ESTRO 2021 Abstract Book

S1251

ESTRO 2021

(19.13 %) to the abdominal/pelvic region and 5 RTs (4.35 %) to extremities. Overall, 31 (26.96 %) of the 115 RTs had an adjuvant treatment intention, 7 (6.09 %) were definitive irradiation treatments, 45 (39.13 %) palliative, 27 (23.48 %) local-ablative, and 3 (2.61 %) were consolidating RT indications. In 23 patients (20.0 %) the TT had been paused for more than one week before starting the irradiation. In 25 patients (21.74 %) the break was less than one week before irradiation and in 42 patients (36.52 %) the TT was not paused at all. The combination of RT and TT has been well tolerated overall. The most common toxicity was radiation dermatitis, with 18 cases of CTCAE grade 1, 3 cases of CTCAE grade 2 and 1 case of CTCAE grade 3 toxicity. Only in 1 patient (0.87 % of the evaluated RTs) treated with Imatinib, the TT was discontinued due to melaena during RT. Other mild CTCAE grade 1-2 toxicity that occurred occasionally included dysphagia, dyspnoea, dry cough, hyperpigmentation, edema and fatigue. Table 1: Targeted therapy substances administered concurrently to radiotherapy:

Conclusion The concurrent treatment with radiotherapy and TT has shown no excessively increased or additional toxicity in our analysis so far.

PO-1527 Single-institution analysis of cancer patients treated with multiple courses of repeat radiotherapy M. Ahmadsei 1 , S.M. Christ 1 , L. Wilke 1 , A. Kühnis 1 , E. Vlaskou Badra 1 , J. Willmann 1 , S. Tanadini-Lang 1 , M. Guckenberger 1 1 UniSpital Zürich, Klinik für Radio-Onkologie, Zurich, Switzerland Purpose or Objective The number of long-term survivors in cancer patients has increased substantially due to major advances in cancer care and treatment. Concurrently, patients may present for several times with oncological situations requiring local radiotherapy in curative or palliative intent. This single-institution analysis aims to report patterns of care and outcomes of patients treated with multiple courses of radiotherapy. Materials and Methods All patients having received radiotherapy over the last decade at the Department of Radiation Oncology, University Hospital Zurich, were screened for this analysis. A course of radiotherapy was defined as all treatment sessions to one anatomical site under one medical indication. Demographics, cancer and treatment characteristics as well as overall survival of patients having undergone multiple courses of irradiation were assessed. Results In 2011, the proportion of patients treated with a minimum 3 or 5 courses of radiotherapy was 2.1% and 0.7%, respectively. By 2019, these numbers increased significantly to 12.5% and 4.5%, respectively. In the 112 patients treated with a minimum of 5 courses, the primary tumor site was lung cancer in 42.0% (n=47), malignant melanoma in 9.0% (n=10) and breast cancer in 8.0% (n=9) of cases. A median of 5 radiotherapy courses was administered with a median interval of 3 years (maximum 8 years) between the first and the last