Impact of Intentional Lad-Blocked Tangents for Enhanced Cardiac Sparing In Left Breast Radiotherapy
Abstract
Purpose
To determine whether adjusting MLC blocking of the left anterior descending artery (LAD) in left breast radiotherapy plans can reduce heart and LAD doses and improve plan robustness while maintaining desired target coverage.
Methods
15 left breast radiotherapy patients, who had free breathing and breath hold 3DCRT plans, were chosen for this retrospective study. The MLC leaves on all fields were adjusted to cover the LAD without compromising clinical coverage goals or reducing the D95% of the lumpectomy PTV and whole breast volume by more than 1% and 1.5%, respectively. For patients who were identified as having a high risk of local recurrence, the MLC blocking was adjusted to not occlude the whole breast volume from the beam’s-eye-view. In the free breathing plans, the mean and maximum LAD and heart doses were computed and compared to the planned doses prior to adjusting the MLC blocking. A dose perturbation function was used to simulate varying levels of breath hold, and the change in the mean LAD dose, averaged across all patients, was determined.
Results
The heart mean dose was reduced by an average of 63 cGy in the free breathing plans. LAD mean dose was reduced by 766 cGy, on average. LAD mean dose was also decreased in the breath hold plans, and the relative increase in the LAD mean dose with displacements of the heart towards the chest wall was smaller after adjusting the MLC blocking, compared to the original plan.
Conclusion
This work indicates that LAD and heart doses for left breast radiotherapy patients can be reduced through adjusting MLC blocking without compromising clinical coverage goals. Breath hold plans were also found to be more robust to varying levels of breath hold.