Author: Won Chang, Vadim L. Stakhursky, Yevgeniy Vinogradskiy 👨🔬
Affiliation: Jefferson Einstein, Alliance Cancer Specialists, Thomas Jefferson University 🌍
Purpose: 4DCBCT is a powerful tool for localization of moving targets when treating lung tumors with hypofractionated regimens (SBRT). However, for patients with implanted cardiac devices (ICD) in close proximity to the targeted area, the dose from imaging procedures could contribute significant dose to the ICD. We develop and validate a technique for limiting 4DCBCT imaging dose to ICDs.
Methods: A lung SBRT patient with a previous history of radiation presented with an ICD implanted 6cm superior to megavoltage treatment isocenter. Varian TrueBeam 4D CBCT imaging workflow allows for a reduction of imaging dose by using KV source blade collimation. We set up a cylindrical phantom with an ion chamber attached 6.0cm away from CBCT volume axial plane and varied KV source collimator opening while recording 4DCBCT (Thorax technique, half beam, Full scan) dose. TLDs (University of Wisconsin, Madison WI) were used to determine in vivo 4DCBCT dose to ICD from full open collimator scan during the first day of patient SBRT treatment and a collimated 4DCBCT scan during the second SBRT fraction.
Results: Phantom study demonstrated that 4DCBCT dose to an ICD may be reduced 7 fold by collimating scanned volume. In vivo measurements of 4DCBCT dose to the patient's ICD were 2.0 cGy for a full range 4DCBCT scan, and 0.6 cGy for a collimated 4DCBCT scan. We reviewed the quality of collimated 4D CBCT image and corresponding 3D average CBCT reconstruction with respect to the full range 4D CBCT image and 3D average reconstruction. No loss of image resolution or contrast were noted on the collimated scan.
Conclusion: 4DCBCT dose to proximal ICD could be reduced using KV beam collimation. For the patient reviewed, ICD imaging dose was reduced from 10 cGy to 3 cGy over the course of 5 fractions.