Dosimetric comparisons of intensity-modulated radiation therapy and three-dimensional conformal radiation therapy for left-sided breast cancer after radical surgery

Abstract

Objective: Postoperative radiotherapy for breast cancer is an effective way to control tumor recurrence; however, there are advantages and disadvantages to different radiotherapy techniques. This study compared dosimetry differences between intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3D-CRT) plans after radical surgery for left-sided breast cancer to provide guidance for clinicians to select a radiotherapy technique. Methods: A total of 50 women who received radiation therapy for left-sided breast cancer after radical surgery in Gansu Provincial Cancer Hospital between 9 January 2017 and 30 November 2017 were included. The prescription dose was 50 Gy/25f. IMRT and 3D-CRT treatment plans were designed for each patient on an Oncentra 4.1 planning system. Statistical analysis of the target dose distribution – conformal index, uniformity index, and irradiation doses to the ipsilateral lung, heart, left ventricle, humeral head, and thyroid – was carried out for the two groups and the differences were compared. Results: When comparing the two plans, the target V95% (z = –5.739, P < 0.001), V105% (t = –3.244, P = 0.002), V110% (t = –9.420, P < 0.001), V115% (z = −5.834, P < 0.001), conformal index (t = 27.711, P < 0.001), and uniformity index (t = –15.761, P < 0.001) for the IMRT plan were better than those for the 3D-CRT plan. Meanwhile, V30 (t = –4.29, P < 0.001) and the maximum dose (z = –5.285, P < 0.001) of the ipsilateral lung, V40 (z = –4.294, P < 0.001) and V50 (z = –5.873, P < 0.001) of the heart, V40 (z = –4.918, P < 0.001) and V50 (z = –5.633, P < 0.001) of the left ventricle, and V50 (z = –4.196, P < 0.001) of the humeral head in the IMRT plan were lower than those in the 3D-CRT plan. However, V5 (t = 30.086, P < 0.001), V10 (z = −6.154, P < 0.001), V20 (t = 8.228, P < 0.001), and the mean dose (z = −4.156, P < 0.001) of the ipsilateral lung, V30 (z = –4.407, P < 0.001) and the mean dose (t = 17.877, P < 0.001) of the heart, V30 (z = −2.920, P = 0.003) and the mean dose (t = 15.324, P < 0.001) of left ventricle, the mean dose (z = −6.144, P < 0.001) of the humeral head, and V40 (z = –6.154, P < 0.001) and the mean dose (z = –5.643, P < 0.001) of the thyroid in the IMRT plan were higher than those in the 3D-CRT plan. There was no statistically significant difference in the V50 (t = 0.825, P = 0.413) of the thyroid between the IMRT and 3D-CRT plans. Conclusions: Both IMRT and 3D-CRT plans for left-sided breast cancer after radical surgery can meet clinical requirements. The prescription dose coverage, conformity, and dose uniformity for the target in the IMRT plan were better than those in the 3D-CRT plan, and the IMRT plan reduced high-dose irradiation volume of the ipsilateral lung, heart, and left ventricle, and better protected the humeral head. The 3D-CRT plan reduced the low-dose irradiation volume and the mean dose to the ipsilateral lung, heart, and left ventricle, and also had more advantages in protecting the thyroid. In clinical settings, it is necessary to consider individual patient condition when selecting a radiotherapy technique.