Dosimetric Comparison between Two Different Intensity Modulated Radiation Therapy and 3D-Conformal Radiation Therapy Planning Techniques for Carcinoma of Breast Following Conservative Surgery

Abstract

Introduction: The anatomy of the chest wall is curved which makes it quite complicated to plan radiation therapy for breast cancer. There are different techniques for delivering external beam radiation therapy. Therefore, it is essential to know the technique by which we can render a better treatment. Aim: To compare and analyse three different planning techniques namely Three Dimensional Conformal Radiation Therapy (3DCRT), two field Intensity Modulated Radiation Therapy (IMRT) and multiple field IMRT using dosimetric parameters. Materials and Methods: In this retrospective dosimetric study, we evaluated 10 breast cancer patients. For each patient, three plans namely 3DCRT, two field IMRT and multiple field IMRT (7 beams) were generated on the computed tomographic images using Oncentra Treatment Planning system. A dose of 50Gy in 25 fractions was prescribed to the Planning Target Volume (PTV). The plans were compared with each other on volume coverage (conformity and homogeneity) and organ-at-risk sparing. Paired t-test was used for identifying statistical differences between the plans. A significance level, p=5% or 0.05 was chosen. Results: The dose conformity was best by multiple field IMRT (p=0.0001). Both two field IMRT and multiple field IMRT provided more homogenous dose distribution with homogeneity index of 1.09±0.01 and 1.08±0.01 respectively when compared to 1.11±0.01 by 3DCRT (p=0.001 and 0.0001, respectively). D2 (dose received by 2% of the tumour volume), a measure of maximum dose was greater in 3DCRT. While dose to the critical organs was considerably less in both two field IMRT and 3DCRT than in multiple field IMRT, two field IMRT achieved lowest doses. Moreover, there was a substantial increase in the Monitor Units (MUs) for multiple field IMRT when compared with the other two techniques. Conclusion: Two field IMRT have the features intermediate of 3DCRT and multiple field IMRT. The two field IMRT is on the beneficial side with homogenous dose distribution in the target and less dose to the critical organs.

Keywords

• breast cancer
• conformal radiotherapy
• conformity index
• inverse planning