INTRODUCTION: Curative chemoradiotherapy of squamous cell carcinoma achieves long-term complete remissions in most patients and minimizing treatment toxicity becomes crucial issue. The aim of the retrospective analysis was to determine an acceptable dose to the bone marrow for radiotherapy planning not leading to increased haematological toxicity. PATIENTS AND METHODS: In the period 2013-2019, 40 patients with squamous cell carcinoma were curatively treated at the Department of Oncology of the University Hospital Motol using intensity modulated radiotherapy (IMRT) /volumetric modulated arc radiotherapy (VMAT) technique. Women make up 90% of the group, the average age at the time of dia-gnosis was 65 years (47-81). Chemotherapy mitomycin C and 5-fluorouracil was given to 68% of patients. The bone marrow was contoured in the Varian Eclipse planning system, version 15.6. RESULTS: Acute hematotoxicity (G3, 4, 5 according to Common Terminology Criteria for Adverse Events - CTCAE) was significantly associated with the concomitant chemoradiotherapy (P = 0.002) and the average dose to the bone marrow 27 Gy (P = 0.011). Late haematological toxicity was mild (maximum grade 1), asymptomatic, and no dependence of late haematotoxicity on any risk factor (age, gender, WHO performance status, bone marrow dose, CHT, BMI, smoking, stage) was proved. The overall survival at 5 years was 100% in stage I, 83% in stage II, 61% in stage III and 0% in stage IV. Local control at 5 years is 100% in stage I, 92% in stage II, 87% in stage III and 0% in stage IV. Local recurrence developed in 5% of radically treated patients. Distant metastases occurred in 8% of radically treated patients. Local recurrences or metastases occurred only during the first 2 years after the treatment. CONCLUSION: Radical chemoradiotherapy in the treatment of squamous cell anal carcinoma is highly effective. IMRT/VMAT enabled to apply a sufficiently effective dose to the tumor and elective areas and reduced not only acute skin, GI and GU toxicity, but also acute haematological toxicity in cases with the dose Dmean to bone marrow lower than 27 Gy. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical, papers.

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