A dosimetric comparison of 3D-CRT, IMRT and IMAT treatment techniques — assessment from radiation protection point of view

Abstract

Background:The purpose was to assess the impact of irradiation technique type and beam energy on the mixed radiation field around the medical linear accelerator (linac) in terms of radiation quality and related radiation protection quantities. Materials and methods:Seven radiotherapeutic plans with Alderson-Rando anthropomorphic phantom [different techniques: conventional three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT) and intensity modulated arc therapy (IMAT), different beams: 6 MV or 18 MV, and their arrangements) were prepared for the case of prostate malignancy. Recombination chambers REM-2 and GW2 were positioned on the treatment couch 100 cm from the beam axis at the height of the isocentre. Recombination chambers REM-2 and GW2 were used for recombination index of radiation quality Q 4 determination, measurement of total tissue dose D t and calculation of gamma and neutron components to D t . Estimation of D t and Q 4 allowed for the ambient dose equivalent H*(10) calculations for each plan.Results: For plans prepared with 6 MV beams, Q 4 values within the limits of uncertainty were equal to one, which confirms the correctness of the measurement method. For plans implemented with 18 MV beams, the value of Q 4 was in the range of 3.7-5.7. Comparison between treatment techniques indicates that the lowest exposure resulting from out-of-field doses comes from 6 MV IMAT (0.7 mSv), whereas the highest one is from 18 MV IMRT (55.1 mSv). Conclusion:With the recombination chambers technique it was confirmed that the choice of beam energy directly affects the generation of photoneutrons. The treatment plan technique can have a significant impact on the out-of-field dose.