Purpose The recently worldwide standard measurement of electron beam reference dosimetry include the International Atomic Energy Agency (IAEA) Technical Report Series (TRS)‐398 and Association of Physicists in Medicine (AAPM) Task Group (TG)‐51 protocols. Muir et al. have modified calibration methods for electron beam calibration based on AAPM TG‐51. They found that the use of cylindrical chambers at low energy gave acceptable results. In this study, we propose and report a modified calibration for electron beam based on IAEA TRS‐398, the standard reference dosimetry protocol worldwide. Methods This work was carried out with energies of 6, 8, 10, 12, and 15 MeV. The electron beam is generated from Elektra Synergy Platform and Versa HD linear accelerator. The charge readings were measured with PTW 30013, IBA CC13, Exradin A1Sl, and Exradin A11 chambers connected to the electrometer. The dose calculation uses an equation of modified calibration for electron beam using the updated kQ${k_Q}$ factor in previous work. The absorbed dose to water for electron beam is expressed in dose per monitor unit (cGy/MU). Thus, we compared dose per monitor unit (D/MU) calculation using a modified calibration to TRS‐398. Results In this work, we have succeeded in implementing the modified calibration of electron beam based on TRS‐398 by applying a cylindrical chamber in all energy beams and using the updated kQ${k_Q}$ factor. The ratio of the absorbed dose to water between original and modified calibration protocols of TRS‐398 (Dw) for the cylindrical chamber was 1.002 on the Elekta Synergy Platform and 1.000 on the Versa HD while for the parallel‐plate chamber it was 1.013 on the Elekta Synergy Platform and 1.014 on the Versa HD. Based on these results, both the cylindrical and parallel‐plate chambers are still within the tolerance limit allowed by the TRS‐398 protocol, which is ±2%. Therefore, modified calibration based on TRS‐398 gives acceptable results and is simpler to use clinically.

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Position verification before the treatment is performed to ensure the actual position to the planning position, so the dose distribution received by the tumor target would be in accordance with the planned dose. In Helical Tomotherapy (HT) treatment, the image of Megavoltage CT (MVCT) could be used to verify the patient’s position by registering the image to Kilovoltage CT (KVCT) image. The aim of this study was to evaluate the comparison from the dose distribution resulted from MVCT and KVCT image registration with and without automatic position correction at high doses. The correction in MVCT image registration to KVCT image was performed with adjustment in four HT degrees of freedom (lateral, longitudinal, vertical and rotational direction). Nine MVCT patient images with Hepatocellular Carcinoma were used with high doses therapy in 4-10 fractions using HT at Cipto Mangunkusumo Hospital. Evaluation of the dose distribution in the verification variation (the corrected and uncorrected position) was analyzed with Homogeneity Index (HI), Conformity Index (CI) and Organ at Risk. The results show that HI ranges from 0.06 to 0.3, while CI varies from 0.7 to 1. Based on these results, the position correction may less contribute to the dose distribution to the tumor target.

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