D. Verellen et al., Assessment of the uncertainties in dose delivery of a commercial system for linac-based stereotactic radiosurgery, INT J RAD O, 44(2), 1999, pp. 421-433
Citations number
33
Categorie Soggetti
Radiology ,Nuclear Medicine & Imaging","Onconogenesis & Cancer Research
Journal title
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
Purpose: Linac-based stereotactic radiosurgery (SRS) was introduced in our
department in 1992, and since then, more than 200 patients have been treate
d with this method. An in-house-developed algorithm for target localization
and dose calculation has recently been replaced with a commercially availa
ble system. In this study, both systems have been compared, and positional
accuracy, as well as dose calculation, have been verified experimentally.
Methods and Materials: The in-house-developed software for target localizat
ion and dose calculation is an extension to George Sherouse's GRATIS(R) sof
tware for radiotherapy treatment planning, and has been replaced by a comme
rcial (BrainSCAN version 3.1; BrainLAB, Germany) treatment planning system
(TPS) for SRS, The positional accuracy for the entire SRS procedure (from i
mage acquisition to treatment) has been investigated by treatment of simula
ted targets in the form of 0.2-cm lead beads inserted into an anthropomorph
ic phantom. Both dose calculation algorithms have been verified against man
ual calculations (based on basic beam data and CT data from phantom and pat
ients), and measurements with the anthropomorphic phantom applying ionizati
on chamber, thermoluminescent detectors, and radiographic film. This analys
is has been performed on a variety of experimental situations, starting wit
h static beams and simple one-are treatments, to more complex and clinical
relevant applications. Finally, 11 patients have been evaluated with both T
PS in parallel for comparison and continuity of clinical experience,
Results: Phantom studies evaluating the entire SRS procedure have shown tha
t a target, localized by CT, can be irradiated with a positional accuracy o
f 0.08 cm in any direction with 95% confidence. Neglecting the influence of
dose perturbation when the beam passes through bone tissue or air cavities
, the calculated dose values obtained from both TPSs agreed within 1% (SD 1
%) for phantom and patient studies. The application of a one-dimensional pa
th length correction for tissue heterogeneity influences the treatment pres
cription 4% on average (SD 1%), which is in compliance with theoretical pre
dictions, The phantom measurements confirmed the predicted dose at isocente
r within uncertainty for the different treatment schedules in this study.
Conclusion: The full SRS procedure applied to an anthropomorphic phantom ha
s been used as a comprehensive method to assess the uncertainties involved
in dose delivery and target positioning. The results obtained with both TPS
s are in agreement with AAPM Report 54, TG 42 and clinical continuity is as
sured. However, the use of a one-dimensional path length correction will re
sult in an increase of 4% in dose prescription, which is slightly more than
that predicted in the literature. (C) 1999 Elsevier Science Inc.