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.