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Quality assurance programme in kilovoltage radiotherapy at University hospital Rijeka: Four-year experience

Introduction Radiation therapy using kilovoltage X-rays can achieve high local control rates for both advanced squamous cell and basal cell carcinomas [1]. The comprehensive quality assurance (QA) programme is required to assure treatment outcome and radiation safety of patients. International recommendations require the implementation of a QA programme for all sources of radiation in medical practices and, as far as possible, regular and independent quality audit reviews of the QA programme for all radiotherapy procedures, including kilovoltage radiotherapy. Nevertheless, it has been shown that a low importance of such equipment is given by regulators, physicists and physicians, in comparison with more complex therapeutic machines [2]. Consequently, written QA/QC protocols regarding kilovoltage radiation therapy are very rare and these devices are not encompassed by audits either. At University hospital Rijeka, we developed our QA protocol and have been implementing periodical procedures for the past four years. The protocol is written according to international reports and publications [3]. Materials and methods The measurements are performed on nine X-ray beams produced by X-Strahl 150, X-ray machine intended for superficial and orthovoltage radiation therapy. Main concern of above mentioned protocol where radiation and dose determination but basic mechanical and safety tests are also included. Dose measurements are performed using electrometer in combination with different ionization chambers in appropriate phantoms whether solid or water respectivelly. HVL measurements are initially performed using Al-filters of high purity but regular checks of beam quality include measurements in raw phantom according to our methodology. Furthermore, IAEA methodology is used for the determination of the absorbed dose to water in a low and medium energy x-ray beams [4]. Periodical tests derived from the commissioning procedures are divided into mechanical, radiation and safety tests. Mechanical and safety tests are not in the scope of this overview. Radiation tests performed are dose output constancy, dose output reproducibility in different conditions, linearity, beam symmetry and beam quality. Results Results showed high beams stability over time which motivated us to revise existing protocols according to our four-year experience. Methodology remained the same, but the frequencies were updated. Quality assurance of kilovoltage radiotherapy machines was initially developed from a high-energy radiotherapy point of view, in terms of rigid tolerances and high frequencies of performing quality control tests. Analysis of the results collected over past four years showed remarkable stability of milovoltage X-ray radiotherapy machine which led us to reduce frequency of majority of tests. It is worth noting that although beams are very stabile the frequency of dose verification procedures remain the same. Discussion Kilovoltage radiotherapy machines should be calibrated following standardised protocols [4] and be subjected to QA programmes to guarantee the accuracy of the treatment. It was shown also that dosimetric quality audit programmes in radiation therapy should be expanded to include dermatological radiation therapy and such audits should include beam quality verification [5].

quality assurance; kilovoltage radiotherapy

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