Background and purpose (extract): Intrafraction motion degrades the efficacy of radiation therapy. We reported on the implementation of focal dose-escalated stereotactic body radiation therapy (HypoFocal-SBRT) for prostate carcinoma on standard linear accelerator, and assessed whether periodic intrafraction image guidance (PIF-IG) improved the accuracy of treatment.
Materials and methods (extract): Twenty prostate cancer patients underwent HypoFocal-SBRT.
Patients had three Gold Anchor markers (Naslund Medical AB, Sweden) implanted 5–7 days before simulation.
Marker positions in stereoscopic projections were registered to their calculated in reference DRRs, and resultant misalignments processed into couch corrections by ExacTrac..
Fiducial marker-based PIF-IG, triggered at pre-defined imaging control point(s) (ICPs), was performed using 1 mm (translations)/1◦ (rotations) action thresholds for online couch corrections.
A scenario representing delivery without image guidance was also simulated by omitting couch corrections. The root-mean-square error (RMSE) of absolute position differences was used as a measure of the geometric uncertainty of treatment with and without PIF-IG.
Results (extract): Interventions occurred at least once in 95% of patients and 83% of fractions. PIF-IG reduced the geometric uncertainty (root-mean-square error) from 1.6 mm, 2.3 mm, and 2.2 mm for the left–right (LR), superior-inferior (SI), and anterior posterior (AP) directions to 0.6 mm, 0.9 mm, and 0.8 mm, respectively. With PIF-IG, target volumes D98% doses with 5% less than planned were observed in 2% of fractions for PTV30 and PTV35, and 0% for PTV40-42, compared to 16%, 12%, and 6% without PIF-IG.
Conclusions (extract): Focal dose-escalated SBRT for prostate cancer can be efficiently and accurately performed on standard accelerator. PIF-IG improved the geometric and delivered dose accuracy.
Article from Physics and Imaging in Radiation Oncology, 2026