Comparison research on three international dosimetry code in ⁶⁰Co γ-ray beams

Objective: The code of practice for radiotherapy dosimetry in our country is not directly based on standards of absorbed dose to water, but based on exposure standards or air kerma standards firstly, and then transform the measurement into absorbed dose by adopting various modifying factors through dosimetry code involved. This essay will probe into the error caused by different codes of practice for radiotherapy dosimetry in terms of absorbed dose. Methods: In this research, we adopt three radiotherapy dosimetry codes including ICRU23, IAEA TRS277 and IAEA TRS398, by which different types of chambers measure the absorbed dose water respectively in ⁶⁰Co γ ray beams under same condition. We analyze the divergence produced by the three codes mentioned above. Results: Having measured the absorbed dose to water through 10 six types of chambers under the same condition of ⁶⁰C0 γ ray beams, we find that three codes in question produce divergences, which are within 2% respectively. Meanwhile, there is certain dispersal among different types of chambers as well. Conclusion: Different measurements of radiotherapy dosimetry codes will produce bigger divergences. To reduce inaccuracy in modern radiation therapy in our nation, we should establish the calibration system of measuring absorbed doses to water as soon as possible. (authors)