Poster — Thur Eve — 61: Intensity Modulated Radiation Therapy: The Relationship between Planar Dose Map Verification and Dosimetric Outcome

Abstract

This work analyses the consequences of random and systematic dose differences in the comparison of calculated against measured planar dose distributions for IMRT from the perspective of a surrogate of the treatment outcome: Equivalent Uniform Dose (EUD). In‐house software was developed to incorporate normally distributed errors in the fluence maps of 3 head and neck (H&N) and 3 prostate plans and simulate dose differences that appear randomly across the planar dose maps. The plans with random errors were grouped according to the following passing rates: 1) 90–95%, 2)85–90% and 3)80–85% during patient specific quality control. The passing criteria included a 3% absolute dose, 3 mm distance to agreement (DTA), and a minimum dose difference of 2 cGy. A systematic 1% dose error could also be incorporated by altering the MUs of each plan with random errors. The impact of random errors on the prescribed EUDs of H&N plans ranged from −2.7 to −1.3% for the CTV and −1.0 to 0.6 Gy for the OARs while in prostate plans they ranged from −1.6 to −0.6% for the CTV and −1.2 to −0.4 Gy for the OARs over the range examined. The criterion of 90% passing rate for 3% absolute dose and 3 mm DTA kept the effects of random errors within a dosimetric goal of 2% change in prescribed EUDs of the targets and 2 Gy for the OARs. Systematic errors, if present, may cause larger effects on clinical dosimetry while still meeting patient specific quality control tolerances.