Recommendations and Clinical Validation of Inguinal Clinical Target Volume Delineation in Penile Cancer

Abstract

This study determined the patterns of distribution of inguinal nodes and the optimal margin needed around the femoral vessels to propose guidelines for inguinal clinical target volume (CTV) delineation in penile cancer. Patients with biopsy-proven penile squamous cell carcinoma with inguinal node metastases were identified on a computed tomography scan. Distribution of nodes and distance of nodes to the nearest femoral vessel and inferior edge of pubic symphysis (IPS) were obtained. A 3-dimensional CTV margin to cover 95% of the nodes was estimated to evolve contouring guidelines. A comprehensive contouring guide with a visual atlas for inguinal CTV delineation was created. The proposed CTV was prospectively validated in 14 consecutive patients with penile squamous cell carcinoma treated with post-operative radiation therapy to the inguino-femoral region. Of the 222 inguinal lymph nodes analyzed in 33 patients, 99% were located anterior (81% antero-medial, 18% antero-lateral) to femoral vessels. A majority (95%) of the antero-laterally located nodes were superior to IPS. Margin around the femoral vessels to cover 95% of the nodes for supra-IPS region in anterior, medial, and lateral directions was 29, 23, and 21 mm, respectively, and for infra-IPS region in anterior and medial directions was 21 and 23 mm, respectively. Cranial and caudal extent of CTV delineation with respect to IPS was at 48 and 50 mm, respectively for 95% nodal coverage. On prospective validation, after a median follow-up of 24 months (range, 5-31), none of the patients developed marginal recurrences. Grade 1 and grade 2 lymphedema was seen in 6 (42.8%) and 4 (28.5%) patients, respectively. This study analyzed pattern of distribution of inguinal nodes and proposes guidelines for inguinal CTV delineation in penile cancer. The proposed guidelines were validated prospectively in a small cohort of patients and found to be implementable and safe.