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Monte Carlo Based Treatment Plan Optimization for Intensity Modulated Proton Therapy

R Kueng1, H A Loebner*1, S Mueller1, D Frei1, W Volken1, D M Aebersold1, M F M Stampanoni2, M K Fix1, P Manser1, (1) Inselspital, Bern University Hospital, and University of Bern, Bern, CH, (2) ETH Zurich and PSI, Villigen, CH

Presentations

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

Room: AAPM ePoster Library

Purpose:
To develop Monte Carlo (MC)-based plan optimization for intensity modulated proton therapy (IMPT) and to compare the resulting spot scanning proton plans to MC re-calculated plans generated in a commercial treatment planning system (TPS).

Methods:
The Eclipse TPS is used to generate a three field IMPT plan for the ProBeam?? spot scanning system (Varian Medical Systems) for a clinically motivated head and neck case. The same spot candidates are used to generate a MC-based in-house IMPT plan using a framework to calculate dose distributions of the individual spots with the proton Macro Monte Carlo (pMMC) algorithm. Fluence map optimization of spot weights is performed using a quasi-Newton L-BFGS algorithm with dose volume objectives set on the target volume and organs at risk. The in-house IMPT plan is compared to the MC re-calculated proton plan created in the commercial TPS by means of dose differences and dosimetric parameters.

Results:
Compared to the MC re-calculation of the TPS plan, the in-house optimized plan shows a more conformal dose distribution to the target volume with dose difference in the normal tissue up to -30% (-20 Gy). PTV homogeneity is improved and dose to organs at risk such as inner ear and lacrimal gland is substantially reduced (mean dose -4.2 Gy and -2.5 Gy, respectively) with the in-house IMPT plan compared to the TPS plan.

Conclusion:
An MC-based in-house framework to generate IMPT plans was successfully developed. MC-based optimization shows dosimetric advantages for conformity, target homogeneity and organ at risk sparing.

Download ePoster [PDF]

Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by Varian Medical Systems.

Keywords

Protons, Optimization, Monte Carlo

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – dose optimization

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