Objective: To evaluate the dosimetric advantages of postmastectomy electron-beam chest-wall irradiation after left mastectomy in patients with breast cancer.
Methods: Electron-beam chest-wall irradiation and tangential field irradiation were planned using Pinnacle7.4f planning systems for 42 patients with left breast cancer after mastectomy. The total prescribed dose for both plans was 5000 cGy/25 fractions. The dose volume histogram was used to compare the dosimetry of the clinical target volume (CTV) and the organs at risk such as the heart and ipsilateral lung.
Results: The maximum dose (Dmax) of the CTV of electron beam chest-wall irradiation plans was significantly higher than that of tangential field irradiation plans (5562±61 vs 5402±82 cGy, t=6.10, P<0.05). The CTV of the electron beam chest-wall irradiation plans showed better heterogeneity than that of the tangential field irradiation plans, with heterogeneity index of 1.18±0.03 and 1.13±0.18, respectively (t=6.50, P<0.05). Electron beam chest-wall irradiation plans had also a better conformal index of the CTV than tangential field irradiation plans (0.77±0.17 vs 0.57±0.17, t=3.49, P<0.05). The V40 of the ipsilateral lung, the maximum dose of the heart, V30 and V40 of the heart in the electron beam chest-wall irradiation plans were smaller than those of the tangential field irradiation plans [(5.86±3.68)% vs (8.73±3.26)%, t=-2.27, P<0.05; 4839±388 cGy vs 5095±176 cGy, t=-2.32, P<0.05; (2.58±1.50)% vs (7.20±2.62)%, t=-4.70, P<0.05; (1.74±1.23)% vs (4.20±2.51)%, t=-3.50, P<0.05].
Conclusion: Compared with the tangential field irradiation plans, electron-beam chest-wall irradiation has better coverage index of the CTV and can decrease the high-dose volume of the normal tissue, but shows a poorer habituation index of the CTV.