Prevalence of Oligometastatic Disease of Solid Tumors and Stereotactic Ablative Body Radiotherapy Adverse Events

Abstract

There is a growing evidence of better outcome of oligometastatic disease (OMD) of solid tumors compared to those with diffuse metastases when treated with stereotactic Ablative body radiotherapy (SABR) and or Stereotactic Radiosurgery (SRS). We reviewed our institution database about the prevalence of OMD in solid tumors, patients’ characteristics and the adverse events due to SABR/SRS. A retrospective review was performed for all solid tumor patients who treated with SABR and/or SRS at our institution from January 2017 to August 2019. Patients were defined to have OMD if ≤ 5 sites of disease were identified at time of diagnosis or first time of development of metastases. univariate analysis was performed to determine the association between treatment toxicity and patient characteristics, treated lesion volume and dose. The chi-square test or Fisher exact test were used as appropriate depending on sample being tested for comparing proportions in categorical variables and the t-test or ANOVA for continuous variables. Late toxicity was graded using the “Common Terminology Criteria for Adverse Events” (CTCAE V.5.0). Of 986 patients with solid tumors reviewed, 109 (11.05%) found to have OMD and treated with SABR and /or SRS for 225 metastatic lesions. The mean age of our OMD population was 57 years. Majority of them had Performance Status (PS) of one (53%) and two (30%) with Charlson Comorbidity index (CCI) of six (67%). Among OMD patients, 47 (43%) had primary colorectal cancer (CRC) followed by non-small cell lung cancer (NSCLC) 21(19%) and breast cancer 17(16%). Of 225 treated sites, 64 (28%) were brain metastatic sites followed by liver and lung (23%) and (21%), respectively. Median SABR dose was 48 Gy (range: 30-54 Gy) in 3 to 5 fractions and the median SRS dose was 21 Gy. Median volume of extracranial lesions was 22cc and 1.8cc for cranial lesions. SABR was well tolerated with infrequent late adverse events. No Grade 4 or 5 toxicity was encountered. Four treated sites (1.8%) in four patients (3.7%) had grade 3 toxicities; 16 treated sites (7%) in 12 treated patients (11%) had grade 2 toxicities. Toxicity correlation with PS, dose or volume was not statistically significant. OMD patients constitute a significant portion of oncology patients. SABR is a safe local treatment modality in OMD patient population. A prospective study with larger sample size is required to confirm these finding and evaluate any correlation between toxicity to SABR/SRS dose and treated lesion volume.