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A practical three‐dimensional dosimetry system for radiation therapy
Author(s) -
Guo Pengyi,
Adamovics John,
Oldham Mark
Publication year - 2006
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 - 10.1118/1.2349686
Subject(s) - dosimeter , dosimetry , scanner , optics , materials science , radiation treatment planning , computer science , medical physics , nuclear medicine , physics , radiation therapy , medicine
There is a pressing need for a practical three‐dimensional (3D) dosimetry system, convenient for clinical use, and with the accuracy and resolution to enable comprehensive verification of the complex dose distributions typical of modern radiation therapy. Here we introduce a dosimetry system that can achieve this challenge, consisting of a radiochromic dosimeter (PRESAGE™) and a commercial optical computed tomography (CT) scanning system (OCTOPUS™). PRESAGE™ is a transparent material with compelling properties for dosimetry, including insensitivity of the dose response to atmospheric exposure, a solid texture negating the need for an external container (reducing edge effects), and amenability to accurate optical CT scanning due to radiochromic optical contrast as opposed to light‐scattering contrast. An evaluation of the performance and viability of the PRESAGE™/OCTOPUS, combination for routine clinical 3D dosimetry is presented. The performance of the two components (scanner and dosimeter) was investigated separately prior to full system test. The optical CT scanner has a spatial resolution of ≤ 1 mm , geometric accuracy within 1 mm , and high reconstruction linearity (with aR 2value of 0.9979 and a standard error of estimation of ∼ 1 % ) relative to independent measurement. The overall performance of the PRESAGE™/OCTOPUS system was evaluated with respect to a simple known 3D dose distribution, by comparison withGAFCHROMIC ®EBT film and the calculated dose from a commissioned planning system. The “measured” dose distribution in a cylindrical PRESAGE™ dosimeter ( 16 cm diameter and 11 cm height) was determined by optical‐CT, using a filtered backprojection reconstruction algorithm. A three‐way Gamma map comparison (4% dose difference and 4 mm distance to agreement), between the PRESAGE™, EBT and calculated dose distributions, showed full agreement in measurable region of PRESAGE™ dosimeter ( ∼ 90 % of radius). The EBT and PRESAGE™ distributions agreed more closely with each other than with the calculated plan, consistent with penumbral blurring in the planning data which was acquired with an ion chamber. In summary, our results support the conclusion that the PRESAGE™ optical‐CT combination represents a significant step forward in 3D dosimetry, and provides a robust, clinically effective and viable high‐resolution relative 3D dosimetry system for radiation therapy.