In vivo dosimetry using EBT3 and EBT-XD radiochromic films for high-energy electron beam in hypofractionation keloid radiotherapy

Radiochromic film is commonly used for in vivo dose verification in radiotherapy. The aim of this study was to investigate the difference in the in vivo dose of high-energy electron beam with single hypofractionation radiotherapy between EBT3 and EBT-XD films in keloid patients. Thirty patients who received postoperative keloid radiotherapy were enrolled in the study (ethics approval: FEMH-IRB-108165). Gafchromic EBT3 and EBT-XD films in the form of 2 × 3 cm2 sheets were used to measure the surface dose to the postoperative keloid scars. The research compared the measurement dose and prescribed dose as well as the difference between EBT3 and EBT-XD radiochromic films. The surface dose in the EBT3 group was 85.5–104.7 % of the prescribed dose and that in the EBT-XD group was 88∼106.6 % of the prescribed dose. The mean percentage differences for thirty measurements were −4.9 % and −2.5 % for the EBT3 and EBT-XD films, respectively. The maximum variation for both film types was −15.3 % and −12.4 % for Patient #6 with a scapula keloid lesion. This investigation also demonstrated that, for 40 % of the patients in the EBT3 group, good agreement (within 5 % variation) was obtained between the dose measurements and the prescribed dose. In contrast, 73 % of the patients in the EBT-XD group agreed well with the expected dose. Moreover, for 10 % of the patients, high agreement (within 1 % variation) was demonstrated for the EBT3 film, and 23 % of the patients were consistent with the EBT-XD film. This study also revealed significant differences between the EBT3 and EBT-XD gafchromic films (p = 0.002). This was not only the first study to perform in vivo dosimetry using EBT-XD film, but also to survey the difference in surface dose between EBT3 and EBT-XD films under the same treatment conditions for clinical patients. For in vivo dosimetry in electron beam radiotherapy, compared with the EBT3 radiochromic film, the EBT-XD film is more suitable for hypofractionation surface dose verification.