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At least 343 records · Page 19Linked to original sources
PubMed1993

Photon activation of iododeoxyuridine: biological efficacy of Auger electrons.

Photon activation therapy is a binary system being investigated as a potential therapeutic modality to improve the treatment of malignancies, particularly the highly lethal and malignant brain tumor, glioblastoma multiforme. Its success relies upon the incorporation of a target atom in the immediate vicinity of a tumor cell's critical site, followed by the activation of this atom with photons of energies suitable for the induction of the photoelectric effect and its concomitant Auger cascades. The collective action of the Auger electrons imparts high-LET type damage at the critical site. Photon activation therapy uses iodine from stable iododeoxyuridine (IdUrd) as the target atom, and monochromatic photons above the K absorption edge of iodine (33.2 keV) as the activating agent. Although IdUrd is a cell-sensitizing agent, work described was designed to separate the biological efficacy due to sensitization from that of the Auger effect. Chinese hamster V79 cells with and without IdUrd in cellular DNA were irradiated at the X17B1 beam line in the National Synchroton Light Source of Brookhaven National Laboratory. Monochromatic photons above (33.4 keV) and below (32.9 keV) the K absorption edge were used to determine if any additional biological damage would accrue from the Auger cascades. The 33.4-keV photons were found to be a factor of 1.4 times more effective than 32.9-keV photons in damaging iodinated cells. The sensitizing effect, evaluated separately, was found to be a factor of 2.2 at 10% survival, regardless of photon energy. Thus the total therapeutic gain was 1.4 x 2.2 = 3.1. Irradiations of noniodinated control cells showed no difference in their response to energies above and below the iodine K edge.

Animals↗
PubMed2004

Two-photon microscopy of cells and tissue.

Two-photon excitation fluorescence imaging provides thin optical sections from deep within thick, scattering specimens by way of restricting fluorophore excitation (and thus emission) to the focal plane of the microscope. Spatial confinement of two-photon excitation gives rise to several advantages over single-photon confocal microscopy. First, penetration depth of the excitation beam is increased. Second, because out-of-focus fluorescence is never generated, no pinhole is necessary in the detection path of the microscope, resulting in increased fluorescence collection efficiency. Third, two-photon excitation markedly reduces overall photobleaching and photodamage, resulting in extended viability of biological specimens during long-term imaging. Finally, localized excitation can be used for photolysis of caged compounds in femtoliter volumes and for diffusion measurements by two-photon fluorescence photobleaching recovery. This review aims to provide an overview of the use of two-photon excitation microscopy. Selected applications of this technique will illustrate its excellent suitability to assess cellular and subcellular events in intact, strongly scattering tissue. In particular, its capability to resolve differences in calcium dynamics between individual cardiomyocytes deep within intact, buffer-perfused hearts is demonstrated. Potential applications of two-photon laser scanning microscopy as applied to integrative cardiac physiology are pointed out.

Animals↗
PubMed2002

[Time resolution spectrum measurements of the process of photon acting on the silver halide materials].

The silver halide material is a very important optical information material. Silver halide material plays a very imperative role in the development of the information science and technology. The time characters of the photon action process determine the quality of the silver halide material to a great degree. We adopt the microwave absorption technology to measure the time characters of the process of the photon acting on silver halide material. A sample of the silver halide material is inserted into a microwave resonant cavity. With the excitation of excimer laser, photogenerated charge carriers are created in the silver halide material. The generation of the photogenerated charge carriers changes the dielectric function of the silver halide material. Therefore, the change of the dielectric function embodies the information of the time characters of the photogenerated change carries. At the same time, the change of the dielectric function results in an alteration of the cavity quality factor. This change leads to a reflected microwave. The reflected microwave contains the information of the time characters of the photon action process. Through the measurement of the reflected microwave, we can obtain the time resolution spectrum of the process of the photon acting on the silver halide material and study the time characters of the photon action process. The time resolution spectra of the process of the photon acting on various silver halide materials were obtained in our experiments. We analyzed the time characters of photon acting on the black-and-white film, color film and X-ray film.

Absorption↗
PubMed1998

Spatially localized ballistic two-photon excitation in scattering media.

We describe spatially localized two-photon excitation in scattering media. Using femtosecond pulses at 770 nm from a Ti: Sapphire laser, we were able to excite fluorophores in capillary tubes under up to 1.5 mm of 0.5% intralipid. Displacement of the laser beam relative to the embedded samples indicates that highly localized excitation was possible with two-photon excitation, whereas one-photon excitation resulted in loss of spatial resolution due to excitation by the diffusely scattered photons. These results indicate that two-photon excitation in the scattering solution is due only to the ballistic photons, a result confirmed by frequency-domain time-resolved measurements. Selective excitation of adjacent embedded samples was found possible for two but not one-photon excitation.

Fat Emulsions, Intravenous↗
PubMed2006

One- and two-photon induced fluorescence of Pacific Blue-labeled human serum albumin deposited on different core size silver colloids.

We studied one- and two-photon induced fluorescence of Pacific Blue (PB)-labeled human serum albumin (HSA) in the presence of different size silver colloids. The PB fluorescence emission intensity was observed with small (30-40 nm) and large (about 120 nm) colloids and compared with PB emission in absence of colloids. For the system with a small core size colloids we did not detect any fluorescence enhancement with one-photon excitation and the enhancement observed with two-photon excitation was about 2.5-fold. In contrast, for large silver colloids we observed about a 2-fold increase in PB fluorescence brightness for one-photon excitation, and the enhancement with two-photon excitation excided 13-folds. Much stronger increases in brightness observed with two-photon excitation, compared to one-photon excitation, indicate a dominant role of enhanced local field in fluorescence enhancement on silver colloids in solutions.

Colloids↗
PubMed1999

Basic aspects of photon transport through matter with respect to track structure formation.

After a short summary of the most important physical aspects of photon interaction with matter and of the main elements of photon transport simulation, some basic features of photon tracks in liquid water are discussed. These include the statistical distribution of the number of photon interactions caused during the complete photon slow-down, the corresponding mean value, the distance distribution of photon interactions, and the spectral distribution of secondary electrons or, which is the same, the spectral distribution of the start energy of secondary electron tracks. The latter distribution can easily be interpreted in terms of the track entity concept of Mozumder and Magee, which, therefore, proves to be the most natural concept of track structure analysis in the case of photon irradiation.

Electrons↗
PubMed2006

Two-photon excited fluorescence energy transfer: a study based on oligonucleotide rulers.

The use of two-photon excitation of fluorescence for detection of fluorescence resonance energy transfer (FRET) was studied for a selected fluorescent donor-acceptor pair. A method based on labeled DNA was developed for controlling the distance between the donor and the acceptor molecules. The method consists of hybridization of fluorescent oligonucleotides to a complementary single-stranded target DNA. As the efficiency of FRET is strongly distance dependent, energy transfer does not occur unless the fluorescent oligonucleotides and the target DNA are hybridized. A high degree of DNA hybridization and an excellent FRET efficiency were verified with one-photon excited fluorescence studies. Excitation spectra of fluorophores are usually wider in case of two-photon excitation than in the case of one-photon excitation. This makes the selective excitation of donor difficult and might cause errors in detection of FRET with two-photon excited fluorescence. Different techniques to analyze the FRET efficiency from two-photon excited fluorescence data are discussed. The quenching of the donor fluorescence intensity turned to be the most consistent way to detect the FRET efficiency. The two-photon excited FRET is shown to give a good response to the distance between the donor and the acceptor molecules.

DNA, Single-Stranded↗
PubMed2006

Photon emissions from rice cells elicited by N-acetylchitooligosaccharide are generated through phospholipid signaling in close association with the production of reactive oxygen species.

Biophotons are ultraweak light emissions from biochemical reactions in a living body. They increase in suspension-cultured rice (Oryza sativa L.) cells when elicited by N-acetylchitooligosaccharide. Biochemical analyses were undertaken to investigate the relationship between disease response and biophotons in order to clarify the emission mechanism of biophotons caused by this elicitor. Photon emissions induced by N-acetylchitohexaose were suppressed when cells were pretreated with the reactive oxygen species (ROS)-generating inhibitors: pyrocatechol-3,5-disulfonic acid disodium salt (Tiron); diphenylene iodonium (DPI); and salicylhydroxamic acid (SHAM). Conversely, exogenously applied ROS (superoxide and hydrogen peroxide) were able to induce photon emissions. The effects of protein phosphorylation (K-252a) and the Ca(2+) signaling inhibitors, ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and LaCl(3), caused photon emissions to decrease. It is clear that photon emissions from rice cells elicited by N-acetylchitohexaose are closely associated with the ROS-generating system, and are regulated by Ca(2+) signaling and protein phosphorylation. Exogenously applied phosphatidic acid (PA), the second messenger in the signal transduction of disease response, raised photon emissions in rice cells. Comparisons of photon emissions from PA and N-acetylchitohexaose regarding time courses, spectral compositions, and the inhibition ratios of several inhibitors, as well as a loss- and gain-of-function assay using the protein synthesis inhibitor cycloheximide (CHX) and PA, showed the possibility that photon emissions from rice cells elicited by N-acetylchitooligosaccharide were generated through PA, an intermediate of phospholipid signaling.

Oligosaccharides↗
PubMed2001

Molecular heterogeneity of O-acetylserine sulfhydrylase by two-photon excited fluorescence fluctuation spectroscopy.

O-acetylserine sulfhydrylase, a homo-dimeric enzyme from Salmonella typhimurium, covalently binds one pyridoxal 5'-phosphate molecule per subunit as a fluorescent coenzyme. Different tautomers of the Schiff base between the coenzyme and lysine 41 generate structured absorption and fluorescence spectra upon one-photon excitation. We investigated the protein population heterogeneity by fluorescence correlation spectroscopy and lifetime techniques upon two-photon excitation. We sampled the fluorescence intensity from a small number of molecules (approximately 10) and analyzed the distribution of photon counts to separately determine the number and the fluorescence brightness of excited protein molecules. The changes in the average number of molecules and in the fluorescence brightness with the excitation wavelength indicate the presence of at least two fluorescent species, with two-photon excitation maxima at 660 and 800 nm. These species have been identified as the enolimine and ketoenamine tautomers of the protein-coenzyme internal aldimine. Their relative abundance is estimated to be 4:1, whereas the ratio of their two-photon cross sections is reversed with respect to the single-photon excitation case. Consistent results are obtained from the measurement of the lifetime decays, which are sensitive to the excited-state heterogeneity. At least two components were detected, with lifetimes of approximately 2.5 and 0.5 ns. The lifetimes are very close to the values measured in bulk solutions upon one-photon excitation and attributed to the ketoenamine tautomer and to a dipolar species formed upon proton dissociation in the excited state.

Biochemistry↗
PubMed2001

Radiotherapy for advanced adenoid cystic carcinoma: neutrons, photons or mixed beam?

PURPOSE: To compare retrospectively radiotherapy with neutrons, photons, and a photon/neutron mixed beam in patients with advanced adenoid cystic carcinoma of the head and neck. Local control, survival, distant failure, and complications were analyzed. MATERIALS AND METHODS: Between 1983 and 1995, 75 patients with inoperable, recurrent, or incompletely resected adenoid cystic carcinoma of the head and neck received radiotherapy that consisted of either fast 14.1 MV DT neutrons (median dose 16 neutron Gy), linac-based photon irradiation (median dose 64 photon Gy), or both (median dose 8 neutron Gy and 32 photon Gy). Follow-up ranged from 1 to 160 months (median 51 months), and the surviving patients had a minimum follow-up of 3 years at the time of analysis. RESULTS: The actuarial 5-year local control was 75% for neutrons, and 32% for both mixed beam and photons (P = 0.015, log-rank). This advantage for neutrons in local control was not transferred to significant differences in survival (P > 0.1). The survival is dictated by the tumor diseases due to distant metastases occurring in 29 (39%) of the 75 patients. Positive lymph nodes were the only significant factor (P = 0.001) associated with the development of distant metastases although negative lymph nodes did not predict absence of distant metastases, but predicted a delay of occurrence. In multivariate analysis postoperative radiotherapy (P = 0.003) and small tumor size (P = 0.01) were associated with high local control, while primary therapy (P = 0.006) and negative lymph nodes (P = 0.01) were associated with longer survival. While acute toxicity was similar in all three radiotherapy groups, severe late grade 3 and 4 toxicity tended to be more prevalent (P > 0.1) with neutrons (19%) than with mixed beam (10%) and photons (4%). CONCLUSION: Fast neutron radiotherapy provides higher local control rates than a mixed beam and photons in advanced, recurrent or not completely resected adenoid cystic carcinoma of the major and minor salivary glands. Neutron radiotherapy can be recommended in patients with bad prognosis with gross residual disease (R2), with unresectable tumors, or inoperable tumors. The type of radiation does not impact survival, which is dominated by the high number of distant metastases.

Adult↗
PubMed2000

Radiotherapy of advanced mycosis fungoides: indications and results of total skin electron beam and photon beam irradiation.

BACKGROUND: The goals of this retrospective study of advanced mycosis fungoides are (1) to describe the indications of a combination of total skin electron beam and photon beam irradiation and (2) to analyze the results of total body or segmental photon irradiation for patients with extension beyond the skin. METHODS: From January 1975 to December 1995, 45 patients with pathologically-confirmed mycosis fungoides or Sézary syndrome received a combination of TSEB and photon beam irradiation for advanced disease: 34 males and 11 females, mean age 61 years (range 27-87 years). The mean follow-up was 111 months (range 18-244 months, median 85 months). Whole-skin irradiation treatment to a depth of 3-5 mm with a 6-MeV electron beam was produced by a linear accelerator to a total dose of 24-30 Gy in 8-15 fractions, 3-4 times a week. In cases of thick plaques or tumors that were beyond the scope of low energy electron beams or for treating nodal areas (especially in the head and neck area or axilla involvement), regional irradiation (RRT) with Co-60 photon beams was followed by whole-skin electron beam irradiation (15 patients). In cases of diffuse erythrodermia, Sézary syndrome, nodal or visceral involvement, total body irradiation was delivered with a 25-MV photon beam using a split-course regimen to prevent hematological toxicity (22 patients). The first course consisted of 1.25 Gy delivered in ten fractions and 10 days. Subsequently, patients received TSEB. Four to 6 weeks after TSEB, they received a second course of 1.25 Gy. The cumulative TBI dose ranged from 2.5 to 3 Gy in about 3 months. Hemi-body irradiation (HB) with Co-60 (and a bolus) was given in cases of multiple regional tumors with large and thick infiltration of the skin to a dose of 9-12 Gy (using fractions of 1-1.5 Gy/day) which, once flattened, were boosted with whole-skin electron beam therapy (8 patients). RESULTS: At 3 months, the overall response rate was 75% with 23/45 (51%) patients in complete response and 24% in partial response; one patient had stable lesions and 1 patient presented progressive disease. The overall response rate was 81% for T3 patients, 61% for T4, 79% for N1 and 70% for N3. The complete response rate was 67% for T3 and 28% for T4. Sixty-four percent of N1 patients and 41% of N3 had a complete response. The 5-year actuarial overall survival was 37% for T3 and 44% for T4 (P = 0.84). Patients with clinically abnormal lymph nodes that were pathologically negative (N1) presented a 5-year survival of 63%. Patients with pathologically positive lymph nodes (N3) experienced a 5-year survival rate of 32% (P = 0.040). CONCLUSIONS: TSEB provides an excellent quality of life by reducing itching and discharge from the skin. Patients with more advanced disease may be treated and cured by the addition of photon beams in combination with TSEB. A selection of patients with advanced skin disease and regional extension may be cured by a combination of TSEB and photon beam irradiation. The regional treatment allows the use of electrons after the reduction of the plaques or thick tumors and a prophylactic irradiation of the adjacent nodal area.

Adult↗
PubMed1999

In vivo imaging of spontaneous ultraweak photon emission from a rat's brain correlated with cerebral energy metabolism and oxidative stress.

Living cells spontaneously emit ultraweak light during the process of metabolic reactions associated with the physiological state. The first demonstration of two-dimensional in vivo imaging of ultraweak photon emission from a rat's brain, using a highly sensitive photon counting apparatus, is reported in this paper. It was found that the emission intensity correlates with the electroencephalographic activity that was measured on the cortical surface and this intensity is associated with the cerebral blood flow and hyperoxia. To clarify the mechanism of photon emission, intensity changes from whole brain slices were examined under various conditions. The removal of glucose from the incubation medium suppressed the photon emission, and adding 50 mM potassium ions led to temporal enhancement of emission and subsequent depression. Rotenone (20 microM), an inhibitor of the mitochondrial electron transport chain, increased photon emission, indicating electron leakage from the respiratory chain. These results suggest that the photon emission from the brain slices originates from the energy metabolism of the inner mitochondrial respiratory chain through the production of reactive oxygen. Imaging of ultraweak photon emission from a brain constitutes a novel method, with the potential to extract pathophysiological information associated with neural metabolism and oxidative dysfunction of the neural cells.

Animals↗
PubMed2004

Benchmark of PENELOPE code for low-energy photon transport: dose comparisons with MCNP4 and EGS4.

The expanding clinical use of low-energy photon emitting 125I and 103Pd seeds in recent years has led to renewed interest in their dosimetric properties. Numerous papers pointed out that higher accuracy could be obtained in Monte Carlo simulations by utilizing newer libraries for the low-energy photon cross-sections, such as XCOM and EPDL97. The recently developed PENELOPE 2001 Monte Carlo code is user friendly and incorporates photon cross-section data from the EPDL97. The code has been verified for clinical dosimetry of high-energy electron and photon beams, but has not yet been tested at low energies. In the present work, we have benchmarked the PENELOPE code for 10-150 keV photons. We computed radial dose distributions from 0 to 10 cm in water at photon energies of 10-150 keV using both PENELOPE and MCNP4C with either DLC-146 or DLC-200 cross-section libraries, assuming a point source located at the centre of a 30 cm diameter and 20 cm length cylinder. Throughout the energy range of simulated photons (except for 10 keV), PENELOPE agreed within statistical uncertainties (at worst +/- 5%) with MCNP/DLC-146 in the entire region of 1-10 cm and with published EGS4 data up to 5 cm. The dose at 1 cm (or dose rate constant) of PENELOPE agreed with MCNP/DLC-146 and EGS4 data within approximately +/- 2% in the range of 20-150 keV, while MCNP/DLC-200 produced values up to 9% lower in the range of 20-100 keV than PENELOPE or the other codes. However, the differences among the four datasets became negligible above 100 keV.

Benchmarking↗
PubMed2006

An assessment of bone marrow and bone endosteum dosimetry methods for photon sources.

The rather complex and microscopic histological structure of the skeletal system generally limits one's ability to accurately model this tissue during dosimetric evaluations. Consequently, various assumptions must be made to evaluate the absorbed dose from external and internal photons to the radiosensitive tissues of the red (or haematopoietically active) bone marrow and the osteogenic tissues of the skeletal endosteum. These various methods for photon skeletal dosimetry have not been inter-compared, partly due to the lack of a realistic reference model that can provide a high-resolution three-dimensional geometry for secondary electron particle transport. In the present study, the paired-image radiation transport (PIRT) model developed by Shah et al (2005 J. Nucl. Med. 45 344) was utilized to evaluate the absorbed dose per incident photon fluence to these skeletal regions from idealized parallel beams of monoenergetic photons. The PIRT model results were then used as a local reference against which absorbed doses via other methods were compared. For red bone marrow dosimetry, four approximate techniques were considered: (1) the dose response function method (DRF method) presented in ORNL/TM-8381, (2) the mass-energy absorption coefficient ratio method (two-parameter MEAC method), (3) the MEAC method with the additional use of energy-dependent dose enhancement factors from King and Spiers (1985 Br. J. Radiol. 58 345) (three-parameter MEAC method), and (4) the three-parameter MEAC method applied at the voxel level through the use image-specific CT numbers (CTN method). For the bone endosteum (i.e., bone surfaces), two approximate techniques were compared: (1) the DRF method for bone surfaces and (2) the homogeneous bone approximation (HBA) method. In each case, the local reference standard was assumed to be that of the PIRT model. Four different ex vivo bone specimens with distinctively different internal structures were used in the study: the cranium, the lumbar vertebra, the os coxae and the left middle rib, each excised from a 66 year male cadaver (body mass index, 22.7 kg m(-2)). High-resolution CT images of these skeletal sites were used to construct computational voxel models for Monte Carlo radiation transport. Study results indicated that skeletal sites with thick cortical regions and thick trabeculae such as in the cranium provide considerable beam attenuation at low photon energies, which is not properly accounted for in methods based on a homogeneous skeletal tissue structure (DRF, MEAC, HBA). For bone marrow dose assessment, the CTN method showed the best agreement with PIRT model results over a broad range of photon energies, while the HBA method showed better agreement with the PIRT model in assessing bone endosteum dose at energies above 100 keV. Bone surface doses were better approximately by the DRF method at energies below 50 keV. Considerable secondary electron escape at photon energies over 1-3 MeV were accounted for in RBM dose assessment only in the PIRT model, as the other methods presume either an infinite expanse of spongiosa (DRF) or the existence of charge-particle equilibrium (MEAC, CTN).

Aged↗
PubMed2006

Monte Carlo simulation of MOSFET detectors for high-energy photon beams using the PENELOPE code.

The aim of this work was the Monte Carlo (MC) simulation of the response of commercially available dosimeters based on metal oxide semiconductor field effect transistors (MOSFETs) for radiotherapeutic photon beams using the PENELOPE code. The studied Thomson&Nielsen TN-502-RD MOSFETs have a very small sensitive area of 0.04 mm(2) and a thickness of 0.5 microm which is placed on a flat kapton base and covered by a rounded layer of black epoxy resin. The influence of different metallic and Plastic water build-up caps, together with the orientation of the detector have been investigated for the specific application of MOSFET detectors for entrance in vivo dosimetry. Additionally, the energy dependence of MOSFET detectors for different high-energy photon beams (with energy >1.25 MeV) has been calculated. Calculations were carried out for simulated 6 MV and 18 MV x-ray beams generated by a Varian Clinac 1800 linear accelerator, a Co-60 photon beam from a Theratron 780 unit, and monoenergetic photon beams ranging from 2 MeV to 10 MeV. The results of the validation of the simulated photon beams show that the average difference between MC results and reference data is negligible, within 0.3%. MC simulated results of the effect of the build-up caps on the MOSFET response are in good agreement with experimental measurements, within the uncertainties. In particular, for the 18 MV photon beam the response of the detectors under a tungsten cap is 48% higher than for a 2 cm Plastic water cap and approximately 26% higher when a brass cap is used. This effect is demonstrated to be caused by positron production in the build-up caps of higher atomic number. This work also shows that the MOSFET detectors produce a higher signal when their rounded side is facing the beam (up to 6%) and that there is a significant variation (up to 50%) in the response of the MOSFET for photon energies in the studied energy range. All the results have shown that the PENELOPE code system can successfully reproduce the response of a detector with such a small active area.

Algorithms↗
PubMed1996

Comparison of exercise stress testing with simultaneous dobutamine stress echocardiography and technetium-99m isonitrile single-photon emission computerized tomography for diagnosis of coronary artery disease.

The object of our study was to compare the value of exercise stress testing with simultaneous dobutamine stress echocardiography and technetium-99m isonitrile single-photon emission computed tomography for the diagnosis of coronary artery disease. Sixty-nine patients with either suspected or proven coronary artery disease underwent simultaneous dobutamine technetium-99m isonitrile single-photon emission computed tomography and stress echocardiography, and treadmill exercise electrocardiography. Dobutamine echocardiography and technetium-99m isonitrile single-photon emission computed tomography revealed a higher overall sensitivity than exercise testing (94 vs 60%, P < 0.001), but dobutamine stress echocardiography showed a higher specificity than both technetium-99m isonitrile single-photon emission computed tomography and exercise testing (86 vs 64%, P < 0.05, for both tests). In addition, the diagnostic accuracy of dobutamine stress echocardiography and technetium-99m isonitrile single-photon emission computed tomography was higher than that of exercise testing (91 vs 61%, P < 0.001; 86 vs 61%, P < 0.001, respectively). Dobutamine stress echocardiography and technetium-99m isonitrile single-photon emission computed tomography are superior to exercise testing in the diagnosis of coronary artery disease, and dobutamine stress echocardiography can act as an alternative to technetium-99m isonitrile single-photon emission computed tomography.

Adult↗
PubMed1994

Two-photon molecular excitation provides intrinsic 3-dimensional resolution for laser-based microscopy and microphotochemistry.

With the development of sensitive and specific fluorescent indicators, modern laser scanning microscopies enable visualization and measurement of submicron, dynamic processes inside living cells and tissues. Here we describe the working principles of new, nonlinear laser microscopies based on two-photon molecular excitation. In these techniques, a pulsed laser produces peak photon densities high enough that when focused into an appropriate medium, excitation by photon energy combinations can occur. For example, two red photons interacting simultaneously with a fluorescent molecule can excite within it a UV electronic transition, one corresponding to twice the energy of each single photon. Because the amount of two-photon excitation depends on the square of the local illumination intensity, this process exhibits a unique localization to the diffraction-limited spot of the beam focus. Elsewhere along the beam, excitation of background and photodamage is virtually nonexistent. Focal point localization of two-photon excitation lends to all visualization, measurement, and photopharmacology studies an intrinsic, three-dimensional resolution. We describe some preliminary biological applications, specifically, imaging of vital DNA stains in developing cells and embryos, imaging of cellular metabolic activity from NADH autofluorescence, spatially resolved measurements of cytoplasmic calcium ion activity, and optically induced micropharmacology using caged bioeffector molecules.

Animals↗
PubMed1995

Alternating conformal neutron and photon irradiation for locally advanced adenocarcinoma of the prostate.

The substantial local failure rate for patients with locally advanced carcinoma of the prostate (LACaP) following photon irradiation, the association of local failure with a poor prognosis, and the promising results of mixed neutron/photon (40%/60%) radiotherapy supplied the rationale for this study. The purpose of this study was to evaluate the combined advantages of mixed neutron/photon (75%/25%) irradiation, 3D treatment planning, as well as fully conformal beam shaping capabilities in reducing the morbidity associated with neutron irradiation. The first 35 patients treated with this technique are the basis for this analysis. After CT stimulation and treatment planning, the normal tissue and target structures were entered into the 3D planning system. The neutron dose was delivered in 15 fractions at 1.0 Gy/fraction (NGy) to the prostate and seminal vesicles (PSV) and 0.6 NGy/fraction to the pelvic lymph nodes (LN). The photon dose was given in 10 fractions of 1.8 Gy each to both the PSV and LN volumes. Neutron and photon dose-volume histograms (DVHs) were generated in each patient for the prostate, seminal vesicles, lymph nodes, bladder, and rectum. The adequacy of the neutron and photon components of the treatment were compared with respect to target volume and normal tissue irradiation. Based on the DVH analysis, the prostate and seminal vesicles received the prescribed dose with both neutrons (99% +/- 2%) and photons (99% +/- 2%). There was no significant difference in the dose to the bladder and rectum for both the neutrons and photons. The acute treatment related reactions have been mild, with only one grade III bladder reaction. The 3D conformal technology utilized in this study has been shown to allow for the delivery of neutron irradiation with no increase in dose to the adjacent normal tissues compared with that achieved with conformal photon treatment. Further follow-up will reveal whether the dosimetric advantage demonstrated by this technique translates into an improved therapeutic ratio.

Adenocarcinoma↗