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SU‐E‐T‐395: Feasibility Study of a Novel Technique to Measure Instantly the Strength of 125I Seeds Being Implanted
Author(s) -
Tanaka K,
Tateoka K,
Asanuma O,
Endo S,
Sato K,
Takeda H,
Kamo K,
Hori M,
Hareyama M,
Takada J
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612349
Subject(s) - detector , measure (data warehouse) , backup , materials science , mathematics , physics , computer science , optics , data mining , database
Purpose: Final goal is to develop a technique to detect the 125I seed and measure its strength during implantation process. This will be a backup tool for QA by offering an additional measurement apart from the pre‐operation measurement. In actual implantation, the speed of the seed varies because it is conducted manually. In order to develop a simple and stable system usable in any speed, this study supposes to use single detector and repeat short‐time measurements. This report summarizes a feasibility test. Methods: The 125I seeds (Oncra Inc. Oncoseed 6711) was moved in speeds up to 200 mm/s by an electric actuator. Its strength was measured with a NaI detector (1″diam. × 1″) set at 170 mm from the needle guiding the seed. The requirement for the counting time was investigated to estimate the strength regardless the seed speed. Results: In the measurement where the seed was set static in needle, the change in counting rate of the NaI detector was 4 % at the 30 mm‐long region along the needle, while the counting rate rapidly decreased outside the region. It is desirable to start‐stop the measurement while the seed is within this region. Assuming 200 mm/s as the maximum speed, 7 to 8 measurements can be performed for the counting time of 20 ms, 3 measurements at 50 ms, 1 measurement at 100 ms. By using the average of the measured results while the seed was within the region, the estimated seed strength agreed within 10 % between the speeds 0 and 200 mm/s at counting time of 100 ms or less. Conclusion: This report shows the feasibility in principle to estimate the 125I seed strength during the implantation operation, regardless the seed velocity.