Real-time dose-guidance in radiotherapy: Proof of principle

PURPOSE: The outcome of radiotherapy is a direct consequence of the dose delivered to the patient. Yet image-guidance and motion management to date focus on geometrical considerations as a practical surrogate for dose. Here, we propose real-time dose-guidance realized through continuous motion-including dose reconstructions and demonstrate this new concept in simulated liver stereotactic body radiotherapy (SBRT) delivery. MATERIALS AND METHODS: During simulated liver SBRT delivery, in-house developed software performed real-time motion-including reconstruction of the tumor dose delivered so far and continuously predicted the remaining fraction tumor dose. The total fraction dose was estimated as the sum of the delivered and predicted doses, both with and without the emulated couch correction that maximized the predicted final CTV D95% (minimum dose to 95% of the clinical target volume). Dose-guided treatments were simulated for 15 liver SBRT patients previously treated with tumor motion monitoring, using both sinusoidal tumor motion and the actual patient-measured motion. A dose-guided couch correction was triggered if it improved the predicted final CTV D95% with 3, 4 or 5 %-points. The final CTV D95% of the dose-guidance strategy was compared with simulated treatments using geometry guided couch corrections (Wilcoxon signed-rank test). RESULTS: Compared to geometry guidance, dose-guided couch corrections improved the median CTV D95% with 0.5-1.5 %-points (p < 0.01) for sinusoidal motions and with 0.9 %-points (p < 0.01, 3 %-points trigger threshold), 0.5 %-points (p = 0.03, 4 %-points threshold) and 1.2 %-points (p = 0.09, 5 %-points threshold) for patient-measured tumor motion. CONCLUSION: Real-time dose-guidance was proposed and demonstrated to be superior to geometrical adaptation in liver SBRT simulations.