SU-G-TeP4-11: Implementation of a Non-Measurement-Based Patient-Specific IMRT QA Program




To implement a comprehensive non-measurement-based verification program for patient-specific IMRT QA


Based on published guidelines, a robust IMRT QA program should assess the following components: 1) accuracy of dose calculation, 2) accuracy of data transfer from the treatment planning system (TPS) to the record-and-verify (RV) system, 3) treatment plan deliverability, and 4) accuracy of plan delivery.


We have implemented an IMRT QA program that consist of four components: 1) an independent re-calculation of the dose distribution in the patient anatomy with a commercial secondary dose calculation program: Mobius3D (Mobius Medical Systems, Houston, TX), with dose accuracy evaluation using gamma analysis, PTV mean dose, PTV coverage to 95%, and organ-at-risk mean dose; 2) an automated in-house-developed plan comparison system that compares all relevant plan parameters such as MU, MLC position, beam iso-center position, collimator, gantry, couch, field size settings, and bolus placement, etc. between the plan and the RV system; 3) use of the RV system to check the plan deliverability and further confirm using “mode-up” function on treatment console for plans receiving warning; and 4) implementation of a comprehensive weekly MLC QA, in addition to routine accelerator monthly and daily QA. Among 1200 verifications, there were 9 cases of suspicious calculations, 5 cases of delivery failure, no data transfer errors, and no failure of weekly MLC QA. These 9 suspicious cases were due to the PTV extending to the skin or to heterogeneity correction effects, which would not have been caught using phantom measurement-based QA. The delivery failure was due to the rounding variation of MLC position between the planning system and RV system.


A very efficient, yet comprehensive, non-measurement-based patient-specific QA program has been implemented and used clinically for about 18 months with excellent results