1.5T MR-guided and daily adapted SBRT for prostate cancer: feasibility, preliminary clinical tolerability, quality of life and patient-reported outcomes during treatment

Abstract

Background Unity Elekta is a unique magnetic resonance (MR)-linac that conjugates a 1.5 Tesla MR unit with a 7 MV flattening filter free accelerator.A prospective observational study for the clinical use of Elekta Unity is currently ongoing in our department. Herein, we present our preliminary report on the feasibility, quality of life, and patient-reported outcomes measures (PROMs) for localized prostate cancer (PC) treated with stereotactic body radiotherapy (SBRT). Methods The SBRT protocol consisted of a 35 Gy schedule delivered in 5 fractions within two weeks. Toxicity and quality of life (QoL) were assessed at baseline and after treatment using the Common Terminology Criteria for Adverse Events v5.0, International Prostatic Symptoms Score (IPSS), ICIQ-SF, IIEF-5, and EORTC-QLQ-C30 and PR-25 questionnaires. Results Between October 2019 and January 2020, 25 patients with localized PC were recruited. The median age was 68 years (range, 54-82); 4 were low risk, 11 favorable intermediate risk (IR) and 10 unfavorable IR. Median iPSA was 6.8 ng/ml (range, 1-19), and 9 of these patients (36%) received concurrent androgen deprivation therapy. Median prostate volume was 36 cc (range, 20-61); median baseline IPSS was 5 (range, 0-10). Median time for fraction was 53 minutes (range, 34-86); adaptive strategy with daily critical structure and target re-contouring and daily replanning (adapt to shape) was performed in all cases. No grade ≥ 3 adverse event was observed, three patients (12%) reported grade 2 acute genitourinary toxicity (urinary frequency, urinary tract pain and urinary retention), while only one patient reported mild rectal pain. No relevant deteriorations were reported in PROMs. Conclusion To the best of our knowledge, this is the first experience reporting feasibility, clinician-reported outcome measurements, and PROMs for 1.5T MR-guided adaptive SBRT for localized prostate cancer. The preliminary data collected here report optimal safety and excellent tolerability, as also confirmed by PROMs questionnaires. Moreover, the data on technical feasibility and timing of online daily adapted planning and delivery are promising. More mature data are warranted.

Daily dosimetric variation between image-guided volumetric modulated arc radiotherapy and MR-guided daily adaptive radiotherapy for prostate cancer stereotactic body radiotherapy

“…In the MR-guided approach, patients start with the bladder half-full, since the time from the first MR acquisition to the delivery is significantly longer and several patients cannot hold the full bladder. To ensure the correct organ positioning we perform a pre-MR, through which was evident a modification only to the upper part of the bladder [11]. Interestingly, MRgRT reported the highest rectum and bladder dosimetric accuracy, as compared to SBRT without fiducials, while the difference was minimal or absent with fiducials.…”

“…Simulation and planning MR-guided RT procedures were described extensively in a previous publication [11]. Before simulation (planning CT and MRI) and each fraction, patients were instructed to have their bladder half full (500 cc of water 15-20 min before the session) and empty rectum.…”

“…More recently, a new concept of MR-guided radiotherapy has been introduced, combining the high MR image quality to the possibility to easily re-adapt treatment plans to the daily anatomy [10]. This approach is characterized by longer treatment sessions, due to the procedures required for the preparation and the re-planning workflow [11]. Whether MRguided RT might improve dose delivery accuracy as compared to standard linac treatments in PCa SBRT has been not deeply explored.…”

MR-Guided Hypofractionated Radiotherapy: Current Emerging Data and Promising Perspectives for Localized Prostate Cancer

“…Currently available evidence reports MR-guided SBRT as a safe and feasible treatment option. Alongi et al [36] reported excellent preliminary results in terms of PROMs in a cohort of 25 patients who received 35 Gy in 5 fractions, with no evidence of acute G ≥ 3 adverse events. Interestingly, the favorable results in terms of quality of life (QoL) outcomes after a median treatment time of 56 min (range, 34-86) per fraction, indicate the tolerability of MR-guided SBRT for prostate cancer and show that the longer treatment time per session has only a minimal impact on QoL.…”

“…For both devices, given the relatively longer treatment time per session, the simulation process is a crucial factor in order to perform an accurate and refined treatment delivery. Based on available literature, most experiences reported a similar protocol in terms of bladder filling and rectal emptying ( [32][33][34][35][36][37][38]-see Table 1). For both the CT scan (performed for dose calculation purposes) and the MRI scan, patients were educated to have a half-full bladder in order to take into account residual volume changes during the plan adaptation phase (Figure 2).…”