Dosimetric consideration of individual 125I source strength measurement and a large-scale comparison of that measured with a nominal value in permanent prostate implant brachytherapy

Yutaka Takahashi, Akira Ito, Iori Sumida, Takuyo Kozuka, Kotaro Gomi, Takayuki Nose, Teruo Ito, Takashi Yamashita

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Purpose. We investigated the difference between measured and manufacturer's nominal source strength in a large sample of a single model of 125I seeds. Physical characteristics of single seed measurement by the well-type ionization chamber were also investigated to provide dosimetric data. Materials and methods. A well-type ionization chamber with a single seed holder was used to measure source strength of all 1935 125I seeds implanted in the initial 28 patients in our hospital. Physical characteristics including linearity of readings for different integral time intervals, reproducibility, isotropy, and axial positional sensitivity were assessed. To calculate the source strength, the integral charge during 30s was measured and converted to air kerma strength. The nominal activity stated by the manufacturer was compared with the measured value. Results. Linearity, reproducibility, and isotropy of the well-type ionization chamber were within 0.2%. Measured source strength was on average 2.1% (range -7.6% to +7.2%), lower than the nominal value. Standard deviation of all measured seeds was 2.0%. The maximum difference between the measured and the manufacturer's nominal source strength in each patient was -3.7%. The standard deviation averaged 1.6%. Conclusion. The nominal source strength of the 125I seeds agreed well with the measured value. Our study can be helpful as guidance for individual 125I seed source strength measurement.

Original languageEnglish (US)
Pages (from-to)675-679
Number of pages5
JournalRadiation Medicine - Medical Imaging and Radiation Oncology
Volume24
Issue number10
DOIs
StatePublished - Dec 2006

Bibliographical note

Funding Information:
Acknowledgments. This study was supported by a Grant-in-Aid for Scientific Research (grant 16591237) of the Japan Society f5or the Promotion of Science. It was also partly supported by a Grant-in-Aid for Scientific Research (grant 17790882) of the Japan Society for the Promotion of Science and for Cancer Research (17-10) of the Ministry of Health, Labour and Welfare.

Keywords

  • I seed
  • Measurement
  • Permanent prostate implant brachytherapy
  • Source strength
  • Well-type ionization chamber

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