Prone-to-Supine; Custom Breast Guard Support for Heart and Lung Dose Reduction

Introduction: Prone setup for Breast irradiation treatments is desired for some women that due to their specific anatomy, treating the breast to a therapeutic dose results in unacceptable doses to the lung and heart, even with deep inspiration breath hold. Prone position will allow a smaller lung and heart exposures, as the breast is stretched away from the OAR by gravity.

Nonetheless, this setup is not comfortable for many patients, and can have more set-up uncertainties. In addition, in some cases, this treatment would not be feasible due to radiation exposure of the contralateral breast in the prone setup and the lack of ability to treat some of the lymph nodes.

We are suggesting a custom made breast guard support to enable the prone breast tissue setup benefits in a supine treatment.

Methods: We have used a patient prone CT SIM to conduct 2 mm ring in a 3D printer. The height of the ring is about 5 cm and is sufficient to support the breast from the chest wall. After the ring is printed, the patient inserts the breast tissue through the ring. The guard is then marked on the patient skin for reproducibility. Then, a supine CT simulation is carried out with the breast guard for the treatment planning and delivery.

Results: Using the breast guard ring allowed a supine treatment with Heart mean dose of 0.59 Gy and Lung mean dose of 0.94 Gy. In the prone treatment, the heart and lung mean doses were 1.1 and 0.42 Gy respectively. To evaluate a supine treatment without the breast guard, we planned two tangential fields on the contralateral right breast.

This plan showed a V20 of 18% for the lung and a 1.8 Gy mean heart dose. This heart dose is underestimated as it was evaluated for a right breast delivery.

Conclusions: The breast guard allowed a reasonably comfortable reproducible immobilization to the breast tissue. It allowed a compatible plan to the prone plan with superior reduction in heart dosage. One should consider this technique for common breast with lymph nodes irradiation, as it shows a significant OAR dose reductions.