Modeling the output ratio in air for megavoltage photon beams

Zhu, Timothy C.; Bjärngard, Bengt E.; Xiao, Ying; Yang, Chuan

doi:10.1118/1.1376639

Cited by 36 publications

(37 citation statements)

References 35 publications

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“…29 We modified the algorithm to require that all parameters (μ a and ) were positive. 30 The effect of this variation of optical properties on the kernels for a point light source was examined. A summary of the average optical properties in each patient before and after PDT is listed in Table I.…”

Section: A Diffusion Theory and Determination Of Optical Propertiesmentioning

confidence: 99%

Optimized interstitial PDT prostate treatment planning with the Cimmino feasibility algorithm

Altschuler

Zhu

et al. 2005

Medical Physics

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The primary aim of this study was to determine whether optimized photodynamic therapy (PDT) treatment planning (seeking optimized positions, lengths, and strengths of the light sources to satisfy a given dose prescription) can improve dose coverage to the prostate and the sparing of critical organs relative to what can be achieved by the standard PDT plan. The Cimmino algorithm and search procedures based on that algorithm were tested for this purpose. A phase I motexafin lutetium (MLu)-mediated photodynamic therapy protocol is ongoing at the University of Pennsylvania. PDT for the prostate is performed with cylindrical diffusing fibers of various lengths inserted perpendicular to a base plate to obtain longitudinal coverage by a matrix of parallel catheters. The standard plan for the protocol uses sources of equal strength with equal spaced (1-cm) loading. Uniform optical properties were assumed. Our algorithms produce plans that cover the prostate and spare the urethra and rectum with less discrepancy from the dose prescription than the standard plan. The Cimmino feasibility algorithm is fast enough that changes to the treatment plan may be made in the operating room before and during PDT to optimize light delivery.

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Section: A Diffusion Theory and Determination Of Optical Propertiesmentioning

confidence: 99%

Optimized interstitial PDT prostate treatment planning with the Cimmino feasibility algorithm

Altschuler

Zhu

et al. 2005

Medical Physics

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“…The calculation is based on the MLC leaffield output subtraction method [16] at the 15 th ICCR. The details are; Zhu and Bjärngard [17] and Zhu and colleagues [18][19][20] introduced the 2D Gaussian-source model for the extended radiation source only with a flattening filter to calculate the in-air output factor (S c ) [21,22] for open jaw or MLC fields. Later, Iwasaki and colleagues [6] proposed the use of this model not only for the flattening filter but also for the X-ray target (or the source (S)).…”

Section: In-air Output Factor Calculation For Open Mlc Fieldsmentioning

confidence: 99%

10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance

Iwasaki¹,

Kimura²,

Sutoh³

et al. 2017

J Radiol Imaging.

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Purposes: This paper highlights a 10-MV X-ray convolution dose calculation method in water using primary and scatter dose kernels formed for energy bins of X-ray spectra reconstructed as a function of the off-axis distance for a linear accelerator equipped with pairs of upper and lower jaws, a multileaf collimator (MLC) and a wedge filter. Methods: The reconstructed X-ray spectra set was composed of 11 energy bins. To estimate the in-air beam intensities at points on the isocenter plane for an MLC field, we employed an MLC leaf-field output subtraction method, using an extended radiation source on each of the X-ray target and the flattening filter as well as simplified twodimensional plates to simulate the three-dimensional jaws and MLC structures. A special correction factor was introduced for nonuniform incident beam intensities, particularly produced at MLC fields. The in-phantom dose calculation was performed by treating the phantom, the wedge filter, the wedge holder and the MLC as parts of a unified irradiated body, where we proposed to use a special factor for the density scaling theorem within the unified irradiated body. Conclusions: The phantom dose was generally separated into nine dosecomponents: the primary and scatter dose-components produced in the phantom; the primary and scatter dose-components emanating from the wedge, the wedge holder and the MLC; and the electron contamination dose-component. From the calculated and measured percentage depth dose (PDD) and off-center ratio (OCR) datasets, we may conclude that the convolution method can achieve accurate dose calculations even under MLC and/or wedge filtration.Keywords: convolution method; X-ray spectra; dose kernels; wedge; multileaf collimation; MLC leaf-field output subtraction Citation: Iwasaki A, Kimura S, Sutoh K, Kamimura K, Sasamori M, Seino M, Komai F, Takagi M, Terashima S, Hosokawa Y, Saitoh H, Miyazawa M. 10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance. J

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“…This algorithm is simple and robust, and converges faster and with more certainty than both the adaptive simulated annealing and the annealed Nelder & Mead approach. We modified the algorithm to require that all parameters (μ a and ) were positive [57].…”

Section: Interstitial Pdt Dosimetry In Vivo Characterization Of Tissumentioning

confidence: 99%

Prostate PDT dosimetry

Zhu

Finlay

2006

Photodiagnosis and Photodynamic Therapy

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SummaryWe provide a review of the current state of dosimetry in prostate photodynamic therapy (PDT). PDT of the human prostate has been performed with a number of different photosensitizers and with a variety of dosimetry schemes. The simplest clinical light dose prescription is to quantify the total light energy emitted per length (J/cm) of cylindrical diffusing fibers (CDF) for patients treated with a defined photosensitizer injection per body weight. However, this approach does not take into account the light scattering by tissue and usually underestimates the local light fluence rate, and consequently the fluence. Techniques have been developed to characterize tissue optical properties and light fluence rates in vivo using interstitial measurements during prostate PDT. Optical methods have been developed to characterize tissue absorption and scattering spectra, which in turn provide information about tissue oxygenation and drug concentration. Fluorescence techniques can be used to quantify drug concentrations and photobleaching rates of photosensitizers.

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Modeling the output ratio in air for megavoltage photon beams

Cited by 36 publications

References 35 publications

Optimized interstitial PDT prostate treatment planning with the Cimmino feasibility algorithm

Optimized interstitial PDT prostate treatment planning with the Cimmino feasibility algorithm

10-MV X-ray dose calculation in water for MLC and wedge fields using a convolution method with X-ray spectra reconstructed as a function of off-axis distance

Prostate PDT dosimetry

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