Dose Distribution Analysis for Electron Beam Irregular Fields In Treatment of Superficial Tumors: A Monte Carlo Study

Document Type : Original Article (s)

Authors

1 MSc Student, Department of Medical Physics and Engineering, School of Medicine And Student Research Committee, Isfahan University of Medical Sciences, Isfahan, Iran

2 Professor, Department of Medical Physics and Engineering, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

Abstract

Background: In the superficial treatment with Electron beam, the Irregular radiation fields are produced because of the shield at the end of the applicator or on the surface of the body in the treatment field. In this situation the dispersion amount in irregular fields change in comparison to the regular field and causes dosimeter value changes.Methods: In this study, in order to study the effect of the shield, the simulation code BEAMnrc based on EGSnrc, which is installed on Linux OS, was used for simulating and calculating R90 irregular fields, which were made of shielding square fields of (15´15)(20´20)(25´25) CM. For experimental measurement a type P silicon diode manufactured by Scanditronix was used. R90 simulated irregular fields were compared with dosimetric amounts gained by methods of equivalent open field and open field.Findings: The depth of R90 changed as a result of change in the shielded area and the shape of the field and there was no specific order in its increasing or decreasing. The amount of change in irregular fields with 6 mega electron volt energy compared to an equivalent field are less than 2 millimeters and compared to an open field are less than 1 millimeter.Conclusion: The study proved that using the open field method is better than the equivalent field method in measuring R90.

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  1. Yoshimura R, Hayashi K, Ayukawa F, shibuya H, Toda K. Electron therapy for orbital and periorbital lesions using customized lead eye shields. J Ophthalmologica 2009; 223(2): 69-101.
  2. Kumar PP, Henschke UK, Nibhanupudy JR. Problems and solutions in achieving uniform dose distribution in superficial total body electron therapy. J Natl Med Assoc 1977; 69(9): 645-7.
  3. Ding GX, Cygler JE, Yu CW, Kalach NI, Daskalov G. A comparison of electron beam dose calculation accuracy between treatment planning systems using either a pencil beam or a Monte Carlo algorithm. Int J Radiat Oncol Biol Phys 2005; 63(2): 622-33.
  4. The physics of radiation therapy. 3rd ed. Baltimore: Lippinott, Williams, wilkins; 2007.
  5. Hogstrom KR, khan FM, Kutchner GJ, Nath R, Prasad SC, Rozenfeld M, et al. Clinical eclectron beam dosimetry. J Med Phys 1991; 18(1): 73-109.
  6. Aird EG. Clinical electron therapy. Report on a meeting organized by the BIR Oncology Committee, held at the British Institute of Radiology, London, 7 November 1997. Br J Radiol 1998; 71(851): 1113-5.
  7. Doucet R, Olivares M, DeBlois F, Podgorsak EB, Kawrakow I, Seuntjens J. Comparison of measured and Monte Carlo calculated dose distributions in inhomogeneous phantoms in clinical electron beams. Phys Med Biol 2003; 48(15): 2339-54.
  8. Chow JC, Grigorov GN. Monte Carlo simulation of backscatter from lead for clinical electron beams using EGSnrc. Med Phys 2008; 35(4): 1241-50.
  9. Davies G, Bidmead M, Lamb C, Nalder C, Seco J. Electron dosimetry of angular fields. Br J Radiol 2007; 80(951): 202-8.
  10. Zhang GG, Rogers DW, Cygler JE, Mackie TR. Monte Carlo investigation of electron beam output factors versus size of square cutout. Med Phys 1999; 26(5): 743-50.