Iranian Journal of Medical Physics

Iranian Journal of Medical Physics

Developing a Verification and Training Phantom for Gynecological Brachytherapy System

Document Type : Original Paper

Authors
Mahbobeh Nazarnejad 1
Seied Rabi Mahdavi 2
Khadijeh Asnaashari 3
Mahdi Sadeghi 1
Alireza Nikoofar 2
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
10.22038/ijmp.2012.328
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
Film Dosimetry
GYN Brachytherapy Phantom
Quality Assurance
Subjects
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Iranian Journal of Medical Physics
Volume 9, Issue 1 - Serial Number 1
March and April 2012
Pages 33-40

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