Evaluation of two-dimensional dose distributions for pre-treatment patient-specific IMRT dosimetry

  • Đeni Smilović Radojčić University Hospital Rijeka Medical Physics Department
  • David Rajlić University Hospital Rijeka Medical Physics Department
  • Božidar Casar Institute of Oncology Department of Radiation Physics
  • Manda Švabić Kolacio University Hospital Rijeka Medical Physics Department
  • Nevena Obajdin University Hospital Rijeka Medical Physics Department
  • Dario Faj University of Osijek Faculty of Medicine and University of Osijek Faculty of dental medicine and health
  • Slaven Jurković University Hospital Rijeka Medical Physics Department and University of Rijeka Faculty of Medicine Department of Physics

Abstract

Introduction

The accuracy of dose calculation is crucial for success of the radiotherapy treatment. One of the methods that represent the current standard for patient-specific dosimetry is the evaluation of dose distributions measured with an ionization chamber array inside a homogenous phantom using gamma method. Nevertheless, this method does not replicate the realistic conditions present when a patient is undergoing therapy. Therefore, to more accurately evaluate the treatment planning system (TPS) capabilities, gamma passing rates was examined for beams of different complexity passing through inhomogeneous phantoms.

Materials and methods

The research was performed using linear accelerator Siemens Oncor Expression, Siemens Somatom Open CT simulator and Elekta Monaco TPS. A 2D detector array (IBA Matrixx I'mRT) is used to evaluate dose distribution accuracy in homogeneous, semi-anthropomorphic and anthropomorphic phantoms. Validation was based on gamma analysis with 3%/3mm and 2%/2mm criteria, respectively.

Results

Passing rates of the complex dose distributions degrade depending on the thickness of non-water equivalent material. It also depends on dose reporting mode used. It is observed that the passing rate decreases with plan complexity. Comparison of the data for all set-ups of semi-anthropomorphic and anthropomorphic phantoms shows that passing rates are higher in the anthropomorphic phantom.

Discussion

Our results raise a question of possible limits of dose distribution verification in assessment of plan delivery quality. Consequently, good results obtained using standard patient specific dosimetry methodology does not guarantee the accuracy of delivered dose distribution in real clinical cases.

Published
2018-09-06
How to Cite
Smilović Radojčić, Đeni, Rajlić, D., Casar, B., Švabić Kolacio, M., Obajdin, N., Faj, D., & Jurković, S. (2018). Evaluation of two-dimensional dose distributions for pre-treatment patient-specific IMRT dosimetry. Radiology and Oncology, 52(3). Retrieved from https://www.radioloncol.com/index.php/ro/article/view/2966
Section
Medical Physics