Room: ePoster Forums
Purpose: Radiotherapy with heavy ion beam is playing an important role in clinical therapy due to its physical characteristics. The uncertainty of correction for the beam factor kQ between 60Co Î³ and heavy ion beam is quite lager than that in other radiotherapy cases, such as high energy photon beam. The work reported here is motivated by the rapid-developing radiotherapy with heavy ion beams and as a pre-study for the upcoming calorimeter measurement.
Methods: The experiment was carried out at a horizontal heavy ion terminal, where a 12C ion beam was produced by a heavy ion research facility. The delivered energy to the terminal was (400Â±0.4) MeV/u and beam intensity was 1.5 nA, a typical heavy ion beam for radiotherapy. A water phantom with the volume of 30 cmÃ—30 cmÃ—30 cm was installed at the iso-center position. During the experiment, 3 farmer type ionization chambers were used to accumulate data one after another.
Results: The polarity and recombination are the basic characteristics for the chambers under a certain beam condition, which were evaluated under heavy ion beam condition in the present work. The normalized absorbed-dose to water of the chambers, in which the number of incident 12C ions is a simultaneous feedback from the heavy ion research facility, are 8.872Ã—10-8, 8.855Ã—10-8, and 8.853Ã—10-8 separately. The discrepancy of the results is approximately 0.7 %, which is far smaller than the currently recommended uncertainty (3%) for the absorbed-dose to water of heavy ion.
Conclusion: A study for the absorbed-dose to water of a 400 MeV/u 12C heavy ion was conducted with the ionometric method. The corrections were also evaluated under the corresponding heavy ion condition. The results from different ionization chambers agree well within uncertainty.
Funding Support, Disclosures, and Conflict of Interest: supported by National Key R&D Program of China (2016YFF0200804)