A. L. Pomeroy1, K. L. Leonard2, and T. A. DiPetrillo3; 1Tufts University School of Medicine, Boston, MA, 2Department of Radiation Oncology, Rhode Island Hospital, Lifespan Cancer Institute, Warren Alpert Medical School of Brown University, Providence, RI, 3Department of Radiation Oncology, Warren Alpert Medical School of Brown University-Lifespan Cancer Institute, Rhode Island Hospital, Providence, RI
Purpose/Objective(s): Ovarian transposition (OT) was first proposed in the 1950s in order to avoid the hormonal and reproductive consequences of pelvic radiation therapy (RT). OT more than 1.5 cm superior to the iliac crest and radiation exposure limited between 120-315 cGy has been associated with preserved function. However, the dose at which immediate ovarian dysfunction is induced in 97.5% of patients decreases with increasing age and a recent meta-analysis discovered the rate of ovarian dysfunction could be as high as 33.1% in patients receiving OT in preparation for lower GI RT. No study has evaluated radiation doses that are typically seen in pelvic anatomic locations in patients being treated for lower GI cancers. Our study measured the distance from isodose lines to the sacral promontory (SP) in patients being treated for lower GI malignancies in order to determine a safe distance for OT. Materials/
Methods: The radiation plans of female patients with lower GI malignancies from one academic institution were reviewed. Isodose lines of 200, 300, 600, 1200, and 1400 cGy were labeled. The distance from the isodose line to the SP was measured to the nearest 100th of a centimeter and the spinal level to which the isodose line corresponded was recorded. Measures of central tendency were calculated. Results: 43 plans were analyzed. The average distance from the SP to the 200 cGy isodose line was 6.28 cm. This corresponded to the superior (n = 13) and middle (n = 14) aspects of L4. The 300 cGy isodose on average fell 5.40 cm from the SP while 600 cGy averaged around 3.76 cm away. 300 cGy corresponded with inferior L4 (n = 18) and L4/L5 (n = 11) or superior L5 (n = 12) for 600 cGy. 1200 and 1400 cGy averaged closest to the SP at only 2.86 and 2.72 cm away respectively, both falling around mid-L5 (n = 14). Conclusion: Based on our data, most OT procedures would need to place the ovaries more than 5-6 cm superior to the SP in order to minimize ovarian dysfunction in female patients undergoing RT for lower GI cancers. In comparison, the average ovary lies around 0.8 cm from the SP. Given that the average female L4 vertebral structure is 2.9 cm in length, this could indicate that the current standard of placing the ovaries at least 1.5 cm from the iliac crest underestimates the minimum safe distance for OT. As the general age of those with GI cancers decreases and the incidence increases, OT could become even more important in order to decrease the incidence of ovarian dysfunction in our female patients.
