Methods to Improve Patient Selection and Predict Dosimetric Benefits for Irradiation of the Left Breast or Chest Wall and Regional Lymph Nodes With Deep-Inspiration Breath-Hold

Abstract

Radiation treatment of left breast cancer patients with deep-inspiration breath-hold (DIBH) can reduce the radiation dose to heart and lung in some patients. This work aims to quantify dosimetric benefits from DIBH based on patient anatomic changes from the CTs acquired under free-breathing (FB) and DIBH conditions, and to determine methods to optimize patient selection for DIBH technique. CT and radiation therapy data from 14 left-sided breast cancer patients who were treated with DIBH using AlignRT (Vision RT, UK) were analyzed. All patients were treated with 50 Gy to breast/chest wall and regional lymph nodes, including supraclavicular and internal mammary nodes, in 25 fractions followed by a boost. Internal mammary nodes were treated with partially wide tangent fields in all cases. 3D treatment plans for DIBH delivery were generated (Elekta XIO). The chest wall excursion with respect to the anterior wall of heart and the diaphragm excursion viewed along the medial tangential angle as well as the left lung volume change between FB and DIBH were measured. The contours of the DIBH plans were populated to the FB CT images by deformable registration using MIM (Cleveland, OH) and manually edited as necessary. The FB plans were calculated on the FB CT images using the DIBH plans as templates to achieve similar coverage for targets. The mean dose and V25 for heart and the mean dose and V20 for the left lung were recorded for both DIBH and FB plans. The dosimetric parameter changes and their correlations to the anatomic changes between DIBH and FB were investigated. The Pearson function was used for correlation study. Between FB and DIBH techniques, the chest wall excursion, the diaphragm excursion and percentage left lung volume change were 6.7±2.8 mm (range 2.0 to 12.3 mm), 24.6.0±10.3 mm (range 10 to 40 mm) and 50.5%±30.0% (range 17.4% to 116.6%). Percentage reduction of mean dose for heart and left lung were 37.3%±13.7% (range 19.1% to 61.7%) and 11.2%±9.5% (range -8.1% to 26.1%). The mean heart and mean left lung dose under DIBH were reduced by 1.27±0.78 Gy (range 0.01 to 2.7 Gy) and 1.98±1.71 Gy (range 0.24 to 4.93 Gy), respectively, comparing to those under FB. V25 and V20 were reduced by 2.0%±1.6% (range 0.0 to 5.8%) and 4.8%±3.6% (range -0.6% to 10.8%) for heart and the left lung, respectively. The reduction of mean heart dose was correlated with the chest wall excursion and the reduction of mean left lung dose was correlated with the diaphragm excursion. However, only the correlation between the reduction of mean heart dose and the chest wall excursion was statistically significant (r=0.65 and p=0.01). The use of DIBH technique in irradiation of left breast cancer and regional lymph nodes results in clear dosimetric benefits. The chest wall excursion could help to identify patients who would benefit from DIBH during treatment to the left chest wall/breast and regional nodes without making an additional FB plan.