PV QA 4 - Poster Viewing Q&A 4
TU_10_3421 - Does Deep Inspiration Breath Hold (DIBH) Impact Dose to Coronary Arteries During Postmastectomy Electron Boost Treatment?
Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3
Does Deep Inspiration Breath Hold (DIBH) Impact Dose to Coronary Arteries During Postmastectomy Electron Boost Treatment?
J. Coster1, S. Rhodes1, J. Turner1, V. L. Massey2, and M. Perry1; 1University of Kansas, Kansas City, KS, 2University of Kansas Medical Center, Kansas City, KS
Purpose/Objective(s): It is well documented that during standard photon radiotherapy for left sided breast cancer, DIBH reduces dose to coronary arteries, resulting in a decrease in adverse cardiac events. We compared point dose to the left anterior descending artery (LAD) during DIBH and free breathing (FB) in the setting of postmastectomy electron boost treatment.
Materials/Methods: We identified 20 consecutive patients with left breast cancer who underwent mastectomy without reconstruction. CT scans were obtained at the time of simulation using both FB and DIBH techniques. Location of the LAD was defined on all CT scans. The shortest distance between the LAD and skin surface of the adjacent left chest wall was determined on each set of scans. Plans were generated using 6 MeV electrons directed en face to the chest wall centered on the point closest to the underlying LAD. Bolus was not incorporated into calculations. Dose to the LAD was calculated for FB and DIBH.
The shortest distance between the LAD and the skin of the overlying left chest wall ranged from 2.67-6.79 cm (median 4.16 cm) with FB, and from 3.35-7.11 cm (median 4.90 cm) with DIBH.
Chest wall thickness along the central ray between the LAD and overlying skin ranged between 0.80-2.33 cm (median 1.54 cm) with FB, and from 0.41-2.49 cm (median 1.33 cm) with DIBH.
Craniocaudal movement of the LAD (using the sternal notch as a stable reference point) during FB versus DIBH ranged between 1.18-3.54 cm (median 2.39 cm).
As a percentage of prescribed dose, the point dose at the LAD closest to the adjacent chest wall ranged from 12%-97% (median 51%, average 53%) with FB, and from 21%-90% (median 54%, average 51%) with DIBH. These differences were not statistically significant.
During the respiratory cycle the spatial relationship between the LAD and the skin of the overlying left chest wall was shown to be complex, impacted by several variables. The LAD typically follows a slightly curvilinear path, and the overlying chest wall is generally convex, however the two did not shift in lockstep during respiration. An electron beam centered on a typical mastectomy incision is directed perpendicular to the chest wall, but the juxtaposition of this beam and the LAD varied greatly in our patient population. While the distance between the skin surface and the LAD increased in 85% of our patients during DIBH versus FB, the LAD moved closer to the center of the electron beam in 58% of patients due to the craniocaudal relationship between the electron path and LAD. Across the entire population the point dose to the LAD was statistically similar during FB versus DIBH.
Conclusion: We have shown that electron dose to the LAD during postmastectomy radiotherapy is similar during FB and DIBH due to the complex spatial juxtapositional relationship between the LAD and overlying skin which is targeted during electron boost treatment.
Author Disclosure: J. Coster: None. V.L. Massey: None. M. Perry: None.