ESTRO 2025 - Abstract Book

S1680

Clinical - Sarcoma & skin cancer & malignant melanoma

ESTRO 2025

planning treatment volume (PTV) 1162/806cc, respectively. The cohort was characterized by unfavourable features in >40%, including 11/69 (16%) retroperitoneal/abdomino-pelvic lesions, 9 (13%) WHOOPS and 9 (13%) recurred/pre treated lesions; 3 of them had undergone previous RT. PTVs/GTVs were defined according to the RTOG 0630 trial. Bolus material (flab) on skin was placed in 51/69 (74%). Induction chemotherapy was given in 2/69 patients (3%). All histologic diagnoses were reviewed/confirmed by our National Sarcoma Reference pathologist. The indication for RT was discussed/determined in all instances during our weekly Swiss Sarcoma Network (SSN; swiss-sarcoma.net) multicenter sarcoma conference. Results: After a mean/median FU time of 27/27 months (2-55), we observed 4/69 (6%) local recurrences diagnosed 4/5/6 and 8 months post uhRT: 1/4 local recurrence after externally performed incomplete surgery (R1) without any further additive therapy, 1/4 was treated for a second local failure, 2/4 in large undifferentiated sarcomas of the medial tight of 1761cc and 1192cc diagnosed with synchronous distant metastases in both cases. Successful salvage surgery was performed in 1/4, translating into a final local control rate of 95%. Early RT tolerance was limited to G0-1, allowing for timely surgery mean/median 20/15 days after uhRT completion (range, 4-60d). R0-resection was achieved in 92%. The wound complication rate (according to CAN-NCIC-SR2 trial) was low with 10% (7/69) [2]. Total treatment time took <1 month in most patients (mean/median 26/23 days (10 75)). Conclusion: We found a 2y local control rate of 94% in our single institution STS cohort treated with uhRT. Local failure was expectable in 2/4 (watch&wait following R1 resection; therapy of a second recurrence). Local failure rate and time to event are well comparable to normofractionated RT literature [3]. References: 1) Hypofractionated Preoperative Radiation Therapy for Soft Tissue Sarcoma: A Systematic Review. Ronan Joyce MB et al. International Journal of Radiation Oncology*Biology*Physics. Available online 5 August 2024. In Press, Corrected Proof 2) Preoperative ultra-hypofractionated radiotherapy for soft-tissue sarcomas: low rate of wound complications. Mattmann A, Glanzmann C, Fuchs B, Bode B, Studer G ( 2024 ). Advances in Radiation Oncology. Volume 9, Issue 10, October 2024 , 101562 3) Local relapse patterns after preoperative radiotherapy of limb and trunk wall soft tissue sarcomas: Prognostic role of imaging and pathologic response factors . M. Cuenin et al. Clinical and Translational Radiation Oncology 48 ( 2024 ) 100825 Digital Poster Definitive radiotherapy in elderly patients with non-melanoma skin cancer: a decision tree algorithm Stefania Martini 1 , Lavinia Spinelli 1 , Paola Critelli 1 , Alberto Fallico 2 , Giuseppe Minniti 2 , Anna Maria Merlotti 1 , Francesca De Felice 2 1 Radiation Oncology, Santa Croce e Carle Hospital, Cuneo, Italy. 2 Radiation Oncology, Policlinico Umberto I, Department of Radiological, Oncological and Pathological Sciences, "Sapienza" University of Rome, Rome, Italy Purpose/Objective: Radiotherapy(RT) can be proposed as curative treatment in non-melanoma (basal and squamous cell carcinoma) skin cancer. This study aimed to develop a classification tree approach to predict clinical complete response(cCR) after definitiveRT in elderly patients using pre-treatment clinical parameters. Keywords: Preoperative uhRT in STS: 2-y local failure 2004