Comparison of Mean Lung and Heart Doses in Three-Dimensional Conformal Radiotherapy Versus Intensity Modulated Radiotherapy in Postmastectomy Breast Cancer Radiation

Abstract

Background: Breast cancer is the leading malignancy among women worldwide, with adjuvant radiotherapy essential for reducing locoregional recurrence following modified radical mastectomy. Optimal radiotherapy technique selection is critical to balance tumor control with the minimization of cardiac and pulmonary toxicity, particularly in left-sided breast cancer. Objective: To compare the dosimetric parameters of mean lung and heart doses, as well as target volume coverage, between three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiation therapy (IMRT) in postmastectomy breast cancer patients. Methods: In this randomized controlled trial conducted at Atomic Energy Cancer Hospital NORI, Islamabad, 60 women with left-sided invasive ductal carcinoma who had undergone modified radical mastectomy were randomized equally to receive adjuvant radiotherapy with either 3DCRT or IMRT (40.05 Gy in 15 fractions). Dosimetric parameters, including mean doses and low- and high-dose volumes for heart and lung, as well as planning target volume (PTV) coverage indices, were assessed using standardized contouring and treatment planning. Group comparisons utilized the Mann-Whitney U test. Results: IMRT achieved significantly superior PTV coverage (PTV 95%: 98.5% vs. 92.96%, p<0.001), but resulted in higher mean lung (15.17 Gy vs. 12.81 Gy, p=0.001) and heart doses (6.88 Gy vs. 4.02 Gy, p<0.001) and increased low-dose exposure (lung V5: 71.5% vs. 45.5%, heart V5: 43.2% vs. 12.8%, both p<0.001), while high-dose volumes (lung V20 and heart V25) did not differ significantly between groups. Conclusion: Although IMRT provides enhanced target volume coverage in postmastectomy radiotherapy, it is associated with greater low-dose irradiation of the heart and lung compared to 3DCRT, highlighting a trade-off that should inform technique selection and further research.