Multimodality Image-based Target and Normal Structure Delineation for Dose Painting of Pancreatic Cancer

Abstract

LC volume reduction. The mean LC maximum depths based on CT1 and CT2 were 6.4 1.3 cm and 5.2 1.3 cm, respectively (p Z 0.0002). Volume encompassed by the boost plan prescription isodose surface (V100%) was reduced in 18/20 (90%) patients after re-planning. V100% was 183.6 142.0 cc based on CT2 plans and 320.6 236.6 cc based on CT1 boost plans (p Z 0.008). While all 20 patients (100%) required a photon mini-tangential boost technique based on CT1, 8 patients (40%) became eligible for electron boost treatment after re-simulation. These 8 patients had a 2.7-fold greater absolute reduction in the mean V100% compared to patients treated with mini-tangents. This difference in mean V100% reduction was further pronounced, 4.5-fold, in 10 patients who experienced an increased LC volume on CT1 relative to pathologic surgical specimen volume. Large CT1 LC volume correlated with an increased reduction in CT2 LC maximum depth (Pearson correlation coefficient Z 0.42, p Z 0.066), and an increased reduction in V100% (Pearson correlation coefficient Z 0.63, p Z 0.003). Conclusions: In breast cancer patients with large lumpectomy cavities and maximum lumpectomy cavity depths >5 cm on initial CT simulation, tumor bed boost planning based on a newly acquired CT toward the end of the whole breast irradiation course is associated with significant treatment volume reduction and may result in a change of treatment technique. This has the potential to improve cosmesis, a clinically important outcome in breast-conserving therapy. Author Disclosure: N. Kovalchuk: None. K.K. Reddy: None. H. Bohrs: None. M.M. Qureshi: None. M.T. Truong: None. A.E. Hirsch: None. J. Willins: None. L.A. Kachnic: None.