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Knox Gelatine™ Effect on Radiation Absorption: An Alternative Bolus

Chiu, Michael; Johansen, Theodore; Porchia, AnthonyAbelson, Jonathan A., M.D.; Crockett, Robert, Ph.D.; San Luis Radiation Oncology Medical Center

BACKGROUND

OBJECTIVES

RESULTS

Material Radiation Dosage (cGy)Superflab (0.5 cm) 85.4

Superflab (1 cm) 98.2Neoprene Mask 57.1

Knox Gelatine™ (0.5 cm) 81.5Knox Gelatine™ (1 cm) 101

Control (no bolus) 42.9

CONCLUSIONS

-1000 -500 0 500 1000 15000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8f(x) = 0.000735339281754904 x + 0.952393157539779R² = 0.951934359460101

Hounsfield Units (HU)

Electron Density (g/cm3)

Electron Density vs. Hounsfield Number

Figure 5. Adherence test for Knox Gelatine™

Figure 6. MOSFET dosimetry testFigure 4. Phantom prepared for CT scanning

Figure 3. Sessile drop test using VCA Optima

Figure 8. HU measurements of Sample L Knox Gelatine™

Figure 9. CT results on the phantomFigure 1. Alternatively used bolus: Superflab (left) and neoprene mask (right) Material

Average Hounsfield Unit (HU)

Electron Density (g/cm3)

Percent Difference in Electron Density

to Water

Superflab -2.967 0.95 5%

Knox Gelatine™-45.933 0.92 8%

Neoprene Mask-761.367 0.419 58%

Figure 7. 3D analysis of Superflab and Knox Gelatine ™

Gelatin Fabrication Conformability

Density

Wettability

Dosimetry

What is Radiation Therapy?

• Radiation formed by momentum transfer

• Light particles excite electrons

• Electron relaxation generates another photon

• Can be used to destroy cancer cells

Bolus Effect

• The radiation beams have characteristic peaks of dosage versus depth

• Peak is below surface of skin

Alternatively Used Bolus by San Luis Radiation

• Superflab and neoprene mask

The Knox Gelatine™ bolus is a viable substitute for Superflab because it is conformable to tight contours, adhesive to skin, and transparent, while maintaining the necessary bolus effect and electron density.

Bolus Must:• Have density close to that

of skin• Be 0.5 to 1 cm thick

• Be conformable to tight contours

• Be transparent

Figure 2. Processing the Knox Gelatine™

Table I. CT density scan Table II. Absorption of radiation at phantom surface

ABSTRACT METHODS RESULTS (CONT.)Skin cancer is the most common form of cancer in the United States, as one in five Americans will develop it in the course of their lifetime. To destroy the cancerous cells, maximum electromagnetic (EM) radiation dose absorption is desired at the surface of the skin. In most cases, however, radiation spares the skin. Enhancement of dermal and epidermal radiation can be achieved using a bolus. An effective bolus must be a one-half to one centimeter thick, homogenous material with an electron density similar to that of skin. The bolus must also be able to conform to tight facial contours. Current bolus materials used at San Luis Radiation Oncology Medical Center are Superflab (a polymeric gel) and a neoprene wetsuit mask. A problem with these bolus materials is their inability to conform to the irregular contours of the face. The purpose of this study is to research and fabricate an alternate bolus material to be used at San Luis Radiation that adheres well to the skin (high wetting ability), has a similar electron density to that of water (1 g/cm3), and yields predictable radiation dosage at the surface of the skin. The validity of Knox Gelatine™ as an alternative bolus was investigated through surface angle testing, computed tomography (CT) scans, and dosimetry measurements. Knox Gelatine™ was found to have a high wetting ability, an electron density similar to water, and predictable surface radiation dose absorption. These results were compared to those of the previously used bolus materials and supported Knox Gelatine™ as an alternative bolus material for radiation therapy.