Dosimetric comparison between IMRT and VMAT in patients undergoing internal mammary lymph node radiotherapy after modified radical mastectomy

Objective: To investigate the dosimetric differences in volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) in patients receiving adjuvant radiotherapy and internal lymph node irradiation after left-sided modified radical mastectomy. Methods: VMAT and IMRT radiotherapy plans were established for 20 patients undergoing left-sided modified radical mastectomy. The dosimetric parameters of the target area and organs at risk were calculated by the dose volume histogram. The categorical variables were tested by X² or Fisher's exact probability test. The continuous variables with normal distribution were analyzed by paired-t test or rank-sum test. Results: Among the two radiotherapy techniques, the homogeneity index of IMRT was significantly higher than that of VMAT (P < 0.05). The time of VMAT treatment was significantly shorter than that of IMRT (P < 0.01). VMAT was superior to IMRT in V_20Gy and V_30Gy of the affected lung (both P < 0.05). VMAT was superior to IMRT in the left anterior descending coronary artery D_mean, D_max, and heart V_30Gy, V_40Gy, D_mean and D_max (all P < 0.01). The esophageal D_mean in the VMAT group was superior to that in the IMRT group (P < 0.05). The V_5Gy and V_10Gy of the contralateral lung and the D_max of the esophagus in the IMRT group were significantly better compared with those in the VMAT group (all P < 0.05). Conclusions: VMAT can significantly reduce the dose of the heart, contralateral lung, spinal cord, esophagus and other vital organs, and shorten the treatment time. For patients who need adjuvant radiotherapy and internal mammary lymph node irradiation after left-sided modified radical mastectomy, VMAT technology can better protect normal tissues than IMRT. (authors)