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Improving IMPT Delivery Efficiency by Increasing Minimum Spot MU in Plan Optimization

Mingyao Zhu, Katja Langen, University of Maryland School of Medicine, Maryland Proton Treatment Center, Baltimore, MD


(Sunday, 7/14/2019) 3:00 PM - 3:30 PM

Room: Exhibit Hall | Forum 7

Purpose: Intensity modulated proton therapy (IMPT) beam delivery time is proportional to target size and can take several minutes for breast treatments. This work explores the possibility of improving beam delivery efficiency for breast IMPT treatments by increasing the minimum spot MU during plan optimization without compromising plan quality.

Methods: A total of ten IMPT plans were created in a commercial TPS for 2 patients, a left-sided breast (patient 1) and a bi-lateral breast (patient 2), both with comprehensive lymph nodes. All plans used a 2-field beam arrangement. The minimum spot MU was set to 1, 2, 3, 4, and 5 MU while optimizing plan 1, 2, 3, 4, and 5, respectively. All plans were optimized to 5040 cGy (180 cGy x 28) covering 95% of the clinical target volume (CTV) and the same organ-at-risk (OAR) constraints were used. The ten plans were subsequently delivered using a clinical IMPT system; the beam-on time was recorded and compared.

Results: The CTVs were 1323 milliliter for patient 1 and 2184 milliliter for patient 2. CTV D1 were 105.10±0.05% for patient 1 and 104.37±0.03% for patient 2; and there was no difference in the OAR doses among the 5 plans for each patient. The delivery time ranges from 1.48 minutes to 5.38 minutes per beam. Plans with higher minimum spot MU delivered within less time; compared with plan 1 (minimum MU was 1MU), the beam-on time reduced 31.9-34.7%, 43.8-47.4%, 46.6-49.5%, and 48.9-51.9% when the minimum MU were increased to 2MU, 3MU, 4MU, and 5 MU, respectively.

Conclusion: Increasing the minimum spot MU reduces the beam delivery time without compromising plan quality. This method can improve IMPT treatment delivery efficiency, decrease the waiting time for multi-room proton treatment facility, and increase patient throughput.


Protons, Optimization


TH- External Beam- Particle therapy: Proton therapy - treatment planning/virtual clinical studies

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