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TU‐FF‐A2‐06: The Verification of Respiratory‐Gated Radiation Treatments Using 3D Dosimetry Techniques
Author(s) -
Brady S,
Sakhalkar H,
Maurer J,
Yoo S,
Adamovics J,
Gluckman G,
Oldham M
Publication year - 2008
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 - 10.1118/1.2962649
Subject(s) - imaging phantom , dosimeter , dosimetry , scanner , materials science , eclipse , nuclear medicine , radius , biomedical engineering , computer science , physics , optics , medicine , astronomy , computer security
Purpose: This work investigates the feasibility of verifying respiratory gated treatments using a new 3D dosimetry system consisting of a radiochromic plastic (PRESAGE™) with optical‐CT readout. Method and Materials: Three identical PRESAGE™ dosimeters (5cm radius × 5cm length) were manufactured for insertion into a CIRS' Dynamic Thorax Phantom. CT scans of the phantom were acquired corresponding to 3 motion scenarios; (1) static CT (no motion), (2) moving non‐gated CT (free‐breathing), and (3) moving gated CT. In the moving scans, the PRESAGE™ insert sinusoidally oscillated in the sup‐inf direction with a 3cm amplitude and 4.5sec period. A simple plan with AP/PA parallel opposed beams was created in the Eclipse planning system to treat a simulated small lung nodule (1.5cm), central to the insert, for all 3 scenarios. The simple plan enabled accurate independent measurement using EBT films. Each plan was then delivered to the phantom twice, first containing the PRESAGE™ insert and second the EBT insert. The gated treatments were delivered using the Varian RPM gating system. The dose recorded in the PRESAGE™ dosimeters was determined by optical‐CT using a novel, fast, in‐house CCD based scanner, which acquired all data in ∼10min. The doses among PRESAGE™, EBT, and Eclipse were compared. Results: In the cases of static and moving gated treatments, excellent agreement (<1mm distance‐to‐agreement) was observed between the PRESAGE™ and EBT measurements. For the moving non‐gated treatment, good agreement was again observed between PRESAGE™ and EBT. Significant differences are seen between the PRESAGE™/EBT films and the Eclipse distribution due to the modeling effects of penumbral broadening at small fields. Conclusion: The combination of small field sizes and sophisticated gating techniques represents a challenging scenario for dosimetry verification. The PRESAGE™ /optical‐CT 3D dosimetry system is demonstrated to achieve high quality, fast, relative dosimetry verification of gating treatments.