ESTRO 2025 - Abstract Book

S4329

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

143%. Lowest achievable doses were compared for 16 organ-at-risk (OAR) constraints. Medians, interquartile ranges and Wilcoxon’s statistical test (two-tailed, confidence interval 95%) were utilised (GraphPad). Bonferroni Dunn and false discovery rate corrections (1%) (5) were applied.

Results:

25 cases were included with a mean tumour diameter of 5.16cm (SD 2.92). Large cases (n=13) ranged between 4.13-13.12cm and small cases (n=12) between 1.64-3.73cm. Median VMAT and CK PTV volumes were 160.48cm 3 and 97.06cm 3 respectively. Median PBT ITV was 95.54cm 3 and 163.76cm 3 (inclusive of 5mm geometric uncertainty). All median OAR dose constraints were met for each technique, with PBT resulting in statistically significant reductions for all OARs except skin in comparison to photons (see Table 1 ). Median small bowel D0.1cc was 18.85Gy (IQR: 11.250-30.080Gy) for VMAT, 16.65Gy (IQR: 13.240-36.950Gy) for CK and 2.25Gy(RBE) (IQR:0.000-26.340GyRBE) for PBT. Figure 1 shows example dosimetry per technique. Skin dose was significantly higher with PBT but in tolerance. Cases with significant overlap between target and bowel were challenging to meet dose constraints with all 3

techniques.

Conclusion: Median OAR doses met constraints with all 3 techniques. PBT significantly reduced dose to small bowel and for all OARs except skin. PBT had higher, but acceptable, skin doses. PBT could be considered where greater bowel sparing may be particularly important e.g. inflammatory bowel disease. Further prospective work is required to clinically investigate PBT in RCC including effective motion management mitigation strategies.

Acknowledgements NIHR RMH Biomedical Research Centre

Keywords: Renal, SABR, protons

References: cell carcinoma. Lancet Oncol. 2022;23(12):1508-16. 2. Green H et al. SBRT for small renal tumours - a dosimetric comparison using VMAT, CK and protons (digital poster). ESTRO abstract book supplement. 2024.