Abstract
Purpose: To integrate the AAPM Task Group 43 (TG‐43) brachytherapy dose calculation formalism directly into a new plastic scintillator dosimeter system. Method and Materials: A novel plastic scintillator system specifically designed to obtain the dose distribution in three dimensions in real time around low‐energy x‐ray‐emitting prostate brachytherapy seeds has been constructed. The small sensitive volume (0.5 mm diameter × 0.5 mm thick) allows unprecedented resolution in dose‐mapping of brachytherapy sources. High sensitivity is achieved by proprietary electronic signal acquisition and processing methods, allowing measurements of the very low dose rates (down to 1 mGy / h) at distances of up to several centimeters from a seed mounted in a water phantom. The computer program that controls this automated dosimeter system has been designed to acquire and display data directly in the format specified by the AAPM TG‐43 protocol for calculating brachytherapy seed dose distributions in terms of radial dose function and anisotropy function. Results: The dose distributions around typical I‐125 and Pd‐103 prostate brachytherapy seeds have been measured. A comparison of the results to published TG‐43 data for several seed models shows excellent agreement in most cases. Anisotropy functions at distances closer to the seed than those published for thermoluminescent dosimeter (TLD) measurements of an I‐125 seed have been measured. In one case, use of this dosimeter allowed the rapid identification of a seed with an anomalous anisotropy function, later confirmed by a radiochromic film contact‐exposure measurement. Conclusions: The automation of this new, high sensitivity, high‐resolution plastic scintillator dosimeter, incorporating the TG‐43 dose calculation formalism, has allowed real‐time characterization of the dose distribution around prostate brachytherapy seeds in a liquid water phantom. Conflict of Interest: This work supported by NIST SBIR Grant SB1341‐03‐W‐0815 and NSF Grant Nos. 0097450 and 0453430.
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