Evaluation of intensity modulated radiation therapy dose painting for localized prostate cancer using 68Ga-HBED-CC PSMA-PET/CT: A planning study based on histopathology reference

Purpose To demonstrate the feasibility and to evaluate the tumour control probability (TCP) and normal tissue complication probability (NTCP) of IMRT dose painting using 68Ga-HBED-CC PSMA PET/CT for target delineation in prostate cancer (PCa). Methods and materials 10 patients had PSMA PET/CT scans prior to prostatectomy. GTV-PET was generated on the basis of an intraprostatic SUVmax of 30%. Two IMRT plans were generated for each patient: Plan77 which consisted of whole-prostate IMRT to 77Gy, and Plan95 which consisted of whole-prostate IMRT to 77Gy and a simultaneous integrated boost to the GTV-PET up to 95Gy (35 fractions). The feasibility of these plans was judged by their ability to adhere to the FLAME trial protocol. TCP-histo/-PET were calculated on co-registered histology (GTV-histo) and GTV-PET, respectively. NTCPs for rectum and bladder were calculated. Results All plans reached prescription doses whilst adhering to dose constraints. In Plan77 and Plan95 mean doses in GTV-histo were 75.8±0.3Gy and 96.9±1Gy, respectively. Average TCP-histo values for Plan77 and Plan95 were 70% (range: 15–97%), and 96% (range: 78–100%, p<0.0001). Average TCP-PET values for Plan77 and Plan95 were 55% (range: 27–82%), and 100% (range: 99–100%, p<0.0001). There was no significant difference between TCP-PET and TCP-histo in Plan95 (p=0.25). There were no significant differences in rectal (p=0.563) and bladder (p=0.3) NTCPs. Conclusions IMRT dose painting using PSMA PET/CT was technically feasible and resulted in significantly higher TCPs without higher NTCPs.