Computed tomography slice-by-slice target-volume delineation for stereotactic proton irradiation of large intracranial arteriovenous malformations: an iterative approach using angiography, computed tomography, and magnetic resonance imaging.
OBJECTIVE
Target-volume delineation for stereotactic irradiation is problematic for large and irregularly shaped arteriovenous malformations (AVMs). The purpose of this report is to quantify modifications in the target volume that result from iterative treatment planning that incorporates multimodality imaging data.


METHODS
Stereotactic neuroimaging procedures were performed for 20 consecutive patients with AVM volumes > 10 cm3. Angiographically defined extrema were transformed into computed tomography (CT) space. The resulting target contours were then modified by a multidisciplinary treatment planning team after iterative review of angiographic, CT, and magnetic resonance imaging (MRI) data. Volumes of interest and dose-volume histograms for proton irradiation were calculated before and after iterative target delineation.


RESULTS
Initial (angiographically defined) target volumes ranged from 15.3 to 96.1 cm3 (mean, 43.6 cm3). Final (iteratively defined) target volumes ranged from 10.7 to 114.0 cm3 (mean, 38.4 cm3). The volume of presumed normal tissue excluded by iterative planning ranged from 2.6 to 47.0 cm3 (mean, 15.5 cm3). Initially untargeted AVM, most commonly obscured by embolization material, was identified in all cases (range, 0.3 to 57.8 cm3; mean, 10.3 cm3). Corresponding dose-volume histograms demonstrated marked differences regarding lesion coverage and sparing of normal tissue structures.


CONCLUSIONS
Iterative target-volume delineation resulted in significant modifications from initial, angiographically defined target volumes. Substantial amounts of apparently normal tissue were excluded from the final target, and additional abnormal vascular structures were identified for incorporation. We conclude that an iterative multimodality approach to target-volume delineation may improve the overall results for stereotactic irradiation of large and complex AVMs.
Levy
R P
RP
Department of Radiation Medicine, Loma Linda University Medical Center, CA 92354,USA.
Schulte
R W
RW
Frankel
K A
KA
Steinberg
G K
GK
Marks
M P
MP
Lane
B
B
Heilbronn
L H
LH
Meinass
H J
HJ
Galindo
R A
RA
Slater
J D
JD
Slater
J M
JM
D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D018810:Magnetic Resonance Angiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013238:Stereotaxic Techniques; D014057:Tomography, X-Ray Computed