Validation of dynamic treatment-couch tracking for prostate SBRT

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Stereotactic body radiation therapy (SBRT) for prostate cancer delivers high doses per fraction with steep dose gradients.
• Intrafractional prostate motion can unpredictably occur during treatment, potentially leading to target miss and reduced efficacy.

Purpose of the Study:

• To investigate the dosimetric benefits of dynamic treatment-couch tracking for motion compensation in prostate SBRT.
• To evaluate the accuracy and feasibility of real-time couch tracking using electromagnetic transponders.

Main Methods:

• Ten prostate cancer SBRT plans with integrated boosts were created.
• Treatments were simulated on a phantom under static, uncompensated motion, and real-time tracked motion conditions using a TrueBeam linear accelerator.
• Dosimetric performance was assessed using Gamma Agreement Indices (GAI) and organ-specific dose parameters.

Main Results:

• Couch tracking drastically reduced the root-mean-square error of prostate motion from 0.8-4.4 mm to 0.2-0.4 mm.
• Significantly improved GAI_1%/1mm (83.4%-100.0% vs. 28.9%-99.7%) and GAI_2%/2mm (98.4%-100.0% vs. 52.3%-100.0%) were observed with tracking.
• Tracking enhanced target coverage and demonstrated a dependency of rectal and bladder doses on motion direction.

Conclusions:

• Dynamic couch tracking significantly improves dosimetric accuracy in prostate SBRT by effectively compensating for intrafractional motion.
• The combination of couch tracking and electromagnetic position monitoring is feasible and enhances treatment delivery accuracy for prostate SBRT.
• Minor residual motion was observed, primarily during abrupt changes in motion direction.