Dose measurements for gamma knife with radiophotoluminescent glass dosemeter and radiochromic film

The small fields in radiotherapy are widely used due to the development of techniques such as intensity-modulated radiotherapy and stereotactic radio surgery. The measurement of the dose distributions for small fields is a challenge. A perfect dosimeter should be independent of the radiation energy and the dose rate and should have a negligible volume effect. The radiochromic (RC) film characteristics fit well to these requirements. However, the response of RC films and their digitizing processes present a significant spatial inhomogeneity problem. The present work uses a method for two-dimensional (2D) measurement with RC films based on the reduction of the spatial inhomogeneity of both the film and the film digitizing process. By means of registering and averaging several measurements of the same field, the inhomogeneities are mostly canceled. Measurements of output factors (OFs), dose profiles (in-plane and cross-plane), and 2D dose distributions are presented. The field sizes investigated are 0.5 × 0.5 cm2, 0.7 × 0.7 cm2, 1 × 1 cm2, 2 × 2 cm2, 3 × 3 cm2, 6 × 6 cm2, and 10 × 10 cm2 for 6 and 15 MV photon beams. The OFs measured with the RC film are compared with the measurements carried out with a PinPoint ionization chamber (IC) and a Semiflex IC, while the measured transversal dose profiles were compared with Monte Carlo simulations. The results obtained for the OFs measurements show a good agreement with the values obtained from RC films and the PinPoint and Semiflex chambers when the field size is greater or equal than 2 × 2 cm2. These agreements give confidence on the accuracy of the method as well as on the results obtained for smaller fields. Also, good agreement was found between the measured profiles and the Monte Carlo calculated profiles for the field size of 1 × 1 cm2. We expect, therefore, that the presented method can be used to perform accurate measurements of small fields.

show abstract

“…It is therefore important to have methods for the precise measurement of the dose for these kinds of fields. [ 1 2 3 ]…”

Section: Introductionmentioning

confidence: 99%

Small fields measurements with radiochromic films

González‐López¹,

Vera-Sánchez²,

Lago-Martin³

2015

J Med Phys

View full text Add to dashboard Cite

show abstract

“…Radiochromic film has been used by several groups for small-field SRS dose measurements (Ralston et al 2012, Gagnon et al 2011, Hsu et al 2011, Hardcastle et al 2011, because it is close to being dosimetrically water equivalent, has high spatial resolution, minimal energy dependence (Butson et al 2010), and provides a two-dimensional map of measured dose, requiring no chemical processing. However it is not a 'real-time' dosimeter and can have large uncertainties stemming from film polarization, non-uniformity as well as scanner and handling techniques (Aland et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Characterization of small-field stereotactic radiosurgery beams with modern detectors

et al. 2013

View full text Add to dashboard Cite

To derive accurate beam models for stereotactic radiosurgery (SRS) planning it is necessary to characterize the beam with dosimetric measurements. The aim of this study is to identify the best detectors for each task in the characterization process. Output ratios, beam profiles and percentage depth doses were measured for SRS cone diameters of 5-45 mm. Commercially available and emerging detectors were used: Gafchromic EBT2 film, an air-core fibre optic dosimeter (FOD) (developed at Royal Prince Alfred Hospital, Sydney), an IBA stereotactic field diode, a PTW 60012 electron diode and an IBA cc01 small volume thimble ion chamber. Analysis of the measured data supported by baseline Monte Carlo simulation data, led to the following recommendations: (1) water-equivalent detectors (Gafchromic EBT2 film or FOD) are the preferred choice for SRS dosimetry, (2) ion chambers (including small volume chambers with high-density central electrodes) should be avoided due to volume averaging effects and energy dependence, (3) if diodes are used, corrections must be made to account for their over-response in small fields.

show abstract

“…Measurements are often performed using a combination of a near-water-equivalent sphere (e.g. a Lucy phantom (Standard Imaging, Middleton, WI)), an ion chamber, and radiochromic films (Ma et al 2000, Bank 2002, Novotny et al 2009, Hsu et al 2011, McDonald et al 2011, Mancosu et al 2015. With the water equivalence of both components, the combination of a PSD with a Lucy phantom appears to be a promising method towards performing reliable quality assurance of the beam.…”

Section: Introductionmentioning

confidence: 99%

Quality assurance for Gamma Knife Perfexion using the Exradin W1 plastic scintillation detector and Lucy phantom

et al. 2019

View full text Add to dashboard Cite

The goal of this work is to validate the use of the Exradin W1 plastic scintillation detector (PSD) to measure profiles and output factors from Gamma Knife Perfexion collimators in a Lucy phantom. The Exradin W1 PSD has a small-volume, near-water-equivalent, energy-independent sensitive element. Output measurements were performed for all 3 collimators (4 mm, 8 mm, and 16 mm) of the Gamma Knife Perfexion system, and these measurements were compared to measurements made with an A16 ion chamber and an EBT3 film and to the nominal values. We showed that a configuration in which the focus or ‘shot’ moves while the detector remains fixed is essentially equivalent to a configuration in which the focus is fixed while the detector moves. A Lucy phantom containing a PSD was moved in small steps to acquire profiles in all three dimensions. EBT3 film was inserted in the Lucy phantom and exposed to a single shot for each collimator. The relative values for output factors measured with the PSD were 1.000, 0.892, and 0.795, for the 16 mm, 8 mm, and 4 mm collimators, respectively. The values measured with EBT3 film were 1.000, 0.881, and 0.793, and the values measured with the A16 ion chamber were 1.000, 0.883, and 0.727. The nominal output factors for the Gamma Knife Perfexion are 1.000, 0.900, and 0.814, respectively. There was excellent agreement between all profiles measured with the PSD and EBT3 as well as with the treatment planning system data provided by the vendor. In light of our results, the Exradin W1 PSD is well suited for beam quality assurance of a Gamma Knife Perfexion irradiator.

show abstract

Dose measurements for gamma knife with radiophotoluminescent glass dosemeter and radiochromic film

Cited by 8 publications

References 4 publications

Small fields measurements with radiochromic films

Small fields measurements with radiochromic films

Characterization of small-field stereotactic radiosurgery beams with modern detectors

Quality assurance for Gamma Knife Perfexion using the Exradin W1 plastic scintillation detector and Lucy phantom

Contact Info

Product

Resources

About