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Title: Evaluation of clinical margins via simulation of patient setup errors in prostate IMRT treatment plans

Abstract

This work evaluates: (i) the size of random and systematic setup errors that can be absorbed by 5 mm clinical target volume (CTV) to planning target volume (PTV) margins in prostate intensity modulated radiation therapy (IMRT); (ii) agreement between simulation results and published margin recipes; and (iii) whether shifting contours with respect to a static dose distribution accurately predicts dose coverage due to setup errors. In 27 IMRT treatment plans created with 5 mm CTV-to-PTV margins, random setup errors with standard deviations (SDs) of 1.5, 3, 5 and 10 mm were simulated by fluence convolution. Systematic errors with identical SDs were simulated using two methods: (a) shifting the isocenter and recomputing dose (isocenter shift), and (b) shifting patient contours with respect to the static dose distribution (contour shift). Maximum tolerated setup errors were evaluated such that 90% of plans had target coverage equal to the planned PTV coverage. For coverage criteria consistent with published margin formulas, plans with 5 mm margins were found to absorb combined random and systematic SDs{approx_equal}3 mm. Published recipes require margins of 8-10 mm for 3 mm SDs. For the prostate IMRT cases presented here a 5 mm margin would suffice, indicating that published recipes maymore » be pessimistic. We found significant errors in individual plan doses given by the contour shift method. However, dose population plots (DPPs) given by the contour shift method agreed with the isocenter shift method for all structures except the nodal CTV and small bowel. For the nodal CTV, contour shift DPP differences were due to the structure moving outside the patient. Small bowel DPP errors were an artifact of large relative differences at low doses. Estimating individual plan doses by shifting contours with respect to a static dose distribution is not recommended. However, approximating DPPs is acceptable, provided care is taken with structures such as the nodal CTV which lie close to the surface.« less

Authors:
; ; ; ;  [1]
  1. Department of Radiation Oncology, Virginia Commonwealth University, P.O. Box 980058, Richmond, Virginia 23298 (United States)
Publication Date:
OSTI Identifier:
20853912
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 1; Other Information: DOI: 10.1118/1.2400842; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; DOSIMETRY; ERRORS; EVALUATION; MODULATION; PATIENTS; PROSTATE; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; RADIOTHERAPY; RANDOMNESS; SIMULATION

Citation Formats

Gordon, J. J., Crimaldi, A. J., Hagan, M., Moore, J., and Siebers, J. V.. Evaluation of clinical margins via simulation of patient setup errors in prostate IMRT treatment plans. United States: N. p., 2007. Web. doi:10.1118/1.2400842.
Gordon, J. J., Crimaldi, A. J., Hagan, M., Moore, J., & Siebers, J. V.. Evaluation of clinical margins via simulation of patient setup errors in prostate IMRT treatment plans. United States. doi:10.1118/1.2400842.
Gordon, J. J., Crimaldi, A. J., Hagan, M., Moore, J., and Siebers, J. V.. Mon . "Evaluation of clinical margins via simulation of patient setup errors in prostate IMRT treatment plans". United States. doi:10.1118/1.2400842.
@article{osti_20853912,
title = {Evaluation of clinical margins via simulation of patient setup errors in prostate IMRT treatment plans},
author = {Gordon, J. J. and Crimaldi, A. J. and Hagan, M. and Moore, J. and Siebers, J. V.},
abstractNote = {This work evaluates: (i) the size of random and systematic setup errors that can be absorbed by 5 mm clinical target volume (CTV) to planning target volume (PTV) margins in prostate intensity modulated radiation therapy (IMRT); (ii) agreement between simulation results and published margin recipes; and (iii) whether shifting contours with respect to a static dose distribution accurately predicts dose coverage due to setup errors. In 27 IMRT treatment plans created with 5 mm CTV-to-PTV margins, random setup errors with standard deviations (SDs) of 1.5, 3, 5 and 10 mm were simulated by fluence convolution. Systematic errors with identical SDs were simulated using two methods: (a) shifting the isocenter and recomputing dose (isocenter shift), and (b) shifting patient contours with respect to the static dose distribution (contour shift). Maximum tolerated setup errors were evaluated such that 90% of plans had target coverage equal to the planned PTV coverage. For coverage criteria consistent with published margin formulas, plans with 5 mm margins were found to absorb combined random and systematic SDs{approx_equal}3 mm. Published recipes require margins of 8-10 mm for 3 mm SDs. For the prostate IMRT cases presented here a 5 mm margin would suffice, indicating that published recipes may be pessimistic. We found significant errors in individual plan doses given by the contour shift method. However, dose population plots (DPPs) given by the contour shift method agreed with the isocenter shift method for all structures except the nodal CTV and small bowel. For the nodal CTV, contour shift DPP differences were due to the structure moving outside the patient. Small bowel DPP errors were an artifact of large relative differences at low doses. Estimating individual plan doses by shifting contours with respect to a static dose distribution is not recommended. However, approximating DPPs is acceptable, provided care is taken with structures such as the nodal CTV which lie close to the surface.},
doi = {10.1118/1.2400842},
journal = {Medical Physics},
number = 1,
volume = 34,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Purpose: The purpose of this study is to determine dose delivery errors that could result from random and systematic setup errors for head-and-neck patients treated using the simultaneous integrated boost (SIB)-intensity-modulated radiation therapy (IMRT) technique. Methods and Materials: Twenty-four patients who participated in an intramural Phase I/II parotid-sparing IMRT dose-escalation protocol using the SIB treatment technique had their dose distributions reevaluated to assess the impact of random and systematic setup errors. The dosimetric effect of random setup error was simulated by convolving the two-dimensional fluence distribution of each beam with the random setup error probability density distribution. Random setup errorsmore » of {sigma} = 1, 3, and 5 mm were simulated. Systematic setup errors were simulated by randomly shifting the patient isocenter along each of the three Cartesian axes, with each shift selected from a normal distribution. Systematic setup error distributions with {sigma} = 1.5 and 3.0 mm along each axis were simulated. Combined systematic and random setup errors were simulated for {sigma} = {sigma} = 1.5 and 3.0 mm along each axis. For each dose calculation, the gross tumor volume (GTV) received by 98% of the volume (D{sub 98}), clinical target volume (CTV) D{sub 90}, nodes D{sub 90}, cord D{sub 2}, and parotid D{sub 50} and parotid mean dose were evaluated with respect to the plan used for treatment for the structure dose and for an effective planning target volume (PTV) with a 3-mm margin. Results: Simultaneous integrated boost-IMRT head-and-neck treatment plans were found to be less sensitive to random setup errors than to systematic setup errors. For random-only errors, errors exceeded 3% only when the random setup error {sigma} exceeded 3 mm. Simulated systematic setup errors with {sigma} = 1.5 mm resulted in approximately 10% of plan having more than a 3% dose error, whereas a {sigma} = 3.0 mm resulted in half of the plans having more than a 3% dose error and 28% with a 5% dose error. Combined random and systematic dose errors with {sigma} = {sigma} = 3.0 mm resulted in more than 50% of plans having at least a 3% dose error and 38% of the plans having at least a 5% dose error. Evaluation with respect to a 3-mm expanded PTV reduced the observed dose deviations greater than 5% for the {sigma} = {sigma} = 3.0 mm simulations to 5.4% of the plans simulated. Conclusions: Head-and-neck SIB-IMRT dosimetric accuracy would benefit from methods to reduce patient systematic setup errors. When GTV, CTV, or nodal volumes are used for dose evaluation, plans simulated including the effects of random and systematic errors deviate substantially from the nominal plan. The use of PTVs for dose evaluation in the nominal plan improves agreement with evaluated GTV, CTV, and nodal dose values under simulated setup errors. PTV concepts should be used for SIB-IMRT head-and-neck squamous cell carcinoma patients, although the size of the margins may be less than those used with three-dimensional conformal radiation therapy.« less
  • Purpose: To evaluate the dose changes to the target and critical structures from rotational setup errors in prostate cancer patients treated with proton therapy. Methods and Materials: A total of 70 plans were analyzed for 10 patients treated with parallel-opposed proton beams to a dose of 7,600 {sup 60}Co-cGy-equivalent (CcGE) in 200 CcGE fractions to the clinical target volume (i.e., prostate and proximal seminal vesicles). Rotational setup errors of +3{sup o}, -3 deg., +5 deg., and -5 deg. (to simulate pelvic tilt) were generated by adjusting the gantry. Horizontal couch shifts of +3 deg. and -3 deg. (to simulate longitudinalmore » setup variability) were also generated. Verification plans were recomputed, keeping the same treatment parameters as the control. Results: All changes shown are for 38 fractions. The mean clinical target volume dose was 7,780 CcGE. The mean change in the clinical target volume dose in the worse case scenario for all shifts was 2 CcGE (absolute range in worst case scenario, 7,729-7,848 CcGE). The mean changes in the critical organ dose in the worst case scenario was 6 CcGE (bladder), 18 CcGE (rectum), 36 CcGE (anterior rectal wall), and 141 CcGE (femoral heads) for all plans. In general, the percentage of change in the worse case scenario for all shifts to the critical structures was <5%. Deviations in the absolute percentage of volume of organ receiving 45 and 70 Gy for the bladder and rectum were <2% for all plans. Conclusion: Patient rotational movements of 3 deg. and 5 deg. and horizontal couch shifts of 3 deg. in prostate proton planning did not confer clinically significant dose changes to the target volumes or critical structures00.« less
  • Purpose: Base of skull meningioma can be treated with both intensity modulated radiation therapy (IMRT) and spot scanned proton therapy (PT). One of the main benefits of PT is better sparing of organs at risk, but due to the physical and dosimetric characteristics of protons, spot scanned PT can be more sensitive to the uncertainties encountered in the treatment process compared with photon treatment. Therefore, robustness analysis should be part of a comprehensive comparison between these two treatment methods in order to quantify and understand the sensitivity of the treatment techniques to uncertainties. The aim of this work was tomore » benchmark a spot scanning treatment planning system for planning of base of skull meningioma and to compare the created plans and analyze their robustness to setup errors against the IMRT technique. Methods: Plans were produced for three base of skull meningioma cases: IMRT planned with a commercial TPS [Monaco (Elekta AB, Sweden)]; single field uniform dose (SFUD) spot scanning PT produced with an in-house TPS (PSI-plan); and SFUD spot scanning PT plan created with a commercial TPS [XiO (Elekta AB, Sweden)]. A tool for evaluating robustness to random setup errors was created and, for each plan, both a dosimetric evaluation and a robustness analysis to setup errors were performed. Results: It was possible to create clinically acceptable treatment plans for spot scanning proton therapy of meningioma with a commercially available TPS. However, since each treatment planning system uses different methods, this comparison showed different dosimetric results as well as different sensitivities to setup uncertainties. The results confirmed the necessity of an analysis tool for assessing plan robustness to provide a fair comparison of photon and proton plans. Conclusions: Robustness analysis is a critical part of plan evaluation when comparing IMRT plans with spot scanned proton therapy plans.« less
  • Purpose: To assess the influence of setup errors and organ motion in terms of the probability of tumor control and normal-tissue complications by tumor control probability and normal-tissue complication probability. Methods and Materials: Twelve patients were treated for prostate cancer with intensity-modulated radiation therapy. Two orthogonal portal images were taken daily. All patients underwent three computed tomography scans during the 8-week treatment time (i.e., baseline, intermediate, and final). The original treatment plans were re-evaluated, taking into account setup errors and organ motion. Results: The mean shifts {+-} standard deviation of the whole patient population in the lateral, anterior-posterior, and craniocaudalmore » direction were 1.0 {+-} 1.5 mm, 0.9 {+-} 2.1 mm, and 1.9 {+-} 2.1 mm, respectively. In most of the recalculated dose-volume histograms, the coverage of clinical target volume was granted despite organ motion, whereas the rectal wall histograms were often very different from the planned ones. Conclusion: We have studied the impact of prostate and rectum motion, as well as setup errors, on dose-volume histograms. The estimate of these effects may have implications for predictive indications when planning intensity-modulated radiation therapy treatments on prostate.« less
  • Purpose: Fast and reliable comprehensive quality assurance tools are required to validate the safety and accuracy of complex intensity-modulated radiotherapy (IMRT) plans for prostate treatment. In this study, we evaluated the performance of the COMPASS system for both off-line and potential online procedures for the verification of IMRT treatment plans. Methods and Materials: COMPASS has a dedicated beam model and dose engine, it can reconstruct three-dimensional dose distributions on the patient anatomy based on measured fluences using either the MatriXX two-dimensional (2D) array (offline) or a 2D transmission detector (T2D) (online). For benchmarking the COMPASS dose calculation, various dose-volume indicesmore » were compared against Monte Carlo-calculated dose distributions for five prostate patient treatment plans. Gamma index evaluation and absolute point dose measurements were also performed in an inhomogeneous pelvis phantom using extended dose range films and ion chamber for five additional treatment plans. Results: MatriXX-based dose reconstruction showed excellent agreement with the ion chamber (<0.5%, except for one treatment plan, which showed 1.5%), film ({approx}100% pixels passing gamma criteria 3%/3 mm) and mean dose-volume indices (<2%). The T2D based dose reconstruction showed good agreement as well with ion chamber (<2%), film ({approx}99% pixels passing gamma criteria 3%/3 mm), and mean dose-volume indices (<5.5%). Conclusion: The COMPASS system qualifies for routine prostate IMRT pretreatment verification with the MatriXX detector and has the potential for on-line verification of treatment delivery using T2D.« less