End-to-end dosimetric audit: A novel procedure developed for Irish HDR brachytherapy centres

Abstract

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.

Evaluation of a new radiochromic film dosimeter, Gafchomic EBT4, for VMAT, SABR and HDR treatment delivery verification

“…The current versions are EBT3 for standard dose range and EBT-XD for extended (higher) dose range (Sorriaux et al 2013, Palmer et al 2015a, 2015b, 2015c, Schoenfeld et al 2016. The high spatial resolution, relative ease of read-out, weak energy dependency and near tissue equivalence make Gafchromic films suitable for dose measurements in a variety of radiotherapy situations, including for dosimetric audit (Palmer et al 2015a, 2015b, 2015c, Bassi et al 2020.…”

3D printed brachytherapy jig for Reference Air Kerma Rate calibration

“…The use of jigs to enable reproducible Farmer chamber measurements has been investigated previously, using both commercially available [9,10] and inhouse designed devices [4,7]. However, although the use of 3D printed jigs for non-reference brachytherapy dosimetry has recently been reported in the literature [11], none of these examples have utilised a 3D printed jig for the purpose of absolute dose measurements for a brachytherapy source using the IAEA protocol.…”

“…3D printing in radiotherapy is a useful tool for optimising clinical practice and workflow [11][12][13][14]. The speed and accuracy with which jigs can be printed are desirable for radiotherapy departments, particularly those that already have a 3D printing programme set up.…”