A first radiotherapy application of functional bulboclitoris anatomy, a novel female sexual organ-at-risk, and organ-sparing feasibility study

Objective: The bulboclitoris (clitoris and vestibular bulbs) is the primary organ responsible for female sexual arousal and orgasm. Effects of radiotherapy on the bulboclitoris are unknown, as its structure/function has yet to be described in radiotherapy, and it overlaps only partially with the external genitalia structure. Our aim was to: describe bulboclitoris structure, function and delineation; compare volume of and dose delivered to the bulboclitoris vs external genitalia; and, compare bulboclitoris-sparing IMRT (BCS-IMRT) to standard IMRT (S-IMRT) to determine reoptimization feasibility. Methods: Our expert team (anatomist, pelvic radiologist, radiation oncologist) reviewed bulboclitoris anatomy and developed contouring guidance for radiotherapy. 20 female patients with anal cancer treated with chemoradiation were analyzed. Sexual organs at risk (OARs) included the external genitalia and the bulboclitoris. Volumes, dice similarity coefficients (DSCs) and dose received using S-IMRT were compared. Plans were reoptimized using BCS-IMRT. Dose–volume histograms (DVHs) for PTVs and all OARs were compared for BCS-IMRT vs S-IMRT. Results: Bulboclitoris structure, function and delineation are described herein. The bulboclitoris occupies 20cc (IQR:12–24), largely distinct from the external genitalia (DSC <0.05). BCS-IMRT was superior to S-IMRT in reducing the dose to the bulboclitoris, with the greatest reductions in V30 and V40, with no significant changes in dose to other OARs or PTV 1/V95. Conclusion: The bulboclitoris can be contoured on planning imaging, largely distinct from the external genitalia. Compared with S-IMRT, BCS-IMRT dramatically reduced dose to the bulboclitoris in anal cancer planning. BCS-IMRT might safely reduce sexual toxicity compared with standard approaches. Advances in knowledge: The structure and function of the bulboclitoris, the critical primary organ responsible for female sexual arousal and orgasm, has yet to be described in the radiotherapy literature. Structure, function and delineation of the bulboclitoris are detailed, delineation and bulboclitoris-sparing IMRT were feasible, and sparing reduces the dose to the bulboclitoris nearly in half in female patients receiving IMRT for anal cancer, warranting further clinical study.