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Session: Proton Therapy I [Return to Session]

A Treatment Planning Study Comparing LET- and Variable RBE-Based Optimization for Intensity-Modulated Proton Therapy

H Moazami Goudarzi1, G Lim2, D Grosshans3, R Mohan4, W Cao5*, (1) University of Houston, Houston, TX, (2) University of Houston, Houston, TX, (3) UT MD Anderson Cancer Center, Houston, TX, (4) UT MD Anderson Cancer Center, Houston, TX, (5) UT MD Anderson Cancer Center, Houston, TX


SU-H330-IePD-F4-4 (Sunday, 7/10/2022) 3:30 PM - 4:00 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 4

Purpose: To evaluate the dosimetric impact of considering linear energy transfer (LET) and variable relative biological effectiveness (RBE) of protons in optimizing intensity-modulated proton therapy (IMPT) plans.

Methods: This study included 10 pediatric brain cancer patients. Three IMPT plans were generated using variable RBE-based, LET-based and constant RBE-based optimization, respectively, for each patient. Optimization algorithms were implemented in a research treatment planning system (matRad), which uses an analytical algorithm to compute physical dose and LET. A phenomenological RBE model was used in variable RBE optimization and evaluation. All plans were normalized to ensure 90% of the clinical treatment volume (CTV) receiving a prescription dose of 54 Gy (RBE).

Results: The homogeneity index and the Paddick conformity index were 1.10±0.02 and 0.85±0.04 for all plans. LET-optimized plans achieved average increases of 18.5% and 17.3% for mean LET in the CTV among the 10 patients compared to variable and constant RBE-optimized plans. The average biological effective EUDs (i.e., based variable RBE-weighted dose) for the CTV among all patients were 55.0 Gy, 64.7 Gy and 66.1 Gy in variable RBE for variable RBE-, constant RBE- and LET-optimized plans, respectively. The corresponding EUDs using a constant RBE of 1.1were 45.6 Gy, 54.8 Gy and 54.6 Gy. The averaged biological effective EUDs of brainstem and spinal cord were 44.8 Gy and 29.0 Gy for variable RBE-optimized plans, but 52.5 Gy and 36.7 Gy for constant RBE-optimized plans and 53.5 Gy and 37.1 Gy for LET-optimized plans.

Conclusion: LET-based optimization outperformed both constant and variable RBE-based optimization in improving LET distribution. Variable RBE-based optimization showed minor advantage in target dose but a significant reduction in dose to normal tissues compared to constant RBE- and LET-based optimization.

Funding Support, Disclosures, and Conflict of Interest: This work is supported partly by NIH R03CA256220 and P01CA261669.


Protons, LET, RBE


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

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