Journal article
An investigation into the robustness of dynamically collimated proton therapy treatments
Medical physics (Lancaster), Vol.47(8), pp.3545-3553
08/01/2020
DOI: 10.1002/mp.14208
PMCID: PMC7429295
PMID: 32338770
Abstract
Purpose To investigate the dosimetric robustness of dynamically collimated proton therapy (DCPT) treatment plans delivered using a dynamic collimation system (DCS) with respect to random uncertainties in beam spot and collimator position as well as systematic offsets in the DCS mounting alignment. This work also demonstrates a technique that can increase plan robustness while preserving target conformity.
Methods Variability in beam spot and collimator positioning can result in changes to a beamlet's dose distribution and incident fluence. The robustness of the DCPT treatment plans was evaluated for three intracranial treatment sites by modeling treatment variability as normally distributed random variables with standard deviations reflecting a clinical system. The simulated treatment plans were then recalculated and compared against their nominal, idealized dose distribution among several trials. It was hypothesized that a plan's robustness to these delivery variables could be reduced by restricting a trimmer's placement toward a beamlet's central axis during collimation.
Results By introducing a minimum trimmer offset of 1.5 mm, the variation of the planning target volume (PTV) D-95% coverage was reduced to within 2% of the prescribed dose. The treatment plans with trimmers that were placed within 0.5 mm of a collimated beamlet's central axis resulted in the greatest healthy tissue sparing but deviations as high as 11.4% to the PTV D-95% were observed. The nominal conformity of these treatment plans utilizing the 1.5 mm trimmer offset was also well maintained. For each treatment plan studied, the 90% conformity index remained within 6.25% of the conformity index achieved without a minimum trimmer offset, and the D-50% of surrounding healthy tissue increased by no more than 3.1 Gy relative to a plan without a trimmer offset.
Conclusions While DCPT can offer a significant reduction in healthy tissue irradiation, the results from this work indicate that special care must be taken to ensure proper PTV coverage amid uncertainties associated with this new treatment modality. A simple approach utilizing a minimum trimmer offset was able to preserve the majority of the target conformity and healthy tissue sparing the DCS technology affords while minimizing the uncertainties in this treatment approach.
Details
- Title: Subtitle
- An investigation into the robustness of dynamically collimated proton therapy treatments
- Creators
- Blake R. Smith - University of Wisconsin–MadisonDaniel E. Hyer - University of IowaWesley S. Culberson - University of Wisconsin–Madison
- Resource Type
- Journal article
- Publication Details
- Medical physics (Lancaster), Vol.47(8), pp.3545-3553
- DOI
- 10.1002/mp.14208
- PMID
- 32338770
- PMCID
- PMC7429295
- NLM abbreviation
- Med Phys
- ISSN
- 0094-2405
- eISSN
- 2473-4209
- Publisher
- Wiley
- Number of pages
- 9
- Grant note
- R37 CA226518 / NCI NIH HHS; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA; NIH National Cancer Institute (NCI)
- Language
- English
- Date published
- 08/01/2020
- Academic Unit
- Roy J. Carver Department of Biomedical Engineering; Radiation Oncology
- Record Identifier
- 9984312975002771
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