The contribution of surgical clips for optimizing highly-conformal image-guided flank irradiation in pediatric renal tumors: a single center experience

Background and aims: Two-opposing photon beams are considered standard of care for flank irradiation in pediatric patients with renal tumors. Nowadays, Image-Guided Radiotherapy (IGRT) techniques allow high-precision dose delivery to complex flank target volumes taking into account postoperative organ shifts and tumor bed motion. This study examines the contribution of a lateral and superior surgical clip on flank target volume delineation intended for IGRT. Methods: Between 01-2015 and 09-2019, 30/162 newly-diagnosed pediatric patients with renal tumors, lateral/superior surgical clips (n = 30/30) and available 4D-CT-scans (n = 27/30), underwent postoperative flank irradiation. The lateral and superior clip, as respective markers for the lateral tumor extension and intrafraction motion, were analyzed. The positive and negative values depict the lateral/dorsal/cranial or the medial/ventral/caudal direction, respectively. Planning target volumes (PTV) were generated based on lateral clips (PTV _latclip), superior clips with 4D-CT technology (PTV _supclip), and both clips combined (PTV _combined), and compared to an approach without clips (PTV _noclip). Results: Indicated by clips, the mean lateral tumor bed extension along the posterior wall was 74° (range: 50°–93°), while mean intrafraction motion was +1.2 mm (range: −1.8/+4.8 mm), +0.6 mm (range: +0.6/+4.9 mm), −0.3 mm (range: −3.8/+0.7 mm) in craniocaudal, ventrodorsal, mediolateral direction, respectively. The median PTV _noclip (556 mL) was statistically different from the median PTV _latclip (454 mL, p = <0.01), median PTV _supclip (373 mL, p = <0.01) and median PTV _combined (348 mL p = <0.01). Conclusion: In pediatric patients with renal tumors, surgical clips at the lateral and superior border of the tumor bed can optimize flank target volume delineation and, consequently, reduce the normal tissue volume receiving high-dose irradiation when IGRT techniques are applied.