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J Korean Soc Ther Radiol Oncol > Volume 24(4); 2006 > Article
The Journal of the Korean Society for Therapeutic Radiology and Oncology 2006;24(4): 280-284.
Evaluation of Biological Characteristics of Neutron Beam Generated from MC50 Cyclotron
Keun Yong Eom, Hong Gyun Wu, Hye Jin Park, Soon Nyung Huh, Sung Joon Ye, Dong Han Lee, Suk Won Park
1Department of Radiation Oncology, Seoul National University College of Medicine, Korea. wuhg@snu.ac.kr
2Institute of Radiation Medicine, Medical Research Center, Seoul National University, Korea.
3Cancer Research Institute, Seoul National University College of Medicine, Korea.
4Department of Radiation Oncology, The Korea Institute of Radiological and Medical Sciences, Korea.
5Department of Radiation Oncology, Chung-Ang University College of Korea, Korea.
To evaluate biological characteristics of neutron beam generated by MC50 cyclotron located in the Korea Institute of Radiological and Medical Sciences (KIRAMS).
The neutron beams generated with 15 mm Beryllium target hit by 35 MeV proton beam was used and dosimetry data was measured before in-vitro study. We irradiated 0, 1, 2, 3, 4 and 5 Gy of neutron beam to EMT-6 cell line and surviving fraction (SF) was measured. The SF curve was also examined at the same dose when applying lead shielding to avoid gamma ray component. In the X-ray experiment, SF curve was obtained after irradiation of 0, 2, 5, 10, and 15 Gy.
The neutron beams have 84% of neutron and 16% of gamma component at the depth of 2 cm with the field size of 26 x 26 cm2, beam current 20 micro A, and dose rate of 9.25 cGy/min. The SF curve from X-ray, when fitted to linear-quadratic (LQ) model, had 0.611 as alpha/beta ratio (alpha=0.0204, beta=0.0334, R2=0.999, respectively). The SF curve from neutron beam had shoulders at low dose area and fitted well to LQ model with the value of R2 exceeding 0.99 in all experiments. The mean value of alpha and beta were -0.315 (range, -0.254 ~ -0.360) and 0.247 (0.220~0.262), respectively. The addition of lead shielding resulted in no straightening of SF curve and shoulders in low dose area still existed. The RBE of neutron beam was in range of 2.07~2.19 with SF=0.1 and 2.21~2.35 with SF=0.01, respectively.
The neutron beam from MC50 cyclotron has significant amount of gamma component and this may have contributed to form the shoulder of survival curve. The RBE of neutron beam generated by MC50 was about 2.2.
Key Words: Cyclotron, Neutron, RBE, Radiation therapy
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