Abstract:
:Proton therapy is very sensitive to daily density changes along the pencil beam paths. The purpose of this study is to develop and evaluate an automated method for adaptation of IMPT plans to compensate for these daily tissue density variations. A two-step restoration method for 'densities-of-the-day' was created: (1) restoration of spot positions (Bragg peaks) by adapting the energy of each pencil beam to the new water equivalent path length; and (2) re-optimization of pencil beam weights by minimizing the dosimetric difference with the planned dose distribution, using a fast and exact quadratic solver. The method was developed and evaluated using 8-10 repeat CT scans of 10 prostate cancer patients. Experiments demonstrated that giving a high weight to the PTV in the re-optimization resulted in clinically acceptable restorations. For all scans we obtained V 95% ⩾ 98% and V 107% ⩽ 2%. For the bladder, the differences between the restored and the intended treatment plan were below +2 Gy and +2%-point. The rectum differences were below +2 Gy and +2%-point for 90% of the scans. In the remaining scans the rectum was filled with air, which partly overlapped with the PTV. The air cavity distorted the Bragg peak resulting in less favorable rectum doses.
journal_name
Phys Med Bioljournal_title
Physics in medicine and biologyauthors
Jagt T,Breedveld S,van de Water S,Heijmen B,Hoogeman Mdoi
10.1088/1361-6560/aa5c12subject
Has Abstractpub_date
2017-06-07 00:00:00pages
4254-4272issue
11eissn
0031-9155issn
1361-6560journal_volume
62pub_type
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