Postoperative radiotherapy for right breast cancer with regional nodal irradiation utilizing the surface-guided radiotherapy based deep inspiration breath hold technique on a TrueBeam HD linear accelerator: A case report.

Introduction: Deep inspiration breath-hold (DIBH) has proven effective in minimizing radiation exposure to organs at risk (OARs) in right-sided breast cancer patients requiring regional nodal irradiation (RNI). However, there has been no dosimetric evaluation comparing DIBH techniques to free-breathing (FB) conditions on the TrueBeam (TB) HD linear accelerator (LINAC). To address this gap and accommodate breast cancer patients requiring RNI on the TB HD LINAC, an innovative method involving a 90-degree rotation of the regional lymph nodes' field during treatment planning was devised.

Case Description: The study focused on a 39-year-old woman who underwent right breast-conserving radical surgery and subsequently required postoperative adjuvant radiotherapy. Both noncontrast FB and DIBH computed tomography (CT) scans were performed using a CT simulator. Due to limitations in MLC field length, a 90-degree rotation was employed for planning the regional lymph nodes' field on the TB LINAC. Patient positioning accuracy was ensured by aligning based on body surface under both FB and DIBH conditions, facilitated by an optical surface management system (OSMS). The target volume and OARs were meet the dose limit on the TB HD LINAC. Noteworthy reductions in radiation exposure to the right lung and liver were evident with DIBH. The mean dose reduction rate for the right lung was 11.9%, while the mean dose reduction rate for the liver was 68.9%. Parameters such as V5, V20, V30, and mean dose (Dmean) also demonstrated decreases with DIBH compared to FB.

Conclusions: This case report underscores the potential of TB HD LINAC for formulating treatment approaches for breast cancer involving RNI. Furthermore, it emphasizes the effectiveness of DIBH radiotherapy in mitigating doses to OARs when implemented on the TB LINAC.