Document Type : Original Research

Authors

Medical Physics Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran

Abstract

Background: One of the main causes of induction of secondary cancer in radiation therapy is neutron contamination received by patients during treatment.
Objective: In the present study the impact of wedge and block on neutron contamination production is investigated. The evaluations are conducted for a 15 MV Siemens Primus linear accelerator.
Methods: Simulations were performed using MCNPX Monte Carlo code. 30˚, 45˚ and 60˚ wedges and a cerrobend block with dimensions of 1.5 × 1.5 × 7 cm3 were simulated. The investigation were performed in the 10 × 10 cm2 field size at source to surface distance of 100 cm for depth of 0.5, 2, 3 and 4 cm in a water phantom. Neutron dose was calculated using F4 tally with flux to dose conversion factors and F6 tally.
Results: Results showed that the presence of wedge increases the neutron contamination when the wedge factor was considered. In addition, 45˚ wedge produced the most amount of neutron contamination. If the block is in the center of the field, the cerrobend block caused less neutron contamination than the open field due to absorption of neutrons and photon attenuation. The results showed that neutron contamination is less in steeper depths. The results for two tallies showed practically equivalent results.
Conclusion: Wedge causes neutron contamination hence should be considered in therapeutic protocols in which wedge is used. In terms of clinical aspects, the results of this study show that superficial tissues such as skin will tolerate more neutron contamination than the deep tissues.

Keywords

  1. In: World Health Organization. IARC-International Agency for Research on Cancer. [2014]. Available from: http://www.who.int/ionizing_radiation/research/iarc/en/.
  2. Price P, Sikora K. Treatment of Cancer, Sixth Edition. London: CRC Press; 2014.
  3. Exposito MR, Sanchez-Nieto B, Terron JA, Domingo C, Gomez F, Sanchez-Doblado F. Neutron contamination in radiotherapy: estimation of second cancers based on measurements in 1377 patients. Radiother Oncol. 2013;107:234-41. doi.org/10.1016/j.radonc.2013.03.011. PubMed PMID: 23601351.
  4. Protection ICoR. ICRP Publication 60: 1990 Recommendations of the International Commission on Radiological Protection:Amsterdam: Elsevier Health Sciences; 1991.
  5. In: National Council on Radiation Protection Measurements. NCRP Report 79, Neutron contamination from medical electron accelerators. [1984]. Available from: http://ncrponline.org/publications/reports/ncrp-report-79/.
  6. Hashemi S, Raisali G, Taheri M, Majdabadi A, Ghafoori M. The effect of external wedge on the photoneutron dose equivalent at a high energy medical linac. Nukleonika. 2011;56:49-51.
  7. Hashemi SM, Hashemi-Malayeri B, Raisali G, Shokrani P, Sharafi AA, Torkzadeh F. Measurement of photoneutron dose produced by wedge filters of a high energy linac using polycarbonate films. J Radiat Res. 2008;49:279-83. doi.org/10.1269/jrr.07066. PubMed PMID: 18460824.
  8. Biltekin F, Ozyigit G, Yeginer M, Celik D, Gurkaynak M. EP-1376 investigating the effect of wedge filter on neutron contamination by using bubble detectors. Radiotherapy and Oncology. 2012;103:S522. doi.org/10.1016/S0167-8140(12)71709-7.
  9. Hashemi SM, Hashemi-Malayeri B, Raisali G, Shokrani P, Sharafi AA, Jafarizadeh M. The effect of field modifier blocks on the fast photoneutron dose equivalent from two high-energy medical linear accelerators. Radiat Prot Dosimetry. 2008;128:359-62. doi.org/10.1093/rpd/ncm421. PubMed PMID: 17875628.
  10. Mesbahi A. A Monte Carlo study on neutron and electron contamination of an unflattened 18-MV photon beam. Appl Radiat Isot. 2009;67:55-60. doi.org/10.1016/j.apradiso.2008.07.013. PubMed PMID: 18760613.
  11. Bahreyni Toossi MT, Behmadi M, Ghorbani M, Gholamhosseinian H. A Monte Carlo study on electron and neutron contamination caused by the presence of hip prosthesis in photon mode of a 15 MV Siemens PRIMUS linac. J Appl Clin Med Phys. 2013;14:52-67. PubMed PMID: 24036859.
  12. Hussien M, Ma A, Spyrou N. Monte Carlo Simulations of the Effective Neutron Dose Received by a Male Anthropomorphic Voxel Phantom outside a Medical Linac Treatment Room. University of Surrey, Guildford, Surrey. 2006.
  13. Zanini A, Durisi E, Fasolo F, Ongaro C, Visca L, Nastasi U, et al. Monte Carlo simulation of the photoneutron field in linac radiotherapy treatments with different collimation systems. Phys Med Biol. 2004;49:571-82. doi.org/10.1088/0031-9155/49/4/008. PubMed PMID: 15005166.
  14. Hashemi SM, Hashemi-Malayeri B, Raisali G, Shokrani P, Sharafi AA, Torkzadeh F. Measurement of photoneutron dose produced by wedge filters of a high energy linac using polycarbonate films. J Radiat Res. 2008;49:279-83. doi.org/10.1269/jrr.07066. PubMed PMID: 18460824.
  15. Zabihinpoor S, Hasheminia M. Calculation of Neutron Contamination from Medical Linear Accelerator in Treatment Room. Adv Studies Theor Phys. 2011;5:421-8.
  16. Pelowitz D. MCNPX user’s manual, version 2.6. 0, LA-CP-07-1473. . New Mexico: Los Alamos National Laboratory; 2008.
  17. Schneider U. Modeling the risk of secondary malignancies after radiotherapy. Genes (Basel). 2011;2:1033-49. doi.org/10.3390/genes2041033. PubMed PMID: 24710304. PubMed PMCID: 3927608.