Stereotactic dose perturbation from an aneurysm clip measured by Gafchromic®EBT film

Abstract

Aneurysm clips within stereotactic treatment volumes enhance spatial accuracy but perturb the dose distribution. The dose perturbations caused by a standard titanium alloy aneurysm clip (Ti6Al4V) have been measured with Gafchromic EBT film. The maximum dose perturbation was an increase of 6 % within 0.5 mm of the beam entry surface of the clip, and a decrease of 7 % within 0.5 mm of the beam exit surface of the clip. Results also showed perturbations to film readout due to the presence of micro dust particles on the film affecting optical properties at high spatial resolution (21um) scanning. Special procedures should be used when film is immersed in water, dried and then read at high spatial resolution. We recommend that films should be immersed only in distilled water and tools such as canned air puffs should be used to clean films without scratches.

Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG‐55

“…RCF can be used to measure beam characteristics, such as output factors, percent depth doses, tissue maximum ratio, and dose profiles (including far off central axis and penumbra) for small fields collimated with jaws, 193–195 MLC 19,174,196–199 and cone applicators 200–207 in conventional linac, CyberKnife (CK) 197 and Gamma Knife (GK), 208 and Helical TomoTherapy (HT) 209 . Most studies for small fields were performed with RCF positioned in a water equivalent solid phantom, and some were carried out in a liquid water phantom 182,200,210 . Raw output factors for small fields using RCF were found to be different than those obtained using MC simulation, diode, and pinpoint ion chambers 195,200,201,203,205,211 .…”

“…Dose distributions in liquid water can be measured accurately. 48,61,83,[181][182][183] RCF can be used for patient-specific QA (PSQA) in conformal radiation therapy 170 and routine machine mechanical QA tasks, including coincidence of the light/radiation field, flatness/symmetry of the radiation field, star pattern for gantry, collimator and couch rotations, and MLC leaf positioning accuracy (e.g., picket fence test). [184][185][186][187] The RTQA2 film with a flatbed scanner is also acceptable for measurement of beam dimensions, as in MLC offsets and secondary jaw calibrations within 0.5 mm accuracy.…”

Dose and absorption spectra response of EBT2 Gafchromic film to high energy x-rays

“…Historically these have included MD-55 and HS film [6][7][8][9][10][11][12] , ISP's films designed specifically for radiotherapy applications where large doses (up to 30 Gy) are required, XR-R films [13][14][15] for high dose diagnostic imaging applications through to films such as XRQA [16][17] which is designed for low dose assessment at kilovoltage x-ray energies. Probably the most used film for radiation dosimetry in therapy applications has been Gafchromic EBT film [18][19][20][21][22][23][24] . Its properties have included lowest energy dependence of any film type dosimeter, radiation sensitivity matched to therapy applications (1-2Gy), flexibility and easy analysis with a common desktop scanner.…”

Scanner uniformity improvements for radiochromic film analysis with matt reflectance backing

“…The low X-ray energy dependence of radiochromic films [1,2] make them clinically useful in both kilovoltage X-ray applications [3][4][5][6][7] and high energy X-ray applications [8][9][10][11]. Radiochromic films that are commonly used in these applications include Gafchromic EBT and EBT2 films.…”