Dosimetric comparison between conventional IMRT and EBCRT combined with IMRT for post-mastectomy left-sided breast cancer patients / 中华放射医学与防护杂志

ABSTRACT

Objective:To investigate the dosimetric differences between conventional IMRT and electron beam conformal radiotherapy (EBCRT) combined with IMRT for post-mastectomy left-sided breast cancer patients.Methods:A total of 20 post-mastectomy left-sided breast cancer patients who were treated in the Ningbo First Hospital from June 2018 to October 2021 were retrospectively studied. The planning target volume (PTV) included the supra-and infra-clavicular regions(PTV sc)and the ipsilateral chest wall (PTV cw), and the prescribed dose was 50 Gy/25 f. All radiotherapy plans were designed using the Varian Eclipse treatment planning system (TPS). After that, the dose distribution of the target volume and the dose exposure of organs at risk (OARs) were compared and analyzed. Results:All the IMRT plans met the clinical requirements, yet 2/20 of the EBCRT combined with IMRT plans were not clinically accepted. For these two patients, the maximum chest wall thickness was 3.7 cm and 4.4 cm each, and the designed electron beam energy was 12 MeV and 15 MeV, respectively. The dose to the ipsilateral lung of these two patients exceeded the institution-specific dose limit standard. For the remaining 18 patients whose chest wall thickness was 3 cm or less, the designed electron beams were 9 MeV or less. All the EBCRT combined with IMRT plans were clinically accepted. The target dose distribution of the conventional IMRT was better than that of the EBCRT combined with IMRT (uniformity index (HI) PTV sc t = -10.20, P<0.05; PTV cw t = -9.24, P<0.05; conformal index (CI) PTV all t = 10.39, P <0.05). For OARs, the V5 Gy, V20 Gy, and Dmean of the ipsilateral lung of EBCRT combined with IMRT were lower than those of IMRT ( t = 5.98, 6.30, 11.30, P <0.05). Specifically, the V25 Gy and Dmean of heart decreased by 8.3% and 4.79 Gy, respectively ( t = 15.23, 15.76, P<0.05), the Dmean of the left anterior descending coronary artery (LADCA) decreased by 44.03% ( t = 11.69, P <0.05), and the V5 Gy and Dmean of the contralateral breast decreased by 7.9% and 0.8 Gy, respectively ( t = 3.66, 4.93, P<0.05). The dosimetric differences of other OARs were not statistically significant ( P > 0.05). Conclusions:For post-mastectomy left-sided breast cancer patients with a chest wall thickness of less than 3 cm, EBCRT combined IMRT can significantly reduce the exposure dose to the heart, the ipsilateral lung, and the contralateral breast, which is beneficial to reducing the potential risk of long-term complications after radiotherapy and can further improve the long-term overall survival rate of patients. For patients with thick chest wall, IMRT plans are more technologically ideal.