Precision dose measurement of 125I seed in solid water through SPECT/CT detecting.

PURPOSE:The aim of the study is to study the feasibility of gamma-ray-detection-based precision dose measurement of 125I seed brachytherapy in solid water. MATERIALS AND METHODS:Seven group 125I seeds with different activities were put into a hole in the center of solid water individually. Each group had ten seeds, and the seed activity ranged from 1.48 × 107 Bq to 3.7 × 107 Bq. Single-photon emission computed tomography/computed tomography (SPECT/CT) was used to scan the seeds perpendicular to the long axis of the seed, with a slice thickness of 3.75 mm. The radioactive count values (x) of the radioactive concentration around the seeds were collected at a distance of 1-15 mm from the center of the seeds, while the corresponding doses (Y) (Gy) were calculated. SPSS 18.0 was used to analyze the relationship between the count value and the dose. RESULTS:With the same seed activity, the count values became smaller according to the distance from the center of the seeds. The count values at the same point had an increasing trend according to the activity. This is similar to the doses calculated at the same point. There was an exponential relationship between the dose around the 125I seeds, and the radioactive count value detected by SPECT/CT. Correlative curves between the dose and radioactive count value detected by SPECT/CT of different-activity 125I seeds were fitted. The formulas of the dose and radioactive count with different seed activity were in the form of Y = b0 (b1)x. The constant b0 ranged from 1.48 to 3.93, according to the seed activity, while b1 was 1.006 for every seed's activity. CONCLUSION:The count value around the 125I seed can be detected accurately by SPECT/CT, and then can be quantified. This study provided useful experiment data for the precision measurement of 125I seed implantation. Radiation detection-based dose measurement may become a new noninvasive technology for the dynamic dosimetry verification method after brachytherapy.