ESTRO 2024 - Abstract Book

S2376

Clinical - Urology

ESTRO 2024

In total 44 treatment fractions with 132 MRIs were included in this analysis. Eight PT-MRIs were excluded due to potential patient movement. The mean deviation and range of the prostate position over all patients and fractions was M=0.0 [-0.5 – 0.3] cm, 0.1 [-0.2 – 1.4] cm, 0.1 [-0.1 – 0.5] cm and 0.3 [0.0 – 1.4] cm for LR, SI, AP and d, respectively (Fig. 1). For the SV positions, mean deviation and range were 0.0 [-0.3 – 0.3] cm, 0.1 [-0.2 – 0.5] cm, 0.2 [- 0.2 – 0.7] cm and 0.3 [0.1 – 0.7] cm for LR, SI, AP and d, respectively. Table 1 summarizes the SDs for random and systematic errors. Overall, position deviations for both targets were small. For SI and AP, more positive shifts were observed, indicating a preference towards inferior and posterior positions of the targets, possibly caused by intrafractional bladder filling.

Conclusion:

This study demonstrated that the residual intrafractional movement of prostate and SV was negligible using a RB, even during lengthy ultrahypofractionated MRIgRT of the prostate. However, when using no RB, the stability of the