## 3 SBRT in Non-Ovarian Gynecologic Primary Oligometastases
The authors reported favorable response in 80.3% of cases and a median 1-year local progression-free survival rate of 75.9%, which was maintained at 3 years. The 1-year and 3-year overall survival rates were 65.4% and 28.7%, respectively. Liver lesions were found to be associated with a less favorable response on multivariate analysis, with only 37.5% of liver lesions with a favorable response. Tumor size < 3.8 cm was associated with a favorable response in the univariate analysis, which trended towards significance in the multivariate analysis. The delivery of a high BED over a small volume with rapid dose fall off is an advantage of SBRT, as seen in Figure 1. However, a limitation of SBRT is its inability to target the adjacent, potentially clinically relevant, at-risk nodal echelon. It has been commonly reported in the literature that despite local ablative radiation to oligometastatic sites, disease progression varies widely, with rates ranging between 23.1% and 75%. Disease progression outside of the radiated field remains the main site of progression and occurs in 78.9-100% of cases [12]. Superior overall survival and progression-free survival have been noted in early detection of oligometastatic lesions and complete response following SBRT [12; 17; 31], which may suggest micrometastatic spread in the neighboring lymphatics that is not clinically apparent at the time of evaluation, resulting in out-of-field progression despite local ablative radiation. Given the high rate of disease progression outside of the SBRT field, elective nodal radiotherapy as metastasis-directed treatment was evaluated in a recently published landmark analysis [26], with a median follow up of 11.7 years. Definitive standard fractionation 2D/3D conformal radiation therapy (CRT) or IMRT including the entire at-risk nodal echelon was delivered to 48 patients with gynecologic oligometastases, resulting in disease-free survival and overall survival of 73 months and 200 months, respectively. Nodal sites were treated to a median dose of 62 Gy to the gross tumor volume (GTV) in 2.0-2.2 Gy per fraction with the clinical target volume (CTV) covering the adjacent nodal echelon to a dose of 45-50 Gy in 1.8-2.0 Gy fractions. Fifty percent of patients in this cohort had recurrence after a median of 28 months, predominantly with an out-of-field component, despite the extension of coverage to neighboring lymphatics. Interestingly, there was a significant improvement in disease-free survival in patients receiving any chemotherapy with radiation as opposed to radiation alone (93 months vs. 34 months, respectively). This highlights the importance of systemic therapies in the treatment of oligometastatic disease. Figure 1: Clinical example of a patient with recurrent and oligometastatic high grade serous carcinoma of the ovary following surgery and multiple lines of systemic therapy. **(A)** Patient was found to have a hypermetabolic nodule medial to the left psoas muscle on positron emission tomography (PET) compatible with metastatic disease. **(B)** Gross tumor volume (GTV) delineation of oligometastatic nodule (red) with 0.5 mm planning tumor volume (PTV) radial expansion (orange). The treatment plan for this patient was generated to deliver a dose of 3000 cGy in 5 fractions prescribed to the PTV. The technique used in this plan is stereotactic body radiotherapy (SBRT) utilizing volumetric modulated arc therapy (VMAT) with a 10 MV beam energy. The plan is prescribed to the PTV. Axial **(C)** and coronal **(D)** images showing dose distribution. There is a max dose of 115.2% of the prescription dose with the PTV. **(E)** Representative axial image of follow-up computed tomography (CT) showing resolution of the treated nodule.