Author: Chia-Lung Chien, Wen C. Hsi, Faraz Kalantari, Pouya Sabouri, Man Yam 👨🔬
Affiliation: Department of Radiation Oncology, University of Arkansas for Medical Sciences (UAMS) 🌍
Purpose:
Reducing treatment delivery time is critical to improving patient throughput and minimizing the risk of intrafraction motion, which can compromise treatment accuracy. This study identifies the optimal minimum monitor unit per energy layer (MMPEL) for intensity modulated proton therapy (IMPT) breast plans delivered using the IBA ProteusOne. By systematically evaluating the trade-offs between delivery efficiency and plan quality, we aim to establish a MMPEL threshold that minimizes beam delivery time while maintaining robust target coverage and dosimetric integrity.
Methods:
Clinical plans for five breast cancer patients were re-optimized in the RayStation treatment planning system (RaySearch Labs, Sweden) by incrementally increasing the minimum MU threshold, without altering any other parameters. MU values were modified starting from a default value of 0.015MU until coverage or OAR doses were compromised. Plan quality was assessed using the worst-case scenario (ensuring at least 95% coverage of the CTV at 95% of the prescribed dose) based on a robustness evaluation with 5mm/3.5% uncertainty. The delivery time was estimated using an in-house tool based on the number of energy layers and of spots in each field.
Results:
No degradation in plan quality was observed until a minimum spot MU of 0.1 which is nearly sevenfold greater than the default minimum MU. Approximately, 20% beam delivery time reduction (~1 minute per field) was observed for this increase. The optimal MMPEL was determined to be around 0.1 MU.
Conclusion:
Increasing the minimum monitor unit per energy layer (MMPEL) to approximately 0.1 MU can significantly reduce treatment delivery time without compromising plan quality. The results highlight the potential for optimizing MMPEL settings to improve clinical efficiency in intensity-modulated proton therapy (IMPT) for breast cancer, thereby enhancing patient throughput while maintaining robust dosimetric outcomes.