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J Korean Soc Ther Radiol Oncol > Volume 19(1); 2001 > Article
The Journal of the Korean Society for Therapeutic Radiology and Oncology 2001;19(1): 66-73.
Dosimetry of the Low Fluence Fast Neutron Beams for Boron Neutron Capture Therapy
Dong Han Lee, Young Hoon Ji, Dong Hoon Lee, Hyun Joo Park, Suk Lee, Kyung Hoo Lee, So Heigh Suh, Mi Sook Kim, Chul Koo Cho, Seong Yul Yoo, Hyung Jun Yu, Ho Shin Gwak, Chang Hun Rhee
1Laboratory. of radiation effect, Korea Cancer Center Hospital, Seoul, Korea.
2Department of Radiation Oncology, Korea Cancer Center Hospital, Seoul, Korea.
3Department of Neurosurgery, Korea Cancer Center Hospital, Seoul, Korea.
For the research of Boron Neutron Capture Therapy (BNCT), fast neutrons generated from the MC-50 cyclotron with maximum energy of 34.4 MeV in Korea Cancer Center Hospital were moderated by 70 cm paraffin and then the dose characteristics were investigated. Using these results, we hope to establish the protocol about dose measurement of epi-thermal neutron, to make a basis of dose characteristic of epi-thermal neutron emitted from nuclear reactor, and to find feasibility about accelerator-based BNCT. METHOD AND MATERIALS: For measuring the absorbed dose and dose distribution of fast neutron beams, we used Unidos 10005 (PTW, Germany) electrometer and IC-17 (Far West, USA), IC-18, EIC-1 ion chambers manufactured by A-150 plastic and used IC-17M ion chamber manufactured by magnesium for gamma dose. There chambers were flushed with tissue equivalent gas and argon gas and then the flow rate was 5 cc per minute. Using Monte Carlo N-Particle (MCNP) code, transport program in mixed field with neutron, photon, electron, two dimensional dose and energy fluence distribution was calculated and there results were compared with measured results.
The absorbed dose of fast neutron beams was 6.47x10-3 cGy per 1 MU at the 4 cm depth of the water phantom, which is assumed to be effective depth for BNCT. The magnitude of gamma contamination intermingled with fast neutron beams was 65.2+/-0.9% at the same depth. In the dose distribution according to the depth of water, the neutron dose decreased linearly and the gamma dose decreased exponentially as the depth was deepened. The factor expressed energy level, D20/D10, of the total dose was 0.718.
Through the direct measurement using the two ion chambers, which is made different wall materials, and computer calculation of isodose distribution using MCNP simulation method, we have found the dose characteristics of low fluence fast neutron beams. If the power supply and the target material, which generate high voltage and current, will be developed and gamma contamination was reduced by lead or bismuth, we think, it may be possible to accelerator-based BNCT.
Key Words: Boron neutron capture therapy (BNCT), Cyclotron, Monte carlo N-Particle (MCNP)
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