(P46) Toxicity Analysis of Concurrent Stereotactic Body Radiotherapy and Immunotherapy for Primary and Oligometastatic Cancer

Abstract

Stereotactic body radiotherapy (SBRT) is a newer modality of radiation therapy that allows the delivery of high doses of radiation, in fewer fractions and with lower rate of side effects. SBRT is the treatment of choice for metastatic cancer with curative intent. Recently, evidence has shown that radiation therapy can elicit a systemic immune response against tumor cells. Furthermore, trials have begun exploring how to incorporate immunotherapy agents, such as immune checkpoint inhibitors, to enhance the local and systemic anti-tumor immune responses achieved by radiation therapy. The purpose of this study was to analyze radiation toxicity in patients who have received concurrent SBRT and immunotherapy. The medical records of 23 consecutive patients who were treated at a single institution between July 2011 and May 2016 were reviewed. These patients received both SBRT and immunotherapy within a one-month window of initiation and completion of SBRT. Excluding sites where SBRT was done as re-irradiation, a total of 40 sites were irradiated among these 23 patients. 12 patients were irradiated for oligometastasis and 11 for primary disease. Sites of treatment with SBRT were classified as: head/neck, liver, lungs/mediastinum, and pelvis/abdomen. The median number of sites irradiated per patient was 1 (range 1 to 5). The median dose was 25 Gy (range 14 to 50). The most common SBRT dose was 18 Gy in 1 fraction (4 patients). Majority of patients received prior chemotherapy (19 patients). Common Terminology Criteria for Adverse Events (CTCAE) and Karnofsky Performance Status (KPS) were analyzed using analysis of variance (ANOVA). Immunotherapy treatment approach was categorized as: Neoadjuvant only (1 patient); Adjuvant only (3 patients); Neoadjuvant + concurrent (2 patients); Concurrent + adjuvant (1 patient); Neoadjuvant + concurrent + adjuvant (16 patients). Immunotherapy drugs administered were Cetuximab, Ipilimumab, Nivolumab, Pembrolizumab, Regeneron 2810, Rituximab, and Durvalumab + Tremelimumab. The median duration of immunotherapy use was 3 months. 21 patients tolerated treatment well with minimal toxicity. A grade 2 toxicity was seen in one patient (pharyngitis), and a grade 3 toxicity was seen in another patient (spinal fracture). While SBRT is the standard of care for treatment of metastatic cancer, a potential side effect is toxicity. This retrospective study found that patients treated with concurrent SBRT and immunotherapy tolerated treatment well. Therefore, toxicity from dual treatment approach was similar to that of monotherapy.