigated the feasibility of adding dose tracking to the routine workflow for radiotherapy. Methods: Daily cone beam computed tomography was conducted for image-guided radiotherapy, and weekly cumulative delivered doses were calculated for dose tracking. Deformable image registration was applied to map weekly dose distributions to the original treatment plan and to create a cumulative dose distribution. The dose-volume histogram (DVH) cutoff points for the rectum and bladder and the planning target volume (PTV), were used to compare the planned and cumulative delivered doses. The additional time required by the departmental staff to complete these duties was recorded. Results: The PTV coverage of the delivered treatment did not satisfy the expected goal for three patients (V98% >98%). In another three patients, the DVH cutoff point for the bladder was higher than the limits, while for the rectum, treatment was as expected in all cases (two patients failed both their bladder constraints and the PTV coverage). Overall, four patients did not satisfy one or more criteria at the end of their treatment. Conclusions: A well-defined strategy for dose tracking assessment is feasible, would have minimal impact on the workload of a radiotherapy department, and may offer objective information to support radiation oncologists in making decisions about adaptive procedures.
Single Institution’s Dosimetry and IGRT Analysis of Prostate SBRT
Radiation Oncology, 2013
Background and purpose: To report single institution's IGRT and dosimetry analysis on the 37 Gy/5 fraction prostate SBRT clinical trial. Materials/methods: The IRB (Duke University Medical Center) approved clinical trial has treated 28 patients with stage T1-T2c prostate cancer with a regimen of 37 Gy in 5 fractions using IMRT and IGRT protocols since 2009. The clinical trial protocol requires CT/MRI imaging for the prostate delineation; a margin of 3 mm in posterior direction and 5 mm elsewhere for planning target volume (PTV); and strict dose constraints for primary organs-at-risks (OARs) including the bladder, the rectum, and the femoral heads. Rigid IGRT process is also an essential part of the protocol. Precise patient and prostate positioning and dynamic tracking of prostate motion are performed with electromagnetic localization device (Calypso) and on-board imaging (OBI) system. Initial patient and target alignment is performed based on fiducials with OBI imaging system and Calypso system. Prior to treatment, conebeam CT (CBCT) is performed for soft tissue alignment verification. During treatment, per-beam corrections for target motion using translational couch movements is performed before irradiating each field, based on electromagnetic localization or on-board imaging localization. Dosimetric analysis on target coverage and OAR sparing is performed based on key DVH parameters corresponding to protocol guidance. IGRT analysis is focused on the average frequency and magnitude of corrections during treatment, and overall intra-fractional target drift. A margin value is derived using actual target motion data and the margin recipe from Van Herk et al., and is compared to the current one in practice. In addition, cumulative doses with and without per-beam IGRT corrections are compared to assess the benefit of online IGRT. Results: 1. No deviation has been found in 10 of 14 dosimetric constraints, with minor deviations in the rest 4 constraints. 2. Online IGRT techniques including Calypso, OBI and CBCT supplement each other to create an effective and reliable system on tracking target and correcting intra-fractional motion. 3. On average ½ corrections have been performed per fraction, with magnitude of (0.22 ± 0.11) cm. Average target drift magnitude is (0.7 ± 1.3) mm in one direction during each fraction. 4. Benefit from per-beam correction in overall review is small: most differences from no correction are < 0.1 Gy for PTV D1cc/Dmean and < 1%/1.5 cc for OAR parameters. Up to 1.5 Gy reduction was seen in PTV D99% without online correction. Largest differences for OARs are −4.1 cc and +1.6 cc in the V50% for the bladder and the rectum, respectively. However, online IGRT helps to catch unexpected significant target motion. 5. Margin derived from actual target motion is 2.5 mm isotropic, consist with current practice. Conclusions: Clinical experience of the 37 Gy/5-fraction prostate SBRT from a single institution is reported. Dosimetric analysis demonstrated excellent target coverage and OAR sparing for our first 28 patients in this trial. Online IGRT techniques implemented are both effective and reliable. Per-beam correction in general provides a small benefit in dosimetry. Target motion measured by online localization devices confirms that current margin selection is adequate.
MRI-based treatment planning for radiotherapy: Dosimetric verification for prostate IMRT
2004
Purpose: Magnetic resonance (MR) and computed tomography (CT) image fusion with CT-based dose calculation is the gold standard for prostate treatment planning. MR and CT fusion with CT-based dose calculation has become a routine procedure for intensity-modulated radiation therapy (IMRT) treatment planning at Fox Chase Cancer Center. The use of MRI alone for treatment planning (or MRI simulation) will remove any errors associated with image fusion. Furthermore, it will reduce treatment cost by avoiding redundant CT scans and save patient, staff, and machine time. The purpose of this study is to investigate the dosimetric accuracy of MRI-based treatment planning for prostate IMRT. Methods and Materials: A total of 30 IMRT plans for 15 patients were generated using both MRI and CT data. The MRI distortion was corrected using gradient distortion correction (GDC) software provided by the vendor (Philips Medical System, Cleveland, OH). The same internal contours were used for the paired plans. The external contours were drawn separately between CT-based and MR imaging-based plans to evaluate the effect of any residual distortions on dosimetric accuracy. The same energy, beam angles, dose constrains, and optimization parameters were used for dose calculations for each paired plans using a treatment optimization system. The resulting plans were compared in terms of isodose distributions and dose-volume histograms (DVHs). Hybrid phantom plans were generated for both the CT-based plans and the MR-based plans using the same leaf sequences and associated monitor units (MU). The physical phantom was then irradiated using the same leaf sequences to verify the dosimetry accuracy of the treatment plans. Results: Our results show that dose distributions between CT-based and MRI-based plans were equally acceptable based on our clinical criteria. The absolute dose agreement for the planning target volume was within 2% between CT-based and MR-based plans and 3% between measured dose and dose predicted by the planning system in the physical phantom. Conclusions: Magnetic resonnace imaging is a useful tool for radiotherapy simulation. Compared with CT-based treatment planning, MR imaging-based treatment planning meets the accuracy for dose calculation and provides consistent treatment plans for prostate IMRT. Because MR imaging-based digitally reconstructed radiographs do not provide adequate bony structure information, a technique is suggested for producing a wire-frame image that is intended to replace the traditional digitally reconstructed radiographs that are made from CT information.