Dosimetric analysis of Deep Inspiratory Breath-hold technique (DIBH) in left-sided breast cancer radiotherapy and evaluation of pre-treatment predictors of cardiac doses for guiding patient selection for DIBH

Abstract

Introduction: The risk of radiotherapy-associated cardiovascular disease has been a concern for decades in breast cancer survivors. The objective of our study is to evaluate the dosimetric benefit of Deep Inspiratory Breath-hold technique (DIBH) on organs-at-risk (OAR) sparing in left-sided breast cancer radiotherapy and to find out pre-treatment predictors of cardiac doses for guiding patient selection for DIBH.

Material and methods: Pre-radiotherapy planning CT scans were done in Free Breathing (FB) and in DIBH [using Active Breathing Coordinator system (ABC™)] in 31 left sided breast cancer patients. 3DCRT plans were generated for both scans. Comparison of anatomical and dosimetric variables were done using paired t test and correlation was evaluated using Pearson correlation. Linear regression was used to get independent predictors of cardiac sparing and Receiver Operating Characteristic (ROC) curve analysis was done to find out the specific threshold of the predictors.

Results: There was a 39.15% reduction in mean heart dose in DIBH compared to FB (2.4 Gy vs 4.01 Gy) (p < 0.001), 19% reduction in maximum Left Anterior Descending (LAD) dose and a 9.9% reduction in ipsilateral lung mean dose (p = 0.036) with DIBH. A significant correlation was observed between reduction in Heart Volume in Field (HVIF) and Maximum Heart Depth (MHD) with reduction in mean heart dose. Reduction in HVIF (ΔHVIF) independently predicted cardiac sparing.

Conclusion: DIBH leads to significant reduction in OAR doses and is suggested for all patients of left-sided breast cancer undergoing radiotherapy. However, HVIF and MHD predicted for cardiac sparing and threshold criteria of ΔHVIF and ΔMHD may be used by centres with high workload to select patients for DIBH.

Keywords: 3DCRT, Three-Dimensional Conformal Radiation Therapy; ABC™, Active Breathing Coordinator™; AUC, Area under the curve; BCS, Breast Conservation Surgery; BMI, Body Mass Index; Breast cancer; CCD, Cardiac Contact Distance; CD, Chest Depth; CLD, Central Lung Distance; CS, Chest Separation; CT, Computer Tomography; DIBH, Deep Inspiratory Breath-hold; DVH, Dose Volume Histograms; Deep inspiratory breath-hold; Dosimetric predictors; EORTC, European Organization for Research and Treatment of Cancer; FB, Free Breathing; HCWD, Heart Chest Wall Distance; HCWL, Heart Chest Wall Length; HH, Heart Height; HV, Heart Volume; HVIF, Heart Volume in Field; IMC, Internal Mammary Chain; LAD, Left Anterior Descending; LOD, Lung Orthogonal Distance; LV, Lung Volume; MHD, Maximum Heart Depth; MRM, Modified Radical Mastectomy; NTCP, Normal Tissue Complications Probability; OAR, Organs-at-risk; PTV, Planning target volume; RNI, Regional Nodal Irradiation; ROC, Receiver Operating Characteristic; RPM, Real-time Position Management; RTOG, Radiation Therapy Oncology Group; Radiotherapy; SCF, Supraclavicular Fossa.

Fig. 1

ROC curve for ΔHVIF predicting for >20% reduction in mean heart dose: AUC was 0.91 (p = 0.001; 95% CI-0.81–0.98) with a cut-off value of 6 cc.

Fig. 2

ROC curve for ΔMHD predicting for >20% reduction in mean heart dose: AUC was 0.768 (p = 0.15; 95%CI 0.58–0.95) with cut-off value of 7 mm.