Clinical evaluation of monitor unit software and the application of ...

Table 1
Overview of institutions and the respective radiotherapy equipment for clinical testing and evaluation of the independent dose verification
software ‘MUV’
Radiotherapy institution TPS and applied algorithm Linacs Energies (MV)
University Umea˚ Helax TMS (V6.1) pencil beam or collapsed cone a
Siemens Primus 6/18
Medical University Vienna Helax TMS (V6.1) pencil beam or collapsed cone a
ELEKTA Precise 6/10/25
GE SAT 43 6/10/25
Medical University Graz Pinnacle (V6.2b) superposition Varian Clinac 2300 CD 6/18
University Basel XiO (V4.2) convolution/superposition ELEKTA Precise 6/18
University Copenhagen Eclipse (V7.3.10) pencil beam Varian Clinac 2300 EX 6/18
a
...applied for lung treatments only.
Results were acquired for 226 individual treatment plans
including a total of 815 radiation fields. Table 2 gives an
overview of the considered cases as a function of treatment
technique and treatment area. All different treatment techniques,
ranging from regular and irregular open fields to
wedged fields using a physical or dynamic wedge, and dynamic
as well as step-and-shoot IMRT could be handled with
MUV and were included in this study.
The accuracy of MUV against measurements, performed
in a homogeneous water phantom, has been demonstrated
during the design and pre-clinical testing phase [17–20].
For example, for irregular MLC shaped fields a standard
deviation of 0.47% was obtained between calculated and
measured output factors (in water or air) for about 300 test
Table 2
Summary of treatment fields, treatment techniques, treatment
sites, etc., for clinical testing of the independent dose verification
software ‘MUV’
Treatment area # of plans # of fields Techniques
Pelvis 98 364 Open 273
Physical wedge 46
Dynamic wedge 38
Step-shoot IMRT 0
Dynamic IMRT 7
Thorax 46 155 Open 95
Physical wedge 17
Dynamic wedge 36
Step-shoot IMRT 7
Dynamic IMRT 0
Head-and-neck 71 271 Open 75
Physical wedge 48
Dynamic wedge 22
Step-shoot IMRT 63
Dynamic IMRT 63
Other 11 25 Open 3
Physical wedge 20
Dynamic wedge 2
Step-shoot IMRT 0
Dynamic IMRT 0
Total 226 815 Open 446
Physical wedge 131
Dynamic wedge 98
Step-shoot IMRT 70
Dynamic IMRT 70
D. Georg et al. / Radiotherapy and Oncology 85 (2007) 306–315 309
cases, where 5, 10, and 20 cm depth were considered together
with four different MLC designs. Maximum deviations
did not exceed 1.7%, even for the most irregular field shapes
[20]. Therefore, the main focus of this study was the clinical
application of the independent MUV software. However,
verification measurements were also performed for a small
number of individual treatment plans encompassing in total
150 beams. Of these more than 100 beams with segmentally
modulated fluence patterns (dynamic wedges and IMRT)
were specifically tested as they were not considered in detail
in previous tests.
Finally, all observed deviations between MUV and the different
TPSs were analysed in order to assess the clinical
application of realistic action levels (AL). For that purpose
current results and previously performed experimental
benchmarking tests of the algorithm implemented in MUV
were combined [17–20].
Results
In general good overall agreement was found between
calculations performed with the different TPS and MUV calculations,
with a mean deviation per field of 0.2 ± 3.5%
(1 SD), and mean deviations of 0.2 ± 2.2% for a composite
treatment. For a more detailed analysis all treatments
and/or fields were binned with respect to treatment area,
treatment technique, and the use of geometrical depth or
radiological depth, respectively.
Treatment site specific deviations
Fig. 1a and b present the fraction of beams with deviations
between the local TPS and MUV that are exceeding a
certain limit, separated for treatment site (pelvis, thorax,
head-and-neck, other) and whether any depth corrections
were performed. While for pelvic treatments less than 10%
of all fields showed deviations larger than 3%, irrespective
of radiological depth corrections, this fraction was almost
40% for thorax fields and 30% for head-and-neck fields.
When using the radiological depth, the fraction of beams
with deviations larger than 3% could be reduced to about
10% for head-and-neck and to 30% for thorax treatments.
For the latter application an agreement between TPS and
MUV calculations for about 90% of all fields could be
achieved only at the 4.5% deviation level (when applying
the radiological depth).