Introduction: With the improvement in prognosis for patients with breast cancer, reducing long-term toxicity from treatment has become
increasingly important. Left breast Radiotherapy (RT usually results in higher dose delivery to the heart and lungs, which are treated as
Organs at Risk (OAR. Heart irradiation increases the risk of radiation induced heart disease and major coronary artery disease in long
Material and methods: After obtaining informed consent, 50 patients were enrolled in the study between October 2020 and
February 2021. Two scans were performed on each patient, one in Free Breathing (FB) and one using Deep Inspiratory Breath Hold technique
(DIBH). Contouring of target volume and Organ at Risk (OAR) were performed on both scans. Dose Volume Histograms
(DVH) was generated for both scans for plan evaluation. Dose parameters were calculated and compared to assess doses to heart
and lungs. In addition, anatomical parameters including Maximum Heart Distance (MHD), Haller Index (HI), Central Long Distance
(CLD), chest wall separation (CWS), Heart Chest Distance (HCD), Lung Volume Difference (LVD), and Cardiac Contact Distance (CCD) in axial
and parasagittal planes were also studied for impact on doses to heart and lung.
Results: The reduction in mean doses using DIBH was statistically significant for both heart and lung. Overall, the mean heart dose in FB
was 5.60 ± 2.20 and in DIBH it is 2.50 ± 1.24 leading to a difference of 3.4 Gy.
About 17 patients (34% failed to attain a difference of ≥2 Gy with DIBH scans. This difference was persistent and significant in V10, V30, V35 of
heart. Similarly, mean left lung dose reduction of 4.89 Gy was seen from 9.42 ± 2.80 in FB to 4.53 ± 2.20 using DIBH scan with statistically
significant (p value=<0.05. Overall, V20 V5 and V10 of both lungs showed no statistical difference in either group (FB and DIBH, respectively.
On contrary to this, the impact of DIBH dose reduction was more pronounced in V20 and V30 of left lung and less marked in V5 and V10. The
mean differences in different anatomical parameters between FB and DIBH scan were significant for all stated parameters except chest wall
separation (FB=20.35 cm, DIBH=20.55 cm, p-value=0.68. The moderate correlation between the anatomical parameters and mean heart dose
reduction was statically significant for CLD (r=-0.36, p- value 0.01, MHD (r=-0.40, p-value=0.007, HCD (r=0.50, p-value=0.001, CCDps
(r=-0.43, p-value=0.002 while the rest of the parameters including CCDax, LVD, CWS and Haller index showed weak correlation with outcome
variable. The Multivariate regression analysis concluded HCD (β=2.02 (CI=1.14-2.89),p -value=0.001)a nd CLD (β-1.499 (CI=-2.448-0.549),p -
value=0.003 two variables that independently predict mean heart dose reduction for patients undergoing DIBH based left sided breast
Conclusion: DIBH is a sublime technique and it is cost effective if used in suitable cohorts of patients. To improve selection criteria, HCD
and CLD can be used as suitable anatomical predictors for reduction in mean doses to organs at risk.