Ovarian Transposition Prior to Pelvic Radiotherapy: Spatial Distribution and Dose Volume Analysis.

Abstract

PURPOSE/OBJECTIVE(S)\nPelvic radiotherapy (RT) is an integral component of local therapy for anorectal and gynecologic malignances. Ovaries are exquisitely radiosensitive, with even 6 Gy exposure leading to a moderate risk of ovarian failure, and 14 Gy resulting in ovarian failure in nearly all patients. To facilitate ovary dose reduction, surgical transposition prior to pelvic RT can be performed, however ovarian function preservation rates remain approximately 50%. Moreover, there is a paucity of data in the modern treatment era analyzing the anatomic locations and dose volume metrics achieved for transposed ovaries, which was examined herein.\n\n\nMATERIALS/METHODS\nRetrospective study including women who underwent ovarian transposition prior to pelvic RT between 2010 and 2020. Measurements (cm) were obtained for 1) the craniocaudal (CC) distance from the plane of the sacral promontory to the ovary centroid and 2) the distance between the nearest edge of the ovary and RT planning target volume (PTV) in any dimension. Area under the receiver operating characteristic curve (AUC) and cut-point analysis estimating ovary location outside the PTV was performed.\n\n\nRESULTS\nThirty-one ovaries were analyzed from 18 patients. Fourteen (77.8%) were treated for cervical cancer and three (16.7%) for rectal cancer. Most (72.2%, n\u202f=\u202f13) were treated with intensity-modulated RT while 27.8% (n\u202f=\u202f5) were treated with 3D-CRT. The median CC distance from the ovaries to sacral promontory was 0.8 cm (interquartile range [IQR] -0.83 - 1.59 cm) and the median distance between the ovary and PTV was 0.9 cm (IQR, -1.0 - 1.9 cm). The majority of ovaries were located above the sacral promontory (64.5%, n\u202f=\u202f20) and outside the PTV (61.3%, n\u202f=\u202f19). AUC and cut-point analysis demonstrated that CC distance from the sacral promontory predicted an ovary to be outside the PTV with an optimal cut-point of 1.2 cm (C-index\u202f=\u202f0.72). The median mean and maximum (Dmax) ovary doses were 15.5 Gy (IQR, 9.6 - 19.4 Gy) and 32.2 Gy (IQR, 24.8 - 45.9 Gy), respectively. When comparing the RT dose of transposed ovaries located outside (n\u202f=\u202f19) vs. within (n\u202f=\u202f12) the PTV, there was a significant decrease in median Dmax (25.4 Gy vs. 46.1 Gy; P < .001), but no significant difference in median mean dose (15.5 Gy vs. 16.4 Gy; P\u202f=\u202f.19). There was a significant inverse correlation between CC distance of transposed ovaries to the sacral promontory and ovary mean dose (-0.73, P < .0001) and Dmax (-0.76, P < .0001).\n\n\nCONCLUSION\nThere was a significant inverse correlation between ovary CC distance from the sacral promontory and ovary RT dose. However, despite the majority of transposed ovaries being located outside the PTV, most patients still received ovary doses associated with a high risk of ovarian failure. These findings provide a deeper understanding of the relationship between ovary location and dose to inform pre-RT planning and suggest that more aggressive ovary-sparing strategies are warranted.