On the Feasibility of RTapp™ as a Daily Delivered Dose Evaluation Tool for Adaptive Lung Stereotactic Body Radiation Therapy (SBRT)

Abstract

RTapp™ is a daily dose evaluation software developed by ©SegAna LLC. It utilizes deformable image registration (DIR) to update patient anatomy based on daily cone-beam CT and assess the dose distribution according to the detected changes. RTapp™ can be a useful tool in lung stereotactic body radiation therapy (SBRT) to avoid underdosing target and overdosing organs at risk (OARs). In this study, the feasibility of RTapp™ to assess the quality of treatment delivered in every fraction was investigated in a retrospective analysis of 20 lung SBRT patients. For each patient, the simulation CT images, treatment structures, plan, and dose from Pinnacle3 treatment planning system, daily CBCT from MOSAIQ record and verify system, and pre-treatment couch alignment information from Varian on-board imaging (OBI) software were imported into the RTapp™ software. Bidirectional DIR was applied to update the planning target volumes and OARs and the dose distribution to the patient's daily anatomy. The ability of RTapp™ to deform structures were validated by evaluating Dice coefficient (DC) and Hausdorff distance (HD) between the deformed RTapp™ ITV (rtITV) and physician-drawn ITV (pITV). The accuracy of dose calculations by RTapp™ was evaluated by recalculating the doses with Pinnacle3 for the target coverage and several dose metrics to lungs, heart, cord, esophagus, and airway. Ten, three, and one out of 20 patients showed more than 5% decrease in PTV V100%, PTV V90%, and both ITV V100% and GTV V100%, respectively. The mean (± standard deviation) values of the DC ranged from 0.75 to 0.81, with a mean of 0.78 ± 0.03, indicating good overlap between the rtITV and pITV. Meanwhile, the average, 95%, and maximum HD had mean values (± standard deviation) 1.44 ± 0.27 mm, 3.61 ±0.62 mm and 6.14 ± 1.24 mm respectively. The difference in the PTV coverage had the largest variation. 97% of the fractions had the ITV and GTV coverage difference within ± 2.5%. The difference in the dose to OARs was the highest in regions with a steep dose gradient, specifically, the dose to lungs. The ability of RTapp™ as a daily dose evaluation tool to maintain the quality of lung SBRT treatment was validated. The fast auto-segmentation and dose distribution updates according to daily anatomical changes provided by the RTappTM software is highly beneficial as a step towards the realization of adaptive radiation therapy without introducing time and resource constraints. However, further studies are necessary to validate the accuracy of RTapp™ DIR for clinical applications.