Mismatch between clinical and pathological T stage among patients with suspected renal cell carcinoma undergoing surgery: Potential implications for target volume delineation and Stereotactic Body Radiotherapy (SBRT) implementation for localized renal masses

Introduction & Objectives: Stereotactic Body Radiotherapy (SBRT) is an emerging treatment option for selected patients with localized renal masses suspected of renal cell carcinoma (RCC). In this regard, identification of the target is critical for SBRT delivery. Ideally, all tumor tissue should be included within treatment volume, and precise identification of disease is crucial to spare normal kidney parenchyma and treat with ablative intent RCC. Correlative data evaluating the concordance between pre-operative imaging and histopathology specimen would allow to choose the best imaging method for this task. Materials & Methods: After Institutional Review Board approval, we retrospectively queried a multi-institutional database promoted by the EAU Young Academic Urologists (YAU) Renal Cancer working group to select patients with a single renal mass suspected of RCC treated with either partial or radical nephrectomy at 13 referral centers worldwide from 2015 to 2022. For this study, we included patients with available preoperative cross-sectional imaging scans (CT or MRI). The Maximum lesion diameters measured on preoperative imaging and histopathology specimens of all patients were compared to evaluate the downstaging or upstaging performance of each imaging method vs pathologic assessment. Mann-Whitney test was performed to compare the mean difference between diameter on pathology specimen and imaging (ΔDiam) in patients undergoing preoperative MRI or CT scan. ΔDiam was significantly smaller for patients undergoing preoperative MRI if compared to CT scan (-0.1 cm vs +0.4 cm, p<0.0001), with a significant trend for upstaging after CT scan (e.g larger than expected lesions on histopathology in these patients). Conclusions: Our data from a surgical registry suggest that a non-negligible proportion of patients may be down-/upstaged by preoperative imaging. Regarding SBRT, this may increase the risk of peripheral underdosage of target lesions, or unnecessary inclusion of normal renal parenchyma inside treatment volume. Of note, MRI may increase reliability of target delineation, and should be probably implemented in clinical practice for this purpose. Whether further refinement of target delineation may be obtained with different imaging (e.g Girentuximab PET/CT) or if MRI-guided SBRT should be considered a preferred approach in this scenario, are potential areas of exploration.