Iranian Journal of Medical Physics

Iranian Journal of Medical Physics

A Feasibility Study to Reduce the Contamination of Photoneutrons and Photons in Organs/Tissues during Radiotherapy

Document Type : Original Paper

Authors
Roya Boodaghi malidarre 1
Rahim Khabaz 2
Mohammad reza Benam 1
Vahid Zanganeh 3
1 Department of Physics, Payame Noor University (PNU), Tehran, Iran
2 Department of Physics, Faculty of Sciences, Golestan University,Gorgan, Iran
3 Golestan university faculty of science, department of physics, Golestan, Iran
10.22038/ijmp.2019.40879.1579
Abstract
Introduction: Due to out-of-field effects in radiation therapy, the determination and reduction of both unwanted photon and photoneutron doses are essential for the reasonable assessment of the risks to healthy tissues.
Material and Methods: By the application of a multilayer shield throughout the phantom and using two models for photoneutron and photon sources, doses were estimated in a 15-MV linac in tissues and organs. Different neutron moderators were used, and the best materials, such as polyethylene, polystyrene, polyvinyl chloride, paraffin, and water, were reported for shielding purpose. Boron carbide and steel were utilized as neutron and gamma absorbents. Various lengths of the shield in line with phantom stature were also assessed in this study.
Results: Except for the target organ, with the shield throughout the phantom, both photoneutron and photon doses approximately reduced by 57-89% and 88-95%, respectively. Extra photoneutron dose in the photon source was also reported due to the shield. Then, unwanted doses, especially photon dose remarkably decreased with increasing the steel thickness. The smaller dimensions of the shield caused also a considerable reduction of the photoneutron and photon doses in the phantom.
Conclusion: The application of a multilayer shield reduces the photon dose remarkably in healthy tissues. Therefore, it is recommended to use shielding materials to decrease photoneutron and photon doses, which can cause a reduction in the risk of secondary cancer. Due to the relatively high mass of the shield, it is necessary to design a proper device to maintain and move the structure.
Keywords
Linac
Radiations
Shielding
Absorbed dose
Subjects

  1.  

    1. Thalhofer JL, Rebello WF, Correa SA, Silva AX, Souza EM, Batista DV. Calculation of dose in healthy organs, during radiotherapy 4-field box 3D conformal for prostate cancer, simulation of the Linac 2300, radiotherapy room and MAX phantom. 2013.
    2. Kry SF, Salehpour M, Followill DS, Stovall M, Kuban DA, White RA, et al. Out-of-field photon and neutron dose equivalents from step-and-shoot intensity-modulated radiation therapy. International Journal of Radiation Oncology* Biology* Physics. 2005;62(4):1204-16. Doi: 10.1016/j.ijrobp.2004.12.091.
    3. Martínez‐Ovalle SA, Barquero R, Gómez‐Ros JM, Lallena AM. Neutron dosimetry in organs of an adult human phantom using linacs with multileaf collimator in radiotherapy treatments. Medical physics. 2012;39(5):2854-66.
    4. Ovalle SA. Neutron dose equivalent in tissue due to linacs of clinical use. Frontiers in Radiation Oncology. 2013;3: 91-112.
    5. Khabaz R. Effect of each component of a LINAC therapy head on neutron and photon spectra. Applied Radiation and Isotopes. 2018; 139:40-5.  Doi: 10.1016/j.apradiso.2018.04.022.
    6. Sánchez-Doblado F, Domingo C, Gómez F, Sánchez-Nieto B, Muñiz JL, García-Fusté MJ, et al. Estimation of neutron-equivalent dose in organs of patients undergoing radiotherapy by the use of a novel online digital detector. Physics in Medicine & Biology. 2012;57(19):6167-91. Doi:10.1088/0031-9155/57/19/6167.
    7. Kry SF, Howell RM, Salehpour M, Followill DS. Neutron spectra and dose equivalents calculated in tissue for high‐energy radiation therapy. Medical physics. 2009;36(4):1244-50. Doi: 10.1118/1.3089810.
    8. Mohammadi N, Miri-Hakimabad H, Rafat-Motavalli L, Akbari F, Abdollahi S. Patient-specific voxel phantom dosimetry during the prostate treatment with high-energy linac. Journal of Radioanalytical and Nuclear Chemistry. 2015;304(2):785-92. Doi: 10.1007/s10967-014-3872-9.
    9. Khabaz R, Boodaghi R, Benam MR, Zanganeh V. Estimation of photoneutron dosimetric characteristics in tissues/organs using an improved simple model of linac head. Applied Radiation and Isotopes. 2018;133:88-94. Doi:10.1016/j.apradiso.2018.04.022.
    10. NCRP. Neutron contamination from medical electron accelerators. NCRP Report No. 79. Bethesda, MD.1984.
    11. ICRP. Recommendations of the international commission on radiological protection. ICRP Report No. 26. 1997.
    12. Garrigó E, Zunino S, Germanier A. Protection of the contralateral breast during radiation therapy for breast cancer. 2008.
    13. Roy SC, Sandison GA. Shielding for neutron scattered dose to the fetus in patients treated with 18 MV x‐ray beams. Medical physics. 2000;27(8):1800-3. Doi:10.1118/1.1287438. Pub Med PMID: 10984226.
    14. Khabaz R. Evaluation of an alternative convenient irradiation system for determination of emission rate of radio-isotopic neutron sources. Journal of Radioanalytical and Nuclear Chemistry. 2014;299(1):5-12. Doi: 10.1007/s 10967-013-2728-z.
    15. Vega-Carrillo HR, Martinez-Ovalle SA, Lallena AM, Mercado GA, Benites-Rengifo JL. Neutron and photon spectra in LINACs. Applied Radiation and Isotopes. 2012;71:75-80. Doi: 10.1016/j.apradiso.2012.03.034.
    16. Sheikh‐Bagheri D, Rogers DW. Monte Carlo calculation of nine megavoltage photon beam spectra using the BEAM code. Medical physics. 2002;29(3):391-402. Doi: 10.1118/1.1445413.
    17. Chu S. Shielding for radiation scattered dose distribution to the outside fields in patients treated with high energy radiotherapy beams. Proccedings of the International Conference on the Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy. Malaga, March; 2001.
Iranian Journal of Medical Physics
Volume 17, Issue 6
November and December 2020
Pages 366-373

  • Receive Date 03 June 2019
  • Revise Date 30 November 2019
  • Accept Date 13 December 2019