Gastrointestinal Cancer

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SU_16_2161 - Outcomes of Stereotactic Body Radiation Therapy for Abdominopelvic Oligometastases

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Outcomes of Stereotactic Body Radiation Therapy for Abdominopelvic Oligometastases
J. Shahi1, J. Peng1, E. Donovan1, R. K. W. Wong1,2, T. Tsakiridis1,2, K. Quan1,2, and A. Swaminath1,2; 1McMaster University, Hamilton, ON, Canada, 2Juravinski Cancer Centre, Hamilton, ON, Canada

Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) allows for the delivery of highly conformal, locally ablative doses of radiation to extracranial targets. Limited data exists in the management of oligometastases (OMs) in the abdominopelvic (AP) space, where the delivery of SBRT poses challenges given the proximity of radiosensitive organs-at-risk, particularly luminal GI structures. We conducted a retrospective chart review to assess clinical outcomes in patients with AP OMs treated with SBRT at our centre. We hypothesize that SBRT can achieve high rates of LC in AP OMs with acceptable toxicity.

Materials/Methods: Eligible patients were those with OMs (defined as disease in ≤3 involved organs and ≤3 total sites) in the AP soft tissues (excluding the liver) treated with SBRT. All primary tumor histologies were included. Minimum follow-up of 3 months was required. Clinical endpoints assessed included progression-free survival (PFS), local control (LC), chemotherapy-free survival (CFS), overall survival (OS) and toxicity (CTCAEv5.0). Descriptive statistical analyses and Kaplan-Meier estimates of LC, PFS, CFS and OS (from date of SBRT completion) were then conducted.

Results: Fifty-one eligible patients with 58 AP OMs were treated with SBRT between January 2011 and December 2015. Median follow-up was 21.9 months. Primary tumors were predominately gynecologic (39%), gastrointestinal (31%), or genitourinary (16%). Eighty-eight percent of patients had a solitary OM. Eighty-three percent of treated OMs were AP lymph nodes (48/58). Median maximal lesion size was 22 mm (range 7-74 mm). All treatments were delivered in 5 fractions with a median dose of 35 Gy (25-40 Gy; BED10 31.25-72 Gy). Initial progression post-SBRT occurred in 38/51 patients (75%) mostly due to distant failures alone (33/38; 87%). Median initial PFS was 5 months (95%CI 2.5-7.5), with a 2-year rate of 29%. Oligometastatic progression occurred in more than half of patients (21/37) who progressed at any time point during follow-up. Of these patients, 48% (10/21) received further SBRT. Resulting 2- and 4-year CFS were 47% and 37%, respectively (median CFS 15 months). Rates of 2- and 4-year LC were 74% and 69%. Median OS was 43 months (95%CI 31-55). Nineteen patients (37%) experienced acute toxicity, predominately grade 1/2, with only one grade 3 toxicity observed. One late non-GI toxicity occurred. No grade 4 or 5 acute or late toxicities were seen.

Conclusion: Despite concerns regarding initial distant PFS, modest BED SBRT for AP OMs was associated with sustained LC without significant toxicity. In this population, excellent OS and CFS were also observed, yet no definitive conclusions can be made if this is solely due to treatment. Oligometastatic disease may behave more indolently and allow for the opportunity to salvage limited-burden local and distant failures and delay chemotherapy; however, prospective validation of our findings is warranted.

Author Disclosure: J. Shahi: None. J. Peng: None. E. Donovan: None. R.K. Wong: None. T. Tsakiridis: None. A. Swaminath: None.

Jeevin Shahi, MD, BS


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SU_16_2161 - Outcomes of Stereotactic Body Radiation Therapy for Abdominopelvic Oligometastases

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