Impact of Breathing Motion on IMRT (Intensity Modulated Radiation Therapy) of the Chest Wall in Postmastectomy Breast Cancer Patients: A Dosimetric Comparison With 3D Conformal Radiation Therapy

Abstract

INTRODUCTION: Radiotherapy forms an essential part of breast cancer treatment. The technology of radiotherapy has developed to give very precise dose to target region with sparing of critical organs. But irradiation of thorax is always influenced by respiratory motion. The influence of respiratory motion on breast cancer radiotherapy and choice of technology based on this has not been studied in detail. We intend to study the effect of respiration on IMRT and 3D conformal radiotherapy of breast cancer. AIM AND OBJECTIVES: To study the dosimetric effect of respiratory motion on intensity modulated radiotherapy to the chest wall in patients with carcinoma breast and compare it with the respiratory motion effect on 3D conformal tangents based plan. MATERIALS AND METHODS: The respiratory parameters of 10 study participants and their dosimetric data on target coverage and dose to organs at risk with IMRT (intensity modulated radiotherapy) and 3D CRT (3D conformal radiotherapy) plans in free breathing, normal inspiration and normal expiration were compared and analysed. RESULTS: Respiratory motion resulted in a significant fall in target coverage (V95) with IMRT when compared to 3D-DRT to chest wall (p=0.007&0.002 vs. 0.174&0.063 with inspiration and expiration respectively) by about 4-5%. Dose inhomogeneity increased in the target volume with respiration, and its minimal dose was decreased by 28% with IMRT in comparison to 14% with 3D-CRT. An analysis of the impact of chest wall movement during IMRT demonstrated that respiration increased the volume of target receiving high radiation dose (11.79% & 20.07% in inspiration and expiration respectively). Evaluation of the dose to organs at risk revealed that there was an overall increasein dose with respiration in IMRT more than 3D-CRT. However, the mean cardiac dose in left sided breast cancer patients crossed the limit of V25 0.68 L and chest wall expansion of >0.5 cm had a poor target coverage with respiration in IMRT (though not significant statistically). The difference in target under-coverage between 3D CRT and IMRT was 11.2% & 5.08% with inspiration and expiration respectively, when tidal volume was >0.68 L. CONCLUSIONS: The dose delivered to target volume is dependent on respiratory movement of chest wall in IMRT technique. It is important to consider the respiratory parameters of a patient prior to choosing the technique of post- mastectomy radiotherapy.