SU-E-T-188: Evaluation of a 3D Patient Relevant Dose QA Tool: Multiple Institutional Studies

To evaluate 3DVHTM as a patient dose-verification and analysis tool through multiple institutional studies. Virtual patient doses were measured and compared among different vendors' treatment planning systems (TPS) and delivered by different vendors' LINACS so that we better understand the uncertainty of entire process within a patient undergone radiotherapy.

One head-and-neck (H&N) and one lung patient were selected in this study. The DICOM images/RT structures along with clinical protocols including prescription doses (59.4Gy for H&N and 70.2Gy for lung) and normal‐tissues tolerances were distributed to six institutions. Based on the same criteria, each institution generated their IMRT plans for the patients. Four different TPS and six different LINACS were used. The conventional per‐beam IMRT QA using MapCHECK was performed by all participants. All the measured and calculated data were sent back to one institution for 3DVH analysis. Through the use of planned-dose-perturbation (PDP)TM algorithm (Sun Nuclear Corp.), the 'actual-DVHs' were generated and then compared to the 'reference-DVHs' from plans. Their differences represented errors induced from the combination of TPS dose-calculation algorithm and beam-delivery systems.

All plans in the study have met the clinical criteria. The 3D matching rates for 3%global/3mm (DD/DTA) ranged from 95.8-99.9% for H&N and 93.5-100% for lung. The dose-difference-histogram for PTV had a mean of 0.67% [0-2%] for H&N cases and 1% [0.6-2.8%] for lung cases. The QA tool was able to spot the doses outside 3%/3mm criteria for critical structures much easier than conventional planar QA methods. In addition, the hot/cold spots at the boundaries of collimators are attributed to the uncertainty of collimator-positioning greater than 1-mm.

The analysis of IMRT plans in this study has shown that 3DVH is a vital QA tool for assessing clinically relevant doses as well as diagnosing potential systematic errors from both TPS and delivery systems.