Program Information
Lung Toxicity Versus CT Number Variation by Hypo-Fractionated Lung Stereotactic Body Radiotherapy (SBRT)
K Dou1*, B Li1, M. Jacobs2, B Laser2, F Lerma1, M Sarfaraz1,(1) RadAmerica Mercy Radiation Oncology, MedStar Health, Baltimore, MD (2) Mercy Medical Center, Radiation Oncology, Baltimore, MD
Presentations
PO-BPC-Exhibit Hall-10 (Saturday, March 7, 2015) Room: Exhibit Hall
Purpose
To study lung injury or toxicity from hypofractionated lung stereotactic body radiotherapy (SBRT) by correlating the lung density variation with computed tomography (CT) number following the hypofractionated lung SBRT.
Methods
Six patients were selected for the retrospective research. Cone beam CT (CBCT) was acquired for obtaining the CT number and then getting the lung density. CBCT numbers were corrected using a CIRS density phantom. Each case had a free breathing simulation CT followed by a respirationgated 4D CT using a Philips CT Big Bore scanner with a Varian RPM respiratory gating system. The internal target volume (ITV) was created from ten phase gated CT images, followed by exporting to the Varian Eclipse TPS for treatment planning with the freebreath and ten phased images. The planned dose was delivered with a 6MV flattened filter free beam of a Varian TrueBeam accelerator.
Results
CBCT numbers were sampled from three locations: visual lung tumor (GTV), normal lung in the tumor seated lobe obtaining 30 percent of the prescribed dose, and reference lung in the normal, tumor-free lobe. The CT number of the lung tumor was found to significantly increase in a range of 7 percent to 313 percent with a radiation scheme of 10Gy by 5 fractions every other day. However, both normal lungs showed a smaller variation in the CT number than that of the tumor. A maximum increase in CT number of post 5th fraction/prior treatment was 313 percent, which leads to more than three times increase in lung density after SBRT treatment.
Conclusion
CBCT can be utilized for not only patient alignment and target localization but also acquirement of CT numbers of the targeted volume and the toxicity or injury can, therefore, be associated with the lung CT number variation deduced from CBCT.
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