A comparative study of volumetric modulated arc therapy plans based on the equivalent uniform dose optimization for left-sided breast cancer

To investigate the effect of equivalent uniform dose (EUD)-based optimization on radiotherapy planning for left-sided breast cancer after mastectomy. Twelve patients treated with left-sided breast cancer using volumetric modulated arc therapy (VMAT) were retrospectively enrolled in this study. Four plans were generated for each patient. Plan A was optimized based on only physical parameters. EUD with α > 0 to organ at risk (OARs) was added in Plan B on the basis of Plan A; EUD with α < 0 to planning tumor volume (PTV) was added in Plan C on the basis of Plan A; EUD constraints were added for both OARs and PTV in Plan D. The quality of plans was evaluated in terms of Vx (volume percent of PTV or OARs received xGy dose), Dx (dose received by volume above x% of PTV or OARs), conformity index (CI), mean dose (Dmean), maximum dose (Dmax) and minimum dose (Dmin). For PTV: Plan A vs. Plan B, the difference of D2 and CI was statistically significant (P < 0.05); Plan A vs. Plan C, the differences in D98, Dmean and HI were statistically significant (P < 0.05); Plan A vs. Plan D, differences in D2, Dmean and HI were statistically significant (P < 0.05). For OARs: Plan A vs. Plan B, and Plan A vs. Plan D, the differences in V5, V10, V20, V30, Dmean of the left lung and V10, V20, V30, Dmean of the heart were statistically significant (P < 0.05), the differences in Dmean of the thyroid and contralateral breast and the D2 and Dmax of spinal cord and spinal cord planning risk volume (PRV) were statistically significant (P < 0.05); Plan A vs. Plan C, only the difference in Dmax of spinal cord was statistically significant (P < 0.05). Compared with DV condition, the dosimetric data with EUD-based optimization for OARs and PTV confer advantages in terms of the mean dose region of the left lung, heart, thyroid and contralateral (right) breast and the maximum dose of the spinal cord, and the improvement of the conformity and homogeneity of the target.