[ 11 C]-Choline PET/CT-guided simultaneous integrated boost to dominant intraprostatic lesions using intensity-modulated radiation therapy with helical tomotherapy technique for dose escalation

Objective The objective of the study is to demonstrate the feasibility of using [ 11 C]-choline positron-emission tomography (PET)/CT to deliver helical tomotherapy (HT) to the prostate with a simultaneous integrated boost to dominant intraprostatic lesions as a biological target volume for dose escalation. Methods Eleven patients with intermediate-risk prostate cancer were included in this virtual planning study. Pretreatment baseline [ 11 C]-choline PET/CT scans were acquired with a PET/CT scanner dynamically in 2-min frames from injection to 40 min post injection. PET data was reconstructed using the RAMLA 3D algorithm and analyzed to identify dominant intraprostatic lesion(s). Dominant lesions were defined as biological target volume(s) (BTV) including all voxels with a standardized uptake value of 75 % or above relative to the maximum standard uptake value (SUV) within the prostate gland. Three target volumes for optimization included the following: PTV78 (BTV + 5 mm margin), PTV68 (prostate + 5 mm posteriorly and 10 mm in all other dimensions), and PTV50 (prostate gland and proximal seminal vesicles + 7 mm margin posteriorly and 10 mm in all other dimensions). Dose constraints on organs at risk were implemented based on a published data using hypofractionated IMRT with long-term follow-up. Helical tomotherapy plans were generated to deliver hypofractionated radiation therapy to these volumes using simultaneous integrated boost in 25 fractions. Results Eight patients had one identifiable contiguous BTV, and the other three patients had two noncontiguous BTVs. The mean BTV ratio to prostate volume ratio was 6.03 % (minimum 0.80 %, maximum 13.44 %). Target volume and normal tissue constraints were met in seven of the 11 patients enrolled in the study. Targets and structures in the four patients that did not meet constraints were the bladder (3 patients), peritoneal cavity (2 patients), rectum (1 patient), PTV68 (1 patient), and PTV50 (1 patient). Conclusion It is feasible in selected patients to use [ 11 C]-choline PET/CT to deliver hypofractionated dose-escalated helical tomotherapy to dominant intraprostatic lesions with simultaneous integrated boost using clinically established normal tissue constraints.