Document Type: Original Article


1 M.Sc Graduated of Medical Physics, Department of Medical Physics, Semnan University of Medical Sciences, Semnan, Iran

2 Assistant Professor, Department of Medical Physics, Semnan University of Medical Sciences, Semnan, Iran

3 Associate Professor, Department of Medical Physics, Semnan University of Medical Sciences, Semnan, Iran

4 Professor, Head of Social Determinants of Health Research Center, Semnan University of Medical Sciences, Semnan, Iran



Medical linear accelerators are one of the most widespread methods for cancer treatment. Despite their advantages, unwanted photoneutrons are produced by high energy linacs. This photoneutrons are as undesired doses to patients and a significant problem for radiation protection of the staffs and patients. Photoneutrons radiological risk must be evaluated because of their high LET and order to achieving this aim, photoneutron spectrum are calculated. The head of linac and a common treatment room was simulated by the MC code of MCNPX. Photoneutron spectrum was calculated in different field sizes, distances from isocenter and different cases (with and without structures and materials such as flattening filter, compensator, air and treatment room walls).The inclusion of the flattening filter and compensator had not any effects on shaping the photoneutron spectrum but neutron fluence and the average neutron energy are reduced obviously. Also effect of air on photoneutron spectrum was negligible. The calculation of photoneutron spectrum with concrete walls show that the component of fast neutrons is decreased and thermal neutrons are increased due to the room-return. In this case, with increasing distance from isocenter, fast neutrons are decreased and thermal neutrons are increased. As the field size is increased from 5×5 to 15×15 cm2, the neutron flux is increased clearly in isocenter. The neutrons flux are decreased near the door due to maze effect. The photoneutron spectrum investigation and risk estimation due to inclusion of neutron contamination in treatment room prevent from secondary cancer mortality.


Main Subjects

Agosteo, S., Para, A.F., Maggioni, B., Angiust, V., Terrani, S., Borasi, G., 1995. Radiation Transport in a Radiotherapy Room. Health. Phys., 68(7), 27-34.
Barquero, R., Méndez, R.P., Iñiguez, M.R., Vega, H., Voltchev, M., 2002. Thermoluminescence measurements of neutron dose around a medical Linac. Radiation Protection Dosimetry, 101(4), 493-496.
Chibani, O., Ma, C.-M.C., 2003. Photonuclear dose calculations for high-energy photon beams from Siemens and Varian linacs. Med. Phys., 30(2), 1990-2000.
Custidiano, E.R., Valenzuela, M.R., Dumont, J.L., McDonnell, J., Rene, L., Rodríguez Aguirre, J.M., 2011. Monte Carlo simulation of spectrum changes in a photon beam due to a brass compensator. Nuclear Instruments and
Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 69(2), 1444-1449.
Difilippo, F., Papiez, L., Moskvin, V., Peplow, D., DesRosiers, C., Johnson, J., Timmerman, R., Randall, M., Lillie, R., 2003. Contamination dose from photoneutron processes in bodily tissues during therapeutic radiation
delivery. Med. Phys., 30(10), 2849-2854.
Esposito, A., Bedogni, R., Lembo, L., Morelli, M., 2008. Determination of the neutron spectra around an 18 MV medical LINAC with a passive Bonner sphere spectrometer based on gold foils and TLD pairs. Radiation Measurements, 43(5), 1038-1043.
Forster, R.A., Godfrey, T.N.K., 1985. MCNP - a general Monte Carlo code for neutron and photon transport, in: Alcouffe, R., Dautray, R., Forster, A., Ledanois, G., Mercier, B. (Eds.), Monte-Carlo Methods and Applications
in Neutronics, Photonics and Statistical Physics. Springer Berlin Heidelberg, 33-55.
Hsu, F.-Y., Chang, Y.-L., Liu, M.-T., Huang, S.-S., Yu, C.-C. 2010. Dose estimation of the neutrons induced by the high energy medical linear accelerator using dual-TLD chips. Radiation Measurements, 45(6), 739-741.

Kry, S.F., Titt, U., Pönisch, F., Vassiliev, O.N., Salehpour, M., Gillin, M., Mohan, R., 2007. Reduced Neutron Production Through Use of a Flattening-Filter–Free Accelerator. Int. J. Radi. Oncol. Biol. Phys., 68(4), 1260-1264.
Lin, J.-P., Chu, T.-C., Lin, S.-Y., Liu, M.-T., 2001. The measurement of photoneutrons in the vicinity of a Siemens Primus linear accelerator. Appl. Radi. Isotop., 55(3), 315-321.
Mao, X.S., Kase, K.R., Liu, J.C., Nelson, W.R., Kleck, J.H., Johnsen, S., 1997. Neutron Sources in the Varian Clinac 21000/23000 Medical Accelerator Calculated by the EGS4 Code. Health. Phys., 72(1), 524-529.
Mesbahi, A., 2009. A Monte Carlo study on neutron and electron contamination of an unflattened 18-MV photon beam. Appl. Radi. Isotop., 67(1), 55-60.
Mesbahi, A., Ghiasi, H., Mahdavi, S.R., 2010. Photoneutron and capture gamma dose equivalent for different room and maze layouts in radiation therapy. Radiation Protection Dosimetry, 140(6), 242-249.
Mesbahi, A., Mehnati, P., Keshtkar, A., Farajollahi, A., 2007. Dosimetric properties of a flattening filter-free 6-MV photon beam: a Monte Carlo study. Radiat Med, 25(7), 315-324.
Pena, J., Franco, L., Gómez, F., Iglesias, A., Pardo, J., Pombar, M., 2005. Monte Carlo study of Siemens PRIMUS photoneutron production. Phys. Med. Biol., 50(24), 5921.
Polaczek-Grelik, K., Orlef, A., Dybek, M., KonefaŁ, A., Zipper, W., 2010. Linear accelerator therapeutic dose— induced radioactivity dependence. Appl. Radi. Isotop., 68(11), 763-766.
Rohrig, N., 2003. Shielding Techniques for Radiation Oncology Facilities, Second Edition. Health. Phys., 84(3), 382.
Schneider, U., Lomax, A., Timmermann, B., 2008. Second cancers in children treated with modern radiotherapy techniques. Radiother. Oncol., 89(2), 135-140.
Simmons, G., 1978. Structural Shielding Design and Evaluation for Medical Use of X-Rays and Gamma Rays of Energies Up to 10 meV. NCRP Report No. 49 Washington, DC, NCRP Publications, 1976, 126 pp, J. Nucl. Med.,
19(2), 228-228.
Vega-Carrillo, H., Ortíz-Hernandez, A., Hernandez-Davila, V., Hernández-Almaraz, B., Montalvo, T., 2010. H*(10) and neutron spectra around linacs. J. Radioanalyt. Nucl. Chem., 283(2), 537-540.
Weinreich, R., Bajo, S., Eikenberg, J., Atchison, F., 2004. Determination of uranium and plutonium in shielding concrete. J. Radioanalyt. Nucl. Chem., 261(2), 319-325.
Wu, R.K., McGinley, P.H., 2003. Neutron and capture gamma along the mazes of linear accelerator vaults. Phys. Med. Biol., 44(2), 25-38.
Zabihinpoor, S., Hasheminia, M., 2011. Calculation of Neutron Contamination from Medical Linear Accelerator in Treatment Room. Adv. Stud. Theor. Phys., 13(5), 421-428.
Zabihzadeh, M., Ay, M.R., Allahverdi, M., Mesbahi, A., Mahdavi, S.R., Shahriari, M., 2009. Monte Carlo estimation of photoneutrons contamination from high-energy X-ray medical accelerators in treatment room and maze: a
simplified model. Radiation Protection Dosimetry, 135(1), 21-32.
Zanini, A., Fasolo, F., Visca, L., Durisi, E., Perosino, M., Annand, J.R.M., Burn, K.W., 2005. Test of a bubble passive spectrometer for neutron dosimetry. Phys. Med. Biol., 50(18), 42-87.