[Automatic definition of prescription isodose for stereotaxic radiation of arteriovenous malformations].
OBJECTIVE
To evaluate dosimetric consequences generated by the automatic definition based on lesion coverage of prescription isodose. A clinical series of 124 arteriovenous malformations was analysed. Plan quality was quantified by the standard deviation of the differential dose volume histogram calculated in the lesion.


METHODS
We define two quantitative protocols based on lesion coverage for the automatic definition of prescription isodose using a volumetric definition of coverage (90% of lesion volume), and an isodose-based definition proposed by RTOG (prescription isodose equals minimum isodose in the lesion divided by 0.9).


RESULTS
We have evaluated the plans obtained for these two protocols, calculating several dose-volume indices. These indices are presented as a function of dose-volume histogram standard deviation in order to quantify the consequences of their variations for this representative series of plans. The margin our team tolerates is such that the sum of underdosed lesion and overdosed healthy tissues factors remains lower than one. Protocol based on volumetric coverage gives results situated within this margin. Protocol based on RTOG definition produces conformation indices that could be greater than 1.


CONCLUSIONS
The absolute dose would be decided taking into account examined dose-volume indices and clinical data. A protocol for automatic definition of prescription isodose using volumetric lesion coverage seems to be more judiciously adapted to arteriovenous malformation conformal plans in stereotactic conditions because of variations observed in the overdosage of healthy tissues.
Dejean
C
C
Unité de radiophysique, hôpital Tenon, 4, rue de la Chine, 75020 Paris, France.
Lefkopoulos
D
D
Foulquier
J N
JN
Schlienger
M
M
Touboul
E
E
D000465:Algorithms; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000532:radiotherapy*; D055656:Prescriptions; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D013238:Stereotaxic Techniques