Stereotactic Body Radiotherapy Use in Prostate Cancer

Stereotactic body radiotherapy (SBRT) use in prostate cancer more than doubled from 2010 to 2015, however it still accounted for less than 10% of all patients undergoing radiotherapy, according to a study published in JAMA Network Open.

Androgen deprivation therapy (ADT) use also increased with risk among patients overall, regardless of if they received SBRT. Additionally, patients who were treated at an academic center, lived in an urban environment, had higher incomes, were healthier, and were diagnosed as having lower-risk prostate cancer were more likely to be administered SBRT. 

“Further investigation is warranted to validate the potential disparities in SBRT implementation to identify and rectify the underlying causes,” the authors wrote. “In addition, the continued use of SBRT will be contingent on ongoing studies reporting long-term outcomes in low-risk prostate cancer and the role of SBRT in higher-risk prostate cancer.”

Using the National Cancer Database, researchers assessed 106,926 patients diagnosed with localized prostate cancer between 2010 and 2015 and who were receiving definitive radiotherapy. The cohort was composed of 77.3% white patients and 18.7% black patients, with 61.2% of the total group using government-issued insurance. Moreover, more than 80% of the participants had a Charlson-Deyo Comorbidity Index score of 0 (range, 0 to ≥3, with lower numbers indicating fewer comorbidities). 

Within the study population, 25.7% had low-risk disease, 26.3% had favorable intermediate-risk disease, 23.3% had unfavorable intermediate-risk disease, and 24.7% had high-risk disease. The proportion of those who underwent radiotherapy and received SBRT (n = 5,395) increased from 3.1% in 2010 to 7.2% in 2015 (OR, 0.36; 95% CI, 0.33-0.40; P < 0.001). Of the entire cohort, patients received a median dose of 36.25 Gy (range, 30-50 Gy). Furthermore, ADT increased significantly as the disease risk level increased among all of the patients receiving radiotherapy (9.5% with low risk to 76.6% with high risk; P = 0.02), as well as among those receiving SBRT (4.1% with low risk to 33.2% with high risk; P = 0.04) or not receiving SBRT (9.9% with low risk to 77.6% with high risk; P = 0.04). 

Researchers indicated that differences in selection of SBRT may be reflective of patient and physician preference for other treatment regimens or modalities with more robust long-term disease-specific control and safety data compared with that of the existing SBRT literature. Additionally, the exposure of physicians and physicists to hypofractionated and stereotactic treatments during training, as well as investing in additional technologies to facilitate effective SBRT delivery, may influence physician selection.

“With more low-risk prostate cancer being managed by active surveillance, which is reflected by decreased external beam radiation therapy [EBRT] in this subset, the observed increasing use of SBRT in this disease subset may be indicative of overtreatment, patient preference, or increased marketing,” the authors wrote. “Thus, the upward-trending use of both active surveillance and SBRT warrant further clarification regarding when to appropriately implement each option in the low-risk disease setting.”

Moreover, researchers also suggested that because the NCDB does not comprehensively capture nuances in the delivery of radiotherapy, future research is necessary to characterize trends in specific radiotherapy planning factors, such as image guidance, use of rectal balloon, spacer or fiducials, treatment platform (CyberKnife vs linear accelerator), and whether all 5 treatment fractions are delivered on consecutive days. 

According to the study, prostate cancer is the most common malignant neoplasm in men, with more than 164,000 new cases diagnosed in 2018. However, with the advent and availability of prostate-specific antigen (PSA) testing allowing for earlier detection of the disease, most men are diagnosed with localized disease. 

Reference:

Mahase SS, D’Angelo D, Kang J, Hu JC, Barbieri CE, Nagar H. Trends in the Use of Stereotactic Body Radiotherapy for Treatment of Prostate Cancer in the United States. JAMA Network Open. doi:10.1001/jamanetworkopen.2019.20471.