Monte Carlo calculation of the relative TG-43 dosimetry parameters for the INTRABEAM electronic brachytherapy source

The INTRABEAM system (Carl Zeiss Meditec AG, Jena, Germany) is an electronic brachytherapy (eBT) device designed for intraoperative radiotherapy applications. To date, the INTRABEAM x-ray source has not been characterized according to the AAPM TG-43 specifications for brachytherapy sources. This restricts its modelling in commercial treatment planning systems (TPSs), with the consequence that the doses to organs at risk are unknown. The aim of this work is to characterize the INTRABEAM source according to the TG-43 brachytherapy dosimetry protocol. The dose distribution in water around the source was determined with Monte Carlo (MC) calculations. For the validation of the MC model, depth dose calculations along the source longitudinal axis were compared with measurements using a soft x-ray ionization chamber (PTW 34013) and two synthetic diamond detectors (microDiamond PTW TN60019). In our results, the measurements in water agreed with the MC model calculations within uncertainties. The use of the microDiamond detector yielded better agreement with MC calculations, within estimated uncertainties, compared to the ionization chamber at points of steeper dose gradients. The radial dose function showed a steep fall-off close to the INTRABEAM source (<= 18years) with spondyloarthritis (SpA) and PsA were included in the trial if they presented with clinical and MRI-positive heel enthesitis. MRI of the affected heel was performed at three time points: screening, Week 24 and Week 52. Inflammatory MRI findings (tendinitis, bursitis and bone marrow oedema [BME]) in the area of the Achilles tendon and/or plantar aponeurosis, periarticular inflammation of the ankle joint and heel erosion were assessed qualitatively (absent/present). In addition, BME and bone erosion were quantitatively assessed based on PsAMRIS, where their proportion was compared to the volume of the affected bone. Mean scores of BME and bone erosion quantification were calculated, and the mean composite score (based on PsAMRIS) was calculated based on the individual score of each subject for periarticular inflammation, BME and bone erosion and further extended for bursitis and tendinitis. Modifications to PsAMRIS were introduced by categorising oedema length as <=/>0.5cm and locating bone erosion.ConclusionsIn ACHILLES, MRI was used to assess and evaluate heel enthesitis. Due to the lack of a validated scoring system for heel enthesitis at the time of ACHILLES initiation, this trial applied quantitative scoring based on PsAMRIS, with specific adaptations for the heel.Trial registrationNational Clinical Trial Registry, NCT02771210. Registered 13 May 2016.