Multiobserver study of the variability in target delineation for meningioma in stereotactic radiosurgery with Leksell Gamma Knife? Perfexion?Helena Sandström1, Håkan Nordström2, Jonas Johansson, PhD3, Iuliana Toma-Dasu11Solna, Sweden 2Elekta Instrument AB 3Stockholm, Sweden Keywords: survey, physics, gamma knife, dose planning, meningioma
Meningioma is one of the tumours prone to pose difficulties in delineation during gamma knife dose planning.
The aim of the study was to quantify the multiobserver variability of target delineation for meningioma and to investigate the dosimetric implications with respect to the plan conformity and dose fall-off.
One patient case was evaluated.
One random patient with meningioma imaged with MR and CT was randomly selected as the subject of the study. Sixteen centres chosen for their high experience with Leksell Gamma Knife® participated in the study and delineated the target based on the same set of images and with the same constraints regarding the delineation of the target and the organs at risk. The analysis of the delineated targets was based on a calculated average target which was assumed to resemble the accurate target if all observers delineate with the same clinical demands. The average target was then compared to each delineated target by the concordance index and discordance index. Each delineated target and resulting plan was also evaluated using the conformity index, Paddick conformity index and gradient index. The difference in target structure location, size and shape was analyzed using the encompassing volume compared to the common volume of all delineated structures.
Target delineation resulted in differences between the participating centers and hence in the average target which resulted to be rather small in comparison to each delineated target volume. Average target volume was 5.90 cm3 while the common volume was 2.60 cm3 and the encompassing volume was 13.14 cm3. These variations translated into corresponding discrepancies in plan conformity resulting into a Paddick conformity index ranging from 0.53 to 0.90 with an average of 0.80. The mean gradient index was 2.83 (2.33-3.78) for all plans.
This was a survey across a limited number of centers.
The differences between the targets delineated by various observers for the investigated case of meningioma appear to be clinically significant.
The resulting plans also show large differences in conformity. The importance of these discrepancies remains to be defined. Project Roles:
H. Sandström (), H. Nordström (), J. Johansson (), I. Toma-Dasu ()