Hurwitz on the Safety Profile of Simultaneous Integrated Boost Plus SBRT in Prostate Cancer

Joshua Hurwitz, medical student, NYU Grossman Long Island School of Medicine, discusses findings from a study investigating the safety of adding multifocal MRI-directed simultaneous integrated boost to stereotactic body radiation therapy (SBRT) in patients with prostate cancer.

This study assessed whether multifocal simultaneous integrated boost using SBRT was associated with increased acute toxicities vs unifocal simultaneous integrated boost using SBRT in patients with prostate cancer who had PI-RADS 3+ lesions identified on pretreatment MRI. Investigators reported genitourinary (GU) and gastrointestinal (GI) toxicities, as well as quality of life (QOL) outcomes. Toxicity and QOL are intimately linked, and QOL outcomes can often reveal unique nuances in the patient experience, Hurwitz says.

Overall, investigators observed no grade 3 or higher toxicities in both the multifocal and unifocal SBRT arms, Hurwitz notes. However, the study reported higher rates of grade 2 GU toxicities than grade 2 GI toxicities in the overall population, at 60% vs 6%, respectively, Hurwitz explains. Questions remain regarding the sensitivity of the CTCAE toxicity grading system, Hurwitz emphasizes. For instance, Hurwitz notes that many patients with prostate cancer receive alpha blockers or 5α-Reductase inhibitors that automatically upstage their toxicities to grade 2. Nonetheless, investigators reported overall favorable GU toxicity levels and limited levels of grade 1 and 2 GI toxicities with multifocal boost relative to unifocal boost. Additionally, most patients in the study received a rectal spacer, which was not associated with a decrease in GI toxicities, Hurwitz says.

The relatively higher rate of GU vs GI toxicities prompted investigators to determine whether the multifocal simultaneous integrated boost was associated with the increased incidence of grade 2 GU toxicities, which was the primary end point of the study, Hurwitz explains. Univariate and multivariate analyses showed no difference in the rates of grade 2 GU toxicities in the patients who received multifocal simultaneous integrated boost vs those who received unifocal simultaneous integrated boost, Hurwitz concludes.