EP-1825: Delivered dose determination in large organ deformations: Pre-requirement for adaptive RT for LACC
Radiotherapy and Oncology
ESTRO 35 2016 S855 ________________________________________________________________________________ Material and Methods: By using a CIRS 062 phantom, conversion curves (Hounsfield Unit, HU, to ρel ) for two different Varian CBCT models and for head and pelvis protocol were measured. Diffusing material was added to the phantom to simulate the typical dimensions of the anatomical districts. A dosimetric analysis was then performed for CIRS phantoms and patients treated for H&N and prostate
... and prostate cancers, by comparing dose distributions calculated on the same CBCT using different HU-ρel conversion curves. For each case, the plan-CT and CBCT images were registered rigidly. A VMAT plan was generated on the plan-CT and transferred to the CBCT. The dose was calculated on the CBCT without heterogeneities corrections, using the plan-CT conversion table and using the CBCT sitespecific conversion tables. The distributions were compared to the reference distribution (Dref) with 3D gamma analysis, Dref being the dose calculated on the plan-CT using its proper conversion curve. For each comparison the net disagreement was calculated, i.e. the percentage of points that exceeded gamma criteria without taking into account discrepancies due to registration errors (DTA = 2mm for phantoms, 3 mm for patients).