Use of Moderate Deep Inspiration Breath Hold for Loco-Regional Radiotherapy of Right Breast Cancer including Internal Mammary Lymph Nodes

Abstract

Loco-regional radiotherapy (RT) of the breast or chestwall may include the internal mammary lymph nodes (IMN). Inclusion of these lymph nodes with a conventional four field technique may give rise to an increased volume of lung in the treated volume. At our centre patients receiving RT to the left breast are usually simulated and treated using a moderate Deep Inspiration Breath Hold (mDIBH) technique in an attempt to reduce dose to the heart. Patients receiving RT to the right breast or chestwall including the IMN may benefit from treatment with the mDIBH technique by reducing doses to organs at risk (OAR). The aim of this work is to compare the dose to OARs for patients receiving loco-regional radiotherapy treatment of the right breast/chestwall including IMN using free breathing and mDIBH CT simulation datasets. Patients who are to receive loco-regional RT to the right breast or chestwall by default are CT simulated while free breathing. The IMN target is contoured by the radiation oncologist. A treatment plan is generated using the free breathing dataset. Review of this treatment plan specifically the volume of right lung receiving 20 Gy (V20) is undertaken. Right lung V20 greater than 35% triggers re-simulation with mDIBH in an attempt to reduce the V20. If a patient is unable to tolerate the mDIBH apparatus, the clinical management may be changed such that IMN may be excluded in the tangent fields thereby ensuring an acceptable dose to the right lung. Simulation and delivery of RT to patients in mDIBH can reduce the ipsilateral lung V20. Resources are impacted by utilizing this treatment technique to the right breast/chestwall loco-regional patient population. Additional resources include the following: additional CT simulation, additional contouring time and treatment plan generation, additional time on the treatment unit to treat in mDIBH, additional cost per fraction for mDIBH consumables. Right breast/chestwall loco-regional RT treatment using a mDIBH technique allows inclusion of the IMN where indicated whilst maintaining acceptable ipsilateral lung doses. In our experience the right lung V20 is reduced by 8% on average for mDIBH technique as compared with the free breathing technique with the reduction in right lung V20 ranging from 3% to 22%. A reduction of 5% in the V20 of both lungs is observed for the mDIBH technique as compared with the free breathing technique. Slight reductions in the mean heart dose are observed for mDIBH as compared with free breathing. When tolerated by patients, the mDIBH treatment enables inclusion of the IMN in the tangential beams where previously the IMN may have been omitted due to ipsilateral lung dose metrics being exceeded. Future direction includes investigating the role of mDIBH for this population as a standard of care considering resources and implementation of a voluntary breath hold delivery technique.