Dosimetric comparison of three different radiotherapy techniques in whole breast radiotherapy after breast-conserving surgery for left breast cancer

Objective: To compare the dosimetry of three different intensity-modulated radiation therapy (IMRT) techniques in patients undergoing whole-breast radiotherapy after breast-conserving surgery for early left breast cancer. Methods: Between March 2019 and August 2019, 12 female patients with early left breast cancer who underwent breast-conservative surgery in the First Affiliated Hospital of Xi'an Jiaotong University were analyzed retrospectively. The patient age was between 32 and 50 years, with an average of 42.4 ± 6.8 years. The IMRT-based hybrid plan (3D conformal radiation therapy or 3DCRT + IMRT), the volumetric modulated arc therapy (VMAT)-based hybrid plan (3DCRT+VMAT), and the tangential VMAT plan (t-VMAT) were designed. The dosimetric parameters of the target and the organs at risk and treatment efficiency were compared among the three plans, and t-test was used for data analysis. Results: Both the dose distribution in the target and dose to the organs at risk can meet the clinical requirements of the three plans. The conformal index (0.84 ± 0.05 vs. 0.74 ± 0.06 vs. 0.79 ± 0.06) and uniformity index (0.10 ± 0.03 vs. 0.14 ± 0.03 vs. 0.13 ± 0.03) of 3DCRT + VMAT were the best, and the difference was statistically significant compared with the two other plans (t = -9.01-6.47, all P < 0.05). The protective effect of 3DCRT + IMRT was the best for V₅ ((35.92 ± 8.01)% vs. (49.33 ± 12.05)% vs. (60.58 ± 12.94)%), V₁₀ ((25.50 ± 6.91)% vs. (26.92 ± 7.23)% vs. (41.25 ± 10.37)%), D_mean ((10.14 ± 2.43) Gy vs. (11.07 ± 2.88) Gy vs. (14.52 ± 3.32) Gy) of the ipsilateral (left) lung, V₅ ((0.50 ± 1.45)% vs. (2.17 ± 3.76)% vs. (3.00 ± 4.94)%), and D_mean ((0.55 ± 0.21) Gy vs. (1.79 ± 0.58) Gy vs. (1.75 ± 0.70) Gy) of the contralateral (right) lung and the V₅ ((0.17 ± 0.58)% vs. (1.92 ± 4.10)% vs. (8.25 ± 8.61)%) and D_mean ((0.86 ± 0.38) Gy vs. (1.65 ± 0.45) Gy vs. (2.46 ± 0.86) Gy) of the contralateral (right) breast. 3DCRT + VMAT was significantly better than 3DCRT + IMRT and t-VAMT in V₃₀ ((4.50 ± 2.88)% vs. (5.00 ± 3.25)% vs. (8.42 ± 2.78)%) and V₄₀ ((2.50 ± 2.11)% vs. (3.25 ± 2.53)% vs. (4.58 ± 2.07)%) of the heart (t = -17.11-3.45, all P < 0.05). The mean monitor unit of 3DCRT + IMRT was the lowest (280.90 ± 52.18), but the treatment time of t-VMAT was the shortest. Conclusions: The protective effect of 3DCRT + IMRT in the low-dose area (< 20 Gy) for the ipsilateral lung, contralateral lung, and contralateral breast was better. 3DCRT + VMAT has obvious advantages in improving the uniformity and conformability of the target area and has better protection in the high-dose area (> 20 Gy) for the contralateral lung and heart. Thus, t-VMAT shortens the treatment time and improves treatment efficiency and patient comfort. (authors)