Abstract
PurposeThe purpose of this study was to investigate daily repositioning accuracy by analyzing inter‐ and intra‐fractional uncertainties associated with patients treated for intracranial or base of skull tumors in a compact proton therapy system with 6 degrees of freedom (DOF) robotic couch and a thermoplastic head mask indexed to a base of skull (BoS) frame.Materials and methodsDaily orthogonal kV alignment images at setup position before and after daily treatments were analyzed for 33 patients. The system was composed of a new type of thermoplastic mask, a bite block, and carbon‐fiber BoS couch‐top insert specifically designed for proton therapy treatments. The correctional shifts in robotic treatment table with 6 DOF were evaluated and recorded based on over 1500 planar kV image pairs. Correctional shifts for patients with and without bite blocks were compared.ResultsSystematic and random errors were evaluated for all 6 DOF coordinates available for daily vector corrections. Uncertainties associated with geometrical errors and their sources, in addition to robustness analysis of various combinations of immobilization components were presented.ConclusionsAnalysis of 644 fractions including patients with and without a bite block shows that the BoS immobilization system is capable of maintaining intra‐fraction localization with submillimeter accuracy (in nearly 83%, 86%, 95% of cases along SI, LAT, and PA, respectively) in translational coordinates and subdegree precision (in 98.85%, 98.85%, and 96.4% of cases for roll, pitch, and yaw respectively) in rotational coordinates. The system overall fares better in intra‐fraction localization precision compared to previously reported particle therapy immobilization systems. The use of a mask‐attached type bite block has marginal impact on inter‐ or intra‐fraction uncertainties compared to no bite block.
Highlights
Patient immobilization is critical to the safe and accurate delivery of radiation therapy
Most commercially available head immobilization devices for proton therapy use a relatively thin layer of carbon fiber composites compared to more rigid construction of their x ray therapy counterparts.[1,2]
Our results show that the addition of a bite block does not enhance immobilization effectiveness
Summary
Patient immobilization is critical to the safe and accurate delivery of radiation therapy. This is especially critical in particle therapy because of strong dependence of beam range on even the smallest variation in patient position with respect to the reference conditions.[1,2] it is important to minimize uncertainties associated with patient motion by understanding limitations of in-room immobilization systems and their performance throughout the course of treatment. Most commercially available head immobilization devices for proton therapy use a relatively thin layer of carbon fiber composites compared to more rigid construction of their x ray therapy counterparts.[1,2] to maintain sharp lateral penumbra, air gap between the aperture and patient needs to be minimal. Despite the widespread use of BoS frame in proton centers, there are few reports evaluating its effectiveness for immobilization with 6 DOF robotic couches.[3]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
