Clinical research is suggesting that stereotactic body radiotherapy (SBRT), in which high doses of radiation are delivered in a targeted fashion to tumors, appears to be an effective and safe treatment approach for patients with oligometastatic disease. An oligometastasis occurs when cancer cells from the original tumor travel through the body and form a small number of (less than five) new tumors elsewhere. Oligometastasis is usually thought of as an intermediate stage between an isolated tumor and widespread metastasis throughout the body, which is often incurable.
The concept of oligometastasis is relatively recent and offers a novel point of therapeutic intervention for individuals with oligometastatic disease. These interventions are now available due to advances in imaging (emission tomography, computed tomography and magnetic resonance imaging) and the identification of novel prognostic markers that enable the increased detection of oligometastatic disease. The appropriate identification and selection of patients with oligometastases is critical for pursuing effective therapy at this stage of disease.
A Growing Need for New Treatment Options
Improvements in systemic and targeted cancer therapies are continually lengthening patient survival. Many of these patients may respond well to systemic and targeted therapies but have a few lesions that do not resolve, and patients who have previously achieved remission may have oligometastatic recurrence. While these patients have historically had few treatment options, new technologies make it possible to aggressively treat unresponsive or recurrent tumors and potentially improve disease-free and ultimately overall survival.
Benefits of SBRT
SBRT is a treatment approach that utilizes stereotactic techniques to precisely deliver high doses of radiation. This allows for local dose escalation at the site of the targeted tumor while sparing surrounding normal tissues. Consequently, SBRT is a potentially ablative treatment approach that can be utilized with a safety and efficacy profile well-suited to oligometastatic disease.
Clinical evidence suggests that SBRT has improved control rates compared with conventional radiation. Local control rates can be quite high, ranging from 70 percent to 90 percent, depending on a variety of factors, including tumor histology, site and treatment dose. Outcomes appear to be similar to metastasectomy and can improve the clinical course in carefully selected patients. Data also suggest that SBRT in combination with newer systemic immunotherapies may have an enhanced synergistic effect, further increasing its potential in the treatment of oligometastatic disease.
Advances in imaging and motion control management and their integration into SBRT systems are enabling improvements in margins, allowing multiple tumors to be treated with radiotherapy without significantly increasing the exposure of healthy tissue. With SBRT, treatment can be tailored to address the size and location of each patient’s tumors, making radiation therapy an essential tool in the era of personalized medicine.
SBRT in Clinical Practice
Within my practice at Cancer Care Northwest and within The Alliance for Cancer Care (The Alliance), we've been using SBRT to treat oligometastases in carefully selected patients with increasing frequency over the past decade.
Use of SBRT at Cancer Care Northwest and The Alliance is increasing due to the growing number of patients diagnosed with oligometastatic disease, improvements in technology, and with improvements in systemic therapy and appropriate patient selection. SBRT offers patients a powerful tool for pursuing aggressive treatment for persistent tumors, which meets an important psychological aspect of living with cancer.
Expanding SBRT in the Treatment of Oligometastasis
SBRT is a promising approach to treating the emerging class of patients with oligometastatic disease. Its ability to target multiple tumors with high specificity and reduced margins supports the development of personalized treatment regimens for these patients, who historically have had few locally aggressive treatment options. Innovations in radiation oncology, including SBRT and stereotactic radiosurgery, demonstrate that radiation therapy remains a foundational treatment for cancer in the era of targeted medical therapies.
The broader use of SBRT in the treatment of oligometastasis will be supported by additional data that define specific patient populations and treatment protocols. Comprehensive clinical studies in different tumor types and anatomical locations and the development of treatment databases are warranted. With a robust body of data to inform treatment decisions, the oncology community can ensure that SBRT is used to provide optimized outcomes for patients with oligometastases.