Stereotactic ablative body radiotherapy (SABR) is an emerging indication for localized renal cell carcinoma (RCC), yet there is a need for standardizing contouring practices, as accurate target delineation is essential to ensure optimal outcomes. Our objective was to develop consensus guidelines for target volume contouring for RCC SABR.

An international panel of RCC SABR experts affiliated with XXXXXX was convened. All were asked to contour target volumes for four relevant clinical scenarios: a large tumor (>10cm) with IVC tumor thrombus; a central tumor abutting the renal hilum; a local recurrence following nephrectomy; and an ablation cavity recurrence after radiofrequency ablation. Participants also contoured two investigational renal substructures: renal cortex and renal hilum. Contours by case were analyzed using a STAPLE algorithm (95% confidence level). Consensus contours & guidelines statements were discussed and refined over two consensus meetings. Measures of variance and agreement, including Dice Similarity Coefficients (DSC), Mean Distance to Agreement (MDA), and Hausdorff Distance (HD), were measured for each case.

In total, 16 radiation oncologists participated. The median DSC was 0.85, and the median MDA/HD were 2.17 mm/9.00 mm respectively. The median DSC was greater than 0.70 for each case, suggesting 'good agreement' among participants. Based on the consensus discussion, any tumor thrombus or ablation cavity should be included in the target volume; organ at risk dose constraints should take priority over target coverage in planning; and the ipsilateral renal cortex should be defined as the ipsilateral renal parenchyma, excluding the target volume, the renal pelvis, renal vasculature, and proximal ureter.

We present the first international consensus contouring guideline for RCC SABR. There was strong agreement amongst experts, yielding high-fidelity consensus contours and guidance statements for each scenario. These results can be used as a guide for radiation oncologists interested in using SABR to treat patients with localized RCC.