3285 - Adjuvant IMRT in Locally Advanced Penile Cancer: Clinical Performance of an Institutional Inguinal Contouring Guideline

Purpose/Objective(s): To report clinical outcomes in patients with locally advanced penile squamous carcinoma (LA-PnSCC) treated with adjuvant IMRT using the published institutional inguinal contouring guideline.

Materials/Methods: For adjuvant IMRT in LA-PnSCC, a novel guideline for inguinal target contouring was developed at our institute based on the observed patterns of failure, and published previously. Clinical performance of this guideline was evaluated after its implementation in routine practice. Consecutive patients with LA-PnSCC treated with radical intent surgery, (neo)adjuvant chemotherapy, and adjuvant IMRT at our center till April 2024, with inguinal target contouring per institutional guideline were eligible. Those with distant metastases or gross locoregional disease without surgery, palliative radiotherapy, or non-IMRT techniques were excluded. Follow up records were extracted from prospectively maintained institutional database. Post-IMRT patterns of recurrence were mapped vis-à-vis the institutional guideline-based contours, and regional recurrences classified as in-field (centroid within PTV), marginal (outside PTV but within 50% isodose), or out of field (beyond 50% isodose). Progression free survival (PFS) and overall survival (OS) were estimated by Kaplan Meier method.

Results: Total 49 patients were eligible for analysis. Almost all (96%) had pN3 disease, treated with radical penectomy (total or partial, 82%), bilateral inguinal dissection (92%), and pelvic nodal dissection (89%). Platinum-based chemotherapy was given for 87% patients (adjuvant 65%, neoadjuvant 22%). Inguinal nodes were irradiated bilaterally in 90% patients, with pelvic nodes included if involved (unilateral 24%, bilateral 57%). Dose prescription was 50.4Gy in 28 fractions, with integrated boost to 56Gy to part of the target volume in 31% patients. IMRT was delivered under daily image guidance. Concurrent weekly cisplatin was given for 78% patients. Over a median follow-up of 27 months (IQR 11-42), recurrence was recorded in 7 patients, with 3 having a regional component (2 in-field, 1 out of field). [Table 1]. None of the recurrences were marginal or in the prepubic fat. Two-year locoregional control was 89.6% (95%CI 88-100%), PFS 80% (68%-95%), and OS 89% (79%-100%) for the study cohort. No patient had toxicity-related interruption or acute toxicity >grade 3. 18% patients had late >grade 2 dermatitis and 43% had grade 1-2 lymphedema. Table 1: Location of recurrence (* in-field)

Conclusion: Clinical implementation of the institutional contouring guideline for adjuvant IMRT showed high regional control in this cohort of LA-PnSCC.