ESTRO 2023 - Abstract Book

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ESTRO 2023

incomplete response after 8 cycles, were subjected, when feasible, to local RT (6 daily fractions of 6Gy). Patients unable to undergo RT or patients recurring after RT were treated with further chemotherapy. Results Out of 19 patients, 2 died from intercurrent reasons before completion of the 4th cycle, and 2 refused to continue therapy after the 2nd cycle, due to long travel distances and/or social/financial reasons. Of the remaining 15, 2 (13.3%) had CR, 10 (66.7%) PR and 3 (20%) had stable disease (SD), after the completion of the 4th cemiplimab cycle. After the 8th cycle, 9 (60%) reached CR, 3 (20%) PR, 2 (13.3%) SD and 1 (6.7%) PgD. All PRs and one patient with SD underwent RT, which led to CR of the disease. The remaining two patients refused further therapy. The overall CR rate was 86.7% (13/15), reaching 100% (13 /13) for patients receiving full treatment according to the treatment algorithm. Within a median follow-up of 12 months (4-24 months), only 1 patient progressed locally, providing an estimated 2-year survival of 82.9%. irAEs included 2 patients with generalized skin toxicity (enforcing immunotherapy interruption), and 2 patients with hypothyroidism. RT tolerance was excellent without higher than grade 1 early or late toxicity.

Conclusion LA-SqSC can be effectively treated with induction cemiplimab immunotherapy followed by a short course hypofractionated RT directed to the residual tumor after the 8th cycle of cemiplimab.

PO-1551 The effect of jaw tracking during radiotherapy for facial non-melanoma skin cancer

S.H. Park 1 , J. Choi 2 , D. Kim 3 , S.H. Ahn 4

1 Jeju National University, Radiation Oncology, Jeju, Korea Republic of; 2 Jeju National Univerisy, Radiation Oncology, Jeju, Korea Republic of; 3 Ulsan University Hospital, Radiation Oncology, Ulsan, Korea Republic of; 4 Ewha Womans University, Ewha Medical Research Institute, Seoul, Korea Republic of Purpose or Objective The higher extent of low dose radiation filed, the worse skin erythema result. In this study, we analyzed dosimetric effects of jaw tracking (VitalBeam, Varian) during the Volumetric Modulated Arc Therapy (VMAT) planning for facial non-melanoma skin cancer (NMSC). Materials and Methods Twenty-two patients with facial NMSC underwent VMAT planning with or without jaw tracking. The target volume (TV) included the primary skin lesion with 1-cm margin around the surface and a 4 mm depth. A total of 55 Gy in 20 fractions was prescribed and the plans were considered acceptable if the TV was covered by 95%-105% of the isodose curve. Dosimetric comparison was performed with volumes of low dose regions which were defined as < 50% of prescription dose (V10-50%). The target coverage was evaluated by homogeneity index (HI) and conformity index (CI). Results The patients’ median TV was 4.07 cc (range: 1.03-10.27 cc). The use of jaw tracking provided mean volume reduction rates in 5.2% (0%-14.4%) for V30%, 10.2% (0.1%-21.0%)for V20%, and 14.7% (1.8%-30%) for V10% (all p < 0.001). Volume changes for V50% and V40% between two groups were 0.4% and 1.7%, respectively (p=0.408, 0.183). No significant differences were observed for HI (0.06) and CI (0.54). Conclusion The application of jaw tracking during VMAT for facial NMSC was associated with significant reduction in the volume of low dose delivered in the radiation field (V10-30%) while maintaining the target coverage. Future analyses should assess whether this volume difference affect treatment-related cosmetic outcome. T. Iwai 1 , T. Imagumbai 2 , S. Hiraoka 1 , T. Kishi 3 , S. Okabayashi 1 , R. Ashida 2 , T. Mitsuyoshi 2 , Y. Matsuo 1 , T. Ishigaki 3 , T. Mizowaki 1 , M. Kokubo 2 1 Kyoto University Graduate School of Medicine, Radiation Oncology and Image-applied Therapy, Kyoto, Japan; 2 Kobe City Medical Center General Hospital, Radiation Oncology, Kobe, Japan; 3 Osaka Red Cross Hospital, Radiation Oncology, Osaka, Japan Purpose or Objective Scalp or face angiosarcoma is a rare cutaneous malignancy with a poor prognosis. Combined therapy including whole scalp radiotherapy (RT) is the treatment for scalp or face angiosarcoma, and volumetric modulated arc therapy (VMAT) is considered to have benefits for target coverage and shorter treatment time. We reviewed the patients with scalp or face angiosarcoma treated with VMAT at several institutions. Materials and Methods Between January 2015 and March 2020, patients with scalp or face angiosarcoma without distant metastasis treated with VMAT at three institutions were evaluated. Both definitive RT and postoperative RT were included. Information regarding patient status, tumor characteristics, treatment characteristics, and outcomes were obtained from the clinical records. Local control probability (LC), overall survival (OS), and progression-free survival (PFS) were calculated by the Kaplan-Meier method from the start date of any first treatment for angiosarcoma. Toxicity was evaluated by CTCAE version 5.0. PO-1552 Scalp or face angiosarcoma treated with volumetric modulated arc therapy, a multicenter study