ESTRO 36 Abstract Book

S757

ESTRO 36 2017

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Purpose or Objective

Anthropomorphic phantoms are used in a variety of ways

in radiation therapy for both research and quality

assurance purposes. Most anthropomorphic phantoms are

of generalized patients, but 3D printing technology can be

used to fabricate patient-realistic phantoms for special QA

and verification procedures. Most 3D printers, however,

can only print in one or two materials at a time, so true

patient heterogeneity is limited. In this study, we

examined two different patient specific, 3D printed

phantoms created based on the same patient to determine

the accuracy of single and multi-material phantoms.

Material and Methods

The phantoms used in this study were designed from the

clinical CT data for a post-mastectomy patient treated at

our institution. The CT data was trimmed to remove the

patient’s head and arms to preserve anonymity and

simplify printing. Phantom 1 was designed by converting

the trimmed CT data into a 3D model with a CT threshold

of >-500 Hounsfield units (HU). This model was sliced into

2.5-cm-thick sagittal slices and printed one slice at a time.

All slices were printed with polylactic acid (PLA)

representing all body tissues, but with air cavities and

lower density regions like the lungs left open. Sagittal

slices were chosen for their superior fit with each other,

and minimal material warping relative to axial slices.

Phantom 2 was designed by converting the CT data into

three separate 3D models with a CT threshold of <-147 HU

for air cavities, -147 to 320 HU for soft tissue, and >320

HU for bone. The models were sliced into 1-cm-thick axial

slices, and printed. The slices were printed from the soft

tissue model using a custom formulated high impact

polystyrene (HIPS) with the air and bone models left open.

After printing, the open bone model sections were filled

with a liquid resin polymer with an equivalent density to

bone.

The phantoms were evaluated for their materials and

overall accuracy to the original patient CT. Blocks of PLA,

HIPS, and the bone resin material were all imaged to

determine their average HU. The phantoms were also each

imaged and registered with each other and the original

patient CT to determine the consistency and accuracy of

each phantom.

Results

The materials used and their properties are summarized

in Table 1. Phantom 1 was fabricated from PLA, which

isn’t particularly tissue equivalent, but did print relatively

consistently. The bone resin and HIPS of phantom 2 more

accurately reflect tissue heterogeneity, but have more

variations in their printed consistency.

Figure 1 shows registered images of the original patient

image (a), phantom 1 (b), and phantom 2 (c). Tissue

density was more accurate in phantom 2, despite some

small holes not being filled with bone resin.

Conclusion

Two phantoms were created, one with a single material,

and a second with two materials (tissue and bone). These

two phantoms provide an ability to more closely simulate

the patient and provide a means to more accurately

measure dose delivered in a patient surrogate.

EP-1436 A newly designed water-equivalent bolus

technique enables BNCT application to skin tumor.

K. Hirose

, K. Arai

, T. Motoyanagi

, T. Harada

, R.

Shimokomaki

, T. Kato

, Y. Takai

Southern TOHOKU BNCT Research Center, Radiation

Oncology, Koriyama, Japan

Purpose or Objective

The accelerator-based boron neutron capture therapy (AB-

BNCT) system was developed in order to enable the

installation of safe hospital BNCT. An important feature of

AB-BNCT system is its capability of delivering great doses

to deep-seated tumors under condition in which a

beryllium target and neutron-beam-sharping assembly are

adjusted for production of epithermal neutron that is

applicable

for

types

tumor

localization.Conversely, AB-BNCT is less suitable for

superficial cancers, such as malignant melanoma. In this

study, we developed a newly water-equivalent bolus

technique that has no production of prompt gamma ray

and no influence on complicating dose calculation, and we

evaluated the effect of this technique on treatment

quality for a case of malignant melanoma patient.

Material and Methods

A water-equivalent bolus was prepared as follows.

Urethane foam was cut down into the size of 3-cm larger

than the superficial lesion, infiltrated with distilled water

with deaeration, and covered with a thin film. The

simulated patient was played by a healthy man and

simulated condition was originated from a malignant

melanoma patient with the lesion of 3-cm diameter

localized in a sole of right foot. The superficial lesion was

bordered by a catheter and covered with a water-

equivalent bolus. Using treatment planning system SERA,

the tumor is depicted as a region surrounded by the

catheter with 5-mm thickness, and also skin is depicted as

the other region except for tumor with 3-mm thickness

from body surface. A water-equivalent bolus was

delineated as water. This was placed into air in calculation

in condition with no bolus. For comparison with bolus-like

effect of a covered collimator, the outline of an imaginary

collimator cover was set as a mass of polycarbonate or a