A quality assurance phantom for IMRT dose verification

Ma, C; Jiang, Steve B; Pawlicki, Todd; Chen, Y.; Li, J.S.; Deng, Jiaojiao; Lee, M.C.; Boyer, Arthur L.

doi:10.1109/iembs.2000.897938

Cited by 7 publications

(9 citation statements)

References 23 publications

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“…On one side, it is known that the dosimeters present some limitations for IMRT fields, due to the presence of high dose gradient, small fields or dynamic beam delivery [3]. On the other side, the use of homogeneous phantoms as a medium to verify measurements cannot provide direct checks of the accuracy of the patient dose calculation, since they do not represent a true and heterogeneous patient geometry [4]. In contrast to the measurements, Monte Carlo dose algorithms have shown to be a more reliable tool to improve dose accuracy, in such situations due to the ability to model realistic radiation transport through the accelerator treatment head, multileaf collimators (MLCs) and patientspecific geometry with heterogeneities.…”

Section: Introductionmentioning

confidence: 99%

The use of non-standard CT conversion ramps for Monte Carlo verification of 6 MV prostate IMRT plans

Zarza-Moreno

Cardoso²,

Teixeira

et al. 2013

Physica Medica

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Monte Carlo (MC) dose calculation algorithms have been widely used to verify the accuracy of intensity-modulated radiotherapy (IMRT) dose distributions computed by conventional algorithms due to the ability to precisely account for the effects of tissue inhomogeneities and multileaf collimator characteristics. Both algorithms present, however, a particular difference in terms of dose calculation and report. Whereas dose from conventional methods is traditionally computed and reported as the water-equivalent dose (D w ), MC dose algorithms calculate and report dose to medium (D m ). In order to compare consistently both methods, the conversion of MC D m into D w is therefore necessary.This study aims to assess the effect of applying the conversion of MC-based D m distributions to D w for prostate IMRT plans generated for 6 MV photon beams. MC phantoms were created from the patient CT images using three different ramps to convert CT numbers into material and mass density: a conventional four material ramp (CTCREATE) and two simplified CT conversion ramps: (1) air and water with variable densities and (2) air and water with unit density. MC simulations were performed using the BEAMnrc code for the treatment head simulation and the DOSXYZnrc code for the patient dose calculation. The conversion of D m to D w by scaling with the stopping power ratios of water to medium was also performed in a post-MC calculation process.The comparison of MC dose distributions calculated in conventional and simplified (water with variable densities) phantoms showed that the effect of material composition on dose-volume histograms (DVH) was less than 1% for soft tissue and about 2.5% near and inside bone structures. The effect of material density on DVH was less than 1% for all tissues through the comparison of MC distributions performed in the two simplified phantoms considering water. Additionally, MC dose distributions were compared with the predictions from an Eclipse treatment planning system (TPS), which employed a pencil beam convolution (PBC) algorithm with Modified Batho Power Law heterogeneity correction. Eclipse PBC and MC calculations (conventional and simplified phantoms) agreed well (<1%) for soft tissues. For femoral heads, differences up to 3% were observed between the DVH for Eclipse PBC and MC calculated in conventional phantoms. The use of the CT conversion ramp of water with variable densities for MC simulations showed no dose discrepancies (0.5%) with the PBC algorithm. Moreover, converting D m to D w using mass stopping power ratios resulted in a significant shift (up to 6%) in the DVH for the femoral heads compared to the Eclipse PBC one. Our results show that, for prostate IMRT plans delivered with 6 MV photon beams, no conversion of MC dose from medium to water using stopping power ratio is needed. In contrast, MC dose calculations using water with variable density may be a simple way to solve the problem found using the dose conversion method based on the stopping power ratio.

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Section: Introductionmentioning

confidence: 99%

The use of non-standard CT conversion ramps for Monte Carlo verification of 6 MV prostate IMRT plans

Zarza-Moreno

Cardoso²,

Teixeira

et al. 2013

Physica Medica

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“…As noted above, the complexity of IMRT plans has created such concern that they are applied to a phantom for confirmation before delivery to the patient (2,3,17). The algorithms used in modern therapy planning software are becoming progressively more sophisticated but, on the other hand, it is still common to find clinics wherein inhomogeneity correction is not applied to lung plans despite clear evidence that this leads to a change in delivered dose (18,19,20).…”

Section: Introductionmentioning

confidence: 99%

An analysis of an implantable dosimeter system for external beam therapy

Black¹,

Scarantino

Mann³

et al. 2005

International Journal of Radiation Oncology*Biology*Physics

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“…Phantoms are typically constructed using either water or water-equivalent plastic. 65,68,[149][150][151][152] Open water phantoms can be used when the beam is perpendicular to the phantom surface, and where great flexibility in detector positioning is desired. With the proper procedures and design, water-equivalent plastic phantoms can support multiple detectors, radiographic film, and rapid and efficient setup reproducibility.…”

Section: Iiia1 Phantom Selection For Imrtmentioning

confidence: 99%

Dosimetry tools and techniques for IMRT

et al. 2011

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Intensity modulated radiation therapy ͑IMRT͒ poses a number of challenges for properly measuring commissioning data and quality assurance ͑QA͒ radiation dose distributions. This report provides a comprehensive overview of how dosimeters, phantoms, and dose distribution analysis techniques should be used to support the commissioning and quality assurance requirements of an IMRT program. The proper applications of each dosimeter are described along with the limitations of each system. Point detectors, arrays, film, and electronic portal imagers are discussed with respect to their proper use, along with potential applications of 3D dosimetry. Regardless of the IMRT technique utilized, some situations require the use of multiple detectors for the acquisition of accurate commissioning data. The overall goal of this task group report is to provide a document that aids the physicist in the proper selection and use of the dosimetry tools available for IMRT QA and to provide a resource for physicists that describes dosimetry measurement techniques for purposes of IMRT commissioning and measurement-based characterization or verification of IMRT treatment plans. This report is not intended to provide a comprehensive review of commissioning and QA procedures for IMRT. Instead, this report focuses on the aspects of metrology, particularly the practical aspects of measurements that are unique to IMRT. The metrology of IMRT concerns the application of measurement instruments and their suitability, calibration, and quality control of measurements. Each of the dosimetry measurement tools has limitations that need to be considered when incorporating them into a commissioning process or a comprehensive QA program. For example, routine quality assurance procedures require the use of robust field dosimetry systems. These often exhibit limitations with respect to spatial resolution or energy response and need to themselves be commissioned against more established dosimeters. A chain of dosimeters, from secondary standards to field instruments, is established to assure the quantitative nature of the tests. This report is intended to describe the characteristics of the components of these systems; dosimeters, phantoms, and dose evaluation algorithms. This work is the report of AAPM Task Group 120.

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A quality assurance phantom for IMRT dose verification

Cited by 7 publications

References 23 publications

The use of non-standard CT conversion ramps for Monte Carlo verification of 6 MV prostate IMRT plans

The use of non-standard CT conversion ramps for Monte Carlo verification of 6 MV prostate IMRT plans

An analysis of an implantable dosimeter system for external beam therapy

Dosimetry tools and techniques for IMRT

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