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correlation between the metrics is shown in figure 2.
Conclusion
Converted Aperture Metric and Edge Area Metric have
successfully been further developed, with retained
correlations as previous study, to account for clinical
aspects of VMAT treatment plans and provide information
about complexity on a control point level.
References
1
Götstedt J, Hauer A K and Bäck A. Development and
evaluation of aperture-based complexity metrics using
film and EPID measurements of static MLC openings. Med.
Phys. 2015; 42(7): 3911-3921
EP-1487 Dosimetric aspects in the development of a
crawl positioning device for prone breast radiotherapy
L. Paelinck
1
, B. Boute
2,3
, L. Veldeman
1,2
, C. De Wagter
1,2
,
B. Speleers
2
, A. Van Greveling
1
, G. Post
2
, W. De Neve
1,2
1
University Hospital Ghent, Radiotherapy, Ghent,
Belgium
2
Ghent University, Radiotherapy and Experimental
Cancer Research, Ghent, Belgium
3
Ghent University, Industrial Design Center, Ghent,
Belgium
Purpose or Objective
A new prone patient positioning device for breast cancer
radiation therapy was developed to treat patients in crawl
position. Prototypes showed excellent patient comfort,
stability, set-up precision and beam access to the regional
lymph nodes. However, two carbon fiber bars of the
external frame may be in beam paths in patients with
pendulous breasts. In this study, the influence of these
carbon fiber bars on the build-up dose and attenuation was
investigated.
Material and Methods
In figure 1 a picture of the patient positioning device is
shown. Beams at gantry angles near 90° or 270° will pass
through the 1 or 2 pullwinded carbon fiber bars of 37/40
mm upstream from the breast. The average distance
between the breast and the closest surface of the medial
bar was estimated 19 cm. Radiochromic film (Gafchromic
EBT2, Ashland Specialty Ingredients, USA) placed in a
slabbed polystyrene phantom was used to measure the
influence of the bars on build-up dose and attenuation.
Measurements were performed with a 6 MV photon beam
at gantry 0° using a distance of 100 cm between the source
and the surface of the phantom. A field size of 10 cm x 10
cm was used. Measurements were performed with or
without bars positioned above the phantom. An air gap of
19 cm between the upper surface of the phantom and the
undersurface of the (lowest) bar was used. The bars were
positioned above each other with parallel longitudinal
axes at 95 mm distance between the axes to mimic the
lay-out of the positioning device. The set-up with bars was
scanned using a large-bore CT scanner (Aquilion, Toshiba
Medical Systems, Tokyo, Japan). Measurements were
performed at 0, 1, 2, 16, 30 and 50 mm depth in the
phantom. Calculations of attenuation were performed
using the Pinnacle convolution-superposition algorithm
which is used in clinical practice.
Results
For irradiation through the bars loss of build-up at the
beam center, calculated by the formula (D-Db)[for depth
>16mm]/D[depth=16mm] was measured as -3.6%, -2.0%
and -1.6% at depths of 0, 1 and 2 mm, respectively.
Hereby, D and Db represent the doses without and with
irradiation through the bars, respectively. Attenuation at
the beam center, calculated by the formula (D-Db)[for
depths >= 16mm]/D[depth=16mm] at depths of 16, 30 and
50 mm depth was measured as 3.6%, 2.7% and 3.2%,
respectively. A typical attenuation measurements is
shown in figure 2. The attenuation through the bars at the
beam center calculated by Pinnacle is 3.7%, 3.1% and 2.8%
at 16, 30 and 50 mm depth, respectively.
Conclusion
Measurements showed that the carbon fiber frame bars
have a clinically irrelevant effect on the build-up dose.
Attenuation by the bars as calculated using Pinnacle and
measurements were in good agreement.
EP-1488 Evaluation of the Efficacy and Accuracy of
Customized bolus by using a 3-dimensional printer
W.K. Choi
1
, S.G. Ju
1
, J.C. Chum
2
, B.J. Min
3
, S.Y. Park
1
,
H.R. Nam
3
, D.H. Lim
1
1
Samsung Medical Center, Radiation Oncology, Seoul,
Korea Republic of
2
Kyonggi University, Computer Science, Suwon, Korea
Republic of