Developing a Verification and Training Phantom for Gynecological Brachytherapy System

Document Type : Original Paper

Authors

1 Science and Research Branch, Islamic Azad University, Tehran, Iran

2 Department of Medical physics, Tehran University of Medical Sciences, Tehran, Iran

3 School of allied medicine, Tehran University of Medical Sciences, Tehran, Iran

Abstract

Introduction
Dosimetric accuracy is a major issue in the quality assurance (QA) program for treatment planning systems (TPS). An important contribution to this process has been a proper dosimetry method to guarantee the accuracy of delivered dose to the tumor. In brachytherapy (BT) of gynecological (Gyn) cancer it is usual to insert a combination of tandem and ovoid applicators with a complicated geometry which makes their dosimetry verification difficult and important. Therefore, evaluation and verification of dose distribution is necessary for accurate dose delivery to the patients.
Materials and Methods
The solid phantom was made from Perspex slabs as a tool for intracavitary brachytherapy dosimetric QA. Film dosimetry (EDR2) was done for a combination of ovoid and tandem applicators introduced by Flexitron brachytherapy system. Treatment planning was also done with Flexiplan 3D-TPS to irradiate films sandwiched between phantom slabs. Isodose curves obtained from treatment planning system and the films were compared with each other in 2D and 3D manners.
Results
The brachytherapy solid phantom was constructed with slabs. It was possible to insert tandems and ovoids loaded with radioactive source of Ir-192 subsequently. Relative error was 3-8.6% and average relative error was 5.08% in comparison with the films and TPS isodose curves.
Conclusion
Our results showed that the difference between TPS and the measurements is well within the acceptable boundaries and below the action level according to AAPM TG.45. Our findings showed that this phantom after minor corrections can be used as a method of choice for inter-comparison analysis of TPS and to fill the existing gap for accurate QA program in intracavitary brachytherapy. The constructed phantom also showed that it can be a valuable tool for verification of accurate dose delivery to the patients as well as training for brachytherapy residents and physics students.  

Keywords

Main Subjects

References

  1. Rodríguez ML, deAlmeida CE. Absorbed dose calculations in a brachytherapy pelvic phantom using the Monte Carlo method. J Appl Clin Med Phys. 2002;3(4):285-92.
  2.  Wilkinson DA. High dose rate (HDR) brachytherapy quality assurance: a practical guide. Biomed Imaging Interv J. 2006;2(2):e34.
  3. Wittkämper FW, Mijnheer BJ, van Kleffens HJ. Dose intercomparison at radiotherapy centres in The Netherlands. 2. Accuracy of locally applied computer planning systems for external photon beams. Radiother Oncol. 1988;11(4):405-14.
  4. Margaret Bidmead, Edith Briot, Janez Burger, and et al. A practical guide to quality control of brachytherapy equipment (2004)
  5. Venselaar J, Bidmead M, Pérez-Calatayud J, Radiology ESfT, Oncology. A Practical Guide to Quality Control of Brachytherapy Equipment: European Society for Therapeutic Radiology and Oncology, ESTRO; 2004.
  6. Ohizumi Y, Akiba T, Imamiya S, Tamai Y, Mori T, Shinozuka T. Vaginal Applicators (ovoids) for Local Control and Alleviation of Rectal Complications of Cervical Cancers Treated by Brachytherapy. Tokai J Exp Clin Med. 1999;24(1):21-7.
  7. Meigooni AS, Meli JA, Nath R. A comparison of solid phantoms with water for dosimetry of 125I brachytherapy sources. Med Phys. 1988;15(5):695-701.
  8. Lewis M, Kafiabadi S, Platten D. Comparative CTDI measurements in Perspex and water equivalent dosimetry phantoms. Presented at the fifth CT Users group meeting. Edinburgh, 2004.
  9. Hill RF, Brown S, Baldock C. Evaluation of thewater equivalence of solid phantoms using gamma ray transmission measurements. Radiat Meas. 2008;43:1258–64.
  10. Rivard MJ, Coursey BM, DeWerd LA, Hanson WF, Huq MS, Ibbott GS, et al. Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys. 2004 Mar;31(3):633-74.
  11. Pai S, Das IJ, Dempsey JF, Lam KL, Losasso TJ, Olch AJ, et al. TG-69: Radiographic film for megavoltage beam dosimetry. Med Phys. 2007;34(6):2228-58.
  12. Kirov A, Williamson JF, Meigooni AS, Zhu Y. TLD, diode and Monte Carlo dosimetry of an I92Ir source for high dose-rate brachytherapy. Phys Med Biol. 1995;40(12):2015-36.
  13. Ochoa R, Gómez F, Ferreira IH, Gutt F, de Almeida CE. Design of a phantom for the quality control of high dose rate 192Ir source used in brachytherapy. Radiother Oncol. 2007;82(2):222-8.
  14. Elfrink RJ, Kolkman-Deurloo IK, van Kleffens HJ, Rijnders A, Schaeken B, Aalbers TH, et al. Determination of the accuracy of implant reconstruction and dose delivery in brachytherapy in The Netherlands and Belgium. Radiother Oncol. 2001;59(3):297-306.
  15. Mostaar A, Hashemi B, Zahmatkesh MH, Aghamiri SM, Mahdavi SR. A basic dosimetric study of PRESAGE: the effect of different amounts of fabricating components on the sensitivity and stability of the dosimeter. Phys Med Biol. 2010;55(3):903-12.
  16. de Almeida CE, Rodriguez M, Vianello E, Ferreira IH, Sibata C. An anthropomorphic phantom for quality assurance and training in gynaecological brachytherapy. Radiother Oncol. 2002;63(1):75-81.
  17. Kutcher GJ, Coia L, Gillin M, Hanson WF, Leibel S, Morton RJ, et al. Comprehensive QA for radition oncology, AAPM task group No.46. Med Phys. 1994;21(4):581-618.
Iranian Journal of Medical Physics
Volume 9, Issue 1 - Serial Number 1
March and April 2012
Pages 33-40

Files

History

  • Receive Date: 19 November 2011
  • Revise Date: 03 March 2013
  • Accept Date: 01 February 2012

Share

How to cite

Statistics