PROSPECTIVE CASE SERIES IN THE USE OF ABDOMINAL AND PELVIC SBRT IN THE CONTEXT OF OLIGO-PROGRESSIVE DISEASE

There is emerging evidence for the “Oligometastatic” state where local therapy for a limited number of metastatic lesions may have benefits for progression free survival (PFS), overall survival (OS) and potentially quality of life. The “Oligo-progressive” state occurs when a patient has several metastatic deposits in which a small number are progressing either on systemic therapy or having just completed a line of treatment. Controlling such lesions with Stereotactic Body Radiotherapy (SBRT) is theorized to extend PFS by either extending an existing chemotherapy course or by delaying the need for commencing a new course. Limited information has been published for treating such lesions in the abdomen and pelvis. We analyzed all oligo-progressing patients treated with 5-fraction SBRT to the abdomen and pelvis 2014-2018. Patients were treated with VMAT using Varian planning software over 2 weeks with abdominal compression employed to reduce breathing amplitude for upper abdominal targets. Patients were categorized in terms of primary diagnosis, target location, target size, dose delivered, PFS and OS from SBRT and time to next treatment. Oligo-progression was defined using an in-house protocol as metastatic patients who progressed radiologically in 1-2 lesions on systemic treatment or within 6 months of completing a course. Local control was evaluated using cross–sectional imaging. Toxicity assessment used CTCAE version 4. Data analysis was conducted as part of an institutional Quality Assurance Process. A total of 35 patients with 42 SBRT courses met inclusion criteria, mean age 62 (range 31–87 years). Their primary tumor types included colorectal 11 (31%), breast 8 (23%), endometrial 4 (11%), lung 4 (11%), and other types 8 (23%). SBRT target organs included liver 26 (62%), para-aortic lymph nodes 5 (12%), adrenal gland 4 (9%), iliac nodes 4 (9%) and others 3 cases (7%). Median PTV prescription dose was 40Gy in 5 fractions (range 25-50Gy) with mean ITV size 98cc (range 0.73-613cc). Median follow-up 300 days. Estimated local control rate was 69% at 1 year and 51% at 2 years, respectively. Median PFS following SBRT was 111 days (95% CI 60-161 days), with estimated 1 year PFS 25%. Median OS was 663 days (95% CI 281-1044 days), with estimated 1-year OS of 67%. Median chemotherapy-free time following SBRT was 133 days (95% CI 61-205 days). One patient developed a grade 4 GI toxicity with a gastro-hepatic fistula, resolved with conservative management. No other grade ≥3 toxicities were observed. There was no association between local control rate or PFS with cancer type, ITV size or prescribed dose. Abdominal and Pelvic SBRT to oligo-progressive targets was well tolerated in this series and could allow either a period of time off chemotherapy or the continuation of existing systemic therapy thereby potentially increasing the remaining chemotherapy options.