The importance of the conformality, heterogeneity, and gradient indices in evaluating Gamma Knife radiosurgery treatment plans for intracranial meningiomas.
OBJECTIVE
To investigate the relationship between the conformality index (CIn), heterogeneity index (HIn), and gradient index (GIn) and the development of toxicity in patients treated with Gamma Knife radiosurgery (GKRS) for intracranial meningiomas.


METHODS
Treatment records of patients treated from 1997 to 2009 with at least 6 months of follow-up were reviewed. The following parameters were collected: CIn, HIn, GIn (ratio of the volume receiving half the prescription isodose to the volume receiving the full prescription isodose), brainstem (BS) maximum dose (MD), BS volume receiving ≥ 12 Gy (V12), optic apparatus (OA) MD, OA V8 Gy, OA V10, number of isocenters, number of isocenters outside target volume, and the occurrence of six toxicities. Univariate and multivariate logistic regression modeling were used for analysis.


RESULTS
This study included 145 patients (148 meningiomas) with a median follow-up time of 27 months (range, 6-113.9 months). The majority of meningiomas were located in the skull base (53%). The median prescription dose was 13 Gy (range, 10-24 Gy) to the 51.50% (range, 50-92%) isodose. A lower HIn was correlated with a higher GIn (p = 0.007). CIn was not associated with any toxicity. Higher HIn was associated with the development of dizziness (odds ratio [OR] 1.9; p = 0.02), whereas a lower GIn was associated with motor deficits (OR 0.38; p = 0.04) and auditory changes (OR 0.59; p = 0.04). The OA MD, V8, and V12 were not associated with visual changes, but visual changes were associated with a higher number of isocenters outside the target volume (OR 1.93; p = 0.07). BS V12 was correlated with the development of auditory changes (OR 1.05; p = 0.05), whereas patients with higher BS MD tended to have increased toxicity.


CONCLUSIONS
Close attention must be paid to all three indices (CIn, HIn, GIn) when optimal treatment plans are determined. We recommend that the target CIn should be ≤ 2.0, the HIn ≤ 2.0, and the GIn ≥ 3.0 for intracranial meningiomas.
Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA.
Ehsan H
EH
Balagamwala
John H
JH
Suh
Gene H
GH
Barnett
Mohammad K
MK
Khan
Gennady
G
Neyman
Rong S
RS
Cai
Michael A
MA
Vogelbaum
Eric
E
Novak
Samuel T
ST
Chao
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001933:Brain Stem / Q000528:radiation effects; D005123:Eye / Q000528:radiation effects; D005260:Female; D006801:Humans; D008297:Male; D008577:Meningeal Neoplasms / Q000473:pathology / Q000601:surgery*; D008579:Meningioma / Q000473:pathology / Q000601:surgery*; D008875:Middle Aged; D009820:Ohio; D058958:Organs at Risk / Q000528:radiation effects; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*; D011879:Radiotherapy Dosage; D012044:Regression Analysis; D012189:Retrospective Studies; D019292:Skull Base Neoplasms / Q000473:pathology / Q000601:surgery; D047368:Tumor Burden; D014786:Vision Disorders / Q000209:etiology; D055815:Young Adult