X-ray fluorescence-based differentiation of neck tissues in a bovine model: implications for potential intraoperative use.

This study explores the possibility of using X-ray fluorescence (XRF)-based trace-element analysis for differentiation of various bovine neck tissues. It is motivated by the requirement for an intra-operative in-vivo method for identifying parathyroid glands, particularly beneficial in surgery in the central neck-compartment. Using a dedicated X-ray spectral analysis, we examined ex-vivo XRF spectra from various histologically verified fresh neck tissues from cow, which was chosen as the animal model; these tissues included fat, muscle, thyroid, parathyroid, lymph nodes, thymus and salivary gland. The data for six trace elements K, Fe, Zn, Br, Rb and I, provided the basis for tissue identification by using multi-parameter analysis of the recorded XRF spectra. It is shown that the combination of XRF signals from these elements is sufficient for a reliable tissue differentiation. The average total abundance of these trace elements was evaluated in each tissue type, including parathyroid and salivary gland for the first time. It is shown that some tissues can unequivocally be identified on the basis of the abundance of a single element, for example, iodine and zinc for the identification of thyroid gland and muscle, respectively.

New prospective for non-invasive detection, grading, size evaluation, and tumor location of prostate cancer.

BACKGROUND: PSA blood test and other present screening tools fail to provide the required sensitivity and specificity and, at early stages, lack correlation with tumor grade, volume, and location. Thus alternative approaches are highly desired. We present and assess a novel method for PCa detection, grading, volume evaluation and tumor location, based on non-invasive zinc concentration mapping in the gland by means of a dedicated rectal probe. METHODS: Zinc-concentration values measured in histologically examined tissue fragments from needle biopsy of 598 patients were analyzed. They were used to generate computer simulated zinc-concentration maps, further analyzed with image-processing tools. The tumor detection performances versus Gleason grade were assessed. RESULTS: A significant increase of zinc depletion with increasing Gleason pattern (grade) classification was established. Tumor detection performance in zinc-concentration maps progressively improves with the cancer's first component score. Reliable information on the location, size and Gleason-grade combination of the lesion can be extracted for clinically relevant volumes. CONCLUSIONS: Zinc depletion in the prostate peripheral zone is the basis for a novel, non-invasive PCa detection, localization, volume evaluation and grading method. Its realization and application as a pre-biopsy and pre-treatment examination, or a follow-up tool, relies on the development of a dedicated transrectal probe. It should have significant impact on biopsy effectiveness, point at a possible extraprostatic extension and provide critical data for focal treatment. The information on tumor grade and distribution may have an important impact on disease management.

A nanodosimetric model of radiation-induced clustered DNA damage yields.

We present a nanodosimetric model for predicting the yield of double strand breaks (DSBs) and non-DSB clustered damages induced in irradiated DNA. The model uses experimental ionization cluster size distributions measured in a gas model by an ion counting nanodosimeter or, alternatively, distributions simulated by a Monte Carlo track structure code developed to simulate the nanodosimeter. The model is based on a straightforward combinatorial approach translating ionizations, as measured or simulated in a sensitive gas volume, to lesions in a DNA segment of one-two helical turns considered equivalent to the sensitive volume of the nanodosimeter. The two model parameters, corresponding to the probability that a single ion detected by the nanodosimeter corresponds to a single strand break or a single lesion (strand break or base damage) in the equivalent DNA segment, were tuned by fitting the model-predicted yields to previously measured double-strand break and double-strand lesion yields in plasmid DNA irradiated with protons and helium nuclei. Model predictions were also compared to both yield data simulated by the PARTRAC code for protons of a wide range of different energies and experimental DSB and non-DSB clustered DNA damage yield data from the literature. The applicability and limitations of this model in predicting the LET dependence of clustered DNA damage yields are discussed.

Evaluating the cancer detection and grading potential of prostatic-zinc imaging: a simulation study.

The present work deals with the analysis of prostatic-zinc-concentration images. The goal is to evaluate potential clinically relevant information that can be extracted from such images. In the absence of experimental images, synthetic ones are produced from clinically measured zinc-concentration distributions in certified benign and cancerous tissue samples, classified by the lesion grade. We describe the method for producing the images and model the effect of counting statistics noise. We present in detail the image analysis, which is based on a combination of standard image processing and segmentation tools, optimized for this particular application. The information on lowest zinc value obtained from the image analysis is translated to clinical data such as tumour presence, location, size and grade. Their confidence is evaluated with the help of standard statistical tools such as receiver operating characteristic analysis. The present work predicts a potential for detecting small prostate-cancer lesions, of grade (4+3) and above, with very good specificity and sensitivity. The present analysis further provides data on the pixel size and image counting statistics requested from the trans-rectal probe that will record in vivo prostatic-zinc maps in patients.

Clinical assessment of the cancer diagnostic value of prostatic zinc: a comprehensive needle-biopsy study.

BACKGROUND: The correlation between Zinc concentration in the prostate's peripheral zone to the onset or presence of malignant process needs to be evaluated in detail. METHODS: Zinc concentration was measured in approximately 1-4 mm3 segments of fresh needle-biopsy cores, with X-ray fluorescence, and correlated with the histological findings of these tissue segments. RESULTS: Local Zinc concentration is correlated with the presence of cancer (PCa); the higher the Gleason score the greater the Local Zinc depletion. The Zinc value averaged over the entire extracted tissue is specific only to Gleason score 8-9 PCa. The results refer to patients avoiding Zinc-rich supplements since those show elevated prostatic Zinc concentration in identified cancer tissue. A computer simulation analysis of randomly located 0.03-3.3 cm3 lesions, with particular Gleason score and the measured Local Zinc concentration, revealed a potential diagnostic approach definitely superior to PSA, with sensitivity to the tumor grade and with excellent detection capability for Gleason score >6. Further clinical studies have been designed, both on full prostates after radical prostatectomy as well as on biopsy cores at higher resolution, to establish the accuracy of the method for Gleason score = 6. CONCLUSIONS: The PCa diagnostic potential of Local Zinc concentration is confirmed and there is indication that the amount of Zinc depletion could be used as a measure of the Gleason score of the tumor. Local Zinc concentration mapping has the potential to improve patient selection for biopsy, biopsy site selection and local therapy (e.g., Cryotherapy, Brachytherapy) site selection.

First attempts at prediction of DNA strand-break yields using nanodosimetric data.

We present the first results of our attempts to correlate yields of ionisation clusters in a gas model of DNA and corresponding double-strand break (DSB) yields in irradiated plasmids, using a simple statistical model of DNA lesion formation. Based on the same statistical model, we also provide a comparison of simulated nanodosimetric data for electrons and published DSB yields obtained with the PARTRAC code.

Dependence of nanodosimetric spectra on the sensitive volume length and ion drift in an ion-counting nanodosemeter.

Nanodosimetric spectra, measured in a well-defined ionisation sensitive volume of an ion-counting gaseous nanodosemeter, may have a valuable predictive value of radiation damage to DNA. In such devices, the distributions of radiation-induced ions are measured after their drift in gas. The sensitive-volume size, corresponding to a DNA segment length, can be tuned by selecting an appropriate time window for ion counting; the method's accuracy depends on the velocity distribution of the drifting ions. The results of ion-drift measurements in an ion-counting nanodosemeter were used for the precise calculation of its sensitive volume length. Monte Carlo simulations of nanodosimetric spectra, performed with the obtained data, are in good agreement with experimental data. The method's limitations, arising from the spread of drift velocities, are discussed.

Ion-counting nanodosemeter with particle tracking capabilities.

An ion-counting nanodosemeter (ND) yielding the distribution of radiation-induced ions in a low-pressure gas within a millimetric, wall-less sensitive volume (SV) was equipped with a silicon microstrip telescope that tracks the primary particles, allowing correlation of nanodosimetric data with particle position relative to the SV. The performance of this tracking ND was tested with a broad 250 MeV proton beam at Loma Linda University Medical Center. The high-resolution tracking capability made it possible to map the ion registration efficiency distribution within the SV, for which only calculated data were available before. It was shown that tracking information combined with nanodosimetric data can map the ionisation pattern of track segments within 150 nm-equivalent long SVs with a longitudinal resolution of approximately 5 tissue-equivalent nanometers. Data acquired in this work were compared with results of Monte Carlo track structure simulations. The good agreement between 'tracking nanodosimetry' data acquired with the new system and simulated data supports the application of ion-counting nanodosimetry in experimental track-structure studies.

Prostatic Zn determination for prostate cancer diagnosis.

We present our studies of prostatic Zn concentration measurements, carried out in the light of a novel prostate cancer (CAP) diagnosis method proposed by us. The method is based on in vivo prostatic Zn mapping by XRF trans-rectal probe. We report on the extensive clinical studies, intended to assess the validity of the novel proposed diagnostic method. Zn content was measured in vitro in needle-biopsy samples from several hundreds of patients, and was correlated with histological findings and other patient parameters. For this purpose, a technique of absolute Zn content determination in approximately 1mm(3) fresh tissue samples by XRF was developed. The experimental details and the main clinical-evaluation results are presented. We further outline the suggested design of the XRF trans-rectal probe for an efficient in vivo detection and mapping of the Zn fluorescence radiation from the prostate through the rectal wall. Laboratory phantom studies, a preliminary design concept and its expected performance are also reported.

Evaluation of lesion clustering in irradiated plasmid DNA.

PURPOSE: To measure the yield of DNA strand breaks and clustered lesions in plasmid DNA irradiated with protons, helium nuclei, and y-rays. MATERIALS AND METHODS: Plasmid DNA was irradiated with 1.03, 19.3 and 249 MeV protons (linear energy transfer = 25.5, 2.7, and 0.39 keV microm(-1) respectively), 26 MeV helium nuclei (25.5 keV microm) and gamma-rays (137Cs or 60Co) in phosphate buffer containing 2 mM or 200 mM glycerol. Single-and double-strand breaks (SSB and DSB) were measured by gel electrophoresis, and clustered lesions containing base lesions were quantified by converting them into irreparable DSB in transformed bacteria. RESULTS: For protons, SSB yield decreased with increasing LET (linear energy transfer). The yield of DSB and all clustered lesions seemed to reach a minimum around 3 keV microm(-1). There was a higher yield of SSB, DSB and total clustered lesions for protons compared to helium nuclei at 25.5 keV microm(-1). A difference in the yields between 137Cs and 60Co gamma-rays was also observed, especially for SSB. CONCLUSION: In this work we have demonstrated the complex LET dependence of clustered-lesion yields, governed by interplay of the radical recombination and change in track structure. As expected, there was also a significant difference in clustered lesion yields between various radiation fields, having the same or similar LET values, but differing in nanometric track structure.

In vivo determination of prostatic zinc: phantom feasibility study.

This paper describes a phantom-based feasibility study for a potential in vivo determination of zinc in prostate, which could bring about improved diagnosis of prostate cancer. An x-ray fluorescence topographic technique was developed, which will permit determination of the Zn content in the prostate through the rectum, namely behind a 2-3 mm thick layer of the rectal wall. The topographic approach, together with a reconstruction method developed here, minimizes the interference of Zn from non-prostatic tissue. The phantom studies show that it will be possible to determine Zn in a prostatic compartment behind a few mm thick layer of tissue using a specially designed transrectal probe. Such a probe is currently under development in our laboratories.

Prostatic zinc and prostate specific antigen: an experimental evaluation of their combined diagnostic value.

PURPOSE: In cancer affected prostate cells lose the ability to concentrate zinc, resulting in a substantial decrease in Zn in the prostate. We investigated the possibility of using prostatic zinc combined with prostate specific antigen (PSA) as a novel tool for the reliable diagnosis of prostate cancer. MATERIALS AND METHODS: Using the x-ray fluorescence method the Zn concentration was determined in vitro in prostate samples extracted by surgery from 28 patients. Clinical records included age, serum PSA, sextant prostate needle biopsy, previous medical therapy, surgical procedure and histological findings. RESULTS: A new relationship was found between Zn in prostate tissue and PSA in blood, which allows improved separation between prostate cancer and benign prostate hyperplasia, and might have a significant impact on the reliable diagnosis of prostate cancer. CONCLUSIONS: Zn concentration is not uniform even in the same anatomical region of the prostate, so that a number of measurements at various locations are required for a diagnostic procedure. The most interesting finding in this study is the relationship between Zn concentration and PSA. A combination of these parameters represents a significant improvement on the diagnostic value of each of them separately and provides a powerful tool for more accurate diagnosis. Although the method may be applied in vitro on biopsy samples, our study underlines the importance of developing a facility for in vivo Zn determination in the prostate.

Ion-counting nanodosimetry: current status and future applications.

There is a growing interest in the study of interactions of ionizing radiation with condensed matter at the nanometer level. The motivation for this research is the hypothesis that the number of ionizations occurring within short segments of DNA-size subvolumes is a major factor determining the biological effectiveness of ionizing radiation. A novel dosimetry technique, called nanodosimetry, measures the spatial distribution of individual ionizations in an irradiated low-pressure gas model of DNA. The measurement of nanodosimetric event size spectra may enable improved characterization of radiation quality, with applications in proton and charged-particle therapy, radiation protection, and space research. We describe an ion-counting nanodosimeter developed for measuring radiation-induced ionization clusters in small, wall-less low-pressure gas volumes, simulating short DNA segments. It measures individual radiation-induced ions, deposited in 1 Torr propane within a tissue-equivalent cylindrical volume of 2-4 nm diameter and up to 100 nm length. We present first ionization cluster size distributions obtained with 13.6 MeV protons, 4.25 MeV alpha particles and 24.8 MeV carbon nuclei in propane; they correspond to a wide LET range of 4-500 keV/microm. We are currently developing plasmid-based assays to characterize the local clustering of DNA damage with biological methods. First results demonstrate that there is increasing complexity of DNA damage with increasing LET. Systematic comparison of biological and nanodosimetric data will help us to validate biophysical models predicting radiation quality based on nanodosimetric spectra. Possible applications for charged particle radiation therapy planning are discussed.

Wall-less ion-counting nanodosimetry applied to protons.

A wall-less ion-counting nanodosemeter, conceived for precise ionisation-cluster measurements in an accelerator environment, is described. The technique provides an accurate means for counting single radiation-induced ions, in dilute gas models of condensed matter. The sensitive volume dimensions, a few tissue-equivalent nm in diameter by a few tens of nm, are tunable by a proper choice of the gas pressure and electric fields; nanometric sub-sections can be electronically selected. Detailed ion-cluster distributions are presented for protons of 7.15, 13.6 and 19.3 MeV, in biologically relevant DNA-like sensitive volumes of low-pressure propane. Experimental results are compared to model simulations.

Modeling of radiation action based on nanodosimetric event spectra.

Assuming that the number of ionizations events within short segments of DNA-size volumes is a major factor of the biological effectiveness of ionizing radiation, we have designed and manufactured a new nanodosimetric detector counting ionization events in small wall-less gas volumes, which simulate such DNA segments. The detector measures individual ionizations in low-pressure (~1 Torr) propane or any other gas corresponding to a tissue-equivalent cylindrical volume of 2-4 nm diameter and up to 30 nm length. While first nanodosimetric event spectra with protons and alpha particles are being obtained, it is important to develop and test a theory that relates these spectra to biological endpoints such as strand breakage, mutations, and lethal cellular events. This paper describes the two-compartment theory, which is based on the premise that energy deposition in nanometer sites can be broadly divided into two categories: a low-energy deposition compartment comprising events with a total number of 2-5 ionizations, and a high-energy deposition compartment comprising events containing 6-10 ionizations. Under standard biochemical conditions, these events will lead to different biological consequences. The fate of DNA lesions produced by low-energy deposition events will mostly depend on the repair capacity of the irradiated cells, whereas events produced by high-energy deposition events will be irreparable. These events are therefore the biologically most relevant lesions, since they inevitably lead to mutation and cell death.