Author: Girish Bal, Thomas I. Banks, Bin Cai, Yesenia Gonzalez, Zohaib Iqbal, Paul M. Medin, Rameshwar Prasad, Chenyang Shen, Robert Timmerman, Yuanyuan Zhang 👨🔬
Affiliation: Department of Radiation Oncology, UT Southwestern Medical Center, University of Texas Southwestern Medical Center, UT Southwestern Medical Center, RefleXion Medical 🌍
Purpose: Each year more than one million pacemakers and 200k cardioverter-defibrillators are implanted in patients worldwide. The presence of a CIED introduces challenges to the delivery of radiation therapy. We present the first clinical evaluation of BgRT treatment of a tumor located in the same transaxial plane as a CIED.
Methods: In this study the patient was injected with 13.8 mCi of FDG and a functional modeling PET scan (used to create a BgRT plan) was acquired 60 minutes post-injection. The patient’s CIED was located near the anterior left chest wall and in the same plane as the tumor. The treatment objective was to deliver 4000 cGy to the tumor in five fractions while limiting CIED dose to 55 cGy. In RefleXion BgRT dose delivery to the tumor is based on real-time 3D PET images which are reconstructed every 100 milliseconds, using the most recent 500 milliseconds of data and the simulation CT for attenuation correction; metal artifact reduction was applied to reduce streaks in the attenuation map.
Results: The patient’s PET uptake values measured during the functional modeling scan were activity concentration = 18.66 kBq/mL and normalized target signal = 7.94. A BgRT treatment plan satisfying the clinical criteria was successfully generated with a total treatment time of 23 minutes. The mean and maximum point doses to the PTV were 4282 cGy and 4682 cGy, respectively, while the mean and max point doses to the pacemaker were 36 cGy and 51 cGy, respectively. The minimum distance between the CIED and 200 cGy isodose line was 19 mm.
Conclusion: The increasing prevalence of patients with CIEDs demands heightened vigilance regarding device failure risks during radiotherapy. This work demonstrates that clinically acceptable BgRT plans can be created for tumors located close to metallic objects.