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SU‐FF‐T‐38: Measurement of the Radial Dose and the Dose Anisotropy Functions for the New 192Ir Varian Source
Author(s) -
GamboadeBuen I,
Díaz P,
Poitevin A
Publication year - 2005
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 - 10.1118/1.1997709
Subject(s) - thermoluminescent dosimeter , imaging phantom , dosimeter , materials science , dosimetry , brachytherapy , nuclear medicine , dose profile , anisotropy , optics , physics , radiation therapy , medicine
Purpose: To measure the radial dose function and the dose anisotropy functions, used in the AAPM Task Group 43 dose calculation formalism, of the new192 Ir Varian Source model VS‐2000 utilized in high dose rate brachytherapy. Method and Materials: The measurements were carried out with TLD dosimeters and radiochromic dye films in a 30 × 30 × 30 cm 3 acrylic phantom with the192 Ir source positioned at the center. The new VariSource has an active length of 0.5 cm, and an active diameter of 0.34 mm. Measurements were made for distances between 2 and 7 cm from the source center using TLD‐100 (LiF:Mg,Ti) chips (3.1 × 3.1 × 0.89 mm 3 ) whereas for distances smaller than 2 cm Gafchromic HD‐810 film were used. TLD irradiations for each distance from the source center were made separately at approximately 2 Gy. TLD's were read using a Harshaw 3500 reader. Because of the high gradient dose near the source, HD‐810 films were exposed at three different doses and then digitized in RBG color scale obtaining three images based on the RGB channels. HD‐810 films were calibrated in a60 Co beam. Results: Dosimetric characteristics of the new Varian192 Ir source have been measured in an acrylic phantom using LiF TLD chips and HD‐810 radiochromic film. These measurements were performed following the AAPM TG‐43 task group recommendation. The radial dose and the dose anisotropy functions were measured in the range of 0.25 cm to 1.5 cm using HD‐810 radiochromic film and for distances between 2.0 cm and 7 cm using LiF TLD‐100 chips. The anisotropy function was measured from 5° to 180° relative to the source axis. Conclusion: Dosimetry data were presented for the new Varian192 Ir HDR source following the AAPM TG‐43 dosimetric formalism, for input and verification purposes in treatment planning systems.