ESTRO 2025 - Abstract Book

S4388

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

Table 2 summarizes the mean values for the main OARs constraints.

Regarding the dose to the OARs, there appears to be greater sparing with the MLC collimator compared to IRIS one, except for the bladder. However the mean values are comparable between the two collimators, and the differences are not significant in almost all cases (Table 2). Conclusion: Preliminary results suggest clear advantages of the MLC collimator over IRIS for CyberKnife SBRT treatment of prostate cancer, particularly in terms of beam on time and monitor units (MUs). As for the key dosimetric parameters, the mean values between the two collimators are comparable, but there are significant differences in the case of CI, nCI, HI, and GI25 (Table 1): • MLC provides a more conformal dose (lower CI and nCI); • IRIS shows greater dose excursion to the target (higher HI); • GI25 is lower with MLC. Further investigation with a larger sample size is needed to determine whether the use of IRIS collimator may offer significant dose sparing to the OARs, potentially allowing for its use in cases of specific toxicity concerns.

Keywords: CyberKnife. SBRT. IGRT.