Session Item

To reduce liver and lung dose during right breast irradiation while maintaining optimal dose to the target volume. This dose reduction has the potential to decrease acute side effects and long-term toxicity.  

Sixteen patients treated with radiation therapy for localized carcinoma of the right breast were included. Six patients were evaluated retrospectively and 10 prospectively. For the planning CT, each patient was immobilised on an indexed board with the arms placed above the head. CT scans were acquired in free-breathing (FB) as well as  with deep inspiration breath hold (DIBH). Both scans were acquired with the same length. Planning target volumes (PTV's) were created with a 5mm margin from the respective clinical target volumes (CTV's) on both CT datasets. The liver was outlined as scanned. Dose metrics evaluated were as follows: differences in PTV coverage, dose to the liver (max, mean, V90%, V50%, V30%), dose to lung (mean, V20Gy, relative electron density) and dose to heart (max). The p-values were calculated using Wilcoxon signed-rank tests. A p-value was significant < 0.05.

Differences in PTV coverage between plans under FB and DIBH were less than 2%. Maximum liver dose was significantly less using DIBH: 40.3Gy versus FB 17.5 Gy (p < 0.001). Dose metrics are summarized in Table 1. The volume of the liver receiving 10% of the dose was significantly less using DIBH with 72.2ccm versus 1.88ccm under FB (p < 0.001). The absolute volume receiving 20Gy in the right lung was larger using DIBH: 291ccm versus 230ccm under FB (p < 0.001), and the relative lung volume was less with DIBH: 11.5% versus 14% in FB (p = 0.007). The relative electron density was less with DIBH: 0.59 versus 0.62 with FB, (p < 0.001). This additionally suggests that the lung tissue receives less dose due to lesser dense lung tissue when using DIBH.

Table 1 - Dose metrics for liver and right lung

Radiation of the right breast using DIBH spares liver and lung tissue significantly and thus carries the potential of a new best practice for localized right sided breast cancer.