Does Overall Treatment Time Impact Toxicity and Clinical Outcomes After Magnetic Resonance Imaging-Guided Stereotactic Body Radiotherapy to the Prostate? An evaluation of the Multi-OutcoMe EvaluatioN of radiation Therapy Using the MR-Linac Repository

AIMS: Prostate stereotactic body radiotherapy (SBRT) can be delivered using magnetic resonance imaging-guided radiotherapy (MRgRT) with the aim of increased precision and reduced toxicity. The overall treatment time (OTT) for SBRT varies, ranging from daily fractions to once-weekly schedules. However, it is unclear whether OTT affects clinical outcomes when using MRgRT. The aim of this study was to establish whether OTT impacts toxicity, quality of life (QoL), and prostate-specific antigen (PSA) control in prostate MRgRT.

MATERIALS AND METHODS: For this study, outcomes from the Multi-OutcoMe EvaluatioN of radiation Therapy Using the MR-Linac (MOMENTUM) study were utilised (NCT04075305). Patients with localised prostate cancer receiving 36.25 Gy to 40 Gy in five fractions, of whom OTT was available, were analysed. Physician-reported Common Terminology Criteria for Adverse Event (CTCAE) toxicity, patient-reported outcomes (PROs) and PSA dynamics were collected at baseline and at three, six, twelve, and 24 months after MRgRT. Univariate ordinal logistic regression and mixed model analysis were performed to study the impact of OTT on changes in genitourinary (GU) and gastrointestinal (GI) toxicity, and QoL and PSA levels compared to baseline, respectively.

RESULTS: A total of 858 patients were included with a median OTT of 14 days, ranging from five to 47 days. Excluding erectile function, no grade ≥3 GU or GI toxicity was reported. The OTT was not associated with acute or late GU toxicity (odds ratio [OR]: 0.97 [95% confidence interval [CI]: 0.92-1.02]; P = 0.21 and OR 0.99 [95% CI: 0.94-1.05]; P = 0.83) or acute and late GI toxicity (OR 0.89 [95% CI: 0.79-1.00]; P = 0.05 and OR 0.99 [95% CI: 0.92-1.07]; P = 0.83). In addition, OTT had no apparent impact on QoL scores and PSA kinetics.

CONCLUSION: This study suggests that OTT, generally between 8 and 18 days, in five-fraction MRgRT for prostate cancer does not affect GU and GI toxicity, QoL and PSA control. Clinicians should consider discussing OTT with patients as this will facilitate treating patients to the time frame that suits them best, reducing the impact of treatment on their QoL, whilst also allowing flexibility for busy departments.