Helical tomotherapy and intensity modulated proton therapy in the treatment of dominant intraprostatic lesion: A treament planning comparison

Purpose: To compare helical tomotherapy (HT) and intensity modulated proton therapy (IMPT) for prostate cancer irradiation while concomitantly boosting dominant intraprostatic lesions (DILs). Methods and materials: Treatment plans of seven patients were designed for HT and IMPT (pencil beam size: 3 mm sigma). The prescribed median PTV/DIL doses were 71.4/100 Gy in 28 fractions, while satisfying "safe" dose constraints for organs at risks (OARS) including rectum, bladder, femoral heads, penile bulb and urethra. The planner could further reduce the dose to OARs if PTV/DIL constraints were reached. Results: IMPT achieved better dose conformity (CI = 1.11 vs 1.31, p < 0.05) and coverage (V95% = 97.3% vs 95.3%, p < 0.05) in PTV. Concerning DIL volumes, both techniques delivered the prescribed dose (Dmedian: HT = 100 Gy, IMPT = 102.1 Gy) with similar dose conformity (CI: HT = 1.49, IMPT = 1.44) and same dose homogeneity, D99%, D1%, while satisfying the OARs constraints. Excepting urethra, the sparing of OARS was significantly better with IMPT; in general, the lower the dose, the greater the benefit of IMPT. Normal tissue complication probabilities for the rectum were in favor of IMPT with an absolute reduction of 3-8%, depending on the NTCP model (p < 0.05). Conclusions: Both techniques allowed delivering 100 Gy to DILs, while complying with the OARs constraints. IMPT was superior in sparing OARs for doses up to approximately 70 Gy, with larger benefit at lower doses. (C) 2013 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 107 (2013) 207-212