Dose rate determination for sup 125 I seeds

Journal Article · Sat Sep 01 00:00:00 EDT 1990 · Medical Physics; (USA)

DOI:https://doi.org/10.1118/1.596586· OSTI ID:6209162

Chiu-Tsao, S ^[1]; Anderson, L L ^[2]; O'Brien, K ^[3]; Sanna, R ^[4]

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1. Department of Radiation Oncology, Henry Ford Hospital, Detroit, MI (USA)
2. Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY (USA)
3. Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ (USA)
4. Radiation Physics Division, Environmental Measurement Laboratory, New York, NY (USA)

Dose rates in water have been determined for the two types of {sup 125}I seed currently used in brachytherapy. The need for such determinations became evident when water/air ratios measured with a silicon diode were found to be lower than expected. Extensive measurements using lithium fluoride thermoluminescent dosimeters (TLD's) have been performed in a solid water phantom, at distances from 0.1 to 10 cm from the seed center and at angular increments of 10{degree}, 15{degree}, or 30{degree} within a plane through the seed axis. Dose calibration of the TLD's was accomplished by irradiation in air with {sup 125}I seeds of the same type and of strengths traceable to a calibration at the National Institute of Standards and Technology (NIST). Relative calibration of TLD's was monitored by irradiation, in an oven-type x-ray machine, of control dosimeters simultaneously and all dosimeters intercurrently with the {sup 125}I irradiations. Values obtained for the dose rate constant, i.e., dose rate per unit air-kerma strength at 1 cm on the transverse axis, were 0.853 and 0.932 cGy h{sup {minus}1} U{sup {minus}1} (1.08 and 1.18 cGy h{sup {minus}1} mCi{sup {minus}1}) for the 6711 and 6702 seeds, respectively. Measured data were supplemented with Monte Carlo-calculated relative dose rate data generated using the MORSE code. These calculations used 100 energy groups from 10 to 35.4 keV and involved energy collection bins ranging from 0.025 to 1.2 cm on an edge. Normalized at 1 cm, transverse axis calculated data are not significantly different from measured data (ours or cited literature) at distances either {lt}2.5 or {gt}8 cm. Normalized at different distances along the transverse axis, our off-axis calculated and measured distributions agree closely at all angles but differ from literature measured distributions at small ({le}1 cm) distances and, for small angles, increasingly at larger distances ({ge}5 cm).

• OSTI ID: 6209162
• Journal Information: Medical Physics; (USA), Journal Name: Medical Physics; (USA) Vol. 17:5; ISSN 0094-2405; ISSN MPHYA
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
655003* -- Medical Physics-- Dosimetry
BETA DECAY RADIOISOTOPES
DAYS LIVING RADIOISOTOPES
DOSE RATES
DOSIMETRY
ELECTRON CAPTURE RADIOISOTOPES
ENERGY RANGE
IMPLANTS
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPES
KEV RANGE
KEV RANGE 10-100
MEDICINE
MOCKUP
MONTE CARLO METHOD
NUCLEAR MEDICINE
NUCLEI
ODD-EVEN NUCLEI
PHANTOMS
RADIATION DOSE DISTRIBUTIONS
RADIATION SOURCE IMPLANTS
RADIATION SOURCES
RADIOISOTOPES
RADIOLOGY
RADIOTHERAPY
STRUCTURAL MODELS
THERAPY
THERMOLUMINESCENT DOSIMETRY