Introduction: Anal cancer is a rare type of malignancy. Basic treatment is a combination of radiotherapy and chemotherapy. Combined therapy allows better healing of the patient, but also causes greater toxicity, with more side effects, acute as well as chronic. With the development of hardware and software in radiotherapy over the years, increasingly advanced irradiation techniques are being used that allow for a better dosage concentrated more on the tumor and less on the surrounding healthy tissue. Purpose: Our purpose was to determine the type of direct toxic effects and their incidence and severity in patients with anal cancer who were undergoing a treatment of IMRT (Intensity Modulated Radiotherapy) or VMAT (Volumetric Modulated Arc Therapy) radiation therapy and compare them with the results of the older 3D CRT (Three-Dimensional Conformal Radiation Therapy) type of treatment. Methods: We conducted a retrospective study, which included review of physical medical records as well as records from the clinical information system WebDoctor and ThinClinical for 93 patients with anal canal cancer who were undergoing a radiotherapy at the Oncology Institute in Ljubljana between November 2012 and November 2019. For statistical data processing, we used the basic frequency statistics for the distribution of acute toxicity and to asses survival rates we used the Kaplan-Meier survival curve. Also we calculated the Cox regression model. Results: Complete response to treatment was reported in 79.1% of patients, while in 20.9% of patients residual or recurrent disease was confirmed, most commonly at the site of tumor onset, followed by distant metastases and least commonly in regional lymph nodes. Locoregional relapse-free survival at five years is 83% and five-year disease-free survival is 77%. Modern radiation techniques demonstrated statistically significant improvements in treatment outcome (p=0,0026). No life-threatening acute side effects were reported in our patients. Grade 3 radiodermatitis was most commonly reported as a more serious adverse reaction in 65.6% of patients, followed by infection in 31.2% of patients, radiomucositis in 7.7% of patients, and nausea with vomiting in 1.1% of patients. Other side effects were milder. When comparing the severity of side effects of the newer and older irradiation techniques, we find that, with the exception of radiodermatitis, they occur in a milder form when using newer radiation techniques. Discussion and conclusion: When using modern, advanced radiation techniques, patients experience milder acute side effects of treatment, which allows for a treatment without detrimental interruptions and consequently more successful treatment.
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