Application of radiochromic gel dosimetry to commissioning of a megavoltage research linear accelerator for small–field animal irradiation studies

Journal Article · Wed Dec 30 00:00:00 EST 2020 · Medical Physics

DOI:https://doi.org/10.1002/mp.14685· OSTI ID:1783602

Ba Sunbul, Noora ^[1]; Oraiqat, Ibrahim ^[2]; Rosen, Benjamin ^[3]; Miller, Cameron ^[3]; Meert, Christopher ^[3]; Matuszak, Martha M. ^[3]; Clarke, Shaun ^[3]; Pozzi, Sara ^[3]; Moran, Jean M. ^[3]; El Naqa, Issam ^[2]

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1. Univ. of Michigan, Ann Arbor, MI (United States); University of Michigan
2. Univ. of Michigan, Ann Arbor, MI (United States); H. Lee Moffitt Cancer Center and Research Inst., Tampa, FL (United States)
3. Univ. of Michigan, Ann Arbor, MI (United States)

To develop and implement an efficient and accurate commissioning procedure for small-field static beam animal irradiation studies on an MV research linear accelerator (Linatron-M9) using radiochromic gel dosimetry. The research linear accelerator (Linatron-M9) is a 9 MV linac with a static fixed collimator opening of 5.08 cm diameter. Lead collimators were manually placed to create smaller fields of 2 × 2 cm², 1 × 1 cm², and 0.5 × 0.5 cm². Relative dosimetry measurements were performed, including profiles, percent depth dose (PDD) curves, beam divergence, and relative output factors using various dosimetry tools, including a small volume ionization chamber (A14), GAFCHROMIC™ EBT3 film, and Clearview gel dosimeters. The gel dosimeter was used to provide a 3D volumetric reference of the irradiated fields. The Linatron profiles and relative output factors were extracted at a reference depth of 2 cm with the output factor measured relative to the 2 × 2 cm² reference field. Absolute dosimetry was performed using A14 ionization chamber measurements, which were verified using a national standards laboratory remote dosimetry service. Absolute dosimetry measurements were confirmed within 1.4% (k = 2, 95% confidence = 5%). The relative output factor of the small fields measured with films and gels agreed with a maximum relative percent error difference between the two methods of 1.1 % for the 1 × 1 cm² field and 4.3 % for the 0.5 × 0.5 cm² field. These relative errors were primarily due to the variability in the collimator positioning. The measured beam profiles demonstrated excellent agreement for beam size (measured as FWHM), within approximately 0.8 mm (or less). Film measurements were more accurate in the penumbra region due to the film’s finer resolution compared with the gel dosimeter. Following the van Dyk criteria, the PDD values of the film and gel measurements agree within 11% in the buildup region starting from 0.5 cm depth and within 2.6 % beyond maximum dose and into the fall-off region for depths up to 5 cm. The 2D beam profile isodose lines agree within 0.5 mm in all regions for the 0.5 × 0.5 cm² and the 1 × 1 cm² fields and within 1 mm for the larger field of 2 × 2 cm². The 2D PDD curves agree within approximately 2% of the maximum in the typical therapy region (1–4 cm) for the 1 × 1 cm² and 2 × 2 cm² and within 5% for the 0.5 × 0.5 cm² field. This work provides a commissioning process to measure the beam characteristics of a fixed beam MV accelerator with detailed dosimetric evaluation for its implementation in megavoltage small animal irradiation studies. Radiochromic gel dosimeters are efficient small-field relative dosimetry tools providing 3D dose measurements allowing for full representation of dose, dosimeter misalignment corrections and high reproducibility with low inter-dosimeter variability. Altogether, radiochromic gels are valuable for fast, full relative dosimetry commissioning in comparison to films for application in high-energy small-field animal irradiation studies.

• Research Organization: Univ. of Michigan, Ann Arbor, MI (United States)
• Sponsoring Organization: National Institutes of Health; US Department of Homeland Security, Countering Weapons of Mass Destruction Office, Academic Research Initiative; USDOE National Nuclear Security Administration (NNSA), Office of Nonproliferation and Verification Research and Development
• Grant/Contract Number: NA0003920
• OSTI ID: 1783602
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 3 Vol. 48; ISSN 0094-2405
• Publisher: American Association of Physicists in Medicine
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
animal irradiator and small-field dosimetry
commissioning
gel dosimetry