Dosimetric advantages of irregular surface compensator technique using flatten filter free (FFF) with deep inspiration breath hold (DIBH) for whole breast with regional nodes irradiation

1. Abstract 1.1. Purpose: Inclusion of internal mammary (IM) lymph nodes as a part of regional nodal breast irradiation has the potential to re- duce local recurrence, distant recurrence, and improve survival in breast cancer patients. However, the increased risk of cardiac tox- icity and lung injury associated with irradiation of the IM lymph nodes has drawn increased scrutiny. The use of deep inspiration breath holds (DIBH) to minimize this toxicity has increased sig- nificantly in recent years, especially for the treatment of left-sided breast cancer. This study evaluates dose delivery techniques for breast cancer patients with IM nodal involvement, including tra- ditional tangential fields with field-in-field (FiF) modulation and flattened beam energy, and tangential fields with irregular surface compensator modulation (ISC) and flattening filter free beam en- ergy (FFF). The effect of DIBH on organ at risk dose was also examined. Finally, treatment efficiency is a significant factor im- pacting the feasibility and accuracy of DIBH treatment, and was also evaluated in this study.