Quantification and comparison of the reference dose measurements using IAEA TRS-398 protocols and its revised version

Area of Science:

• Medical Physics
• Radiotherapy Dosimetry

Background:

• The International Atomic Energy Agency (IAEA) established Technical Report Series (TRS-398) for absorbed dose measurement in external radiotherapy.
• TRS-398 offers a standardized method for using calibrated ionization chambers traceable to metrology institutes to determine absorbed dose to water.
• Accurate dosimetry is crucial for effective and safe radiotherapy treatments.

Purpose of the Study:

• To compare reference dosimetry, specifically dose at 10 cm depth (D10), between the original TRS-398 protocol and its revised version.
• To evaluate the impact of using different ionization chambers and beam types on dosimetry comparisons.
• To assess the influence of the absorbed dose conversion factor (kQ,QO) on measurement accuracy.

Main Methods:

• Reference dosimetry was performed for flattened (FF) and flattening filter-free (FFF) photon beams (6, 10, 15 MV) using both TRS-398 and its revised version.
• Two IBA ionization chambers (0.65 cm³ FC65-G and 0.13 cm³ CC13) with traceable calibration coefficients were employed.
• Absorbed dose to water (Dw) standards were used for calibration.

Main Results:

• Differences in D10 between the protocols ranged from 0.03% to 0.63% for the FC65-G chamber and -0.40% to -0.77% for the CC13 chamber.
• The revised protocol showed variations up to 0.63% (FC65-G) and -0.77% (CC13) compared to the old TRS-398.
• Using the old kQ,QO value led to an average overestimation of 0.5% and an underestimation of up to -0.77% depending on the chamber and beam type.

Conclusions:

• The revised TRS-398 protocol impacts reference dose measurements, with variations observed depending on the ionization chamber and beam characteristics.
• The choice of kQ,QO value significantly affects dosimetry accuracy, potentially leading to over or underestimation of the absorbed dose.
• Adherence to the revised protocol is recommended for accurate and consistent radiotherapy dosimetry.