This study reported the justification and selection of acceptable γ criteria with respect to low (6 MV) and high (15 MV) photon beams for intensity-modulated radiation therapy quality assurance (IMRT QA) using the Gafchromic external beam therapy 3 (EBT3) film.

Five-field step-and-shoot IMRT was used to treat 16 brain IMRT patients using the dual-energy DHX-S linear accelerator (Varian Medical System, Palo Alto, CA, USA). Dose comparisons between computed values of the treatment planning system (TPS) and Gafchromic EBT3 film were evaluated based on γ analysis using the Film QA Pro software. The dose distribution was analysed with gamma area histograms (GAHs) generated using different γ criteria (3%/2 mm, 3%/3 mm and 5%/3 mm) for the 6 and 15 MV photon beams, to optimise the best distance-to-agreement (DTA) criteria with respect to the beam energy.

From the comparison between the dose distributions acquired from the TPS and EBT3 film, a DTA criterion of 3%/2 mm showed less dose differences (DDs) with passing rates up to 93% for the 6 MV photon beams, while for the 15 MV a relaxed DTA criterion of 5%/3 mm was consistent with the DD acceptability criteria with a 95% passing rate.

Our results suggested that high-energy photon beams required relaxed DTA criteria for the brain IMRT QA, while low-energy photon beams showed better results even with tight DTA criteria.

The data used in brachytherapy planning are obtained from homogeneous mediums. In practice, the heterogeneous tissues and materials affect the dose distribution of brachytherapy. It is aimed to investigate the effect of air cavities on brachytherapy dose distribution using a specially designed device.

In this study, the special device designed with different volumes of air and water to be irradiated and measured at different depths using EBT3 Gafchromic films. EBT3 Gafchromic films were preferred for this study because they can be cut to the shape of the experimental geometry, are water resistance and double directional usability.

In our study, sudden dose increases and decreases were observed at the water–air–water interfaces. Increases were 9, 11·8 and 15% in the 13, 18 and 22 mm apparatus, respectively. These effects were expected and the results were consistent with the literature and within the tolerance limits stated in the clinical dose guidelines. The most important result is that the percent depth–dose curve of the radiation passing through the air to the water and only passing through the water medium is different. The average differences were 1·97, 2·97 and 2·31% for the 13, 18 and 22 mm apparatus, respectively.

Although the effect of heterogeneity may be neglected according to clinical guidelines, it is suggested that the dose effect of heterogeneity is taken into account so that the dose can be estimated sensitively. Brachytherapy plans using dose data without considering air gaps may cause erroneous dose distributions due to heterogeneity of tissue.

The purpose of this study was to analyse the comparison of intensity-modulated radiation therapy quality assurance (IMRT QA) using Gafchromic® EBT3 film, Electronic portal imaging device (EPID) and MapCHECK®2.

Pretreatment authentication is the main apprehension in advanced radiation therapy treatment plans such as IMRT.

A total of 20 patients were planned on Eclipse treatment planning system using 6 and 15 MV separately.

Gamma index of EBT3 film results shows the following average passing rates: 97% for 6 MV and 96·6% for 15 MV using criteria of ±5% of 3 mm, ±3% of 3 mm and ±3% of 2 mm for brain. However, by using ±5% of 3 mm and ±3% of 3 mm criteria, the average passing rates were 95·4% on 6 MV and 95·2% on 15 MV for prostate. For EPID, the results show the average passing rates as 97·8% for 6 MV and 97·2% for 15 MV in for brain. In cases in which ±5% of 3 mm and ±3% of 3 mm were used, the average passing rates were 96·6% for 6 MVand 96·1% for 15 MV for prostate. MapCHECK®2 results show average passing rates of 96·4% for 6 and 96·2% for 15 MV, respectively, for brain using criteria of ±5% of 3 mm, ±3% of 3 mm and ±3% of 2 mm, whereas for ±5% of 3 mm and ±3% of 3 mm the average rates are 95·2% for 6 and 94·7% for 15 MV in prostate.

The EPID results are better than the other methods, and hence EPID can be used effectively for IMRT pretreatment verifications.