A comprehensive review on photon-counting computed tomography: Principles, technical hurdles and analysis of clinical applications / 生物医学工程学杂志

In recent years, photon-counting computed tomography (PCD-CT) based on photon-counting detectors (PCDs) has become increasingly utilized in clinical practice. Compared with conventional CT, PCD-CT has the potential to achieve micron-level spatial resolution, lower radiation dose, negligible electronic noise, multi-energy imaging, and material identification, etc. This advancement facilitates the promotion of ultra-low dose scans in clinical scenarios, potentially detecting minimal and hidden lesions, thus significantly improving image quality. However, the current state of the art is limited and issues such as charge sharing, pulse pileup, K-escape and count rate drift remain unresolved. These issues could lead to a decrease in image resolution and energy resolution, while an increasing in image noise and ring artifact and so on. This article systematically reviewed the physical principles of PCD-CT, and outlined the structural differences between PCDs and energy integration detectors (EIDs), and the current challenges in the development of PCD-CT. In addition, the advantages and disadvantages of three detector materials were analysed. Then, the clinical benefits of PCD-CT were presented through the clinical application of PCD-CT in the three diseases with the highest mortality rate in China (cardiovascular disease, tumour and respiratory disease). The overall aim of the article is to comprehensively assist medical professionals in understanding the technological innovations and current technical limitations of PCD-CT, while highlighting the urgent problems that PCD-CT needs to address in the coming years.

Photosynthesis of Physalis peruviana under different densities of photons and saline stress

Physalis peruviana L. is a solanacea that has been gaining prominence due to its fruits presenting good acceptance in the national and international market. However, several abiotic factors, such as salinity, can cause physiological disturbances in plants, and these changes may be of greater or lesser intent according to species. Therefore, the objective of the present work was to evaluate the physiological behavior of P. peruviana submitted to different fluxes of photosynthetically active photons (PPFD) and saline stress. The experimental design was a randomized block design with three saline levels (ECw) (0.5, 2.75 and 5.00 dS m-1) with four replications. Gas exchange measurements were performed with a portable infrared gas analyzer. Liquid CO2 assimilation, stomatal conductance, internal CO2 concentration, water use efficiency and instantaneous carboxylation efficiency were measured. Data were subjected to analysis of variance by F test and in cases of significance applied to regression analysis. The increase in PPFD provided reductions in stomatal conductance up to the density of approximately 400 µmol m-2s-1, being more pronounced in ECw of 2.75 and 5.0 dS m-1. The maximum CO2 assimilation rates in the three salinities are different according to the PPFD. The salinity of irrigation water reduced the quantum efficiency of photosynthesis in P. peruviana plants.

Perfil clínico, epidemiológico y descripción de los resultados de la Tomografía ósea computarizada con emisión simple de fotones (SPECT) en pacientes con dolor de cuello y espalda. Estudio de cohorte transversal / Clinical and epidemiological profile and description of the results of bone single photon emission computed tomography (SPECT) in patients with neck and back pain: Cross-sectional study

Introducción La tomografía ósea computarizada (TAC) con emisión simple de fotones (SPECT: single photon emission computed tomography) es una herramienta diagnóstica importante en los pacientes con dolor de cuello y espalda. Es una prueba funcional que se adelanta a los cambios estructurales en algunas patologías de columna. El objetivo del estudio es definir el perfil epidemiológico de pacientes con dolor axial crónico y/o subagudo en la columna vertebral. Materiales y Métodos Serie de casos cuyo objetivo general es presentar las características clínicas y sociodemográficas, así como los resultados de TAC con SPECT de los pacientes que consultaron al Hospital en un periodo de tiempo con diagnóstico de dolor de cuello o espalda y se les solicitó dicho examen. Resultados 77 pacientes cumplieron los criterios de inclusión, La mediana para la edad fue de 48 años, 57.1% eran hombres y 42.9% mujeres. 57 pacientes tenían localización única del dolor (74%) y 20 pacientes tenían localización múltiple (26%), los segmentos afectados fueron 57 lumbar (74%), cervical 15 (19.5%) y sacro 1 (1.3%). La impresión diagnóstica preexamen más común fue enfermedad facetaría en 25 casos para un 32.5%. En cuanto a los resultados del SPECT el radiofármaco captó en 48 ocasiones (62.3%) y los sitios en que captó el radiofármaco se distribuyeron así: facetas 13 (16.9%), cuerpo vertebral 28 (36.4%), Pars Interarticularis 3 (3.8%), disco intervertebral 1 (1.3%), 3 (3.8%) captaron en sitios diferentes al raquis, El índice de concordancia diagnóstica luego del SPECT se dio en 33 casos (42.85%). Discusión La mayoría de las gammagrafías con captación fueron en los cuerpos vertebrales, en el contexto de nuestro hospital como centro de trauma y que muchos de los pacientes tenían dolor secundario a accidentes de tránsito o accidentes laborales, se correlacionan con microfracturas o contusiones óseas. La gammagrafía con SPECT sigue siendo una prueba funcional que nos puede ayudar en el diagnóstico, pronóstico y enfoque terapéutico de los pacientes con dolor raquídeo axial en sus diferentes estadios.

Background SPECT bone scan with is an important diagnostic tool in patients with neck and back pain. It is a functional test that anticipates structural changes in some spinal pathologies. Aim of study is to define the epidemiological profile of patients with chronic and/or subacute axial spine pain. Methods A retrospective descriptive study whose general objective is to present the clinical and sociodemographic characteristics, as well as the results of the SPECT scans of the patients who visited the Hospital in a period of time with a diagnosis of neck or back pain and were requested such an examination. Results Seventy-seven patients met the inclusion criteria. The median age was 48 years, 57.1% were men and 42.9% were women. Fifty-seven patients had a single location of pain (74%) and 20 patients had multiple location (26%), the affected segments were 57 lumbar (74%), cervical 15 (19.5%) and sacrum 1 (1.3%). The most common pre-examination diagnostic impression was facet disease in 25 cases for 32.5%. Regarding the SPECT results, the radiopharmaceutical captured on 48 occasions (62.3%) and the sites where it captured the radiopharmaceutical were distributed as follows: facets 13 (16.9%), vertebral body 28 (36.4%), pars interarticularis 3 (3.8%).), intervertebral disc 1 (1.3%), 3 (3.8%) captured in sites other than the spine. The diagnostic concordance index after SPECT occurred in 33 cases (42.85%). Discussion Most of the uptake scans were in the vertebral bodies, beneath the context of our hospital, as a trauma center, and that many of the patients had pain secondary to traffic accidents or work behavior accidents, they are correlated with micro-fractures or bone contusions. SPECT scintigraphy continues to be a functional test that can help us in the diagnosis, prognosis and therapeutic approach of patients with axial spinal pain in its different stages.

Kinetic characterization and modeling of a microalgae consortium isolated from landfill leachate under a high CO2 concentration in a bubble column photobioreactor

BACKGROUND: The determination of kinetic parameters and the development of mathematical models are of great interest to predict the growth of microalgae, the consumption of substrate and the design of photobioreactors focused on CO2 capture. However, most of the models in the literature have been developed for CO2 concentrations below 10%. RESULTS: A nonaxenic microalgal consortium was isolated from landfill leachate in order to study its kinetic behavior using a dynamic model. The model considered the CO2 mass transfer from the gas phase to the liquid phase and the effect of light intensity, assimilated nitrogen concentration, ammonium concentration and nitrate concentration. The proposed mathematical model was adjusted with 13 kinetic parameters and validated with a good fit obtained between experimental and simulated data. CONCLUSIONS: Good results were obtained, demonstrating the robustness of the proposed model. The assumption in the model of DIC inhibition in the ammonium and nitrate uptakes was correct, so this aspect should be considered when evaluating the kinetics with microalgae with high inlet CO2 concentrations.

Recent trends in two-photon auto-fluorescence lifetime imaging (2P-FLIM) and its biomedical applications

Two photon fluorescence microscopy and the numerous technical advances to it have served as valuable tools in biomedical research. The fluorophores (exogenous or endogenous) absorb light and emit lower energy photons than the absorption energy and the emission (fluorescence) signal is measured using a fluorescence decay graph. Additionally, high spatial resolution images can be acquired in two photon fluorescence lifetime imaging (2P-FLIM) with improved penetration depth which helps in detection of fluorescence signal in vivo. 2P-FLIM is a non-invasive imaging technique in order to visualize cellular metabolic, by tracking intrinsic fluorophores present in it, such as nicotinamide adenine dinucleotide, flavin adenine dinucleotide and tryptophan etc. 2P-FLIM of these molecules enable the visualization of metabolic alterations, non-invasively. This comprehensive review discusses the numerous applications of 2P-FLIM towards cancer, neuro-degenerative, infectious diseases, and wound healing.

Advances in the simulation of light–tissue interactions in biomedical engineering

Monte Carlo (MC) simulation for light propagation in scattering and absorbing media is the gold standard for studying the interaction of light with biological tissue and has been used for years in a wide variety of cases. The interaction of photons with the medium is simulated based on its optical properties and the original approximation of the scattering phase function. Over the past decade, with the new measurement geometries and recording techniques invented also the corresponding sophisticated methods for the description of the underlying light–tissue interaction taking into account realistic parameters and settings were developed. Applications, such as multiple scattering, optogenetics, optical coherence tomography, Raman spectroscopy, polarimetry and Mueller matrix measurement have emerged and are still constantly improved. Here, we review the advances and recent applications of MC simulation for the active field of the life sciences and the medicine pointing out the new insights enabled by the theoretical concepts.

Radioembolization for the Treatment of Primary and Metastatic Liver Cancers / 대한핵의학회잡지

Radioembolization using ⁹⁰Y microspheres (glass or resin) has been introduced as an effective intraarterial therapy for unresectable primary and metastatic liver cancers. Although the basic therapeutic effect of chemoembolization results from ischemia, the therapeutic efficacy of radioembolization comes from radiation. Furthermore, compared with surgical resection and local ablation therapy, radioembolization is available with less limitation on the sites or number of liver cancers. The radioisotope ⁹⁰Y is a β-radiation emitter without γ-radiation, with the emission of secondary bremsstrahlung photons and small numbers of positrons. Administration of ⁹⁰Y microspheres into the hepatic artery can deliver a high dose of radiation selectively to the target tumor with limited radiation exposure to the surrounding normal parenchyma, and has low systemic toxicity. In general, radioembolization has been considered for patients with unresectable primary or metastatic liver-only or liver-dominant cancers with no ascites or other clinical signs of liver failure, life expectancy of > 12 weeks, and good performance status. Here, we review the current radioactive compounds, pretreatment assessment, and indications for radioembolization in patients with hepatocellular carcinoma, intrahepatic cholangiocarcinoma, and liver metastases from colorectal cancer.

Simulation of dose distribution in bone medium of 125I photon emitting source with Monte Carlo method / 北京大学学报(医学版)

OBJECTIVE@#To present a theoretical analysis of how the presence of bone in interstitial brachytherapy affects dose rate distributions with MCNP4C Monte Carlo code and to prepare for the next clinical study on the dose distribution of interstitial brachytherapy in head and neck neoplasm.@*METHODS@#Type 6711,125I brachytherapy source was simulated with MCNP4C Monte Carlo code whose cross section library was DLC-200. The dose distribution along the transverse axis in water and dose constant were compared with the American Association of Physicists in Medicine (AAPM) TG43UI update dosimetry formalism and current literature. The validated computer code was then applied to simple homogeneous bone tissue model to determine the affected different bone tissue had on dose distribution from 125I interstitial implant.@*RESULTS@#125I brachytherapy source simulated with MCNP4C Monte Carlo code met the requirements of TG43UI report. Dose rate constant, 0.977 78 cGy/(h×U), was in agreement within 1.32% compared with the recommended value of TG43UI. There was a good agreement between TG43UI about the dosimetric parameters at distances of 1 to 10 cm along the transverse axis of the 125I source established by MCNP4C and current published data. And the dose distribution of 125I photon emitting source in different bone tissue was calculated. Dose-deposition capacity of photons was in decreasing order: cortical bone, spongy bone, cartilage, yellow bone marrow, red bone marrow in the same medium depth. Photons deposited significantly in traversal axis among the phantom material of cortical bone and sponge bone relevant to the dose to water. In the medium depth of 0.01 cm, 0.1 cm, and 1 cm, the dose in the cortical bone was 12.90 times, 9.72 times, and 0.30 times of water respectively.@*CONCLUSION@#This study build a 125I source model with MCNP4C Monte Carlo code, which is validated, and could be used in subsequent study. Dose distribution of photons in different bone medium is not the same as water, and its main energy deposits in bone medium surface, so we should consider the effect of bone medium when we design the target area adjacent to the bone tissue in 125I sources implantation plan.

Transcriptional and translational responses of rapeseed leaves to red and blue lights at the rosette stage / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Under different red (R):blue (B) photon flux ratios, the growth performance of rapeseed (Brassica napus L.) is significantly different. Rapeseed under high R ratios shows shade response, while under high B ratios it shows sun-type morphology. Rapeseed under monochromatic red or blue light is seriously stressed. Transcriptomic and proteomic methods were used to analyze the metabolic pathway change of rapeseed (cv. "Zhongshuang 11") leaves under different R:B photon flux ratios (including 100R:0B%, 75R:25B%, 25R:75B%, and 0R:100B%), based on digital gene expression (DGE) and two-dimensional gel electrophoresis (2-DE). For DGE analysis, 2054 differentially expressed transcripts (|log2(fold change)|≥1, q<0.005) were detected among the treatments. High R ratios (100R:0B% and 75R:25B%) enhanced the expression of cellular structural components, mainly the cell wall and cell membrane. These components participated in plant epidermis development and anatomical structure morphogenesis. This might be related to the shade response induced by red light. High B ratios (25R:75B% and 0R:100B%) promoted the expression of chloroplast-related components, which might be involved in the formation of sun-type chloroplast induced by blue light. For 2-DE analysis, 37 protein spots showed more than a 2-fold difference in expression among the treatments. Monochromatic light (ML; 100R:0B% and 0R:100B%) stimulated accumulation of proteins associated with antioxidation, photosystem II (PSII), DNA and ribosome repairs, while compound light (CL; 75R:25B% and 25R:75B%) accelerated accumulation of proteins associated with carbohydrate, nucleic acid, amino acid, vitamin, and xanthophyll metabolisms. These findings can be useful in understanding the response mechanisms of rapeseed leaves to different R:B photon flux ratios.

Fontes de obtenção de medicamentos para tratamento de hipertensão arterial no Brasil: análise da Pesquisa Nacional de Saúde, 2013 / Sources for obtaining drugs for hypertension in Brazil: results from the National Health Survey, 2013

RESUMO: Objetivo: Analisar as diferenças sociodemográficas dos indivíduos adultos hipertensos, em relação às fontes de obtenção de medicamentos para tratar hipertensão arterial no Brasil. Métodos: Análise secundária dos dados oriundos da Pesquisa Nacional de Saúde, 2013; os desfechos considerados nas análises foram representados pelas fontes de obtenção de medicamentos para tratar a hipertensão arterial. Resultados: Foram entrevistados 10.017 indivíduos. A grande maioria dos hipertensos em uso de medicamentos (74,0%) utiliza uma fonte única de obtenção de medicamentos 7,3% (IC95% 6,4 - 8,4) referiu obter todos os medicamentos por meio dos planos de saúde privados; 22,7% (IC95% 21,0 - 24,4) em farmácias do sistema público de saúde; 21,8% (IC95% 20,2 - 23,4) no Programa Farmácia Popular do Brasil; e 29,5% (IC95% 27,7 - 31,4) exclusivamente pelas farmácias comerciais. A obtenção no sistema público de saúde como fonte única diminuiu com o avanço da idade, apresentou-se menor nas pessoas de cor da pele branca, diminuiu fortemente com o aumento da escolaridade e evidenciou-se menor entre os residentes na região Norte do país; no Programa Farmácia Popular do Brasil, a fonte única de obtenção também foi menor para as pessoas com maior escolaridade. A obtenção nas farmácias comerciais esteve associada positivamente com um perfil do sexo masculino, de maior escolaridade, de idade mais elevada, tendo declarado cor da pele branca. A ocorrência de mais de uma fonte de obtenção mostrou-se associada positivamente ao aumento da idade e inversamente ao aumento da escolaridade. Conclusões: Os resultados possibilitaram identificar diferentes estratégias para obtenção de medicamentos usados no tratamento da hipertensão, de modo a explicar como são obtidos os medicamentos no país e qual o impacto das políticas públicas nesse setor.

ABSTRACT: Objective: To analyze the sociodemographic differences among adults with hypertension regarding the sources for obtaining drugs for hypertension treatment in Brazil. Methods: This is a secondary analysis of data from the National Health Survey 2013; the outcomes considered for the analysis were the sources for obtaining drugs for treating high blood pressure. Results: The great majority (74%) of patients with hypertension taking drugs use a single source for obtaining them, 7.3% (95%CI 6.4 - 8.4) reported getting all the drugs through private health plans, 22.7% (95%CI 21.0 - 24.4) by pharmacies of the public health system, 21.8% (95%CI 20.2 - 23.4) by the Popular Pharmacy Program, and about one-third (29.5%; 95%CI 27.7 - 31.4) exclusively by commercial pharmacies. Having the public health system as the single source for obtaining the drugs was found to decrease with age, was lower in white people, decreased strongly with increase in education, and was lower for residents in the North region. Exclusive obtainment through the Popular Pharmacy Program was lower for people with higher education. Obtainment in commercial pharmacies was positively associated with being male, with higher education level, being older, and having white skin color. Obtainment using more than one source was positively associated with increasing age and inversely associated with higher education levels. Conclusions: The results allowed the identification of a trajectory of patients in obtaining drugs for the treatment of hypertension, aiming at explaining how the drugs are obtained and the impact of public policies in this sector in the country.

Analysis of Optical Coherence Tomography Based on Monte Carlo Simulation Model / 中国医疗器械杂志

A Monte Carlo model for optical coherence tomography of human skin is proposed. The new model includes importance sampling technique which is designed to suit for the multi-layer human skin, new rules for back scattered photon classification are correspondingly proposed. Based on the new simulation model, we analyzed the focusing of Gaussian beam through skin and the maximum detecting depth of optical coherence tomography. The experimental results show that there exists focus distortion when beam propagates in skin, including focus shift and diffusion. Object lens with greater NA will lower the maximum detecting depth of optical coherence tomography.

Monte Carlo study on beam hardening effect of physical wedges

Physical wedges are still widely used as beam modifiers in external beam radiotherapy. However the presence of them in the beam trace may cause beam hardening which may not be considered in many treatment planning systems. The aim of this study is to investigate the beam hardening effect generated by physical wedges via different beam quality indexes as photon spectrum, half value layer, mean energy and tissue-phantom ratio. The effect of physical wedges on the photon beam quality of a 6-18MV Varian 2100C/D accelerator was studied with the BEAMnrc Monte Carlo code. Good agreements were obtained between measured and calculated depth doses and beam profiles for open and wedged photon beams at both energies. It was noticed that for 6 MV photon beams, physical wedges have more significant effects on beam quality than for 18 MV. Also it was obtained that at 18 MV photon beam as the wedge angle increased, the effect of wedge on beam quality becomes reversed and beam softening occurred. According to these results, it is recommended that beam hardening and softening of physical wedges should be considered in treatment planning systems in order to increase the accuracy in dose delivery

Production of a novel high strength heavy concrete using tourmaline and galena for neutron and photon radiation shielding

High density concrete is extensively used for efficient radiation attenuation in radiotherapy rooms and nuclear reactors. Over the past eight years, some efficient galena-based concrete samples for shielding X or gamma rays was produced. The goal of this study was to produce a novel high density concrete against neutron and photon radiations using tourmaline and galena. Attenuation of gamma photons was measured using a Farmer type ionization chamber with a standard [60]Co buildup cap on a Theratron[60] Co therapy unit. Neutron shielding characteristics were measured by using an Am-Be source. The MCNP4C radiation transport computer code was used to investigate the effects of various shield thicknesses on the attenuation of gamma-ray photons and neutrons. The concrete samples had a density of 4.0- 4.2 g/cm[3]. The compressive strength was 326 - 560 kg/cm2. The calculated value for Half Value Layer [HVL] of the tourmaline-galena concrete samples for 60Co gamma rays was 2.72 cm, which is much less than that of ordinary concrete [6.0 cm]. The MC-derived HVL for photons with the same energy was 2.77 cm, which is in a good agreement with the experimental data. Moreover, ToGa concrete had up to 10 times greater neutron attenuation compared to that of the reference concrete. Tourmalin-Galena Concrete opens a new horizon in economic and efficient gamma/neutron shielding in high-energy radiotherapy bunkers, nuclear power plants, and shielding of radioactive sources

Research on increasing X-ray protection capability based on photonic crystal technology / 生物医学工程学杂志

Light cannot be propagated within the range of photonic crystal band gaps. Based on this unique property, we proposed a method to improve anti-radiation capability through one-dimensional photonic crystal coating. Using transmission matrix method, we determined the appropriate dielectric materials, thickness and periodic numbers of photonic crystals through Matlab programming simulation. Then, compound one-dimensional photonic crystal coating was designed which was of high anti-radiation rate within the range of X-ray. As is shown through simulation experiments, the reflection rate against X-ray was higher than 90 percent, and the desired anti-radiation effect was achieved. Thus, this method is able to help solve the technical problems facing the inorganic lead glass such as thickness, weightiness, costliness, high lead equivalent, low transparency and high cost. This method has won China's national invention patent approval, and the patent number is 201220228549.2.

The effect of resin thickness on polymerization characteristics of silorane-based composite resin

OBJECTIVES: This study examined the influence of the resin thickness on the polymerization of silorane- and methacrylate-based composites. MATERIALS AND METHODS: One silorane-based (Filtek P90, 3M ESPE) and two methacrylate-based (Filtek Z250 and Z350, 3M ESPE) composite resins were used. The number of photons were detected using a photodiode detector at the different thicknesses (thickness, 1, 2 and 3 mm) specimens. The microhardness of the top and bottom surfaces was measured (n = 15) using a Vickers hardness with 200 gf load and 15 sec dwell time conditions. The degree of conversion (DC) of the specimens was determined using Fourier transform infrared spectroscopy (FTIR). Scratched powder of each top and bottom surface of the specimen dissolved in ethanol for transmission FTIR spectroscopy. The refractive index was measured using a Abbe-type refractometer. To measure the polymerization shrinkage, a linometer was used. The results were analyzed using two-way ANOVA and Tukey's test at p < 0.05 level. RESULTS: The silorane-based resin composite showed the lowest filler content and light attenuation among the specimens. P90 showed the highest values in the DC and the lowest microhardness at all depth. In the polymerization shrinkage, P90 showed a significantly lower shrinkage than the rest two resin products (p < 0.05). P90 showed a significantly lower refractive index than the remaining two resin products (p < 0.05). CONCLUSIONS: DC, microhardness, polymerization rate and refractive index linearly decreased as specimen thickness linearly increased. P90 showed much less polymerization shrinkage compared to other specimens. P90, even though achieved the highest DC, showed the lowest microhardness and refractive index.

Determination of the attenuation coefficient for megavoltage photons in the water phantom

Attenuation coefficient [micro] plays an important role in calculations of treatment planning systems, as well as determination of dose distributions in external beam therapy, dosimetry, protection, phantom materials and industry. So, its exact measurement or calculation is very important. The aim of this study was to evaluate the micro in different points in the water phantom analytically as a formula, in addition to derive and parameterize it with dosimetry measurements data results. To find the attenuation coefficients at each point along the central axis of the beam in the phantom for every size of the fields, the first mathematical approach was performed for derivation of micro s from percentage depth dose [PDD] formula. Then by dosimetry for different fields in different depths of water phantom, one can parameterize the obtained formula for micro in any field and depth. By comparing the mathematical and dosimetry results, the parameters of the micro-expression were derived in terms of the dimension of square field in different depths. From this formula one can find the micro for any field in different depths for two energies of the Varian 2100CD linear accelerator, 6, 18MV with the statistical coefficient of determination of R2>0.98. The measurement of the micro in each field size and depth has some technical problems, but one can easily measure the micro for every point of central axis of the beams in any field size

Basics of particle therapy II: relative biological effectiveness

In the previous review, the physical aspect of heavy particles, with a focus on the carbon beam was introduced. Particle beam therapy has many potential advantages for cancer treatment without increasing severe side effects in normal tissue, these kinds of radiation have different biologic characteristics and have advantages over using conventional photon beam radiation during treatment. The relative biological effectiveness (RBE) is used for many biological, clinical endpoints among different radiation types and is the only convenient way to transfer the clinical experience in radiotherapy with photons to another type of radiation therapy. However, the RBE varies dependent on the energy of the beam, the fractionation, cell types, oxygenation status, and the biological endpoint studied. Thus this review describes the concerns about RBE related to particle beam to increase interests of the Korean radiation oncologists' society.

Influence of Couch and Collimator on Dose Distribution of RapidArc Treatment Planning for Prostate Cancer in Radiation Therapy / 의학물리

We investigated the influence of photon energy, couch and collimator angle differences between arcs on dose distribution of RapidArc treatment planning for prostate cancer. RapidArc plans were created for 6 MV and 10 MV photons using 2 arcs coplanar and noncoplanar fields. The collimator angle differences between two arcs were 0degrees, 15degrees, 30degrees, 45degrees, 60degrees, 75degrees and 90degrees. The plans were optimized using same dose constrains for target and OAR (organ at risk). To evaluate the dose distribution, plans were analyzed using CI (conformity index), HI (homogeneity index), QOC (quality of coverage), etc. Photon energy, couch and collimator angle differences between arcs had a little influence on the target and OAR. The difference of dosimetric indices was less than 3.6% in the target and OAR. However, there was significant increase in the region exposed to low dose. The increase of V15% in the femur was 6.4% (left) and 5.5% (right) for the 6 MV treatment plan and 23.4% (left), 24.1% (right) for the noncoplanar plan. The increase of V10% in the Far Region distant from target was 54.2 cc for the 6 MV photon energy, 343.4 cc for the noncoplanar and 457.8 cc for the no collimator rotation between arcs.

Comparison of calculation precision of photon dose between the two algorithms for the situation with air cavity and small fields / 生物医学工程学杂志

In order to evaluate the calculation precision of the pencil beam (PB) algorithm and convolution-superposition(CS) algorithm for the situation with air cavity and small fields, we built a water phantom with an air cavity slab, in which the depth dose (DD) and off-axis ratio (OAR) for field 1cm x 1cm to field 7cm x 7cm were calculated by PB algorithms, CS algorithms and Monte Carlo (MC) simulation. The evaluation of algorithms by MC simulation was achieved by comparisons of DD with the spread penumbras of OAR curve self-defined as the width between isodose lines of 10% and 90%. It was shown that PB algorithm and CS algorithm both overestimated the DD but the degree overestimated by PB algorithm was more serious. The CS algorithm showed a better agreement with the MC simulation for the OARs, which spread to both laterals, while that was not predicted accurately by PB algorithm. It was indicated that PB algorithm and CS algorithm do not have high calculation precision whereas CS algorithms is relatively better for the situation with air cavity and small fields.

Verification of the accuracy of Monte Carlo-based dose calculation algorithm, DPM, in homogeneous and inhomogeneous tissues / 生物医学工程学杂志

The present paper is to verify the accuracy of DPM, a Monte Carlo-based dose calculation algorithm, in homogeneous and inhomogeneous tissues. DPM was applied to calculate (1) depth dose curves and off-axis ratios at a depth of 10 cm in water using a 6 MeV photon beam with a 3 cm x 3 cm field and phase space file simulated Varian 60 degrees C medical linear accelerator with a 10 cm x 10 cm field at SSD = 100 (cm); (2) depth dose curves using 6 MeV photon beam in inhomogeneous tissues, such as water (6 cm)/lung (6 cm)/water (8 cm) with a 3 cm x 3 cm field and water (6 cm)/ bone (2 cm)/water (12 cm) with a 10 cm x 10 cm field; (3) depth dose curves using 6 MeV photon beam based on the CT data of a patient's head and abdomen. The doses based on DPM are compared to the doses calculated by DOSXYZnrc under the same condition. The error was within 3% in water phantom while the error was within 3% in inhomogeneous tissues, except a few points. It has been concluded that the DPM can accurately predict the dose to homogeneous and inhomogeneous tissues.