Stereotactic Body Radiotherapy: Past and Future Challenges

ONA: Has the evidence base regarding late radiotoxicity associated with SBRT matured? What’s better understood about the risks for delayed adverse effects?

Dr Yom: We now understand that SBRT can cause a very significant amount of necrosis and fibrosis in the treated area and potential scarring or severe damage to serial organ structures that are very close to the treated area (eg, spinal cord, nerve plexuses, and esophagus must be carefully accounted). This understanding and specific dosimetric planning for SBRT have greatly improved safety. Additionally, an American Association of Physicists in Medicine (AAPM) workgroup on SBRT has organized an effort called HyTEC, under which a series of papers that describe hypofractionated planning and physics criteria, is being developed for publication in the International Journal of Radiation Oncology • Biology • Physics (Red Journal) over the coming year. These papers will be a valuable educational resource on treatment techniques for clinicians and, we hope, will further improve the quality of outcomes for patients.  Data on late toxicities of various organs from individual centers or consortia also have been published, to help guide safe practice.

ONA: Has SBRT lived up to its promise over the past 10 years? What have been major milestones and major challenges or barriers to its wider use?

Dr Yom: SBRT has more than lived up to its promise, and the vast majority of radiation oncologists see the value of SBRT for their patients. There are few barriers to its use, and only in isolated sectors. These barriers unfortunately include:

Habit There remain lingering, and in most cases unfounded, concerns about safety held over from very early experiences.

Education Radiation oncologists are not used to SBRT across so many different body sites and the indications are expanding very rapidly, faster than some can keep up with.

Financial Impact Or, at the least, the fear among some of a negative impact. SBRT is a high-value treatment method, and it can provide cost efficiencies in cases where it replaces a conventional — and longer — course of radiation treatments. It offers versatility and a well-tolerated, noninvasive way to treat cancers that have been treated more commonly with other modalities in the past.

Patient and Consultant Relationships Radiation oncologists are used to having long-term relationships with patients; there is concern that because SBRT is so short and technically oriented, that radiation oncologists might be called in a procedural manner rather than remaining an integral part of the oncology team. This can be easily addressed of course by radiation oncologists continuing to refine the science and complexity of SBRT-based treatments and developing a new expertise in this arena.

ONA: What exciting areas of research or significant developments in SBRT do you anticipate seeing by 2030?

Dr Yom: There are several:

• Greater range of indications and uses
• Improved biologic understanding of various cancers with planning and delivery approaches tailored to the unique disease characteristics
• Integration of SBRT with immunotherapy (using SBRT as a vaccine)
• Increased integration of MRI and proton therapy into SBRT approaches
• Development of the science of oligometastatic disease where SBRT is uniquely effective.

ONA: Do you think proton therapy or other radiotherapeutic modalities might displace SBRT to any significant degree?

Dr Yom: Proton therapy can be used to deliver SBRT; they will cooperate, not compete. Whether proton therapy or photon (IMRT) therapy is used to deliver SBRT, the SBRT philosophy is the same: small volumes, high doses, and steep dose fall-off. Challenges with the delivery of stereotactic body proton therapy include the lack of cone beam CT (volumetric or 3D verification) in most proton centers, and more severe scattering from metal creating a dosimetric issue when there are metallic implants.

ONA: Are there advances in other facets of radiotherapy, such as radiogenomics, that have implications for SBRT?

Dr Yom: Radiogenomics and other nuanced understanding of biology will lead to more specific, effective, nuanced approaches for SBRT. SBRT will become more specific and individualized. SBRT came onto the scene from the periphery of the field but quickly found its way onto center stage in radiation oncology, and patients have benefited as a result. It is here to stay and will only continue to improve but I also can’t wait for the “next SBRT,” the thing we don’t even yet know is in the building that will emerge and add meaningful improvement to our patient care in the decade ahead.