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Session: Therapy: Particle Therapy Verification [Return to Session]

Validation of a Commercial Treatment Planning System for Small-Field Patient-Specific Apertures in Pencil Beam Scanning Proton Therapy

J Holmes1*, J Shen1, J Shan1, W Wong1, R Foote2, S Patel1, M Bues1, W Liu1, (1) Mayo Clinic, Phoenix, AZ, (2) Mayo Clinic, Rochester, MN


TU-IePD-TRACK 5-3 (Tuesday, 7/27/2021) 3:00 PM - 3:30 PM [Eastern Time (GMT-4)]

Purpose: Patient-specific apertures are increasingly being studied and developed for pencil beam scanning proton therapy. RayStationᵀᴹ, a commercial treatment planning system, is capable of simulating apertures and has previously been validated for general use, however validation is needed for small fields with apertures. This work aims to validate the modelling of apertures with small openings in RayStationᵀᴹ by comparison to in-water point-dose and film measurements and by cross-validation in patient geometries with MCsquare, an open source Monte Carlo dose calculation engine.

Methods: The original MCsquare does not support apertures. We enhanced MCsquare to support apertures for cross-validating RayStationᵀᴹ. Apertures with openings of 1,2,3,4, and 5 cm have been manufactured and used in the irradiation of proton beams in a water phantom. Two setups were used in the irradiation, one with a range shifter and the other without. The doses were measured in the phantom using point-dose detectors and films and were cross-validated by the enhanced MCsquare. We further cross-validated MCsquare and RayStationᵀᴹ for 10 small-field treatment plans in patient geometries.

Results: Comparing to the absolute point-dose in-water measurements, MCsquare differed by 1.8% ± 3.6% while RayStationᵀᴹ differed by 1.2% ± 1.0%. Compared to the in-water film measurements, MCsquare and RayStationᵀᴹ both performed well with an average 2D Gamma passing-rate of 99.7% and 99.4% (3%/3mm) respectively. A t-test by comparing the film measurements’ agreement to the calculation results between MCsquare and RayStationᵀᴹ suggests that the dose distributions calculated by MCsquare and RayStationᵀᴹ are statistically indistinguishable. Directly comparing the dose calculations between MCsquare and RayStationᵀᴹ over 10 patients resulted in 3D Gamma passing-rates of 98.5% (3%/3mm) and 94.1% (2%/2mm) respectively, where the average target volume size was 8.3 cc.

Conclusion: RayStationᵀᴹ and the enhanced MCsquare were validated for small field dose calculation with patient-specific apertures in pencil beam scanning proton therapy.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by Arizona Biomedical Research Commission Investigator Award, the Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, and the Kemper Marley Foundation.



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