Author: Jon Burns, Angela J Da Silva, Andrew Groll, Gopinath Kuduvalli, Manoj Narayanan, Jeffrey Schmall, Sanchit Sharma, Timothy Pok Chi Yeung ๐จโ๐ฌ
Affiliation: Reflexion Medical Inc,, RefleXion Medical ๐
Purpose: Biology-guided radiotherapy uses positron emissions from FDG-avid tumor volumes to provide a of the planned prescribed dose with high accuracy. The purpose of this work is to characterize BgRTโs dosimetric performance for static targets as a function of FDG-avid lesion size, while the ratio of tumor radioactivity concentration relative to the background is kept constant.
Methods: The prototype phantom used for experimental setup was a volumetric cylinder that encapsulated interchangeable 3D printed spherical targets of 40 mm, 50 mm, and 60 mm diameter. This phantom and the targets were filled with FDG and water solution with an activity concentration aiming for a target-to-background ratio (TBR) close to 8:1. The treatment planโs conformality and the TBR of the activity contrast fill were intentionally kept similar for all three experiments. The Sun Nuclear ArcCHECK was used as a primary diagnostic tool for this experiment. EBT-XD monochromatic x-ray films were sandwiched between the two hemispheres of the spherical target for a more detailed dosimetric analysis within the PTV. The activity concentration used for the targets were 48.64 kBq/ml, 52.18 kBq/ml, and 49.45 kBq/ml, for 40 mm, 50 mm, and 60 mm targets, respectively, while the background activity concentration was kept between 5 - 6 kBq/ml. The RefleXionยฎ X1 system was utilized to create the plans and deliver 1000 cGy dose in a single fraction for each target size. Absolute dose gamma was then measured for each experiment.
Results: The 3%/3 mm absolute dose gamma obtained for 40 mm, 50 mm, and 60 mm targets were 96%, 96.7%, and 99.8%, respectively. The delivered dose profiles on the EBT-XD monochromatic x-ray films demonstrated good agreement with the planned dose.
Conclusion: The assessment of the delivered dose with larger spherical targets demonstrated good agreement with the planned dose.