SU-E-J-171: The Dosimetric Consequence of a Failed Breath Hold for Left-Sided DIBH Breast Treatment

Authors


Abstract

Purpose:

The purpose of this work is to determine the dosimetric consequence of a failed breath hold which may arise out of failure to prompt the patient before initiating treatment or lack of compliance from the patient in taking or maintaining the breath hold. In this context, the patient is assumed to be aligned properly for treatment to the breath hold surface.

Methods:

Ten left-sided breast cancer patients were simulated for treatment in the free-breathing (FB-CT) and deep-inspiration breath hold (DIBH-CT) positions using a bellows device to monitor respiration. The CT scans were fused using a common rigid coordinate system in the underlying couch allowing the analysis of the identical setup position for either FB-CT or DIBH-CT. The breast tissue, lumpectomy cavity, heart, and lungs were contoured on each CT. Patients were planned for treatment to 50Gy using a tangent field-in-field technique on the DIBH CT scan. The treatment plan was subsequently copied to the free-breathing scan in the same geometric position and recalculated.

Results:

No statistically significant dose difference was found for the heart (V30, V20, mean, and maximum) or lumpectomy cavity (mean, maximum, minimum, and V95). However, in two cases, the lumpectomy cavity V95 was 20% less for FB-CT. The lung V20 decreased by an average of 3.7±1.0% (p=0.004) for FB-CT. No statistically significant dose difference was found for the mean and maximum breast dose. The minimum breast dose (16.9±3.4 for DIBH) decreased by an average of 11±3.4% (p=0.0001), and the breast V95 (84.7±2.0% for DIBH) decreased by an average of 13.9±7.2% (p=0.003).

Conclusion:

Our results show that a failed breath hold would not negatively affect the surrounding organs and increased lung sparing. In our study, the lumpectomy cavity remained satisfactorily targeted in 8 out of 10 cases. However, the minimum and V95 breast doses decreased considerably.

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