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| Dissertation / PhD Thesis | GSI-2016-00157 |
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2015
Abstract: Radiation therapy for prostate carcinoma (PCa) is challenged in part by large target dislocations between single fractions (interfraction motion). To prevent geometrical target misses, in clinical practice the volume to be irradiated is enlarged by so called safety margins of typically 5 to 12 mm, in some cases even up to 15 mm, in any direction. The extension causes an unnecessary dose delivered to healthy tissue and radiation sensitive organs like the bladder and the rectum. Toxicity in these organs restricts the maximum target dose which has been found to improve tumor control if increased. In this work, adaptive radiation therapy (ART) strategies have been analyzed for their possible application in prostate cancer therapy. For this purpose, scanned ion beam therapy, which is known to feature a highly conformal dose delivery, was combined with two ART strategies: image guided target definition and daily plan re-optimization. As a proof of concept, the treatment planning software for particles TRiP, developed at GSI Helmholtz Center for Heavy Ion Research (GSI) in Darmstadt, Germany, has been optimized for calculation speed. A reduction of computation time from 4 hours to 6 min for a two-field prostate plan demonstrated the plausibility of daily plan re-optimization. In addition a treatment simulation study on a dataset containing 60 computed tomography scans (CTs) of ten prostate cancer patients has been designed comparing the performance of image guided target definition and daily plan re-optimization with conventional one plan radiotherapy. In the presented dataset 20% of the patients showed considerable motion (mean 3D vector length > 4 mm). The fraction of the target volume receiving at least 95% of the prescribed target dose in 5% of all fractions (V955%) for these patients was lower than 0.64 (mean 0.87) and lower than 0.66 (mean 0.91) for conventional one-plan particle therapy and image guided target definition, respectively. In patients showing only small motion(mean 3D vector length < 4 mm), image guided target definition reduced the mean rectal volume receiving more than 60% target dose (V60mean) by 13% at slightly but significantly improved target coverage. Daily re-optimization, the most versatile correction method, kept target coverage in all patients above 95% of the prescribed dose and reduced the rectal V60mean by 37% and 47% for patients with large and small motion, respectively, due to the possible margin reduction. It has been shown in this work that treatment replanning can become possible in the future. Patients exhibiting large prostate motion will greatly benefit of such on line adaptation strategies, while adaptation could be completely omitted in patients showing small prostate displacements only. For motion classification, pre treatment motion assessment, using repeated imaging sessions, would be the preferable approach. The best suited treatment modality/protocol that way can be determined before a therapy course is started and reduce the additional workload coming from adaptation protocols to a minimum. Treatment replanning still waits for advances in hard- and software development, to ease the entire TRP process and thereby permit integration in a clinical environment. Based on the findings of this work, dedicated motion management is indicated for one fifth of the patients in PT of the prostate.
- ddc:610
Note: The Thesis is presented as a cumulative work of two publications (see linked works). https://repository.gsi.de/record/96010 and https://repository.gsi.de/record/184394 .
Note: Friedrich-Alexander-Universität Erlangen-Nürnberg, Diss., 2015
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Appears in the scientific report 2015
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Journal Article
Scanned ion beam therapy for prostate carcinoma : Comparison of single plan treatment and daily plan-adapted treatment
Strahlentherapie und Onkologie 192(2), 118-126 (2015) [10.1007/s00066-015-0925-0]
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Journal Article
Fast optimization and dose calculation in scanned ion beam therapy
Medical physics 41(7), 071703 (2014) [10.1118/1.4881522]
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