Rolling tangential IM-segment beam in the irradiation for the breast / 中华放射肿瘤学杂志

ABSTRACT

Objective Studies on IMRT technique demonstrates that the improved dose homogeneities throughout the breast as well as reduction in dose to the heart and the ipsi-and control-lateral lungs. Methods Based on the physical principle of rolling tangential technique, a treatment plan for a patient has been planned by using Pinnacle aperture-based inversion software. The rolling tangential IM-beam was pre-determined at each pre-selected gantry angle with normally angle separation of 5?, 10? or 15?. Each beam's width was so chosen that the inner-and outer-edge of the beam should be tangential to the inner chest wall and target outer surface respectively. For the starting and ending tangential beam, a pair of opposing beam was designed. The beam's orientation was suggested to be reversed to its opposite angle when the tangential beam's gantry angle reached 90? or 270?. Each beam's shape and size were adjusted on its BEV map. For each tangential beam, 7 sub-segment beams were chosen for each tangential beam. Then, planning system was allowed to do optimization according to the clinical dose prescriptions. Results The calculated dose distributions in target(CTV), left & right lungs, and heart showed that the volume received the prescribed dose 50?Gy V_ 50 was 0.95; The volume in target enclosed with 95%, 105%, 110%, 115% isodose lines V_ 95% , V_ 105% , V_ 110% , V_ 115% was 0.98, 0.84, 0.53, 0.18, respectively. The volume of V_ 10 ,V_ 20 , V_ 30 , V_ 40 V_ 50 , in the lungs and heart were significantly decreased when compared to the current IMRT techniques published in the literature(Table 1).Conclusions The rolling tangential IM-segment irradiation technique for the breast developed by the author is able to offer not only a better dose distribution and better dose conformity throughout the target, but also reduce significantly the dose to the lungs and heart, with the patient's set up and localization process being very simple. The treatment planning for individual patient is optimal in any treatment planning system with Aperture-Optimization inverse software. This technique is certainly to offer more benefit to the patient if some measures are taken to limit or to follow the movement of the chest wall during irradiation.