Characterization of dose-dependent Young's modulus for a radiation-sensitive polymer gel.

Radiation-sensitive polymer gels for clinical dosimetry have been intensively investigated with magnetic resonance imaging (MRI) because the transversal magnetic relaxation time is dependent on irradiation dose. MRI is expensive and not easily available in most clinics. For this reason, low-cost, quick and easy-to-use potential alternatives such as optical computed tomography (CT), x-ray CT or ultrasound attenuation CT have also been studied by others.

Diffusion-weighted imaging in cervical cancer with an endovaginal technique: potential value for improving tumor detection in stage Ia and Ib1 disease.

Purpose: To establish apparent diffusion coefficients (ADCs) of invasive cervical carcinoma compared with nontumor cervical epithelium and determine sensitivity and specificity of diffusion-weighted (DW) magnetic resonance (MR) imaging used in conjunction with T2-weighted MR imaging to help detect invasive cervical carcinoma in patients with stage Ia and Ib1 disease.

Materials And Methods: Local research ethics committee approval was obtained with written consent from each subject. Group 1 comprised patients (mean age, 38.

Investigation of metabolite changes in the transition from pre-invasive to invasive cervical cancer measured using (1)H and (31)P magic angle spinning MRS of intact tissue.

The aim of this study was to determine the metabolic changes in the transition from pre-invasive to invasive cervical cancer using high-resolution magic angle spinning (HR-MAS) MRS. Biopsy specimens were obtained from women with histologically normal cervix (n = 5), cervical intraepithelial neoplasia (CIN; mild, n = 5; moderate/severe, n = 40), and invasive cancer (n = 23). (1)H HR-MAS MRS data were acquired using a Bruker Avance 11.

Planning lung radiotherapy using 4D CT data and a motion model.

This work is a feasibility study to use a four-dimensional computed tomography (4D CT) dataset generated by a continuous motion model for treatment planning in lung radiotherapy. The model-based 4D CT data were derived from multiple breathing cycles. Four patients were included in this retrospective study.

A new way of adapting IMRT delivery fraction-by-fraction to cater for variable intrafraction motion.

In this paper a technique is presented for adaptive therapy to compensate for variable intrafraction tissue motion. So long as the motion can be measured or deduced for each fraction the technique modifies the fluence profile for the subsequent fractions in a repeatable cyclic way. The fluence modification is based on projecting the dose discrepancies between the cumulative delivered dose after each fraction and the expected planned dose at the same stage.

Treatment of lung cancer using volumetric modulated arc therapy and image guidance: a case study.

Background: Volumetric modulated arc therapy (VMAT) is a radiotherapy technique in which the gantry rotates while the beam is on. Gantry speed, multileaf collimator (MLC) leaf position and dose rate vary continuously during the irradiation. For optimum results, this type of treatment should be subject to image guidance.

A margin model to account for respiration-induced tumour motion and its variability.

In order to reduce the sensitivity of radiotherapy treatments to organ motion, compensation methods are being investigated such as gating of treatment delivery, tracking of tumour position, 4D scanning and planning of the treatment, etc. An outstanding problem that would occur with all these methods is the assumption that breathing motion is reproducible throughout the planning and delivery process of treatment. This is obviously not a realistic assumption and is one that will introduce errors.

Diffusion-weighted magnetic resonance imaging: a potential non-invasive marker of tumour aggressiveness in localized prostate cancer.

Aim: To evaluate diffusion-weighted magnetic resonance imaging (DW-MRI) as a marker for disease aggressiveness by comparing tumour apparent diffusion coefficients (ADCs) between patients with low- versus higher-risk localized prostate cancer.

Method: Forty-four consecutive patients classified as low- [n = 26, stageT1/T2a, Gleason score < or = 6, prostate-specific antigen (PSA)< 10 (group 1)] or intermediate/high- [n = 18, stage > or = T2b and/or Gleason score > or = 7, and/or PSA > 10 (group 2)] risk, who subsequently were monitored with active surveillance or started neoadjuvant hormone and radiotherapy, respectively, underwent endorectal MRI. T2-weighted (T2W) and DW images (5 b values, 0-800 s/mm(2)) were acquired and isotropic ADC maps generated.

Anatomical imaging for radiotherapy.

The goal of radiation therapy is to achieve maximal therapeutic benefit expressed in terms of a high probability of local control of disease with minimal side effects. Physically this often equates to the delivery of a high dose of radiation to the tumour or target region whilst maintaining an acceptably low dose to other tissues, particularly those adjacent to the target. Techniques such as intensity modulated radiotherapy (IMRT), stereotactic radiosurgery and computer planned brachytherapy provide the means to calculate the radiation dose delivery to achieve the desired dose distribution.

Dosimetric investigation of lung tumor motion compensation with a robotic respiratory tracking system: an experimental study.

The benefits of using Synchrony Respiratory Tracking System (RTS) in conjunction with the CyberKnife robotic treatment device to treat a "breathing tumor" in an anthropomorphic, tissue-equivalent, thoracic phantom have been investigated. The following have been studied: (a) Synchrony's ability to allow the CyberKnife to deliver accurately a planned dose distribution to the free-breathing phantom and (b) the dosimetric implications when irregularities in the breathing cycle and phase differences between internal (tumor) and external (chest) motion exist in the course of one treatment fraction. The breathing phantom PULMONE (phantom used in lung motion experiments) has been used, which can imitate regular or irregular breathing patterns.

Improving recruitment to clinical trials for cancer in childhood.

Clinical trials have underpinned progress in the treatment of cancer in childhood: about 75% of children newly diagnosed with cancer can expect to be long-term survivors. This success has been achieved because most children with cancer have participated in available clinical trials. This high level of engagement of the childhood-cancer community relies on the so-called therapeutic alliance that begins between doctors and families when a child is diagnosed with cancer.

Computationally efficient vascular input function models for quantitative kinetic modelling using DCE-MRI.

A description of the vascular input function is needed to obtain tissue kinetic parameter estimates from dynamic contrast enhanced MRI (DCE-MRI) data. This paper describes a general modelling framework for defining compact functional forms to describe vascular input functions. By appropriately specifying the components of this model it is possible to generate models that are realistic, and that ensure that the tissue concentration curves can be analytically calculated.

Combatting cancer in the third millennium--the contribution of medical physics.

In this invited opening Plenary Lecture at the 1st European Conference on Medical Physics, I indicated some of the roles of medical physics, and specifically medical radiation therapy physics, in the development of improved cancer care for the third millennium. It is said that you are only asked to predict the future if you are seriously old and/or will not be around long enough to know if you were correct. Hopefully, however, I will be able to contribute to this field for many years to come and many of my suggestions will be enacted.

The spatio-temporal strain response of oedematous and nonoedematous tissue to sustained compression in vivo.

Poroelastic theory predicts that compression-induced fluid flow through a medium reveals itself via the spatio-temporal behaviour of the strain field. Such strain behaviour has already been observed in simple poroelastic phantoms using generalised elastographic techniques (Berry et al. 2006a, 2006b).

Adapting IMRT delivery fraction-by-fraction to cater for variable intrafraction motion.

This paper presents a technique for coping with variable intrafraction organ motion when delivering intensity-modulated radiation therapy (IMRT). The strategy is an adaptive delivery in which the fluence delivered up to a particular fraction is subtracted from the required total-course planned fluence to create an adapted residual fluence for the next fraction. This requires that the fluence already delivered can be computed, knowing the intrafraction motion during each fraction.

Characterization of the ultrasonic attenuation coefficient and its frequency dependence in a polymer gel dosimeter.

Research on polymer-gel dosimetry has been driven by the need for three-dimensional dosimetry, and because alternative dosimeters are unsatisfactory or too slow for that task. Magnetic resonance tomography is currently the most well-developed technique for determining radiation-induced changes in polymer structure, but quick low-cost alternatives remain of significant interest. In previous work, ultrasound attenuation and speed of sound were found to change as a function of absorbed radiation dose in polymer-gel dosimeters, although the investigations were restricted to one ultrasound frequency.

Intrafraction motion compensation by highly constrained iterative deconvolution of organ motion.

This short paper investigates highly constrained organ-motion deconvolution in the context of the delivery of radiotherapy. Whereas unconstrained and unphysical deconvolution of regular intrafraction motion can generate a dose distribution exactly matching the plan (made on a supposedly static object), the addition of fluence-positivity, fluence-smoothing and fluence-capping constraints to create constrained, physically valid, deconvolution reduces the goodness of fit. However, the generated modulations are physically acceptable and essentially are 'for free', no added delivery technology being needed and they improve on the 'do nothing about motion' strategy.

Single-cell dosimetry for radioimmunotherapy of B-cell lymphoma patients with special reference to leukemic spread.

Aims: Many lymphoma patients have both macroscopic tumors and single-cell manifestations of their disease. Treatment efficacy could, therefore, depend on the radionuclide used. The aim of this study was to investigate dosimetry at a cellular level for three isotopes of radioiodine.

A quality-control method for SPECT-based dosimetry in targeted radionuclide therapy.

Dosimetry for targeted radionuclide therapy is necessary for treatment planning and radiation protection. Currently, there are no standard methods either for performing dosimetry or to evaluate the uncertainties inherent in the dosimetric calculations. In this paper, we present an experimental method using polymer gel dosimeters, whereby absorbed-dose distributions resulting from nonuniform distributions of activity may be determined directly from T(2) magnetic resonance imaging (MRI) as well as from scintigraphic images.

Tumor dosimetry on SPECT (186)Re-HEDP scans: variations in the results from the reconstruction methods used.

The aim of this work was to estimate tumor-absorbed doses delivered from the administration of fixed activities of (186)Re-HEDP for the treatment of bone metastases from prostate cancer. The variations and reproducibility in the estimated absorbed dose owing to the reconstruction algorithm used (OSEM vs. FBP) were also analysed.

Bayesian estimation of pharmacokinetic parameters for DCE-MRI with a robust treatment of enhancement onset time.

When applying pharmacokinetic (PK) models to dynamic contrast enhanced MRI (DCE-MRI) data it is important to appropriately deal with the enhancement onset time, because errors in the onset time will affect the PK parameter estimates. This paper presents a Bayesian approach to the estimation of the PK parameters k(ep) and K(trans) that robustly treats the onset time. This approach involves the computation of an analytically intractable integral, so two approximate methods are developed.

Magnetic resonance imaging in prostate cancer: the value of apparent diffusion coefficients for identifying malignant nodules.

The aim of this work was to determine the potential of diffusion weighted magnetic resonance imaging (DW-MRI) for identifying prostate cancer by comparing apparent diffusion coefficients (ADCs) from malignant peripheral zone (PZ) nodules with values from the non-malignant PZ and the predominantly benign central gland (CG). 33 patients with elevated prostate specific antigen (PSA) aged 52-78 years (30 patients with biopsy proven prostate cancer) underwent endorectal MRI with T2 weighted and echo planar diffusion weighting (b = 0 mm2 s(-1), 300 mm2 s(-1), 500 mm2 s(-1) and 800 mm2 s(-1)) sequences. ADCs were measured from 30 malignant PZ nodules (identified on T2 weigting and positive biopsy; median region of interest (ROI) size 41 mm2), 33 CG regions (predominantly benign nodules; median ROI size 218 mm2) and 18 non-malignant PZ regions (ipsilateral biopsies all benign; median ROI size 54.

Reference tissue quantification of DCE-MRI data without a contrast agent calibration.

The quantification of dynamic contrast-enhanced (DCE) MRI data conventionally requires a conversion from signal intensity to contrast agent concentration by measuring a change in the tissue longitudinal relaxation rate, R(1). In this paper, it is shown that the use of a spoiled gradient-echo acquisition sequence (optimized so that signal intensity scales linearly with contrast agent concentration) in conjunction with a reference tissue-derived vascular input function (VIF), avoids the need for the conversion to Gd-DTPA concentration. This study evaluates how to optimize such sequences and which dynamic time-series parameters are most suitable for this type of analysis.

Comparison of inverse-planned three-dimensional conformal radiotherapy and intensity-modulated radiotherapy for non-small-cell lung cancer.

Purpose: Lungs are the major dose-limiting organ during radiotherapy (RT) for non-small-cell lung cancer owing to the development of pneumonitis. This study compared intensity-modulated RT (IMRT) with three-dimensional conformal RT (3D-CRT) in reducing the dose to the lungs.

Methods: Ten patients with localized non-small-cell lung cancer underwent computed tomography (CT).

Towards an acoustic model-based poroelastic imaging method: II. experimental investigation.

Soft biological tissue contains mobile fluid. The volume fraction of this fluid and the ease with which it may be displaced through the tissue could be of diagnostic significance and may also have consequences for the validity with which strain images can be interpreted according to the traditional idealizations of elastography. In a previous paper, under the assumption of frictionless boundary conditions, the spatio-temporal behavior of the strain field inside a compressed cylindrical poroelastic sample was predicted (Berry et al.