Evaluation of a new software prototype for frameless radiosurgery of arteriovenous malformations

Schmidhalter, Daniel; Henzen, Dominik; Herrmann, Evelyn; Volken, Werner; Mackeprang, Paul-Henry; Ermis, Ekin; Hemmatazad, Hossein; Honegger, Jonas; Haas, Benjamin; Fix, Michael; Manser, Peter (2019). Evaluation of a new software prototype for frameless radiosurgery of arteriovenous malformations. Radiation oncology, 14(1), pp. 1-13. BioMed Central 10.1186/s13014-019-1422-x

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Background: In order to locate an arteriovenous malformation, typically, a digital subtraction angiography (DSA) iscarried out. To use the DSA for target definition an accurate image registration between CT and DSA is required. Carrying out a non-invasive, frameless procedure, registration of the 2D-DSA images with the CT is critical. A newsoftware prototype is enabling this frameless procedure. The aim of this work was to evaluate the prototype interms of targeting accuracy and reliability based on phantom measurements as well as with the aid of patient data. In addition, the user’s ability to recognize registration mismatches and quality was assessed.
Methods: Targeting accuracy was measured with a simple cubic, as well as with an anthropomorphic headphantom. Clearly defined academic targets within the phantoms were contoured on the CT. These referencestructures were compared with the structures generated within the prototype. A similar approach was used withpatient data, where the clinically contoured target served as the reference structure. An important error source decreasing the target accuracy comes from registration errors between CT and 2D-DSA. For that reason, the tools in BC provided to the user to check these registrations are very important. In order tocheck if the user is able to recognize registration errors, a set of different registration errors was introduced to the correctly registered CT and 2D-DSA image data sets of three different patients. Each of six different users rated thewhole set of registrations within the prototype.
Results: The target accuracy of the prototype was found to be below 0.04 cm for the cubic phantom and below 0.05 cm for the anthropomorphic head phantom. The mean target accuracy for the 15 patient cases was found tobe below 0.3 cm. In the registration verification part, almost all introduced registration errors above 1° or 0.1 cm were detected bythe six users. Nevertheless, in order to quantify and categorize the possibility to detect mismatches in the registration process more data needs to be evaluated.
Conclusion: Our study shows, that the prototype is a useful tool that has the potential to fill the gap towards aframeless procedure when treating AVMs with the aid of 2D-DSA images in radiosurgery. The target accuracy of the prototype is similar to other systems already established in clinical routine.

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