3328 - Prostate Reirradiation with Online Daily-Adaptive Stereotactic Body Radiotherapy (SBRT) on 1.5T MR-Linac
Presenter(s)
A. Romei1, L. D. Nicosia2, M. Rigo1, A. G. Allegra1, C. De-Colle1, N. Giaj-Levra1, C. Orsatti1, E. Pastorello1, F. Ricchetti1, R. Ruggieri3, and F. Alongi4; 1Department of Advanced Radiation Oncology, IRCSS "Sacro Cuore Don Calabria Hospital" Cancer Care Center, Negrar di Valpolicella (VR), Italy, 2Department of Advanced Radiation Oncology, IRCCS "Sacro Cuore Don Calabria Hospital" Cancer Care Center, Negrar di Valpolicella (VR), Italy, 3Department of Advanced Radiation Oncology, IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Negrar di Valpolicella, Italy, 4Varian, Milpitas, CA, Uganda
Purpose/Objective(s): Prostate re-irradiation is an attractive treatment option in the case of local relapse after previous radiotherapy, either in the definitive or in the post-operative setting. In this scenario, the introduction of MR-linacs may represent a helpful tool to improve the accuracy and precision of the treatment.
Materials/Methods: Patients with exclusive local relapse to the prostate or the prostate bed after primary RT were treated with a second course of SBRT on 1.5T MRL. The clinical target volume (CTV) was represented by the entire prostate gland in non-operated patients or the macroscopic relapse to the prostatic bed in operated patients. In those last cases, the target was identified by the combination of MRI and PET-TC. Disease relapse was defined according to the Phoenix criteria and diagnostic imaging was requested in all patients. No confirmatory biopsy was performed due to technical difficulties of patients’ refusal for invasive procedures. The CTV was expanded by 5 mm in all direction to obtain the corresponding planning target volume (PTV). Planning mandatory goals for the urethra, the bladder and the rectum were V30Gy <1 cc.
Results: 46 patients were treated with re-SBRT with the dose of 30 Gy in 5 fractions daily (10) or every-other-day (40). The median follow-up was 14 months (range 6-56). Primary RT was: conventionally fractionated RT (56.5%), prostate bed salvage RT after surgery (28.5%), SBRT (8.5%), brachytherapy (6.5%). Initial Gleason score was: 3+3 (19.5%), 3+4 (32.5%), 4+3 (15%), 4+4 or higher (19.5%), unknown (13.5%) The median time to local relapse was 76 months (range 11-189). The median IPSS at recurrence was 4 (range 0-10). All patients were staged with PET-TC PSMA (44) or choline (2). Worst acute GU toxicity was: G1 (32.5%), G2 (8.5%), G3 (2%). Worst acute GI toxicity was: G1 (35.5%). At the median follow-up only one patient had further intraprostatic relapse for which androgen deprivation therapy (ADT) was initiated.
Conclusion: MRL permits to safely delivery a second SBRT course in patients with exclusive local relapse after a first course of RT. Toxicity was acceptable using online daily plan adaptation and local relapse were uncommon in short-term follow-up. Further studies including treatment margin reduction are ongoing at our institution.