An investigation of a new amorphous silicon electronic portal imaging device for transit dosimetry

Grein, Ellen; Lee, Richard; Luchka, K.

doi:10.1118/1.1508108

Cited by 77 publications

(63 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Their response characteristics with respect to various input parameters have been investigated by sev-eral groups, [4][5][6][7][8][9][10][11] which suggest the appropriateness of using this type of EPID for dose measurement. Throughout this paper, EPID refers to the amorphous silicon-based EPID unless otherwise stated.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo-based adaptive EPID dose kernel accounting for different field size responses of imagers

et al. 2009

View full text Add to dashboard Cite

The aim of this study is to present an efficient method to generate imager-specific Monte Carlo ͑MC͒-based dose kernels for amorphous silicon-based electronic portal image device dose prediction and determine the effective backscattering thicknesses for such imagers. EPID field sizedependent responses were measured for five matched Varian accelerators from three institutions with 6 MV beams at the source to detector distance ͑SDD͒ of 105 cm. For two imagers, measurements were made with and without the imager mounted on the robotic supporting arm. Monoenergetic energy deposition kernels with 0-2.5 cm of water backscattering thicknesses were simultaneously computed by MC to a high precision. For each imager, the backscattering thickness required to match measured field size responses was determined. The monoenergetic kernel method was validated by comparing measured and predicted field size responses at 150 cm SDD, 10ϫ 10 cm 2 multileaf collimator ͑MLC͒ sliding window fields created with 5, 10, 20, and 50 mm gaps, and a head-and-neck ͑H&N͒ intensity modulated radiation therapy ͑IMRT͒ patient field. Field size responses for the five different imagers deviated by up to 1.3%. When imagers were removed from the robotic arms, response deviations were reduced to 0.2%. All imager field size responses were captured by using between 1.0 and 1.6 cm backscatter. The predicted field size responses by the imager-specific kernels matched measurements for all involved imagers with the maximal deviation of 0.34%. The maximal deviation between the predicted and measured field size responses at 150 cm SDD is 0.39%. The maximal deviation between the predicted and measured MLC sliding window fields is 0.39%. For the patient field, gamma analysis yielded that 99.0% of the pixels have ␥ Ͻ 1 by the 2%, 2 mm criteria with a 3% dose threshold. Tunable imager-specific kernels can be generated rapidly and accurately in a single MC simulation. The resultant kernels are imager position independent and are able to predict fields with varied incident energy spectra and a H&N IMRT patient field. The proposed adaptive EPID dose kernel method provides the necessary infrastructure to build reliable and accurate portal dosimetry systems.

show abstract

Section: Introductionmentioning

confidence: 99%

Monte Carlo-based adaptive EPID dose kernel accounting for different field size responses of imagers

et al. 2009

View full text Add to dashboard Cite

show abstract

“…Although it is implemented in several different departments as the routine method for IMRT pre-treatment verification [20][21][22][23][24][25][26][27], little information is available in the literature on the criteria to use for the analysis and acceptance/rejection of the acquired data. In addition, the commercially available solution suffers from a suboptimal calibration procedure that limits the achievable accuracy for larger field sizes or highly asymmetrical fields.…”

mentioning

confidence: 99%

Practical guidelines for routine intensity-modulated radiotherapy verification: pre-treatment verification with portal dosimetry and treatment verification within vivodosimetry

Vinall¹,

Williams²,

Currie³

et al. 2010

BJR

View full text Add to dashboard Cite

ABSTRACT. The purpose of this work is to provide guidelines for the routine use of portal dosimetry and in vivo diode measurements to verify intensity-modulated radiotherapy (IMRT) treatments. To achieve tolerance levels that are sensitive enough to intercept problems, both the portal dosimetry and the in vivo procedure must be optimised. Portal dosimetry was improved by the introduction of an optimised twodimensional (2D) profile correction, which also accounted for the effect of backscatter from the R-arm. The scaled score, indicating the fraction of points not meeting the desired gamma evaluation criteria within the field opening, was determined as the parameter of interest. Using gamma criteria of a 3% dose difference and 3 mm distance to agreement, a ''scaled score'' threshold value of 1.5% was chosen to indicate excessive tongue and groove and other problems. The pre-treatment portal dosimetry quality assurance (QA) does not encompass verification of the patient dose calculation or position, and so it is complemented by in vivo diode measurements. Diode positioning is crucial in IMRT, and so we describe a method for diode positioning at any suitable point. We achieved 95% of IMRT field measurements within ¡5% and 99% within ¡8%, with improved accuracy being achieved over time owing to better positioning. Although the careful preparation and setup of the diode measurements can be time-consuming, this is compensated for by the time efficiency of the optimised procedure. Both methods are now easily absorbed into the routine work of the department. In many radiotherapy departments, routine treatment verification for conventional static treatment fields is performed during the first treatment session. This verification often consists of in vivo measurements with diodes (mostly on the beam axis) in combination with portal imaging of the treatment-field shapes superimposed on the patient's anatomy. Before the first treatment session, the treatment parameters are carefully reviewed by a qualified person and independent monitor unit (MU) calculations may be performed as an additional check.For dynamic intensity-modulated radiotherapy (IMRT) fields, a more extensive quality assurance (QA) protocol is considered to be good practice, the reasons for this being at least fourfold:(1) Both delivery and dose calculations are considerably more complex for dynamic IMRT fields than for conventional static fields.(2) Conventional portal imaging of the treatment fields provides images that are difficult to interpret because the modulated fluence is superimposed on the patient's anatomy.(3) Because of the presence of many dose gradients within the IMRT fields, conventional in vivo dosimetry on the beam axis is prone to large deviations, or can be meaningless when little dose is delivered on the beam axis.(4) Dosimetric treatment parameters, such as MU and multileaf collimator (MLC) shape (or movement pattern), depend on the individual patient plan and can vary substantially among patients as a function of the modulation. Hence,...

show abstract

“…Different QA measurement techniques in IMRT exist, making use of 2D detector array [5][6][7][8], single ion chamber in phantom for point dose measurements [9][10][11] or using specific phantoms with 2D dose measurement devices and 3D dose reconstruction software [12][13][14]. One disadvantage of these approaches is that measurements are generally compared with calculations by the TPS and it is difficult to give interpretation and to address the deviations between calculated and measured doses to failures of the accelerator performance or to the calculation algorithm.…”

Section: Introductionmentioning

confidence: 99%

Primo software as a tool for Monte Carlo simulations of intensity modulated radiotherapy: A feasibility study

et al. 2016

View full text Add to dashboard Cite

Background: IMRT provides higher dose conformation to the target and dose sparing to surrounding tissues than 3DCRT. Monte Carlo method in Medical Physics is not a novelty to approach dosimetric problems. A new PENELOPE based code named PRIMO recently was published. The most intriguing features of PRIMO are the user-friendly approach, the stand-alone property and the built-in definition of different linear accelerators models. Nevertheless, IMRT simulations are not yet implemented. Methods: A Varian Trilogy with a Millennium120 MLC and a Varian Novalis with 120HD MLC were studied. A RW3 multi-slab phantom was irradiated with Gafchromic films inserted between slabs. An Expression 10000XL scanner (Seiko Epson Corp., Nagano, Japan) was used to digitalize the films. PTW-Verisoft software using the global Gamma Function (2%, 2 mm) was used to compare simulated and experimental results. The primary beam parameters were adjusted to best match reference data previously obtained in a water phantom. Static MLC simulations were performed to validate the MLC models in use. Two Dynamic IMRT preliminary tests were performed with leaves moving with constant and variable speed. A further test of an in phantom delivery of a real IMRT field allowed simulating a clinical-like MLC modulation.

show abstract

An investigation of a new amorphous silicon electronic portal imaging device for transit dosimetry

Cited by 77 publications

References 42 publications

Monte Carlo-based adaptive EPID dose kernel accounting for different field size responses of imagers

Monte Carlo-based adaptive EPID dose kernel accounting for different field size responses of imagers

Practical guidelines for routine intensity-modulated radiotherapy verification: pre-treatment verification with portal dosimetry and treatment verification within vivodosimetry

Primo software as a tool for Monte Carlo simulations of intensity modulated radiotherapy: A feasibility study

Contact Info

Product

Resources

About