Measurement of the strength of iodine-125 seed moving at unknown speed during implantation in brachytherapy

Abstract

The aim of this study is to demonstrate the feasibility of estimating the strength of the moving radiation source during patient implantation. The requirement for the counting time was investigated by comparing the results of the measurements for the static source with those for the source moving at 2, 5, 10 and 20 cm s−1. The utilized source was 125I with an air-kerma strength of 0.432 U (μGym2h–1). The detector utilized was a plastic scintillation detector (8 cm × 5 cm × 2 cm in thickness) set at 8 cm away from the needle to guide the source. Experiments were conducted in order to determine the most desirable counting time. Analysis using the maximum of the measured values while the source passed through the needle indicated that the results for the moving source increased more than those for the static source as the counting time decreased. The combined standard uncertainty, with the coverage factor of 1, was within 4% at the counting time of 100 ms. This investigation supported the feasibility of the method proposed for estimating the source strength during the implantation procedure, regardless of the source speed. The method proposed is a potential option for reducing the risk of accidental replacements of sources with those of incorrect strengths.

Anin vitroverification of strength estimation for moving an 125I source during implantation in brachytherapy

“…Similarly, the length of the region in which the change in the counting rate was ~10% was ~30 to 50 mm. These lengths are comparable to those in the previous study [ 9 ]. The previous study showed the uncertainty from a source speed variation of 2–20 cm/s was within 2.3% for a counting time of 50 ms [ 9 ].…”

“…These lengths are comparable to those in the previous study [ 9 ]. The previous study showed the uncertainty from a source speed variation of 2–20 cm/s was within 2.3% for a counting time of 50 ms [ 9 ]. In this study, the source speed was assumed to be 10–20 cm/s.…”

“…A method for estimating the strength of a source while it is being implanted has been proposed as a backup for quality assurance [ 9 ]. The method for estimating the moving-source strength is briefly described here, and is described in detail in other publications [ 9 , 10 ]. Source strength measurement has been shown to be difficult during actual implantations because the speed of the source varies, as the source is moved manually.…”

“…The feasibility of the proposed method has been verified experimentally using a clinical source moving at different constant speeds for both a loose source [ 9 ] and linked sources [ 10 ]. In the present study, the validity of the proposed method was investigated for a source that was manually driven.…”

Strength estimation of a moving 125Iodine source during implantation in brachytherapy: application to linked sources

“…If necessary, the dose could then be reduced by increasing the distance between the sources. The estimation method proposed here has previously been suggested for use in loose 125 I source implants [ 9 , 10 ]. In the present study, this method has been applied to linked sources.…”