核医学与放射治疗

Evaluation of Doses to Organ at Risk with Deep Inspiratory Breath Hold Compared to Free Breathing in Left Sided Breast Cancer and Assessment of Patient Related Anatomical Factors

Abstract

Tabinda Sadaf*, Samaha Nawaz, Asma Rashid, Aqueel Shahid, Amna Munawar, Raheel Mukhtar, Sana Mazhar and Muhammad Abubakar

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 term survivors.

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 radiotherapy.

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.