A Dosimetric Study Comparing 3D-CRT vs. IMRT vs. VMAT in Left-Sided Breast Cancer Patients After Mastectomy at a Tertiary Care Centre in Eastern India

Introduction Post-mastectomy radiation in left-sided breast cancer in women continues to pose a significant risk to the underlying lungs and heart. This study analyzed the difference in planning target volume (PTV) coverage and dose to the organs at risk (OAR) by using three different planning methods for the same patient - threedimensional conformal radiotherapy (3D- CRT), intensity-modulated radiotherapy (IMRT), and volumetricmodulated arc therapy (VMAT). Material and methods Thirty-five left-sided breast cancer patients' post-mastectomy were included in this study, and three different plans for adjuvant radiation were created using 3D-CRT, IMRT, and VMAT. The prescribed dose was 50Gy in 25 fractions. Kruskal-Wallis analysis of variance (ANOVA) was done, followed by a pairwise t-test to establish a hierarchy of plan quality and dosimetric benefits. The plans were compared with PTV95, homogeneity index (HI), conformity index (CI), hotspot (V107%), left lung V20Gy, mean lung dose, heart V25Gy, mean heart dose, and integral dose (ID) to the body. Results Both VMAT and IMRT led to improved PTV95% coverage (95.63 +/- 1.82%, p=0.000 in VMAT; 93.70 +/- 2.16 %, p=0.000; 81.40 +/- 6.27% in 3D-CRT arm) and improved CI (0.91 +/- 0.06 in IMRT [p<0.05] and 0.96 +/- 0.02 for VMAT plans [p<0.05]) as compared to 3D-CRT (0.66 +/- 0.11), which was statistically significant on pairwise analysis. In contrast, the difference in HI and reduction in hotspots were not significantly different. Left lung V20 was statistically very different between the three arms with the highest values in IMRT (36.64 +/- 4.45) followed by 3D-CRT (34.80 +/- 2.24) and the most negligible value in VMAT (33.03 +/- 4.20). Mean lung dose was also statistically different between the three arms. There was a statistically significant difference in mean heart dose between the three arms on pairwise analysis. Both the inverse planning methods led to a statistically significant increase in low dose volume (V5 and V10) of the ipsilateral lung, opposite lung, and heart, and increased ID to the body excluding the PTV. Conclusion While both the inverse planning modalities led to increased coverage, better CI, and better HI and decreased high dose volumes in OARs, there was increased low volume irradiation of heart, lungs, and body with VMAT faring marginally better than IMRT in coverage and decreasing lung irradiation with comparable heart irradiation.

Automated summary

In post-mastectomy radiation for left-sided breast cancer, intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) provide better target coverage and conformity index compared to three-dimensional conformal radiotherapy (3D-CRT). However, they also result in increased low dose irradiation to organs at risk, such as heart, lungs, and body.