Influence Of Photon Energy Research Articles

Performance testing of dosimeters used in interventional radiology: Results from the VERIDIC project

Interventional procedures in radiology and cardiology are associated with high dose to the patient. Accurate dosimetry is essential and calibration of the equipment is a means to provide the necessary accuracy of dose assessment.The objective of this work is to investigate the performance of dosimeters used in interventional procedures in different standard and non-standard X-ray radiation qualities, and to investigate potential uncertainties related to dose measurements, thus improving accuracy of patient dosimetry in interventional procedures.Four new reference radiation qualities dedicated to interventional cardiology applications have been established, allowing calibration of dosimeters used in clinical conditions with appropriate traceability to primary standards. Testing of solid-state semiconductor detectors and thermoluminescent dosimeter properties, e.g. influence of photon energy, angle of incidence and dose rate, was performed in the standard and non-standard radiation qualities.Both dosimeter types showed good performance in the non-standard beams during all performance tests. Solid-state dosimeters displayed weak dependence on energy, angle of incidence and dose rate, in the range defined by the manufacturer and requirements of the international standard. Thermoluminescent dosimeters displayed excellent linearity and angular dependence. The influence of energy dependence on measurement uncertainty can be reduced if appropriate radiation quality is selected for calibration.

How crystal configuration affects the position detection accuracy in pixelated molecular SPECT imaging systems?

It is well known that inter-crystal scattering and penetration (ICS–P) are major spatial resolution limiting parameters in dedicated SPECT scanners with pixelated crystal. In this study, the effect of ICS–P on crystal identification in different crystal configurations was evaluated using GATE Monte Carlo simulation. A 99mTc pencil-beam toward central crystal element was utilized. Beam incident angle was assumed to vary from 0° to 45° in 5° steps. The effects of various crystal configurations such as pixel-size, pixel-gap, and crystal material were studied. The influence of photon energy on the crystal identification (CI) was also investigated. Position detection accuracy (PDA) was defined as a factor indicating performance of the crystal. Furthermore, a set of 99mTc point-source simulations was performed in order to calculate peak-to-valley (PVR) ratio for each configuration. The results show that the CsI(Na) manifests higher PDA than NaI(Tl) and YAP(Ce). In addition, as the incident angle increases, the crystal becomes less accurate in positioning of the events. Beyond a crystal-dependent critical angle, the PDA monotonically reduces. The PDA reaches 0.44 for the CsI(Na) at 45° beam angle. The PDAs obtained by the point-source evaluation also behave the same as for the pencil-beam irradiations. In addition, the PVRs derived from flood images linearly correlate their corresponding PDAs. In conclusion, quantitative assessment of ICS–P is mandatory for scanner design and modeling the system matrix during iterative reconstruction algorithms for the purpose of resolution modeling in ultra-high-resolution SPECT.

Studies on energy absorption and exposure buildup factors in some solutions of alkali metal chlorides

Buildup of photons has been investigated through the solutions LiCl, NaCl and KCl with different salt contents in the energy region 0.015-15 MeV up to a penetration depth of 40 mean free paths. Two types of buildup factors, the gamma ray energy absorption () and exposure buildup factors () have been calculated simultaneously using the five parameter geometric progression (G-P) fitting formula. The influence of photon energy, penetration depth and chemical composition on the buildup factors has been studied. Also, a comparison has been made between the values of and if any significant variation occurs between them. Moreover, the Monte Carlo simulation study has been made for the purpose of the comparison. Key words: Gamma ray buildup factor, energy absorption, exposure, solution, Monte Carlo method.

Influence of photon energy on the quality of prostate intensity modulated radiation therapy plans based on analysis of physical indices

The goal of the present study was to study the effects of low- and high-energy intensity-modulated photon beams on the planning of target volume and the critical organs in cases of localized prostate tumors in a cohort of 8 patients. To ensure that the difference between the plans is due to energy alone, all other parameters were kept constant. A mean dose volume histogram (DVH) for each value of energy and for each contoured structure was created and was considered as completely representative for all patients. To facilitate comparison between 6-MV and 15-MV beams, the DVH-s were normalized. The different parameters that were compared for 6-MV and 15-MV beams included mean DVH, different homogeneity indices, conformity index, etc. Analysis of several indices depicts more homogeneous dose for 15-MV beam and more conformity for 6-MV beam. Comparison of all these parameters showed that there was little difference between the 6-MV and 15-MV beams. For rectum, 2 to 4 % more volume received high dose with the 6-MV beam in comparison with the 15-MV beam, which was not clinically significant, since in practice much tighter constraints are maintained, such that Normal Tissue Complication Probability (NTCP) is kept within 5 %. Such tighter constraints might increase the dose to other regions and other critical organs but are unlikely to increase their complication probabilities. Hence the slight advantages of 15-MV beam in providing benefits of better normal-tissue sparing and better coverage cannot be considered to outweigh its well-known risk of non-negligible neutron production.

Influence of Photon Energy on Carcinoma of Cervix IMRT Plans

Influence of Photon Energy on Carcinoma of Cervix IMRT Plans

Influence of photon energy on the efficiency of photochemotherapy

It is found that when indotricarbocyanine dye in HeLa cells is exposed to photons with different energies the efficiency of cell damage is wavelength independent provided the photosensitizer absorbs the same number of photons per unit time. In vivo animal experiments with two strains of tumor show that when the wavelength of the irradiating light is increased (668, 740, and 780 nm) and the number of photons absorbed per unit time per unit volume of the tumors is held constant, the damage depth increases by a factor of 1.5 and 3, respectively. The observed changes are related both to differences in the in vivo tissue optical transmission with increasing wavelength and an increased local concentration of oxygen owing to photodissociation of oxyhemoglobin.

In situ gamma-ray spectrometry for environmental monitoring: a semi empirical calibration method

In situ gamma spectrometry using high-purity germanium (HPGe) detectors is a frequently used method for the determination of radionuclide ground deposition levels. Such measurements do, however, require an efficiency calibration based on detector sensitivity and parameters such as soil density and vertical activity distribution. In this work, a novel expression is used for the detector efficiency, incorporating both the influence of photon energy and incidence angle. Detector-specific efficiency data are determined empirically. For the theoretical calculation of the photon fluence at the detector, a three-layer model of finite thickness is developed for the description of soil density and vertical activity distribution. In order to facilitate the calibration of in situ measurements, a PC program has been developed to enable rapid, on-site calculations of radionuclide ground deposition levels. The semi empirical calibration method was tested on in situ measurements with two different detectors, and the results show good agreement with results obtained from traditional soil sampling.

Influence of photon energy on the processes of irreversible photochanges of polymethine dyes

Influence of photon energy on the processes of irreversible photochanges of polymethine dyes

Resolving power of radioactive solution level gauging

The response and resolving power functions were developed for a radiation source whose intensity, geometry and location vary with the property measured. The approach is demonstrated for the measurement of the level of radioactive solution in a container. The measurement system should include an interpretation/control program which accumulates information from a few detector assemblies located externally or inside the container. The functions show that as filling starts a saturation layer is formed and later it is pushed upward in the container. The influence of photon energy, half-life, homogeneity of the solution and filling history is discussed. The approach is a useful tool at the design step for choosing between options. The system's memory and algorithms depend on the characteristics of the solutions and the historical data. With suitable design a resolving power of 5% in the measured volume may be achieved.