Risks of genitourinary and gastrointestinal toxicity were reduced significantly, but longer follow-up is necessary to examine potential future issues.
Data from 29 clinical studies showed that using magnetic resonance-guided daily adaptive stereotactic body radiotherapy (MRg-A-SBRT) as a guide can make radiation therapy safer for patients with prostate cancer, according to authors of a recent analysis posted in Cancer. Compared to other techniques, this imaging technology can help clinicians aim radiation beams more precisely, allowing them to avoid tissue that neighbors the prostate, including the bladder, urethra, and rectum.1
According to the authors, MRg-A-SBRT provides more detailed images, which can be used to adjust a patient’s radiation plan daily to take possible anatomical changes into consideration. Further, to ensure the treatment is directed accurately, MRg-A-SBRT can monitor the position of the patient’s prostate in real time while the radiation beam remains on. However, the technique requires more time and resources than more standard procedures and it was previously unclear whether MRg-A-SBRT has an impact on clinical outcomes and adverse effects (AE) compared with other methods of delivering radiation.1
From the trials, acute toxicity rates associated with MRg-A-SBRT was compared to a more conventional method, computed tomography-guided non-adaptive prostate SBRT (CT-SBRT). Unlike MRg-A-SBRT, this method is not adjusted daily, meaning it may not be as accurate.
Combining data from 29 clinical trials between January 1, 2018, and August 31, 2022, the researchers tested prostate SBRT. Random and fixed effects were used to estimate pooled toxicity rates, while meta-regression was performed to compare toxicity between the 2 treatments. A total of 2547 patients with prostate cancer were evaluated in order to determine potential AEs that occur after the use of MRg-A-SBRT and CT-SBRT.2
“The study is the first to directly evaluate the benefits of MR-guided adaptive prostate radiation in comparison to another more standard and conventional form of radiation, and it provides support for use of this treatment in the management of prostate cancer,” said lead researcher Jonathon E. Leeman, MD, of the Dana-Farber Cancer Institute and Brigham and Women’s Hospital, in a press release.1
Furthermore, the analysis found that MRg-A-SBRT was associated with a significantly reduced risk of acute grade 2 or higher (G2+) genitourinary (GU) and gastrointestinal (GI) toxicity in comparison to CT-SBRT. The risks of short-term urinary and bowel AEs were reduced by 44% and 60%, respectively. The pooled estimates for MRg-A-SBRT were 16% (95% confidence interval [CI], 10%–24%) and 4% (95% CI, 2%–7%) and for CT-SBRT they were 28% (95% CI, 23%-33%) and 9% (95% CI, 6%-12%), respectively. 2
Additionally, for meta-regression, the odds ratios for acute G2+ GU and GI toxicities comparing MRg-A-SBRT and CT-SBRT were 0.56 (95% CI, 0.33–0.97, p = .04) and 0.40 (95% CI, 0.17–0.96, p = .04), respectively. Despite this, longer follow-up is necessary to evaluate potential late toxicity and disease control outcomes.2
It is unknown which aspect of the technology is responsible for the improved outcomes that were recorded in the clinical trials; however, Leeman suggests the ability to change the imaging during treatment is a factor. “It could potentially be the capability for imaging-based monitoring during the treatment or it could be related to the adaptive planning component. Further studies will be needed to disentangle this,” said Leeman.1
Additionally, further investigation is required because MRg-A-SBRT is a relatively new treatment. It is unknown whether these short-term benefits could lead to long-term benefits and which would be more impactful for patients.1
1. Image-guided adaptive radiation treatments reduce short-term side effects for patients with prostate cancer. News release. July 24, 2023. Accessed on July 27, 2023. http://bit.ly/3YdnZhZ
2. Leeman J, Shin K, Chen, Y, et al. Acute toxicity comparison of magnetic resonance-guided adaptive versus fiducial or computed tomography-guided non-adaptive prostate stereotactic body radiotherapy: A systematic review and meta-analysis. CANCER. 2023. doi:10.1002/cncr.34836