## 2 SBRT in Ovarian Primary Oligometastases  
Radiation was historically used to treat metastatic ovarian cancer in a palliative setting, with a well-established efficacy in the treatment of pain and bleeding [6; 7; 8]. Local recurrence within the abdomen or pelvis remained a significant factor contributing to poor prognosis despite multiple courses of chemotherapy. Definitive intent treatment using involved field radiation therapy (IFRT) resulted in modest benefits in overall survival and in-field disease control [9; 10]. Intensity-modulated radiation therapy (IMRT) was more promising, with 2-year local control (LC) and overall survival (OS) rates of 82% and 63%, respectively, in refractory disease despite a median of three regimens of chemotherapy for recurrence within the abdomen or pelvis [11]. More recently, the use of SBRT has been evaluated in oligometastatic ovarian cancer. A recent systematic review on SBRT in gynecologic malignancies [12] analyzed sixteen studies including one prospective phase II trial, two prospective phase I trials and thirteen retrospective reviews dating back to 2009. A total of 667 patients with 1071 oligometastatic lesions from varying ROMGC histological subtypes were evaluated. More than half (57.6%) of patients had primary ovarian oligometastases and 65.4% had a single lesion treated. Most lesions that were treated were at nodal sites (64%) within the abdomen (44.2%) or pelvis (18.8%) to a median BED\({}_{10}\) of 50.7 Gy with response rates and local control exceeding 75% and 80%, respectively. Despite the high local control rates, disease progression occurred outside of the SBRT field. In addition, over half (56%) of the studies found no grade 3 or higher toxicities, suggesting that SBRT is well tolerated overall. Although this is representative of a mixed cohort of primary malignancies, a significant portion of patients in this review are from one retrospective review, the Multicenter Italian Trial in Ovarian cancer and gynecologic (MITO) RT1 study, which specifically evaluated the role of SBRT in ovarian primary oligometastases. The MITO RT1 study is the largest retrospective review of ovarian primary oligometastases treated with SBRT, including 261 patients with 449 oligometastatic lesions with a median follow up of 22 months [13]. Most patients had a single lesion (55.9%) in abdominal lymph nodes (65%) with a median size of 15.7 cc. Inclusion criteria included any site of disease and up to five synchronous lesions. The most common histology was high-grade serous in 71.3% of patients. All patients underwent chemotherapy prior to radiation and 88.2% were treated with SBRT while 11.8% were treated with single-fraction radiotherapy (SRS). The median SBRT dose was 27 Gy (range 18-75) with a median BED\({}_{10}\) of 48 Gy (range, 28-262.5). The most frequent SBRT prescriptions were 8 Gy \(\times\) 3 fractions, 5 Gy \(\times\) 5 fractions and 9 Gy \(\times\) 3 fractions. Complete response was achieved in 65.2% of patients, with a 2-year actuarial local control of 81.9%, 2-year progression-free survival of 15.4%, and 2-year overall survival of 73.6%. On multivariate analysis, the following factors were identified as independent predictors for a higher likelihood of complete response and increased local control: patients younger than 60 years old, planning target volume (PTV) \(<\) 18 cc, lymph node disease and BED\({}_{10}\)\(>\) 70. SBRT was well tolerated with 95.1% late toxicity-free survival. Two other studies have reported comparable complete response rate with SBRT in oligometastatic ovarian cancer. An Italian retrospective study reported their experience with SBRT in 26 patients with 44 metastatic lesions [14]. Most patients had lymph node metastases (63.6%) treated to a median total dose of 45 Gy (range, 36-60 Gy) in six fractions (range, 4-8). After a median follow-up of 28.5 months, complete response was 59.1%, the 2-year local control was 92.9% and the median progression-free survival was 19 months. No grade 3 or 4 toxicities were reported [14].