Dosimetric comparison of IMRT versus 3DCRT for post-mastectomy chest wall irradiation

To compare the dose distribution of three-dimensional conformal radiation therapy (3DCRT) with intensity-modulated radiation therapy (IMRT) for post-mastectomy radiotherapy (PMRT) to left chest wall.

One hundred and seven patients were randomised for PMRT in 3DCRT group (n = 64) and IMRT group (n = 43). All patients received 50 Gy in 25 fractions. Planning target volume (PTV) parameters-D_near-max (D₂), D_near-min (D₉₈), D_mean, V₉₅, and V₁₀₇-homogeneity index (HI), and conformity index (CI) were compared. The mean doses of lung and heart, percentage volume of ipsilateral lung receiving 5 Gy (V₅), 20 Gy (V₂₀), and 55 Gy (V₅₅) and that of heart receiving 5 Gy (V₅), 25 Gy (V₂₅), and 45 Gy (V₄₅) were extracted from dose-volume histograms and compared.

PTV parameters were comparable between the two groups. CI was significantly improved with IMRT (1.127 vs. 1.254, p < 0.001) but HI was similar (0.094 vs. 0.096, p = 0.83) compared to 3DCRT. IMRT in comparison to 3DCRT significantly reduced the high-dose volumes of lung (V₂₀, 22.09% vs. 30.16%; V₅₅, 5.16% vs. 10.27%; p < 0.001) and heart (V₂₅, 4.59% vs. 9.19%; V₄₅, 1.85% vs. 7.09%; p < 0.001); mean dose of lung and heart (11.39 vs. 14.22 Gy and 4.57 vs. 8.96 Gy, respectively; p < 0.001) but not the low-dose volume (V₅ lung, 61.48% vs. 51.05%; V₅ heart, 31.02% vs. 23.27%; p < 0.001).

For left sided breast cancer, IMRT significantly improves the conformity of plan and reduce the mean dose and high-dose volumes of ipsilateral lung and heart compared to 3DCRT, but 3DCRT is superior in terms of low-dose volume.