Verification of absorbed dose and single-field dosimetry of MLC-shaped IMRT photon beams in Hubei province

Abstract

Objective To verify the absorbed dose and two-dimensional dosimetry delivered by MLC-shaped IMRT photon beams using thermoluminescent dosimeters (TLDs) and radiochromic films. Methods Different types of medical linear accelerators at 7 third-grade first-class hospitals in Hubei were selected for this audit study. Besides TLDs and films, a small polystyrene phantom measuring 15 cm×15 cm×15 cm, supplied by the International Atomic Energy Agency (IAEA), was also used. The TPS dose calculation were performed with 6 MV X-ray beam and by delivering 6 Gy dose to the TLDs or films at 10 cm depth for 5 cm×5 cm field size at 90 cm SSD. After irradiation, comparations were conducted of dose derivations between TPS-calculated values and TLD- or film-measured values. The two-dimensional dosimetry audit was carried out by using 30 cm×30 cm homogeneous solid phantoms in which a 25 cm×25 cm film was located at 5 cm depth. A single-filed profile generated by TPS was delivered to the film, and the film was measured. And then, two-dimensional dose distribution was analyzed using the film analysis system. Results The results suggested that the relative deviations of TLD and film to TPS dose was -8.5% and -1.9% for accelerator 1, 5.4% and 0.5% for accelerator 7, respectively, whereas those for other accelerators were within ±5%. The passing rates for two-dimensional dose distribution at all accelerators were all higher than 90%. Conclusions TLD and film quality audit for IMRT can be applied for a wide range of application in view of its simplicity, reliability and postal convenience. Key words: Intensity modulated radiotherapy; Thermoluminescent dosimeter; Film; Absorbed dose; Two-dimensional dose distribution