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Development of Measurement Technique to Determine Beam Quality Conversion Factor for High-Energy Electron Beams

K Hirayama1,2*, T Saitou1,2, M Shimizu2, Y Morishita2, S Seno3, N Kinoshita4, H Oguchi3, M Hoshina1 (1) Komazawa Univ., Setagaya-ku, Tokyo (2) National Metrology INstitute of Japan, AIST, Tsukuba-shi, Ibaraki (3) Nagoya Univ., Nagoya-shi, Aichi (4) University of Fukui hospital, Yoshida-gun, Fukui


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: In order to reduce the uncertainty of absorbed dose to water in high-energy electron beams, the National Metrology Institute of Japan is developing a measurement technique by a calorimetric method. Absorbed dose to water in high-energy electron beams was determined by a compact graphite calorimeter in a water phantom.

Methods: The compact graphite calorimeter was positioned at the reference point in a water phantom. Absorbed dose to graphite determined using a temperature rise of the calorimeter core during the beam irradiation. We measured the absorbed dose to graphite for 9, 12, 15 and 18 MeV high-energy electron beams from a clinical linac (Precise, Elekta Inc.). The absorbed dose was converted from graphite to water using an EGS5 Monte-Carlo code. Several Farmer-type ionization chambers were calibrated with absorbed dose to water in high-energy electron beams determined by the calorimeter.

Results: The absorbed dose to water in 9, 12, 15 and 18 MeV electron beams were determined with a relative expanded uncertainty of 1.2 % (k=2). The dominant factor of the uncertainty is the long-term reproducibility of the absorbed dose measurement by the calorimeter: 0.4 % (k=1). The relative uncertainty of the conversion factor were estimated as 0.3 % (k=1). The present beam quality conversion factors were about 1% larger than those of TRS-398, TG-51 and the calculation results by Muir, although these differences were smaller than the present uncertainty.

Conclusion: The absorbed dose to water in high-energy electron beam was measured with the relative expanded uncertainty of 1.2 % (k=2). Our results are in agreement with those in other publications.


Ionization Chamber, Calibration, Linear Accelerator


TH- External beam- electrons: dose measurement

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