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Calibration procedures for seeds preloaded in cartridges
Ryan S Brame1, Gil'ad N Cohen, Marco Zaider
1Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021, USA.
Medical Physics
|September 13, 2006
Summary
Evaluating radioactive seed inspection, this study finds that batch inspection of unshielded cartridges is the only practical method to meet regulatory requirements while saving time. Other methods often require individual seed assays, negating efficiency gains.
Area of Science:
- Medical Physics
- Radiological Sciences
- Nuclear Medicine
Background:
- Radioactive seeds used in brachytherapy require strict regulatory oversight for air kerma strength (SK) verification.
- Current regulations mandate accounting for all seeds and independent SK verification, posing challenges for efficient inspection schemes.
- The viability of aggregate seed inspection methods is of interest to balance regulatory compliance with practical time savings.
Purpose of the Study:
- To determine conditions under which cartridge inspection can satisfy regulatory requirements for radioactive seeds.
- To assess the practical benefits, specifically time savings, of cartridge inspection schemes compared to traditional single-seed assays.
- To evaluate manufacturer-specific inspection schemes, considering the prevalence of in-calibration seeds.
Main Methods:
- Comparison of two cartridge inspection schemes: (a) measuring SK of each cartridge in a batch, and (b) measuring a single randomly sampled cartridge.
- Evaluation against established standards: AAPM TG40, AAPM TG56, and ACR standards for brachytherapy sources.
- Analysis focused on Oncura model 6711 125I seeds in shielded and unshielded Mick cartridges.
Main Results:
- The batch inspection scheme applied to unshielded cartridges is identified as the only practically useful method.
- Other inspection schemes result in high false positive rates, necessitating the 10% single-seed assay at least 80% of the time.
- The effectiveness of inspection schemes is manufacturer-specific and depends on the prevalence of in-calibration seeds.
Conclusions:
- Batch inspection of unshielded cartridges offers a viable regulatory-compliant and time-saving alternative to single-seed assays.
- Random sampling and shielded cartridge inspections are generally impractical due to high false positive rates.
- Future inspection schemes should consider manufacturer-specific data and seed calibration prevalence for accurate assessment.
