ESTRO 2024 - Abstract Book

S4635

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

Material/Methods:

Full institutional approval was obtained for this dual-centre study. Adult cases with small RCCs were identified from sequential diagnostic CT scans of RCC. These anonymised cases underwent renal SBRT planning using VMAT, CK and PBS PBT platforms across 2 institutions. For VMAT and CK, a 5mm expansion from ITV and CTV respectively was used to PTV. For CK, ITV was not used as fiducial marker insertion was assumed for real-time tracking. For PBS PBT, static serial organs and target volume coverage (ITV) were evaluated under robustness for uncertainties of 5mm (geometric) and 3.5% (range). A dose prescription in routine use for SBRT was utilised; 42Gy in 3 fractions[2]. Cases were stratified to left and right-sided tumours. For all techniques, SBRT plans were created to ensure D95%=100%, with a Dmax between 123-143%. For PBT, target volume coverage was mandated in the worst case scenario. Lowest achievable organ at risk (OARs) doses were then reported for each technique. National dose constraints for 3 fraction SBRT were utilised. Doses to skin, spinal cord, cauda equina, small bowel, duodenum, large bowel, stomach, liver, pancreas, spleen, ipsilateral normal and contralateral kidney were recorded. Means and standard deviations (SD) were calculated.

Results:

Mean tumour diameter was 2.95cm (SD 1.04). Mean volumes for VMAT and CK PTV were 73.58cm 3 and 41.42 cm 3 respectively. CK volumes required a PTV expansion from CTV only. PBT ITV was 38.80cm 3 and 73.70cm 3 including 5mm geometric expansion for robust analysis. All OAR dose constraints were met for each technique (see Table 1). Mean small bowel D0.1cc was 14.8Gy, 12.60Gy and 2.13Gy(RBE), with SD in Table 1, for VMAT, CK and PBT respectively. Mean large bowel D0.1cc was 19.10Gy, 17.78Gy and 8.69Gy(RBE) respectively for VMAT, CK and PBT. Liver doses were minimal. For ipsilateral normal kidney, Dmean was 11.86Gy, 11.20Gy and 6.80Gy(RBE) for VMAT, CK and PBT respectively. Skin D1.5cc was 10.27Gy, 10.50Gy and 20.89Gy(RBE) for VMAT, CK and PBT respectively.