Measurement of brachytherapy sources using MAGIC gel

Heard, M

doi:10.1088/1742-6596/3/1/032

Cited by 6 publications

(4 citation statements)

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“…Hence, the significant sensitivity increase observed cannot be attributed to the low energy of 125 I. In view of corresponding reported findings (Heard andIbbot 2004, De Deene 2004), this sensitivity increase should be considered in relation to the low dose rate of 125 I sources and/or the prolonged irradiation time period required to achieve sufficient absorbed dose values.…”

Section: Polymer Gel Response To the 125 I Energiesmentioning

confidence: 70%

“…This agreement serves as an indirect confirmation of the calibration curve measured from data for source 1, and especially the increased dose sensitivity value measured for 125 I, irrespective of the reasons accounting for this behaviour. In view of these findings for the gel dose response in 125 I irradiations, a feasible experimental procedure for the dosimetry of 125 I and other low dose rate sources, which could be used at least supplementary to the established experimental setup of TLDs in solid water phantoms, is to irradiate the same gel sample with both a wellcharacterized source and a new source as originally proposed by Heard and Ibbot (2004) and performed in this work. This would allow for the derivation of a dose response calibration curve using experimental data obtained from the well-characterized source, which then could be used to perform absolute dosimetry for the new source design.…”

Section: Absolute Polymer Gel Dosimetrymentioning

confidence: 98%

“…To our knowledge, there are only two polymer gel dosimetry studies of an 125 I source in the literature (Ibbott et al 1999, Heard and. Ibbott et al (1999) used BANG polymer gel calibrated using a 6 MV LINAC photon beam, while Heard and Ibbot (2004) used MAGIC polymer gel calibrated using a well-characterized 125 I source to measure the dose distribution of a different type of 125 I source. However, results presented in both studies were limited and were either not compared (Ibbott et al 1999) or in disagreement (Heard and Ibbot 2004) with expected, relative dose distributions.…”

Section: Introductionmentioning

confidence: 99%

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Polymer gel dosimetry close to an¹²⁵I interstitial brachytherapy seed

et al. 2005

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Despite its advantages, the polymer gel-magnetic resonance imaging (MRI) method has not, as yet, been successfully employed in dosimetry of low energy/low dose rate photon-emitting brachytherapy sources such as 125I or 103Pd interstitial seeds. In the present work, two commercially available 125I seed sources, each of approximately 0.5 U, were positioned at two different locations of a polymer gel filled vial. The gel vial was MR scanned with the sources in place 19 and 36 days after seed implantation. Calibration curves were acquired from the coupling of MRI measurements with accurate Monte Carlo dose calculations obtained simulating the exact experimental setup geometry and materials. The obtained gel response data imply that while linearity of response is sustained, sensitivity (calibration curve slope) is significantly increased (approximately 60%) compared to its typical value for the 192Ir (or 60Co and 6 MV LINAC) photon energies. Water equivalence and relative energy response corrections of the gel cannot account for more than 3-4% of this increase, which, therefore, has to be mainly attributed to physicochemical processes related to the low dose rate of the sources and the associated prolonged irradiation time. The calibration data obtained from one 125I source were used to provide absolute dosimetry results for the other 125I source, which were found to agree with corresponding Monte Carlo calculations within experimental uncertainties. It is therefore suggested that, regardless of the underlying factors accounting for the gel dose response to 125I irradiations, polymer gel dosimetry of new 125I or 103Pd sources should be carried out as originally proposed by Heard and Ibbot (2004 J. Phys.: Conf. Ser. 3 221-3), i.e., by irradiating the same gel sample with the new low dose rate source, as well as with a well-characterized low dose rate source which will provide the dose calibration curve for the same irradiation conditions.

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Section: Polymer Gel Response To the 125 I Energiesmentioning

confidence: 70%

Section: Absolute Polymer Gel Dosimetrymentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Polymer gel dosimetry close to an¹²⁵I interstitial brachytherapy seed

et al. 2005

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“…The large and varied body of literature pertaining to polymer gel dosimetry applications confirms the value and versatility of the technique. In addition, the recent gel dosimetry conference, DOSGEL2004, had many contributions on the applications of polymer gel dosimetry using MRI [176][177][178][179][180][181][182][183] and OCT [134,135], including one novel application to diagnostic imaging [142]. The large number of these very recent papers highlights the increasing relevance of such work.…”

Section: Gel Applicationsmentioning

confidence: 99%

Investigations in x‐ray computed tomography polyacrylamide gel dosimetry

Hilts¹

2005

Medical Physics

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Polyacrylamide gels (PAGs) are radiosensitive materials currently under development for use as three dimensional (3D) dosimeters in radiation therapy. Dose information is recorded in the gels and extracted through imaging. X-ray computed tomography (CT) has emerged as a promising gel imaging method due to a change in gel density that occurs upon irradiation. The accessibility of CT technology to cancer hospitals makes CT read-out clinically attractive, however the technique remains of limited clinical use due in part to poor dose resolution. This thesis investigates the use of CT for extracting dose information from PAG with an overall goal to improve achievable dose resolution. Thesis results are divided into three studies: a gel compositional study, a study of noise and dose resolution and a digital filtering study. The first study investigates the effects of gel composition on PAG CT dose response and the underlying density change. Systems for irradiating and imaging gels are designed and tested and dose response reproducibility is established. Results indicate dramatic variation in CT dose response sensitivity and range with gel composition. A model is developed to describe gel density change with dose, revealing two fundamental properties of the density to dose response: the density change that occurs per unit polymer yield is highest for gels with low and high concentrations of crosslinking molecule (%C) and the dose response sensitivity is linearly dependent on the total concentration of monomer in the gel. The second study investigates strategies for minimizing noise in x-ray CT polymer gel dosimetry and assesses system performance. Specifically, the effects of phantom design, scanning technique and image voxel size on image noise are investigated. This work leads to the establishment of a method of predicting image noise for any given CT imaging protocol. Image uniformity is also assessed, in the context of noise levels in gel dosimetry. The effect of scanning protocol on imaging time is established and the dose resolution achievable with an optimized system is calculated given voxel size and imaging time constraints. These results, when compared with published values for MRI and optical CT gel dosimetry indicate that CT dose resolution (e.g. 5%, 1x1x3 mm 3 voxels), is still not at the level of the best MRI or optical CT techniques, however fast imaging times makes the rapid acquisition of volumetric data most feasible with x-ray CT. The third study investigates the potential of image filtering for improved dose resolution in CT gel dosimetry. CT image noise is characterized as Gaussian distributed and independent of signal strength and niters for reducing spatially invariant noise are investigated: mean, median, midpoint, adaptive mean, alphatrimmed mean, sigma mean and a relatively new filter called SUSAN. The filters are tested on a CT image of a PAG irradiated with a clinically relevant dose distribution. Filter performance varies greatly in both achieved dose resolution and affects on the spatial di...

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Radiation Dosimetry, Three‐Dimensional

Ibbott

2006

Encyclopedia of Medical Devices and Instrumentation

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Accurate delivery of radiation therapy is essential for the treatment to have the greatest probability of success. Determining the dose delivered by radiation beams and radioactive sources requires complex dosimetry procedures and sophisticated computerized treatment planning software. Validating the software to assure its accuracy is an essential component of the quality assurance program in a radiation therapy department. In recent years, radiation therapy has evolved to take advantage of new treatment delivery capabilities and ever‐more complex treatment planning techniques. These techniques allow the dose distribution to be tailored to closely match the shape of the target volume and avoid nearby sensitive tissues. Consequently, dosimetric validation devices must also allow the accurate measurement of dose in three dimensions. Conventional dosimetry systems measure the dose at a point or in a plane, and mapping a 3D dose distribution is difficult at best. As a result, there is a need for a reliable 3D radiation dosimetry system, with the capability of integrating the dose from a complex, and possibly dynamic treatment, so that the delivered dose can be mapped and compared with computer simulations. Today, the only true 3D dosimeters are radiosensitive gels and plastics that can be constructed to fill volumes and conform to complex surfaces. The science behind these dosimeters is developing rapidly, and their routine use in the clinic is believed to be imminent.

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Measurement of brachytherapy sources using MAGIC gel

Cited by 6 publications

References 4 publications

Polymer gel dosimetry close to an¹²⁵I interstitial brachytherapy seed

Polymer gel dosimetry close to an¹²⁵I interstitial brachytherapy seed

Investigations in x‐ray computed tomography polyacrylamide gel dosimetry

Radiation Dosimetry, Three‐Dimensional

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Measurement of brachytherapy sources using MAGIC gel

Cited by 6 publications

References 4 publications

Polymer gel dosimetry close to an125I interstitial brachytherapy seed

Polymer gel dosimetry close to an125I interstitial brachytherapy seed

Investigations in x‐ray computed tomography polyacrylamide gel dosimetry

Radiation Dosimetry, Three‐Dimensional

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Polymer gel dosimetry close to an¹²⁵I interstitial brachytherapy seed

Polymer gel dosimetry close to an¹²⁵I interstitial brachytherapy seed