ESTRO 2021 Abstract Book

S1157

ESTRO 2021

mediastinal lymphoma in the area of radiation. One case report shows an adult patient without secondary malignancy at 57 months follow-up and made a comprehensive literature review of radiotherapy outcomes in adult patients with GS. Another case series evaluated the use of radiotherapy in 3 adult patients with 17 BCCs treated and complete remission without carcinogenic effects was reached in all treated lesions, with a mean follow-up of 30.35 months.

Conclusion There is evidence that shows how radiotherapy can induce tumors in pediatric patients, so it is recommended to avoid the use of radiotherapy in these patient population. In the limited literature available, there is no evidence that radiotherapy induces tumors in adult patients with GS. The recommend treatment for BCCs in GS patients is surgical excision, but CO2 laser, electrocauterization, cryotherapy and photodynamic therapy may be used. In addition, imiquimod cream 5%, topical 5-fluorouracil and vismodegib in locally-advanced and metastatic forms are other treatment options. However, in selected adult patients with BCC not candidates for other treatments, radiotherapy could also provide a favorable outcome. PO-1408 Establishment of a national database for non-melanoma skin cancer treated with radiotherapy J.G. Eriksen 1 , Z.G. Zimling 2 , C.K. Lønkvist 3 , A.L. Linnet Nielsen 3 , P. Lassen 1 , K. Nowicka-Matus 4 , N. Gyldenkerne 5 , G. Hanahan 6 , J. Friborg 2 , J. Overgaard 1 , A. Gothelf 2 1 Aarhus University Hospital, Dept. of Experimental Clinical Oncology, Aarhus, Denmark; 2 Copenhagen University Hospital, Dept. of Oncology, Copenhagen, Denmark; 3 Herlev Hospital, Dept. of Oncology, Herlev, Denmark; 4 Aalborg University Hospital, Dept. of Oncology, Aarhus, Denmark; 5 Odense University Hospital, Dept. of Oncology, Odense, Denmark; 6 Vejle Hospital, Dept. of Oncology, Vejle, Denmark Purpose or Objective Treatment of skin cancer with radiotherapy (RT) dates back to 1899. Despite this, very few large data sets exist on treatment and outcome in non-melanoma skin cancer (NMSC). In 2019 an initiative was taken to establish a national collaboration and database between the departments treating NMSC with radiotherapy. Nation-wide registration started January 2020. The aim is to create evidence from large unbiased cohorts in order to optimize treatment and outcome of RT in NMSC. Materials and Methods A database accessible online using two-step login was established. Key parameters regarding patient, tumor and treatment characteristics are recorded as well as follow-up (incl. photos documentation as a part of a standardized cosmetic follow-up). Results During the first year 824 patients (pts) with NMSC was registered. Male-female balance were 51% vs. 49%. Median age was 75 years (27-100 years). The majority of pts had WHO performance status 0-1 (89%). In total 45% had one or more risk factors predisposing to NMSC: 309 pts (38%) had prior NMSC; 44 (5%) were organ transplanted or received immunosuppressive drugs for other reasons; 23 pts (3%) had previously received RT to the involved skin area or bucky rays for benign diseases. None were registered having hereditary diseases that predisposes to NMSC. In total, 77% were basal cell carcinomas (BCC), mostly of nodular type (63%). The rest were squamous cell carcinomas (SCC). Frequent localizations of BCC were: nose (68%), forehead (8%) and ears (6%). Tumors had a median thickness of 2.5 mm and a diameter of 10 mm and 86% had UICC8 Stage I disease. Less than 1% had nodal or distant metastases. Frequent localizations of SCC’s were: lips (21%), nose (13%) and cheeks (13%). Tumors had a median thickness of 7 mm and a diameter of 20 mm. 80% had UICC8 Stage I-II disease. Initially, 20% presented with node- positive disease and 6% with distant metastases. 38% of the pts were discussed at NMSC dedicated multidisciplinary tumor boards. In total 7 different dose