Stereotactic Body Radiotherapy: Past and Future Challenges

The editors of Oncology Nurse Advisor present a review of one of the past decade’s groundbreaking radiologic therapies as part of our 10-year anniversary celebration. In this interview, Bryant Furlow, a long-time contributing writer covering radiation therapy, sat down with Sue S. Yom, MD, PhD, to talk about the evolution of stereotactic body radiotherapy (SBRT) over the past decade and what’s next.

Dr Yom is professor at the Helen Diller Family Comprehensive Cancer Center and vice chair and the Jacobs Distinguished Professor of Head and Neck Cancer in the Department of Radiation Oncology, with a co-appointment in Otolaryngology-Head and Neck Surgery; all at the University of California, San Francisco (UCSF). Dr Yom is also deputy editor of the International Journal of Radiation Oncology • Biology • Physics.

Oncology Nurse Advisor (ONA): What can you tell us about the origins of SBRT? How did intracranial radiosurgery contribute to its development?

Dr Yom: The principles of intracranial stereotactic radiosurgery (SRS) — small volumes, high doses, precision of imaging and tumor localization, and rapid fall-off of radiation dose away from the target — were essentially translated to the rest of the body to make SBRT. The connections were actually very direct, with major practitioners such as Bob Timmerman, when he was at Indiana University, studying with leaders in SRS such as David Larson at UCSF.

ONA:  What significant advances have improved SBRT planning and delivery since 2010?

Dr Yom: The planning and delivery processes have both become routine and incredibly efficient compared with those of 2010. When I was in residency, an SBRT delivery could take many hours; the same treatment is now given in a fraction of that time. Furthermore, the simulation processes to account for motion (4DCT, breath-hold or active breathing control, respiratory gating) were literally being invented as SBRT became popular. Now, those technologies are available as commercial packages and have become accessible to community practices.

ONA: What about the evidence base for SBRT applications in cancer treatment? What additions to the tumor types and/or stages that can be treated with SBRT were developed over the past decade?

Dr Yom: The indications for stereotactic radiation continue to grow as doctors and patients become more familiar with both the efficacy and convenience of the technique. For example, use of SRS has expanded into the skull base, and SBRT, first used in the spine and lung, is now being used regularly in cases of gastrointestinal (liver and pancreas) tumors, prostate cancer, and even mucosal head and neck cancers. SBRT has also been utilized to tackle limited metastases (ie, oligometastatic cancer) in an aim to prolong survival.

New applications continue to be analyzed and established. For example, just in the past year or 2, the International Radiosurgery Oncology Consortium for Kidney (IROCK) presented and published several reports on SBRT for renal cell carcinoma, which led to the approval of SBRT as a standard treatment for this disease in Japan. There is emerging evidence for the use of SBRT with selected patients who have recurrent gynecologic cancer, breast cancer, and cardiac arrhythmia, although further investigations are needed to better define the role of SBRT in those diseases.

ONA: Have there been advances over the past decade specifically regarding tumor/target volume motion management?

Dr Yom: Motion management techniques (breath hold, active breathing control, gating, 4DCT) and image-guided radiation therapy (IGRT; faster cone beam CT) have evolved simultaneously with SBRT. More and more clinics routinely incorporate these methods into everyday practice as access to SBRT has expanded.

ONA: Have the acute toxicity profiles of SBRT changed much over the past decade? In what ways?

Dr Yom: Toxicity profiles are much better as diagnostic and localization imaging become more precise and margins around the tumor volume can be decreased. When these margins are decreased, the volume treated is smaller. Better motion management also means that these margins/volumes can be decreased. With the accumulated experience and data in the literature, we now better understand the factors predicting acute side effects during and after SBRT, and we can proactively use strategies to minimize the risks.

One more important advance for prostate cancer SBRT is that we now have an implantable spacer that can give some separation between the rectum and the back of the prostate. This is a way to reduce the risk of GI side effects in that setting.

ONA: Have SBRT dose-fractionation schedules changed meaningfully over the past 10 years? If so, how?

Dr Yom: They have not changed very much. Five fractions remains the popular schedule. In the spine, treatment with 1 to 3 fractions is fairly routine, and in lung and prostate cancer, there are ongoing experiments to reduce this to fewer fractions. Outside of the United States, up to 6 to 8 fractions may be designated as SBRT, and an 8-fraction regimen has been increasingly used in situations where constraints of certain organs at risk cannot be met (eg, ultracentrally located lung tumors).