Multiobserver study of the variability in target delineation for anaplastic astrocytoma in stereotactic radiosurgery with Leksell Gamma Knife® Perfexion™

Helena Sandström1, Håkan Nordström2, Jonas Johansson, PhD3, Iuliana Toma-Dasu1

1Solna, Sweden 2Elekta Instrument AB, Stockholm, Sweden 3Stockholm, Sweden

Keywords: gamma knife, anaplastic astrocytoma, dose planning, technique, survey

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     The targeting of glioma volumes for radiosurgery can be challenging.
     The aim of the study was to quantify the multiobserver variability of target delineation for anaplastic astrocytoma and to investigate the dosimetric implications with respect to the plan conformity and dose fall-off.
     For anaplastic astrocytoma, a tumour which presents a high degree of invasion of the neighbouring tissue the issue of accurate delineation is extremely critical. The subject of this study was a randomly selected patient with anaplastic astrocytoma planned for stereotactic radiosurgery with Leksell Gamma Knife® Perfexion™. Several images of the brain taken with different techniques were available for delineating the target: MRI-FLAIR, MRI-T2 and PET. Fourteen centres chosen for their high experience with Leksell Gamma Knife® participated in the study and delineated the target. The analysis of the delineated targets was based on a calculated average target which 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 large differences in the planned target volume. Average target volume was 2.06 cm3 and the common volume was extremely small, only 0.05 cm3 while the encompassing volume was 43.27 cm3. These variations translated into corresponding discrepancies in plan conformity resulting into a Paddick conformity index ranging from 0.42 to 0.83 with an average of 0.69. The mean gradient index was 3.41 (2.76-6.82) for all plans.
     This was a limited survey using data from one case.
     The differences between the targets delineated by various observers for the investigated case of anaplastic astrocytoma appear to be clinically significant.
     The resulting plans also show large differences in conformity due to the high complexity of the disorder.


Project Roles:

H. Sandström (), H. Nordström (), J. Johansson (), I. Toma-Dasu ()