I‐125 ROPES eye plaque dosimetry: Validation of a commercial 3D ophthalmic brachytherapy treatment planning system and independent dose calculation software with GafChromic^® EBT3 films

Abstract

The doses calculated by PS and RADCALC(®) for uniformly loaded ROPES plaques in full and uniform scattering conditions were validated by the EBT3 film measurements. The stainless steel plaque backing was observed to decrease the measured dose by 4%. Through the introduction of a scalar correction factor (0.96) in PS, the dose homogeneity effect of the stainless steel plaque backing was found to agree with the measured EBT3 film measurements.

AAPM recommendations on medical physics practices for ocular plaque brachytherapy: Report of task group 221

“…This prototype device can determine the dose distribution from plaques loaded with 125 I, and may be useful with other low‐energy photon‐emitting radionuclides such as 103 Pd and 131 Cs . Measurements for dose‐rate distribution of 125 I plaques as stipulated in the TG‐129 report have used diodes, X‐Omat V radiographic film, MD‐55 radiochromic film, and more recently GafChromic EBT3 ® film …”

A Polymer-Gel Eye-Phantom for 3D Fluorescent Imaging of Millimetre Radiation Beams

“…For a cell containing an RFG gel the values were 0.89 and 0.47 Gy/min; a decrease by 0.528. The decrease in dose rate between the incident and exit films is due to the conical expansion of the beam from z1 (47.6 cm) to z2 (50.0 cm) and to photon attenuation in the intervening media, D'(z2)/D'(z1) = (z1/z2) 2 In (3) M, ρ and δ are the mass attenuation coefficient, the gravimetric density and the length of the attenuating medium respectively. For the air-containing cell the attenuation by the cell contents is negligible and the overall decrease by a factor of 0.71 leads to a value of 2[Mρδ]glass = 0.244.…”

Radiochromic film calibration for low-energy seed brachytherapy dose measurement

“…The reference dose was determined using TG-43 tabulated data 8 in water with a conversion factor 25 of 1.14 ± 1.5% applied to account for the PMMA material of the phantom. This setup was used as opposed to previously described I-125 film calibration methods 9,26 so that any azimuthal variations in the seed construction could be averaged as well as variations in the film thickness, as recommended by the film manufacturer. 22 The films were irradiated to nine different reference dose levels ranging from 13.4 to 3408 cGy in geometric progression.…”

“…Due to the spatially nonuniform dose delivery by the I-125 brachytherapy seed, the measurement region was reduced to a smaller 2.47 × 2.47 mm 2 area in the centre of the film within the maximum exposure region to determine the impact this would have on the resulting calibration curve. Previous film measurements using brachytherapy seeds for calibration used regions much smaller than those suggested by the film manufacturer, 9,14,26 who recommends using film pieces at least 25 cm 2 in size. 40 Such a large measurement area is required to ensure an average film response that is not affected by local heterogeneities in the film, which may not be achieved if the measurement area is too small.…”