Purpose: This study aims at evaluating the potential clinical efficacy of prostate low dose rate (LDR) brachytherapy when a simultaneously integrated boost (SIB) is incorporated in treatment planning. The boost dose is focused to the dominant intra-prostatic lesion (DIL) determined by 68Ga-Prostate specific membrane antigen (PSMA) PET combined with multi-parametric MRI.
Methods: Seven patients with unfavourable-risk prostate cancer were imaged with PSMA-PET/mpMRI in order to determine the extent of the DIL. All the patients received 110 Gy with D95% of the CTV > 100% of the prescribed dose and 115% < D90% < 120%. Additional seeds were placed in the area of DIL until the tolerance doses of the organs at risk (OARs) were reached. Another set of plans was created in which a standard loading procedure was used without the information by PSMA-PET/mpMRI. The tumor control (TCP) and normal tissue complication probabilities (NTCP) of the targets and OARs were calculated.
Results: Higher TCP values were found for the plans created with SIB to the DIL (97.6±2.2%) compared to standard loading (85.5±26.4%). The DIL V95 value for the two sets of plans were (96.3±8.1%) and (91.0±9.4%), respectively. The NTCP values of rectum were similar (1.4±1.0%) versus (0.8±1.0%) with and without SIB to DIL, respectively. For urethra the NTCP values were negligible in both sets of plans (~0.0%).
Conclusion: The findings of the comparison indicate that higher TCP values are achieved in the plans created with simultaneously integrated boost to the dominant intra-prostatic lesion defined by the PSMA-PET/mpMRI input relative to the plans with standard loading (without SIB to the DIL), while the NTCP values to the OARs are similar. The use of the PSMA-PET/mpMRI technique to delineate the radioresistant intra-prostatic tumors may prove to be effective in LDR brachytherapy in centers with such imaging capabilities.