Room: AAPM ePoster Library
To assess the feasibility of using a CBCT-based monitoring system for detecting dosimetric deviations from plan and the need for corrective action during a course of conventionally fractionated treatment for advanced stage lung cancer.
A novel in-house monitoring framework was used to retrospectively analyze a dataset consisting of 15 patients, treated post-kV X-ray image guidance. The IGRT protocol included either daily or weekly CBCTs. The framework is based on a set of scripts automatizing the monitoring of new IGRT data acquisitions, data transfer, planning CT-to-CBCT registrations and dose recalculation on CBCTs using the RayStation™ treatment planning system. From dose calculated on all 287 CBCTs we analyzed DVH metrics and a measure of correlation (Pearson Correlation Coefficient, PCC) between HU of the target ROIs in planning CT and each of the CBCTs. DVH metrics changes larger than 5% and PCCs below 0.75 were considered thresholds for plan review and modification.
Of 15 patients, 8 showed relatively stable PCC and DVH metrics, 7 exhibited a progressive PCC decrease to below threshold – and of these, 3 were rescanned and replanned, due to weight loss, tumor response or position changes. D98 exhibited some correlation with PCC in 3 out of the 7 decreasing trends. The PTV coverage degradation correlated with below-threshold PCC in 3 patients.
Tracking changes in PCC and DVH metrics in lung radiation treatment reduces reliance on purely visual examination of IGRT data. Predetermined criteria for replan may help clinical staff to act sooner in dealing with dosimetric deficiencies. To optimize the use of quality metrics and fully validate this approach we plan on further patient accrual to this study.