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Aim: To determine the energy and dose dependence of GafChromic EBT3-V3 film over an energy range 0.2 mm Al HVL to 6 MV. Background: The decay scheme of a brachytherapy source may be complex and the spectrum of energy can be wide. LiF TLDs are the golden standard recommended for dosimetric measures in brachytherapy, for their energy independence, but TLDs could be not available in some centres. An alternative way to perform dose measurements is to use GafChromic films, but they show energy dependence. Methods and materials: Films have been irradiated at increasing dose with three different beams: 6 MV beam, TPR20, 10 = (0.684 ± 0.01), HVL = (2.00 ± 0.01)mmAl and HVL = (0.20 ± 0.01)mmAl. Calibration curves were generated using the same dose range (0cGy to 850cGy) for the three energies. Using the 6 MV calibration curve as reference, the film response in terms of net optical density (OD) was evaluated. Results: The difference in the calibration curve obtained by irradiating the film with 6 MV and 2 mm Al HVL energy beams is less than 3 %, within the calibration uncertainty, in the dose range 500-850cGy. The OD of EBT3-V3 film is significantly lower at 0.2 mmAl HVL compared to 6 MV, showing differences up to 25 %. Conclusion: Within the range 6 MV-2 mm Al HVL and dose higher than 500cGy, GafChromic EBT3-V3 films are energy independent. In this dose range, films can be calibrated in a simple geometry, using a 6 MV Linac beam, and can be used for brachytherapy sources dose measures. The use of EBT3 films can be extended to reference dosimetry in Ir-192 clinical brachytherapy.

A dosimetric audit of Ir-192 high dose rate (HDR) brachytherapy remote after-loading units was carried out in 2019. All six brachytherapy departments on the island of Ireland participated in an end-to-end test and in a review of local HDR dosimetry procedures. Materials and methods: A 3D-printed customised phantom was created to position the following detectors at known distances from the HDR source: a Farmer ionization chamber, GafChromic film and thermoluminescent dosimeters (TLDs). Dedicated HDR applicator needles were used to position an Ir-192 source at 2 cm distance from these detectors. The end-to-end dosimetry audit pathway was performed at each host site and included the stages of imaging, applicator reconstruction, treatment planning and delivery. Deviations between planned and measured dose distributions were quantified using gamma analysis methods. Local procedures were also discussed between auditors and hosts. Results: The mean difference between Reference Air Kerma Rate (RAKR) measured during the audit and RAKR specified by the vendor source certificate was 1.3%. The results of end-to-end tests showed a mean difference between calculated and measured dose of 2.5% with TLDs and less than 0.5% with Farmer chamber measurements. GafChromic films showed a mean gamma passing rates of >95% for plastic and metal applicators with 2%/1 mm global tolerance criteria. Conclusions: The results of this audit indicate dosimetric consistency between centres. The 'end to end' dosimetry audit methodology for HDR brachytherapy has been successfully implemented in a multicentre environment, which included different models of Ir-192 sources and different treatment planning systems. The ability to create a 3D-printed water-equivalent phantom customised to accurately position all three detector types simultaneously at controlled distances from the Ir-192 source under evaluation gives good reproducibility for end-to-end methodology.

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In medical radiography, a large area of the human body sometimes needs to be investigated by means of X-ray examinations, for example, the lower spine. With computed radiography (CR) cassettes, due to their large surface area, it is possible to make this type of investigation with a single exposure and use of a single cassette. With flat-panel digital detectors (DR detectors), due to their smaller size and their large cost, it is not possible to make the investigation with a single exposure, but multiple exposures are required according to the extent of the surface to be irradiated, with merging of two or more radiographic images. This operation is called "stitching" because several images are stitched together. We have tested three different modes of performing stitching examinations: linear, rotational and wide. Our purpose was to highlight the differences and issues, taking into account the quality of the images and the simplicity of use, with the goal of choosing the best technique. We evaluated the methods by three different parameters: the image quality, the ease of use (taking into account the time for performing an examination), and the simplicity of development. Each method has good qualities, but also its own problems: choosing the best technique is not easy, because each has advantages and disadvantages. Nowadays, rotational stitching is the most used because the quality of the images is very good and we are confident that the images have no parallax errors. However, this is not an easy system to develop because there are two different mechanical movements to be managed. For this reason, we are improving linear stitching, which is easier, but has a worse image quality. Wide stitching is the system closer to the CR system and has very good image quality, but the difficulty of developing a collimator that allows one to perform the technique presents a big hurdle. We conclude that, even though rotational stitching is complex and expensive, it is the best technique among those investigated.