International Harmonization of Technical Approaches to Kidney SABR – An International Radiosurgery Consortium of the Kidney (IROCK) Contouring Project

Stereotactic ablative body radiotherapy (SABR) is an emerging treatment for patients with primary renal cell carcinoma (RCC), however variation in treatment protocols can exist between institutions. The goals of this study were to measure the variation in contouring RCC tumors for patients being treated with SABR and to develop consensus recommendations. An international panel of 16 radiation oncologists was created from the IROCK meeting during ASTRO 2023. Four patient cases were: Case 1, a renal tumor greater than 10 cm in size with an IVC tumor thrombus; Case 2, a central renal tumor abutting the renal hilum; Case 3, a local recurrence of RCC post-nephrectomy; and Case 4, a residual tumor post-radiofrequency ablation (RFA). For each Case, panelists were asked for radiation planning details and to contour the target volumes on representative axial images using a computer-based training tool. Comparison of panelist contours with the were performed using the Dice-Similarity Coefficient (DSC), the Mean Distance to Agreement (MDA) and the Hausdorff Distance (HD). The DSC measures the overlap between two contours, so a higher DSC suggests greater agreement. The MDA and HD represent the mean and maximum distances between points on the two contours, so higher MDA and HD represent lower agreement. Consensus target volumes were derived using the STAPLE algorithm and discussed amongst the panel. Altogether, the panel included radiation oncologists from Canada, the USA, Australia, the Netherlands, and India. All panelists had previously treated at least 10 patients with SABR for primary RCC. Table 1 shows the DSC, MDA and HD for each case. Using an ANOVA analysis, for all Cases, the DSC, MDA and HD were not statistically different between participants (p = 0.32, p = 0.24, and p = 0.23, respectively). On qualitative inspection of participant contours, Case 4 showed the most agreement, followed by Case 3, Case 2, and then Case 1. There was good agreement from our international expert panel on contouring renal tumors in all four Cases, with Case 4 having the greatest agreement, and Case 1 having the least agreement. Consensus recommendations based on this study may help improve the quality of SABR for RCC moving forward.