How Effective is Deep Inspiration Breath Hold in Minimizing Cardiac Doses During Hybrid Radiotherapy Treatment for Left-Sided Breast Cancer with Comprehensive Regional Nodes?

Abstract

Background: In the context of left breast cancer radiotherapy, long term cardiopulmonary toxicity has been well-documented, significant efforts have been undertaken to mitigate such toxicity by using 4D gating, deep inspiration breath-hold(DIBH) and active breath control(ABC) techniques.

Purpose: To evaluate and compare the cardio-pulmonary radiation doses incurred during postmastectomy radiotherapy (PMRT) in two distinct breathing conditions such as DIBH and Free Breathing (FB), with a specific focus on the left chest wall with comprehensive regional nodal irradiation.

Materials and methods: A prospective dosimetric study was conducted on 15 patients who received adjuvant loco-regional radiotherapy of chest-wall (CW), supraclavicular fossa(SCF), and internal mammary region(IMC), with or without axilla. Two sets of planning CT scans were taken in DIBH and FB conditions. The dosimetric difference between DIBH CT and FB CT plans analyzed using Wilcoxon signed-rank test, employing SPSS software version 21.0.

Results: Comparison of DIBH and FB parameters for target coverage revealed a statistically significant advantage with DIBH in SCF(D95, V90, p<0.017) and IMC(D98, V90 & V95, p<0.03). Dosimetric characteristics of heart and LAD exhibited statistically significant lower doses with DIBH (V20, V25, and Dmean, p<0.001) compared to FB plans. Lung doses were similar with no discernible advantage of one technique over the other. Other OARs such as contralateral breast (p=0.027) and esophagus (p=0.001) received lower doses with the DIBH technique while the spinal cord (p=0.691) and thyroid(p=0.496) showed no significant difference. Maximum heart distance (p= 0.001), central lung distance (p= 0.011) and Haller index (p= 0.001) exhibited statistical significance between the two techniques, whereas chest wall separation showed no significant statistical difference (p=0.629).

Conclusion: DIBH demonstrates a substantial reduction in cardiac and LAD doses compared to the FB technique. This study underscores the efficacy of DIBH as a viable strategy for mitigating cardiac and LAD radiation doses in left-sided breast cancer patients undergoing PMRT of chest wall with comprehensive regional nodes.

Keywords: Cardiopulmonary toxicity; deep inspiration breath hold; free breathing; postmastectomy radiotherapy; regional nodal irradiation.

Figure 1

Dosimetric Comparison between A) Deep inspiration breath hold and B) Free breathing technique.

Figure 2

Measurement Indices: A) Chest wall separation (CWS); B) Central lung distance (CLD) and maximum heart distance (MHD)

Figure 3

Dosimetric Box Plot of Deep Inspiration Breath Hold and Free Breathing: A) Homogeneity index with significant p value (p=0.002); B) Conformity index with no significant p value (p=0.615).

Figure 4

Dosimetric Box Plot of Deep Inspiration Breath Hold and Free Breathing: A) Dosimetric box plot of V20 of Heart with significant p value (p=0.001); B) Dosimetric box plot of Dmean of heart with significant p value (p=0.001); C) Dosimetric box plot of V₉₀ of Internal mammary node with significant p value (p=0.008). (FB, Free breathing; DIBH, Deep inspiration breath hold)