SU‐E‐T‐829: Dosimetric Comparison of Three Different External Beam Partial Breast Irradiation Techniques: Three‐Dimensional Conformal Radiotherapy, Intensity‐Modulated Radiotherapy and Volumetric Modulated Arc Radiotherapy

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Purpose: To compare the dosimetric differences of three‐dimensional conformal radiotherapy (3D‐CRT), inverse intensity‐modulated radiotherapy (IMRT) and volumetric modulated arc radiotherapy(V‐MAT) for external beam partial breast irradiation. Methods: Twelve patients with breast cancer receiving breast‐conserving surgery and external beam partial breast irradiation were enrolled in the study.Three treatment techniques including 3D‐CRT, IMRT and V‐MAT were designed for each patient.The dose distribution in the target,the dose to the organs at risk,total MU and delivery time were compared. Results: 3D‐CRT plans showed the worst conformity in target.V‐MAT plans provided the lowest target coverage and homogeneity in target.All three plans met the clinical requirement.3D‐CRT plans showed the lowest values for the V5,V10 and mean dose and the highest values for V30 in the ipsilateral lung. No statistically significant differences were observed in V20 of the ipsilateral lung between three plans.The ipsilateral normal breast volume receiving 5Gy,10Gy,30Gy and 34Gy doses were significantly lower in IMRT and V‐MAT compared with 3D‐CRT.V‐MAT showed the lowest values in ipsilateral normal breast volume receiving 15Gy,20Gy and 25Gy doses.For V5,mean and max dose in heart,the mean dose in contralateral lung and the mean,max dose in thyroid, IMRT and 3D‐CRT showed the highest and lowest value respectively.The MUs were 417.6±34.4,772.8±54.4 and 631.0±109.0 respectively in 3D‐CRT,IMRT and V‐MAT.The delivery times were 9–10min, 8–10min and 1–1.1 min respectively in 3D‐CRT,IMRT and V‐MAT. V‐MAT could significantly reduced the delivery time. Conclusions: All three plans met the clinical requirement.V‐MAT significantly reduced the irradiated volume of high dose region in the ipsilateral normal breast,but the other dosimetric parameters didnˈt show better in V‐MAT compared with IMRT.V‐MAT significantly decreased the delivery time.Overall,V‐MAT showed a similar or better dose distribution and could significantly reduce the delivery times compared with 3D‐CRT and IMRT.