Stereotactic Body Radiation Therapy: A Radiosurgery Society Guide to the Treatment of Localized Prostate Cancer Illustrated by Challenging Cases.

Traditionally, external beam radiotherapy (EBRT) for localized prostate cancer (PCa) involved lengthy courses with low daily doses. However, advancements in radiation delivery and a better understanding of prostate radiobiology have enabled the development of shorter courses of EBRT. Ultrahypofractionated radiotherapy, administering doses greater than 5 Gy per fraction, is now considered a standard of care regimen for localized PCa, particularly for intermediate-risk disease. Stereotactic body radiotherapy (SBRT), a specific type of ultrahypofractionated radiotherapy employing advanced planning, imaging, and treatment technology to deliver in five or fewer fractions, is gaining prominence as a cost-effective, convenient, and safe alternative to longer radiotherapy courses. It is crucial to address practical considerations related to patient selection, fractionation scheme, target delineation, and planning objectives. This is especially important in challenging clinical situations where clear evidence for guidance may be lacking. The Radiosurgery Society endorses this case-based guide with the aim of providing a practical framework for delivering SBRT to the intact prostate, exemplified by two case studies. The article will explore common SBRT dose/fractionation schemes and dose constraints for organs-at-risk. Additionally, it will review existing evidence and expert opinions on topics such as SBRT dose escalation, the use of rectal spacers, the role of androgen deprivation therapy in the context of SBRT, SBRT in special patient populations (e.g., high-risk disease, large prostate, high baseline urinary symptom burdens, and inflammatory bowel disease), as well as new imaging-guidance techniques like Magnetic Resonance Imaging for SBRT delivery.