ESTRO 2022 - Abstract Book

S126

Abstract book

ESTRO 2022

Conclusion While OS differences between the cohorts likely reflect selection bias, there was no difference in MCC-specific survival and very few in-field recurrences in the two cohorts, despite lower EQD2 dosing in the hypo-RT group. Most recurrences occurred out-of-field as in-transit or distant recurrences. Our data suggest that hypo-RT may be a reasonable and more convenient option for select pts, but future prospective studies are needed.

MO-0152 Hypofractionated versus conventional adjuvant radiotherapy for lymph node metastases of melanoma

L.H. Holtkamp 1,2 , S.N. Lo 1,3 , M. Drummond 1 , J.F. Thompson 1,3,4 , O.E. Nieweg 1,3,4 , A.M. Hong 1,3

1 The University of Sydney, Melanoma Institute Australia, Sydney, Australia; 2 University Medical Center Groningen, Department of Surgical Oncology, Groningen, The Netherlands; 3 The University of Sydney, Faculty of Medicine and Health, Sydney, Australia; 4 Royal Prince Alfred Hospital, Department of Melanoma and Surgical Oncology, Sydney, Australia Purpose or Objective Adjuvant post-operative radiotherapy (RT) has been shown to reduce the risk of recurrence in a lymph node field following therapeutic dissection for high-risk stage III melanoma. However, the optimal fractionation schedule is unknown and both hypofractionated and conventionally fractionated adjuvant RT have been used. The aim of this study was to compare the oncological outcomes of these two approaches in an era before effective systemic immunotherapy became available. The primary endpoint was node field recurrence (as a first recurrence). Secondary endpoints were recurrence-free survival (RFS) and overall survival (OS). Risk factors associated with node field recurrence as a first recurrence, RFS and OS were also assessed. Materials and Methods This retrospective, single-institution study involved 335 patients with stage III melanoma who received adjuvant radiotherapy after therapeutic regional lymph node dissection for metastatic melanoma between 1990 and 2011. Information on tumour characteristics, radiotherapy and patient outcomes was retrieved from the Melanoma Institute Australia database and patients’ medical records. Results Hypofractionated RT (median dose 33 Gy in six fractions over three weeks) was given to 95 patients (28%) and conventionally fractionated RT (median dose 48 Gy in 20 fractions over four weeks) to 240 (72%). Five-year lymph node field control rates were 86.0% (95% CI 78.4-94.4%) in the hypofractionated group and 85.5% (95% CI 80.5-90.7%) in the conventional fractionation group (P=0.87), see figure. There were no significant differences in RFS (41.7% (95% CI 32.5-53.5) vs. 31.9% (95% CI 26.1-38.9), P=0.18) respectively, and OS (41.2% (95% CI 32.1-52.8) vs. 45.0% (95% CI 38.7-52.4) P=0.77). On multivariate analysis, extranodal spread was associated with decreased RFS (P=0.04). The number of resected lymph nodes containing metastatic melanoma was associated with decreased RFS (P=0.0006) and OS (P=0.01).