A dosimetric comparison of intensity-modulated radiotherapy versus conventional tangential irradiation for breast cancer after breast-conserving surgery

Abstract

Objective To evaluate the dosimetric benefits of intensity-modulated radiotherapy (IMRT) for early stage breast cancer after breast-conserving surgery. Methods Ten patients with stage Tis～2N0M0 breast cancer receiving breast-conserving surgery were selected for the study. Six cases were on the left, four were on the right. A dosimetric comparison of IMRT with conventional wedged tangential technique was performed on each patient using three dimensional treatment planning. The total prescribed dose for both plans was 50 Gy/25 fractions. Dose volume histograms (DVH) were used to compare the planning target volume (PTV) and organs at risks(OARS). Results The PTV coverage in IMRT plan was similar to that of the conventional plan (97.83 % vs 97.61%). A better dose uniformity throughout the whole breast was achieved by IMRT plan. The percentage of PTV receiving less than 95 % prescribed dose and more than 103 % prescribed dose (inhomogeneity index IHI), decreased from 25.42 % to 2.71%: the percentage of PTV receiving more than 105 % prescribed dose (V105 %) decreased from 25.79 % to 1.08 %. A better amelioration of IHI and reduction of V105 % in IMRT plans were observed in the relatively large PTV subgroup. The Dmean and percentage of volume receiving more than 30 Gy (V30) of heart from 6.72 Gy to 4.95 Gy, and from 7.23 % to 1.04 %. the Dmean and percentage of volume receiving more than 20 Gy (V20) of ipsilateral from 9.19 Gy to 7.65 Gy, and from 22.34 % to 20.18 %; the Dmean of contralateral breast decreased from 5.12 Gy to 3.52 Gy;the Dmean of contralateral lung decreased from 2.76 Gy to 1.79 Gy; the Dmean of liver decreased from 7.23 Gy to 1.04 Gy for right side patients. Conclusion Forward planning IMRT based on a standard tangential beam arrangement significantly improves the dose homogeneity throughout the target volume of intact breast and reduces the dose to OARS, especially in patients with large breast volumes who might be proposed as candidates of IMRT for intact breast. Key words: Breast neoplasms; Radiotherapy; Intensity modulation radiation therapy; Threedimensional treatment planning; DVH; Breast-conserving surgery