3294 - A Comprehensive Evaluation of an Independent Quality Assurance System for Intensity Modulated Proton Therapy Treatment Plans and Deliveries

Z. Su¹, W. C. Hsi¹, M. Oneil², and P. Sabouri³; ¹Department of Radiation Oncology, University of Arkansas for Medical Sciences, Little Rock, AR, ²IBA (Ion Beam Applications), Louvain-la-Neuve, United States, ³Department of Radiation Oncology, UAMS Winthrop P. Rockefeller Cancer Institute, University of Arkansas for Medical Sciences, Little Rock, AR

Purpose/Objective(s): To perform quality assurance (QA) of initial patient IMPT treatment plans and monitoring dose delivered of each fractional, a software, myQA Ion PT (myQA-ION) system was validated and evaluated using commissioning data and patient data. Materials/

Methods: In myQA-ION, the Monte Carlo (MC) dose engine was commissioned for the Proteus One (P1) proton system based on measured commissioning data, which was also used for commissioning of P1 in our treatment planning system (TPS). Single spots and 10x10cm² single layers for 7 energies ranging from 70 to 226MeV. The spot sizes, R90 and distal falloff of the extracted PDDs of the 7 energies were compared to the measured commissioning data. The 3D Gamma values (down to 1%,1mm) were obtained to validate the myQA-ION system against TPS for these single spot and single layer plans. Patient IMPT plans from sites of brain, HN, thoracic, and pelvic were sent to myQA-ION for 3D gamma comparisons. Treatment delivery logs of each proton beam of these patients were also imported into the myQA-ION to calculate per beam fractional dose on patient simulation CTs. Gamma tests of the irradiated volumes, PTV, and OARs were also obtained.
Results: The myQA-ION P1 model calculated spot size, range, distal falloff, and field size of the single spot and square fields are in good agreement with the commissioning measurement data. The 3D gamma comparisons of single spot and energy layers showed minimum 97.7% for 1% and 1mm criteria (see Table) for 70MeV, which has sharpest dose fall off, thus was partially affected by 1mm dose grid resolutions of both TPS and myQA-ION. For patient plans, the global gamma (3%, 3mm) of irradiate volume has the values of 99.5% +/- 0.6%; gamma of PTV has the values of 99.9% +/- 0.12%; gamma of OARs has the values of 99.9% +/- 0.04%. For recalculated patient dose of treatment logs, the gamma of irradiated volume per beam has the values of 98.5% +/- 1.2%, the gamma values for PTV and OAR has the minimum values of 98.8% +/- 0.2%. The trend of gamma test of treatment log to TPS dose is consistent among different fractions.
Conclusion: The validation of myQA-ION system demonstrated high fidelity between its calculated spots and PDDs and the commissioning data and proved by their high gamma pass rate (1%,1mm criteria) of the 3D dose between TPS and myQA-ION. The independent myQA-ION calculated treatment plans and the treatment log-based dose verification provides safe and more efficient delivery based IMPT QA and per fraction dose auto monitoring.

Abstract 3294 – Table 1

		Gamma Analyses (TPS vs myQA-ION)					R90 Difference	Distall falloff Difference	Spot Size Difference
Energy (MeV)	Type	3%, 3mm	2%,2mm	1%, 2mm	2%, 1mm	1%, 1mm	(MC-Measured) (mm)	(MC-Measured) (mm)	(MC-Measured) (mm)
70	spot	99.97	99.92	99.88	98.12	97.66	-0.2	0.1	0.01
100	spot	100	99.99	99.95	99.18	99.04	0	0.1	-0.01
125	spot	100	99.98	99.96	99.32	99.14	-0.1	0	-0.01
150	spot	100	99.98	99.97	99.57	99.47	-0.1	0	0.05
175	spot	100	99.99	99.98	99.65	99.5	-0.3	0	0.03
200	spot	100	99.99	99.98	99.74	99.48	-0.4	0.2	0.01
226	spot	100	99.99	99.9	99.76	99.33	-0.1	0	-0.01