Dosimetry Study Of Left Breast Under Imrt Precisely Outline The Heart And Its Sub-structure

Objective:To evaluate the feasibility that64-slice spiral CT coronary angiography(CTA) method display and outline sub-structure of the heart in patients of left breast-conserving surgery; and compare the dosimetry differences between target and organs at risk under the prone and supine two kinds of position in breast intensity-modulated radiation therapy.Methods:From January to December in2011,20patients of left breast-conserving surgery were enrolled. The CTA method was used separately for each patient prone and supine position scanning. Two sets of sequence scanning were done at the same time. One is a conventional sequence, the other is a special sequence (CTA). CT images of the two sequences were transmitted to the Master Plan radiation planning system for integrated. On the conventional sequence, the clinical target volume (CTV) of the whole breast, planning target volume (PTV), bilateral lung (L-Lung, R-Lung), spinal cord, the contralateral breast (R-Breast) and Heart were outlined; On the special sequence, left ventricular (LV), left anterior descending coronary artery (LAD) and LAD’s planning risk volume (LAD-PRV)(LAD1cm outside the expanded form) were outlined. For each patient, two kinds of IMRT plans were developed under supine and prone position, a total of20plans. In the dose-volume histogram, the following indicatorswas compared:PTV:Dmean, D95; the ipsilateral lung(L-Lung):Dmean, V5, V20; heart and its sub-structures(LAD-PRV、LV): Dmea、V10、V20、V30、V40; the contralateral lung(R-Lung):Dmean> V5; R-breast:Dmax、Dmean.Results:CTA method outline sub-structure of the heart is very intuitive, easy to sketch, economic and worthy of promotion. PTV’s dose has reached the radiation treatment planning requirements both in the supine and prone position.The dose distribution of the two positions is recognized. PTV’s dose of the two positions has no significant.The plans of prone position significantly reduced the exposure doses of LAD, LV, heart and the ipsilateral lung. LAD-PRV’s Dmean reduced445.83cGy (P=0.043),V25reduced8.57%(P=0.042); LV’s Dmean reduced575.00cGy (P=0.003), V20reduced15.21%(P=0.026), V25reduced12.54%(P=0.042);Heart’s Dmean reduced402.00cGy (P=0.039),V10reduced28.31%(P=0.029), V20reduced12.59%(P=0.011), V25reduced8.70%(P=0.019), V30reduced5.54%(P=0.034);L-Lung’s Dmean reduced553.33.00cGy (P=0.004),V05reduced27.86%(P=0.031),V20reduced10.62%(P=0.006)Conclusion:1. The method that CTA outlines sub-structure of the heart is very intuitive, easy to sketch, economic and worthy of promotion.2.For most Asian women with medium size of breast after BCT, comparing with supine position, prone position IMRT radiation can reduce the ipsilateral lung’s, heart’s, and its sub-structure’s exposure doses, which may reduce the incidence of cardiovascular events after radiotherapy.3.The dose-volume limit value of the sub-structure of the heart such as LV、LAD need to be further explored.