(Saturday, 4/7/2018) 10:30 AM - 12:30 PM
Room: Marquis Ballroom 5-8
Purpose: To demonstrate a system for real-time dose accumulation and prediction of equivalent uniform dose for multi-metastasis single isocenter stereotactic radiosurgery.
Methods: Stereotactic radiosurgery plans were created for two example brain metastases. Each plan consisted of a coplanar arc and two non-coplanar arcs at ±45° couch angles. One plan targeted a 20-mm sphere centered at isocenter, and the other targeted an 8-mm sphere positioned 4 cm away. The position of this latter target represented the case where multiple targets are treated simultaneously using a single isocenter. The different sizes and positions of the two targets made them differ in their sensitivity to rotational errors. For each plan, the dose delivered by each arc under the influence of clinically-relevant rigid transformations was determined. At time points prior to the delivery of each arc, possible cumulative doses to be delivered were predicted by combining the dose already delivered under theoretical error conditions (1 mm & 1° and 0.2 mm & 0.2°) with 1,000 predictions of the possible remaining dose. These cumulative doses were used to make dynamic statistical predictions of the final dose volume histogram (DVH) and equivalent uniform dose (EUD).
Results: The distributions of possible DVHs and EUDs were observed to change dynamically throughout treatment in a way that depended on the size and position of the target, as well as on observed treatment delivery (p<0.01). Smaller, off-axis targets were more sensitive to positional errors, with a possible EUD change of over 1 Gy. Larger positional errors caused coverage losses regardless of size and position.
Conclusion: In stereotactic radiosurgery, the delivered dose depends on patient- and plan-specific factors as well as on intrafractional delivery effects. Monitoring cumulative dose and radiobiological metrics during treatment would give clinicians greater awareness of the delivered dose and also greater ability to achieve their clinical goals.
Contact Email
