Tri-phasic contrast enhanced CT simulation with bolus tracking for pancreas SBRT target delineation

Publication date: Available online 13 April 2017
Source:Practical Radiation Oncology
Author(s): Devon J Godfrey, Bhavik N Patel, Justus D Adamson, Ergys Subashi, Joseph K Salama, Manisha Palta
PurposeBolus-tracked multi-phasic contrast CT is often employed in diagnostic radiology to enhance the visibility of pancreas tumors, but is uncommon in radiotherapy pancreas CT simulation, and its impact on GTV delineation is unknown. This study evaluates the lesion conspicuity and consistency of pancreas SBRT GTVs contoured in the different contrast phases of tri-phasic CT simulation scans.Methods and MaterialsTri-phasic, bolus-tracked planning CT simulation scans of ten consecutive pancreas SBRT patients were acquired, yielding images of the pancreas during the late arterial (LA), portal venous (PV), and either the early arterial (EA) or delayed phase (DP). GTVs were contoured on each phase by a GI-specialized radiation oncologist and reviewed by a fellowship-trained abdominal radiologist who specializes in pancreatic imaging. The volumes of the registered GTVs, their overlap ratio, and the 3-dimensional margin expansions necessary for each GTV to fully encompass GTVs from the other phases were calculated. The contrast difference between tumor and normal pancreas was measured, and two radiation oncologists rank ordered the phases according to their value for the lesion contouring task.ResultsTumor-to-pancreas enhancement was on average much larger for the LA and PV than the DP or EA phases and the LA and PV phases were also consistently preferred by the radiation oncologists. Enhancement differences amongst the phases resulted in highly variable GTV volumes with no observed trends. Overlap ratios ranged from 18-75% across all three phases, improving to 43-91% when considering only the preferred LA and PV phases. GTV expansions necessary to encompass all GTVs ranged from 0.3–1.8cm for all three phases, improving slightly to 0.1–1.4cm when considering just the LA and PV phases.ConclusionsFor pancreas SBRT, we recommend combining the GTVs from a multi-phasic CT simulation with bolus-tracking, including, at a minimum, a Boolean "OR" of the LA and PV phases.



http://ift.tt/2pdwdsb