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Figure 2. This will help in determining whether the
effective energy of radiation beam is less than or greater
than the E
max
.
Conclusion
This work presents some possible TLD tandem systems
consisting of three types TL materials which are better
able to estimate effective energy of a radiation beam in
the 30 to 100 keV range than the presently used two TL
material tandem systems. This can potentially improve
dosimetry in situations where information about the
effective energy of radiation is crucial such as personal
monitoring. Considering the high sensitivity TLD100H, the
TL material increasingly being used in personal dosimetry,
tandem combinations of TLD100H,TLD200 & TLD500 or
TLD100H, TLD400 & TLD500 are recommended for x or
gamma radiation energy discrimination in the 30 to 120
keV range.
PO-0765 Preparation and Fabrication of a Full-scale
Patient-specific 3D-Printed Radiotherapy Phantom
D. Craft
1
, R. Howell
1
1
The University of Texas MD Anderson Cancer Center,
Radiation Physics, Houston- TX, USA
Purpose or Objective
Phantoms are used in a wide variety of ways for
radiotherapy research and quality assurance. Generally,
however, these phantoms are limited in size and
complexity to represent only small treatment areas or
generalized patients. 3D printing technology can make the
fabrication and design of patient-specific phantoms simple
and inexpensive, but has also been limited by size and
complexity due to the limited size of most 3D printers and
the tendency of materials to warp while being printed. We
aimed to overcome these limitations by developing an
effective 3D printing workflow that could be used to
design and fabricate large, full-scale, patient-specific
phantoms with negligible material warping errors. To
demonstrate the viability of our technique we produced a
full-scale phantom of a post-mastectomy patient treated
at our institution.
Material and Methods
The clinical CT data for a post-mastectomy patient at our
institution was converted into a 3D model, and then
trimmed to remove the patient’s head and arms to
simplify printing. The model was next sliced into eleven
2.5-cm-thick sagittal slices, which fit better and have less
warping relative to axial slices. Each slice was printed
using polylactic acid to represent all body tissues at 100%
infill. Air cavities and lower density regions like the lungs
were left open and unfilled. The slices were printed on an
inexpensive and commercially available 3D printer with
the inferior aspect of the patient on the printing surface.
The slices were individually and collectively imaged and
examined for printing accuracy. The original patient CT
scan and the assembled phantom CT scan were registered
together to assess the overall accuracy of the phantom
construction.
Results
The slices took an average of 24 hours and 19 minutes to
print, and the total material cost of the phantom was
$524. Figure 1 shows images of the phantom with the left-
most slices removed to show the interior anatomy (a), and
the entire phantom assembled (b). As can be seen, the
phantom fits together well, and has a high level of detail.
Figure 2 shows a comparison of slices in the axial, sagittal
and coronal orientations from the original patient CT
image (a), and slices from the phantom CT image (b) in
the same location and orientation. While material
heterogeneity has been lost due to using only one material
in the phantom, the anatomical and structural details
agree very well between the printed phantom and the
source image. The only disagreement is in the lungs,
where unsupported nodules were removed prior to
printing the phantom. Analysis of individual slices
revealed that measurable dimensions were accurate
within 0.5 mm, and the average volumetric discrepancy
between printed slices and their models was 1.37%.
Figure
1:
Figure
2: