Dosimetric Comparison of Intensity-modulated Radiation Therapy versus Three-dimensional Conformal Radiation Therapy in Postmastectomy Chest Wall Radiotherapy in Breast Cancer

A BSTRACT Background: Breast cancer is the most common cancer affecting women globally. Postmastectomy radiotherapy (PMRT) of the chest wall improves the locoregional control and survival in node positive breast cancer patients after mastectomy. Data on the effect of intensity-modulated radiation therapy (IMRT) to chest wall in postmastectomy breast cancer patients are scarce in the literature. This study was conducted to know if IMRT is as safe and effective as three-dimensional conformal radiation therapy (3DCRT). Objectives: To determine and compare the dose parameters of organs at risks (OARs) in IMRT versus 3DCRT in patients receiving PMRT and also to compare the clinical toxicities caused by IMRT versus 3DCRT. Materials and Methods: This study was conducted among 60 patients receiving PMRT. Thirty patients each were recruited to IMRT and 3DCRT arm. All patients were treated with 6MV photon linear accelerator. Dose volume histograms of the 3DCRT and IMRT plans were generated and dosimetric parameters of heart, lung, esophagus, contralateral breast, and spinal cord were compared. Patients were monitored weekly during the treatment and every month for 3 months after treatment. At each follow-up, every patient was assessed for Cutaneous Reactions and Esophagitis and was graded according to CTCAE version 5.0. Results: The Conformity Index and Heterogeneity index for planning target volume is significantly better with IMRT. V5 Gy of heart, ipsilateral and contralateral lung were significantly high in IMRT in comparison to 3DCRT. There was no significant difference in terms of mean doses and high dose volumes of heart and lung between IMRT and 3DCRT. Maximum dose of the esophagus and spinal cord were significantly high in IMRT arm. Mean dose received by the contralateral breast was significantly higher in IMRT than 3DCRT. Conclusion: IMRT provides better target coverage and higher dose to OAR in terms of low dose volumes and also decreases the incidence of moist desquamation and Grade 2 esophagitis. The advantages of improved coverage of the target area and lower adverse events can be weighed against the consequences of irradiating larger volume of healthy tissues. Hence, the treating technique can be carefully chosen on individual basis. Both IMRT and 3DCRT can be considered for postmastectomy chest wall radiation.