CTBS Sterilization Methods 4 — Questions and Answers
Question 1: Which radiation dose range is typically used by tissue banks for terminal sterilization of allografts to achieve SAL 10⁻⁶?
- 1–5 kGy
- 5–10 kGy
- 15–25 kGy (Correct answer)
- 50–75 kGy
Correct answer: 15–25 kGy
Most tissue banks use doses between 15 and 25 kGy for terminal sterilization, balancing sterility assurance with tissue integrity.
Question 2: During ETO sterilization, relative humidity inside the chamber is critical because:
- High humidity inactivates ETO gas rapidly
- Moisture hydrates spore coat, enabling ETO penetration (Correct answer)
- Humidity prevents pressure buildup
- Low humidity improves ETO gas distribution
Correct answer: Moisture hydrates spore coat, enabling ETO penetration
Adequate moisture (30–80% RH) is needed to hydrate the spore coat, allowing ETO to penetrate and alkylate cellular components effectively.
Question 3: A tissue bank switches its radiation sterilization source from Co-60 to e-beam. Which limitation of e-beam must be addressed?
- Higher radiation-induced collagen damage
- Limited penetration depth for dense or thick products (Correct answer)
- Inability to validate with biological indicators
- Requirement for higher sterilization temperatures
Correct answer: Limited penetration depth for dense or thick products
E-beam electrons have limited penetration compared to gamma photons, restricting its use to thinner or lower-density tissue configurations.
Question 4: Which chemical parameter is MOST critical to monitor and control during an ETO sterilization cycle?
- pH of the chamber atmosphere
- ETO gas concentration, temperature, humidity, and time (Correct answer)
- Oxygen partial pressure
- UV absorbance of the sterilant
Correct answer: ETO gas concentration, temperature, humidity, and time
ETO efficacy depends on the precise control of gas concentration, temperature, humidity, and exposure time — all four must be within validated ranges.
Question 5: What does the term 'bioburden' mean in the context of tissue sterilization?
- The number of prions detected on a tissue surface
- The total number of viable microorganisms present on a product before sterilization (Correct answer)
- The endotoxin load on processed tissue
- The weight of microbial debris after sterilization
Correct answer: The total number of viable microorganisms present on a product before sterilization
Bioburden is the total count of viable microorganisms on or in a product before terminal sterilization, used to calculate the required sterilization dose.
Question 6: Under AATB standards, which type of tissue graft is specifically prohibited from terminal sterilization with high-dose radiation due to loss of osteoinductive properties?
- Cortical strut allografts
- Demineralized bone matrix (DBM) (Correct answer)
- Cancellous bone chips
- Periosteal patches
Correct answer: Demineralized bone matrix (DBM)
High-dose radiation degrades the growth factors and BMP proteins in DBM that are responsible for its osteoinductive activity.
Question 7: A tissue bank discovers that a validation lot was sterilized at a humidity level below the validated range for ETO. The correct action is:
- Release the lot since temperature and concentration were met
- Quarantine the lot; humidity is a critical parameter that invalidates the cycle (Correct answer)
- Re-aerate the lot to compensate
- Reprocess with a higher ETO concentration
Correct answer: Quarantine the lot; humidity is a critical parameter that invalidates the cycle
Humidity is a critical ETO cycle parameter; if it falls outside the validated range, the cycle is invalid and the lot must be quarantined pending investigation.
CTBS Sterilization Methods 4
Which radiation dose range is typically used by tissue banks for terminal sterilization of allografts to achieve SAL 10⁻⁶?