Evaluation of a systemic change of Superficial X-ray tube characteristics

Introduction: Very low, Low and Medium X-ray machines are used extensively for Superficial Radiation Therapy mostly used for Basal Cell, Squamous Cell Carcinoma, and Melanoma skin cancers. In most of cases, Superficial X-ray Therapy (SXRT) is preferred to Electron beams generated using a linear accelerator. SXRT tube characteristics may vary with the use of the machine for a long time. This study investigates the variation of machine output characteristics acquired during machine commissioning and applied for treatment planning system. Materials and Methods: A Gulmay D3150 Superficial Unit was used for all data collected. At the first stage, beam quality index, half Value Layer (HVL), radiation beam profiles in different depths for a range of applicator for all available applicators were collected. At the end, machine output was also compared with baseline established during the machine commissioning. Results: Result shows that there is a systemic variation of the beam quality index up to 4.3%. Although results are found to be within tolerance, but a systemic variation of the data acquired shows that machine characteristics are modified. Conclusion: As a systemic change of machine output is observed, based on data achieved, more detailed QA checks, annual QA program and re-commissioning of the machine for more accurate treatment is recommended.