Dose-escalation using intensity-modulated radiotherapy for prostate cancer - Evaluation of the dose distribution with and without 18F-choline PET-CT detected simultaneous integrated boost

Background and purpose: The aim of the study was to evaluate the impact of a dose escalation to an 18F-choline PET-CT defined simultaneous integrated boost (IB) on the dose distribution and changes of the equivalent uniform dose (EUD). Materials and methods: PET-CT was performed in 12 consecutive patients for treatment planning. An intraprostatic lesion was defined by a tumour-to-background uptake value ratio >2 (GTVPET). Dose escalation was focused only on the intraprostatic lesion. Two comparisons were evaluated: whole prostate irradiation to 76 Gy ± boost to 80 Gy (C1) and whole prostate irradiation to 66.6 Gy ± boost to 83.25 Gy (C2). Results: PTV/GTVPET + margins were covered by a mean EUD of 75.9/76.1 Gy vs. 77.1/80.1 Gy (C1) and 66.5/66.2 Gy vs. 71.1/82.9 Gy (C2) (p < 0.01, respectively). Concerning the organs at risk, EUD increased slightly with an additional boost (mean EUD for bladder: C1 53.2 Gy vs. 53.8 Gy; C2 43.0 Gy vs. 45.1 Gy; for rectum: C1 52.0 Gy vs. 52.6 Gy; C2 43.0 Gy vs. 45.4 Gy; p < 0.01, respectively). The distance to the organs at risk had a significant impact on the respective maximum doses in the treatment plans with IB. Conclusions: Treatment planning with IB allows an individually adapted dose escalation. The therapeutic ratio can be improved by a considerable dose escalation to the macroscopic tumour, but only minor EUD changes to the bladder and rectum.