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Evaluation of Range Robustness for a Dynamically Collimated Proton Therapy Treatment Plan

L Bennett1*, D Hyer1, K Erhart2, B Smith3, N Nelson3, T Geoghegan1, P Hill3, R Flynn1, (1) University of Iowa, Iowa City, IA, (2) .decimal LLC, Sanford, FL, (3) University of Wisconsin, Madison, WI

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To assess the robustness of proton therapy treatment plans generated using a dynamic collimation system (DCS) to range uncertainty. The use of a DCS sharpens the lateral dose distributions at all beam energies and has the potential to increase the sensitivity of dose distributions to range uncertainty, decreasing robustness.


Methods: Two patients that were previously treated for brain tumors using traditional pencil beam scanning (PBS) proton therapy were re-planned in the Astroid Proton Treatment Planning System (.decimal, Sanford, FL). For each patient, both an uncollimated PBS plan and a DCS proton beam treatment plan were generated and optimized using multicriteria optimization. Range uncertainty was evaluated for each case by recalculating the dose from the optimized plans with ± 3% error in the relative stopping power distribution to simulate systematic overshoot and undershoot, resulting in a total of six plans for each patient.


Results: DCS plans were marginally less robust than uncollimated plans. Mean CTV dose for DCS plans had a mean error of 0.23% compared with a mean error of 0.05% for PBS plans with no collimation. Max CTV dose demonstrated similar errors, with DCS plans generating a mean error of 2.24% compared with 1.68% for uncollimated PBS plans. OAR doses demonstrated comparable errors, with mean error in dose to the 10 mm expansion around the PTV of 3.75% for DCS plans and 3.25% for uncollimated PBS plans. For the patient with the most affected organs at risk, mean error in maximum dose to the pituitary, hypothalamus, and optic chiasm was 14.60% (DCS) and 13.58% (PBS), 6.17% (DCS) and 6.26% (PBS), and 2.29% (DCS) and 2.56% (PBS).


Conclusion: DCS plans maintain an acceptable degree of robustness while providing superior target conformity and healthy tissue sparing.

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Funding Support, Disclosures, and Conflict of Interest: Research reported in this abstract was supported by the National Cancer Institute of the National Institutes of Health under award number R37CA226518. Hyer, Flynn, and Hill are co-inventors on a patent that has been licensed to IBA.

Keywords

Protons, Beam Shaping, Collimation

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – Development (new technology and techniques)

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