(P074) The Use of Stereotactic Body Radiotherapy in Lieu of Brachytherapy in Patients With Cervical or Endometrial Cancer

Nabila L. Waheed, DO, Michelle Ludwig, MD, PhD, Celestine Tung, MD, Marian Williams-Brown, MD, Creighton L. Edwards, MD, Concepcion Diaz-Arrastia, MD, Matthew L. Anderson, MD, PhD, Lois Ramondetta, MD, Timothy Wagner, MD, Joshua Asper, PA, Danny Tran, CMD, Umang Patel, MD, Mark Bonnen, MD; Department of Radiation Oncology, Department of Obstetrics and Gynecology, Baylor College of Medicine; Department of Gynecologic Oncology, UT MD Anderson Cancer Center

PURPOSE: To evaluate the use of stereotactic body radiation therapy (SBRT) as an alternative treatment method to brachytherapy in patients with cervical or endometrial carcinoma with anatomically difficult-to-implant tumor volumes or other contraindications to brachytherapy.

MATERIALS AND METHODS: A total of seven patients undergoing radiation therapy with curative intent for cervical or uterine cancer were identified after they had been deemed ineligible for brachytherapy due to unfavorable anatomy, including large tumor size, location, and/or prior hysterectomy. Patients diagnosed with either cervical (n = 5) or endometrial (n = 2) cancer were treated using 45–48.6 Gy external beam radiation to the pelvis +/− para-aortic lymph nodes. Either three-dimensional (3D) radiation or intensity-modulated radiotherapy (IMRT) was followed by Linac-based SBRT to the cervix or vaginal cuff at a dose of 5–6 Gy in five daily fractions to a total of 25–30 Gy. Median age was 52 years (range: 47–64 yr). The International Federation of Gynecology and Obstetrics (FIGO) stage was I (n = 1), II (n = 2), and IV (n = 1); the remaining three patients had vaginal cuff recurrence. All patients were simulated and treated after insertion of a Foley urinary catheter with manual bladder filling to a predetermined volume. Patients also underwent bowel preparation at the time of simulation and before each treatment fraction, and daily cone-beam image-guided radiotherapy (IGRT) was utilized. The dose-volume histograms for planning target volumes, as well as organs at risk, were all analyzed.

RESULTS: SBRT was well tolerated. No acute severe urinary or gastrointestinal toxicity > grade 2 was observed during treatment or up to 5 months posttreatment. Target volume of 95% gross tumor volume (GTV) coverage goal was > 95% (range: 95%–99%). D_0.2cc to the bladder was kept at or below 90 Gy (range: 87.3–90 Gy). Total bladder D_0.2cc contribution from SBRT for all five fractions was 20.5–40 Gy. D_0.2cc to the rectum was kept at or below 75 Gy (range: 69–73.8 Gy). Total rectal D_0.2cc contribution from SBRT for all five fractions was 13.1–23.8 Gy. No patient has had any sign of progression or local failure at follow-up thus far, with a median follow-up of 3 months.

CONCLUSION: SBRT boost appears to be an effective and well-tolerated alternative treatment method for patients with gynecologic malignancies who cannot undergo brachytherapy. Target coverage and dose to organs at risk with SBRT appear to be comparable with those of brachytherapy. Acute toxicity is minimal. These initial clinical results substantiate the need for further evaluation of this treatment approach and its long-term efficacy and safety.

Proceedings of the 97th Annual Meeting of the American Radium Society- americanradiumsociety.org