Evaluating Biology-Guided Radiotherapy (BgRT) Dose Conformity for Complex PET-Avid Targets Under Static and Motion Conditions
Abstract
Purpose
To examine the dose conformity during planning and delivery for complex C-shaped targets in an investigational RefleXion X2 platform under static and motion conditions.
Methods
The RefleXion X2 platform has an increased PET-FOV (four times the X1 platform), and this study added a developmental BgRT Anchor Point Tracking algorithm with a goal of improving the accuracy of BgRT. 18F-FDG–fillable inserts representing a C-shaped target and a 22-mm spherical organ-at-risk (OAR) were placed in a homogeneous phantom containing an FDG–water background. The phantom was inserted in an ArcCHECK detector array to measure the delivered BgRT doses. Target and OAR-to-background activity ratio of 8:1 was used for both static and motion deliveries, with activity maintaining ~5 kBq/ml for the background. First, a static functional modeling was performed to create a plan, followed by a static delivery to the C-shape target. In the second study, the phantom was placed on CIRS motion platform, and a cos4 motion profile with 15 mm peak-to-peak amplitude and a 4 s period was used during functional modeling and treatment of the C-shape target. An EBT-XD film was placed in the coronal plane of C-shape target for the motion test. All treatments were delivered on the prototype RefleXion X2 system and evaluated using 3%/2 mm gamma analysis.
Results
For static C-shaped target plan, the conformity index (CI) was 1.04 and the CI50 was 3.91. The periodic motion C-shaped target plan had a CI of 1.07 and the CI50 was 4.54. Treatment delivery was completed for both static and motion tests which resulted in a 3%/2 mm gamma pass rates of 99.0% and 98.6%, respectively.
Conclusion
The system achieved high dose conformity for planning and delivery for the complex C-shaped target under static and periodic motion conditions, carving out the dose in the middle of the C-shaped target.