Dosimetric Comparison between 3D-Conformal Radiotherapy and Volumetric Modulated Arc Therapy for the Heart in Left- Sided Breast Irradiation

Background: After breast-conserving surgery, irradiation to whole breast
lowers the rate of recurrence. Deep inspiration breath-hold technique is the most
effective way to lower radiation doses to the heart and if it is not accessible,
alternative options like intensity-modulated radiation therapy (IMRT),
volumetric modulated arc therapy (VMAT) or three-dimensional conformal
radiation therapy(3D-CRT) must be chosen. We aimed for comparing the
dosimetric measurements affecting the target and organs-at-risk (OAR) in
VMAT+SIB and 3D-CRT+SIB.
Methods: A comprehensive sample of 54 were included in the study. Patients
were allocated into 2 Arms, arm A received 3D-CRT+SIB, arm B received
VMAT+SIB, each arm received WBI 40 Gy/15 fractions with SIB 8 Gy/15
fractions. Comparison of both arms, treatment plans evaluation, Dose Volume
Histograms especially dose constrains to heart and coronary artery, target dose
coverage, conformity index, monitor units’ number and homogeneity index
were analyzed.
Results: A significant difference between two groups was seen regarding to
target coverage dosimetry. VMAT demonstrated higher mean CTV than 3D-
CRT. Also, a significant difference was noted regarding OAR dosimetry, as the
VMAT was associated with higher doses to the heart, right lung, and right
breast. In contrast, the 3D-CRT delivered a higher minimum, maximum and
mean left anterior descending coronary artery (LAD) doses. The VMAT
demonstrated significantly higher CI and MU but HI among both groups did not
differ significantly.
Conclusion: multi-fields and arcs arrangements (VMAT) considerably
decreased the doses to the LAD and improved doses to the target, although
approaches with tangential fields arrangement (3DCRT) provided better OARs
dosimetry.