J. Wulf et al., Stereotactic radiotherapy of extracranial targets: CT-simulation and accuracy of treatment in the stereotactic body frame, RADIOTH ONC, 57(2), 2000, pp. 225-236
Citations number
27
Categorie Soggetti
Radiology ,Nuclear Medicine & Imaging","Onconogenesis & Cancer Research
Background and purpose: Evaluation of set-up accuracy and analysis of targe
t reproducibility in the stereotactic body frame (SBF), designed by Blomgre
n and Lax from Karolinska Hospital, Stockholm. Different types of targets w
ere analyzed for the risk of target deviation. The correlation of target de
viation to bony structures was analyzed to evaluate the value of bones as r
eference structures for isocenter verification.
Materials and methods: Thirty patients with 32 targets were treated in the
SBF for primary or metastatic peripheral lung cancer, liver metastases, abd
ominal and pelvic tumor recurrences or bone metastases. Set-up accuracy and
target mobility were evaluated by CT-simulation and port films. The contou
rs of the target at isocenter level, bony structures and body outline were
compared by matching the CT-slices for treatment planning and simulation us
ing the stereotactic coordinates of the SBF as external reference system. T
he matching procedure was performed by using a 3D treatment planning progra
m.
Results: Set-up accuracy represented by bony structures revealed standard d
eviations (SD) of 3.5 mm in longitudinal, 2.2 mm in anterior-posterior and
3.9 mm in lateral directions. Target reproducibility showed a SD of 4.4 mm
in longitudinal, 3.4 mm ap and 3.3 mm in lateral direction prior to correct
ion. Correlation of target deviation to bones ranged from 33% (soft tissue
targets) to 100% (bones).
Conclusion: A security margin of 5 mm for PTV definition is sufficient, if
CT simulation is performed prior to each treatment to correct larger target
deviations or set-up errors. Isocenter verification relative to bony struc
tures is only safe for bony targets but not for soft tissue targets. (C) 20
00 Elsevier Science Ireland Ltd. All rights reserved.