Comparison and Evaluation of the Effects of Rib and Lung Inhomogeneities on Lung Dose in Breast Brachytherapy using a Treatment Planning System and the MCNPX Code

Salehi Yazdi, Hossein; Shamsaei, Mojtaba; Shabani, Hamid Reza; Jaberi, Ramin; Setayeshi, Saeed

doi:10.22038/ijmp.2010.7250

Comparison and Evaluation of the Effects of Rib and Lung Inhomogeneities on Lung Dose in Breast Brachytherapy using a Treatment Planning System and the MCNPX Code

Document Type : Original Paper

Authors

Hossein Salehi Yazdi ¹

Mojtaba Shamsaei ²

Hamid Reza Shabani ³

Ramin Jaberi ⁴

Saeed Setayeshi ⁵

¹ M.Sc. Student of Medical Radiation Engineering , Nuclear Engineering and Physics Dept., Amirkabir University of Technology, Tehran, Iran

² Assistant Professor, Nuclear Engineering and Physics Dept., Amirkabir University of Technology, Tehran, Iran

³ M.Sc. Student of Medical Physics, Medical Physics Dept., Tehran University of Medical Sciences, Tehran, Iran

⁴ Radiotherapy Physicist, Cancer Institute, Imam Khomeini Hospital, Tehran, Iran

⁵ Associate Professor, Nuclear Engineering and Physics Dept., Amirkabir University of Technology, Tehran, Iran

10.22038/ijmp.2010.7250

Abstract

Introduction: This study investigates to what extent the computed dose received by lung tissue in a commercially available treatment planning system (TPS) for 192Ir high-dose-rate breast brachytherapy is accurate in view of tissue inhomogeneities and presence of ribs.
Materials and Methods: A CT scan of the breast was used to construct a patient-equivalent phantom in the clinical treatment planning system. An implant involving 13 plastic catheters and 383 programmed source dwell positions were simulated using the MCNPX code.
Results: The results were compared with the corresponding commercial TPS in the form of isodoses and cumulative dose–volume histogram in breast, lung and ribs. The comparison of Monte Carlo results and TPS calculation showed that the isodoses greater than 62% in the breast that were located rather close to the implant or away from the breast curvature surface and lung boundary were in good agreement. TPS calculations, however, overestimated dose in the lung for lower isodose contours and points that were lying near the breast-air boundary and relatively away from the implant.
Discussion and Conclusions: Taking into account the ribs and entering the actual data for breast, rib and lung, revealed an average overestimation of dose in lung in the TPS calculation.

Keywords

Breast Cancer

Brachytherapy

High Dose Rate

Inhomogeneity

MCNPX

Treatment Planning System

Subjects