Therapy Medical Physics

A radionuclide has an initial dose rate of 4.1 cGy/hr will deliver a cumulative dose of 8,500 cGy over its life. What is the radionuclide?

• Pd-103
• Ir-192
• Co-60
• Iodine-125

Answer explanation

I-125 has a half-life of 59.4 days. By how much does activity decline in 1 day?

• 2.4%
• 1.8%
• 0.8%
• 1.2%

Answer explanation

Accurate proton dose calculation requires knowledge of what?

• Tissue electron density
• Tissue stopping power
• Tissue linear attenuation coefficient
• Tissue physical density

What device provides the oscillating electromagnetic wave used to propel electrons down the linac accelerating waveguide?

• Thyratron
• Magnetron
• Betatron
• Half-wave rectifier

Which of the following is not an advantage of HDR afterloading?

• Out patient procedures
• Ability to optimize dose distributions
• Reduced dose to staff
• Less QA required

True or false: BSF is independent of SSD.

• True
• False

What is the radius of an circular field equivalent to a 5cm by 6cm field?

• 3.1cm
• 2.8cm
• 5.5cm
• 1.7cm

Answer explanation

Physical penumbra is typically defined as the lateral distance between what two isodose lines?

• 66.7% and 33.3%
• 80% and 20%
• 80% and 50% (FWHM)
• 90% and 10%

A sample of Au-198 has an initial activity of 8Ci. What is its activity after 14 days?

• 5.7 x 10^8 Bq
• 3.4 x 10^8 Bq
• 8.1 x 10^9 Bq
• 7.4 x 10^10 Bq

What energy electron beam would you select to treat to the 80% isodose line at a depth of 3cm?

• 9 MeV
• 6 MeV
• 15 MeV
• 12 MeV

Answer explanation