Accuracy of volume and DVH parameters determined with different brachytherapy treatment planning systems.
OBJECTIVE
To determine the uncertainties in dose volume histogram (DVH) analysis used in modern brachytherapy treatment planning systems (TPSs).


METHODS
A phantom with three different volumes was scanned with CT and MRI. An inter-observer analysis was based on contouring performed by 5 persons. The volume of a standard contour set was calculated using seven different TPSs. For five systems a typical brachytherapy dose distribution was used to compare DVH determination.


RESULTS
The inter-observer variability (1SD) was 13% for a small cylindrical volume, 5% for a large cylinder and 3% for a conical shape. A standardized volume for a 4mm CT scan contoured on seven different TPS varied by 7%, 2%, and 5% (1SD). Use of smaller slice thickness reduced the variations. A treatment plan with the sources between the large cylindrical shape and the cone showed variations for D(2cc) of 1% and 5% (1SD), respectively. Deviations larger than 10% were observed for a smaller source to cylinder surface distance of 5mm.


CONCLUSIONS
Modern TPSs minimize the volumetric and dosimetric calculation uncertainties. These are comparable to inter-observer contouring variations. However, differences in volume result from the methods of calculation in the first and last slice of a contoured structure. For this situation and in case of high dose gradients inside analyzed volumes, high uncertainties were observed. The use of DVH parameters in clinical practice should take into account the method of calculation and the possible uncertainties.
Kirisits
Christian
C
Department of Radiotherapy, Medical University of Vienna, Vienna, Austria. Christian.Kirists@meduniwien.ac.at
Siebert
Frank-André
FA
Baltas
Dimos
D
De Brabandere
Marisol
M
Hellebust
Taran Paulsen
TP
Berger
Daniel
D
Venselaar
Jack
J
D001918:Brachytherapy; D006801:Humans; D008279:Magnetic Resonance Imaging; D015588:Observer Variation; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*