A survey among German-speaking radiation oncologists on PET-based radiotherapy of prostate cancer

Marco M. E. Vogel, Sabrina Dewes, Eva K. Sage, Michal Devecka, Jürgen E. Gschwend, Matthias Eiber, Stephanie E. Combs, Kilian Schiller

Positron emission tomography-(PET) has evolved as a powerful tool to guide treatment for prostate cancer (PC). The aim of this survey was to evaluate the acceptance and use of PET-especially with prostate-specific membrane antigen (PSMA) targeting tracers-in clinical routine for radiotherapy (RT) and the impact on target volume definition and dose prescription. We developed an online survey, which we distributed via e-mail to members of the German Society of Radiation Oncology (DEGRO). The survey included questions on patterns of care of RT for PC with/without PET. For evaluation of doses we used the equivalent dose at fractionation of 2 Gy with α/β = 1.5 Gy [EQD2(1.5 Gy)]. From 109 participants, 78.9% have the possibility to use PET for RT planning. Most centers use PSMA-targeting tracers (98.8%). In 39.5%, PSMA-PET for biochemical relapse after prior surgery is initiated at PSA ≥ 0.5 ng/mL, while 30.2% will perform PET at ≥ 0.2 ng/mL (≥ 1.0 ng/mL: 16.3%, ≥ 2.0 ng/mL: 2.3%, regardless of PSA: 11.7%). In case of PET-positive local recurrence (LR) and pelvic lymph nodes (LNs), 97.7% and 96.5% of the participants will apply an escalated dose. The median total dose in EQD2(1.5 Gy) was 70.00 Gy (range: 56.89-85.71) for LR and 62.00 Gy (range: 52.61-80.00) for LNs. A total number of ≤ 3 (22.0%) or ≤ 5 (20.2%) distant lesions was most often described as applicable for the definition as oligometastatic PC. PSMA-PET is widely used among German radiation oncologists. However, specific implications on treatment planning differ among physicians. Therefore, further trials and guidelines for PET-based RT are warranted.