S. Sharma, A. Groll, A. Da Silva, M. Narayanan, and G. Kuduvalli Ph.D; RefleXion Medical, Inc., Hayward, CA
Purpose/Objective(s): Biology-guided radiotherapy utilizes direct photon emissions from a positron emission tomography (PET)-avid tumor to direct planned prescription dose to the tumor. The purpose of this work is to characterize the tracked dose delivery and dosimetric performance of BgRT as a function of changes in tumor location during treatment, while contrast of tumor radioactivity relative to the background concentration is kept constant. Materials/
Methods: Themedical technology X1 system was utilized to create a conformal plan and deliver 1000 cGy dose in a single fraction. The experimental setup consisted of a cylindrical volumetric assembly (phantom) encapsulating a 22 mm ball target structure and a d avoidance structure. These structures were filled with F-18 fluorodeoxyglucose (FDG) and water solution with an activity concentration of 56.99 kBq/ml while the background was filled with 6.84 kBq/ml, providing a target-to-background ratio (TBR) of 8.18:1. Ashland EBT-XD monochromatic x-ray film was used as a primary diagnostic tool to characterize the tracked dose delivery and dosimetric performance of the system. A 5 cm by 10 cm piece of x-ray film was placed in between the two hemispheres of the 22 mm ball target. The patient-specific quality assurance (PSQA) is a helical assembly of 1,386 semiconductor diodes, widely used for quality assurance of radiation therapy plans. It measures the dose delivered by linear accelerator and compares it with the planned dose. The activity filled phantom was sealed and loaded in the patient-specific quality assurance (PSQA). Before proceeding to a 10 mm linear shift in the +IEC y-axis was applied to the 22 mm ball target with respect to the to simulate a sudden patient shift.After treatment completion the x-ray film was analyzed using green channel to obtain estimation of 3%/3 mm absolute dose gamma within the planning treatment volume (PTV) and dose profiles. Results: The irradiated x-ray film demonstrated 3%/3 mm gamma within the PTV of 95.08%. Conclusion: X-ray film analysis demonstrated that the delivered dose closely followed the 10 mm linear shift in the +IEC y-axis, and good dosimetric agreement was achieved between planned and delivered dose within the target.
