A Study Comparing Dosimetric Parameters and Clinical Outcomes in Inversely Planned Intensity-Modulated Radiotherapy (IMRT) and Field-in-Field Forward Planned IMRT for Breast Cancer Treatment

This study aimed to evaluate IP IMRT with field-in-field FP IMRT in patients undergoing adjuvant radiation after a modified radical mastectomy (MRM) for breast cancer. In the treatment of breast cancer, radiotherapy has been an essential component of the multimodality strategy. Dose distribution was improved by newer methods such as three-dimensional radiation. Intensity-modulated radiation (IMRT) improved homogeneity much further. The purpose of this study was to evaluate dosimetric characteristics and clinical results of inverse planned IMRT (IP IMRT) and field-in-field forward planned IMRT (FP IMRT) in patients with breast cancer receiving post-modified radical mastectomy (MRM) adjuvant radiation. Fifty patients with breast cancer who had MRM and needed adjuvant radiation were randomly randomized to one of two groups (25 each) using IP IMRT and FP IMRT procedures. The recommended dose was 50 Gy spread out over five weeks in 25 portions. In IP IMRT, five to seven tangential beams were employed for the chest wall, nodal volumes were set at appropriate angles using beam optimization, and the analytical anisotropic technique was used to calculate. In order to ensure uniform dose distribution to the planned target volume (PTV), minimize hot spot areas, and restrict exposure to the ipsilateral lung and contralateral breast, two opposing tangential fields were developed for FP IMRT. The dosimetric parameters in terms of PTV are better for IP IMRT plans compared to FP IMRT plans (V95%: 92.3% vs 75.2%, p = 0.0001; D90%: 47.4 Gy vs 42.9 Gy, p = 0.0001; D95%: 44.9 Gy vs 37.1, p = 0.0004). The ipsilateral lung (V10Gy: 71.9% vs 41%, p = 0.00001; V20Gy: 42.14% vs 36.35%, p = 0.03; V40Gy: 17.31% vs 26.95%, p = 0.00004; Dmean: 20.91 Gy vs 17.88 Gy, p = 0.01) and contralateral lung (V5Gy: 31.8% vs 0.1%, p < 0.00001; V10Gy: 6.2% vs 0.08%, p = 0.0001) received statistically significant lesser doses in terms of low dose parameters in FP IMRT. In the heart, the dosimetric parameter V5 was significantly lower for FP IMRT (61.7% vs 9.7%, p = 0.00001) along with Dmean (10.92 Gy vs 4.01 Gy, p = 0.001). Similarly, LAD parameters showed comparable high dose volumes (V40Gy: 21.02% vs 16.26%; p = 0.29) in both groups and a trend toward reduction in mean dose (17.1% vs 9.2%; p = 0.05) in FP IMRT group, although low dose volumes were higher in IP IMRT group. In contralateral breast, doses in smaller volumes were better for FP IMRT plans (V0.5Gy: 59.7% vs 43.8%, p = 0.01; V0.6Gy: 54.07% vs 37.6%, p = 0.007; V1Gy: 40.9% vs 22.1%, p = 0.001; V2Gy: 28.7% vs 9.4%, p = 0.00003; V5Gy: 12.07% vs 4.2%, p = 0.0001). In esophagus, statistically significant lower doses were seen only in terms of Dmean (10.29 Gy vs 5.1 Gy; p = 0.03) with FP IMRT. No significant difference in terms of skin reactions and dysphagia was seen in both the groups. Both IP IMRT and FP IMRT offer benefits and drawbacks, and the superiority of one approach over the other cannot be proved in this study. The decision to choose one approach over another can also be influenced by patient-related criteria such as the risk of loco-regional recurrence vs the danger of radiation-induced sequelae.