Modified electron beam output calibration based on IAEA Technical Report Series 398

Abstract

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.

A multicenter study of modified electron beam output calibration

“…In TRS‐398, the position of the reference point for the parallel‐plate chamber was at the reference depth ($${z}_{ref}),\ $$and on the inner surface of the entrance window, at the center of the window, whereas for the cylindrical chamber, it was at the effective point of measurement, 0.5 $${r}_{cyl}\ $$deeper than $${z}_{ref}$$. This is different for measurements using modified calibration procedure by Muir 17 and Pawiro et al., 18 where the position of the reference point for the cylindrical chamber was with the central axis at $${z}_{ref}.$$ The measurement of $${z}_{ref}$$ in the absolute dosimetry of the electron beam is calculated as follows: $$$$\begin{equation}{Z}_{ref} = \ 0.6{R}_{50} - 0.1\ \left( {{\mathrm{cm}}} \right),\end{equation}$$$$where $${R}_{50}\ $$is the depth at which dose falls 50% of the maximum for 10 cm × 10 cm field size. The types of linear accelerators, $${R}_{50},\ $$and $${z}_{ref}$$ used in the measurements are listed in Table 4.…”

“…The determination of the beam quality conversion factor in the modified calibration, denoted as $$k{^{\prime}}_Q$$, was the same as that of Pawiro 18 and Muir's work 17 . The factor of $$k{^{\prime}}_Q$$ of a chamber is determined by substituting the power fitting parameter for a cylindrical chamber to the equation based on the Monte Carlo calculation proposed by Muir and Rogers 9 .…”

“…The importance of achieving high accuracy and precision in radiotherapy has always been recognized, and dosimetry plays a crucial role in achieving this goal. Pawiro et al 18 recently compared the absolute dose ratio using the modified calibration procedure and TRS-398 protocols. The results showed that the absolute dose ratios obtained with the cylindrical chamber were 1.002 and 1.004.…”

Modified calibration protocols in electron beam dosimetry: comparison with IAEA TRS-398 and AAPM TG-51

“…A recent publication presented a modified calibration for electron beam reference dosimetry [5] using the formalism proposed by Muir, which yielded smaller deviations than TG-51. A modified reference dosimetry formalism for the electron beam was also applied and compared with TRS-398, which showed a dose ratio of 1.000-1.014 between TRS-398 and modified calibration [7]. These results were within the allowable tolerance limit of ±2% [2].…”

Implementation of TRS-398 Protocol in Routine Calibration of Linac by Determination of Slab Phantom on Water Phantom Correction Factor

“…As a guide to dose measurement in ionometric dosimetry, two standard dosimetry protocols have been developed are IAEA Technical Report Series No.398 (TRS-398) and American Association of Physicists in Medicine Task Group No.51 (AAPM TG-51) [12][13][14]. However, TRS-398 protocol is the most commonly adopted and applied radiation dosimetry protocol worldwide [11,15]. Almost all radiotherapy units in Indonesian hospitals use the IAEA TRS-398 dosimetry protocol as their dosimetry guidelines.…”