[The correlation between blood glucose level and muscle mass, strength and function in an elderly population].

Objective: To explore the correlation between blood glucose levels and the three factors of sarcopenia (muscle mass, strength and function) in older Chinese community dwellers. Methods: This is a retrospective study conducted by collecting the data of patients in Jiangsu Huaqiao Road Community Health Service Center from 2018 to 2019. Two hundred and fifty people aged 60 years or elder were selected. Among them, 101 were men and 149 were women. According to the American Diabetes Association diagnostic criteria for diabetes mellitus in 2018, they were divided into normal glucose tolerance (NGT) group, pre-diabetes group and diabetes group. The patients were assessed for sarcopenia as well. Results: Compared with those in the NGT group, muscle mass and upper limb muscle strength did not change in the diabetic group, but lower limb muscle strength and body function [walking speed, balance, short physical performance battery (SPPB)] decreased significantly in the diabetic group. Pearson correlation analyses showed that fasting plasma glucose(FPG) was negatively correlated with walking speed (r=-0.248, P=0.001), three-pose balance (r=-0.166, P=0.013) and SSPB (r=-0.213, P=0.001). Glycosylated hemoglobin A1c(HbA1c) was positively correlated with sitting and standing time (r=0.205, P=0.002), and negatively correlated with three-pose balance (r=-0.186, P=0.006) and SSPB (r=-0.154, P=0.024). Multiple regression analyses showed that FPG was negatively associated with walking speed (ß=-0.125, P=0.005) and SPPB (ß=-0.034, P=0.012), and that HbA1c was positively associated with sitting and standing time (ß= 0.218, P =0.006) and negatively associated with three-pose balance (ß=-0.143, P=0.012), and SPPB (ß=-0.117, P =0.036). Conclusions: There is no significant correlation between blood glucose levels and muscle mass in the elderly; however, FPG is closely correlated with gait speed, and HbA1c is closely correlated with muscle strength of lower limbs and balance ability in the elderly.

[Measurement of corneal nerve fiber parameters in patients with Parkinson's disease].

Objective: To analyze the characteristic changes of corneal nerve fibers in patients with Parkinson's disease (PD) by corneal confocal microscopy (CCM) and investigate the association of corneal nerve fiber parameters with disease severity and motor symptoms. Methods: Forty-two patients with PD were recruited from the Department of Neurology, Henan University People's Hospital from June 2018 to October 2019. Meanwhile, 40 healthy controls who visited the hospital for physical examination at the same period were enrolled. Corneal nerve fibers in both eyes of all participants were detected by using CCM. The differences of corneal nerve fibers were comparatively analyzed between PD group and healthy controls. Associations of corneal nerve parameters with clinical characteristics such as course of disease, Hoehn and Yahr stage (H-Y stage), unified Parkinson disease rating scale (UPDRS), levodopa equivalent daily dosage (LEDD) were analyzed by using partial correlations. The receiver operating characteristic (ROC) curve was used to analyze the capability of corneal nerve fibers for distinguishing patients with PD from healthy controls. Results: Corneal nerve fiber density (CNFD) in PD group ((19±3)/mm2) was significantly decreased compared with healthy controls ((28±4)/mm2) (t=10.798, P<0.001). However, corneal nerve branch density (CNBD) was significantly increased in PD group ((25±11)/mm2) compared with healthy controls ((18±6)/mm2) (t=-3.427, P=0.001). Meanwhile, corneal nerve fiber length (CNFL) was decreased in PD group ((11.0±2.5) mm/mm2) in comparison with healthy controls ((12.5±1.6) mm/mm2) (t=3.139, P=0.002). ROC curve analysis revealed that CNFD could discriminate PD patients from healthy controls, with an area under the curve of 0.961 3 (95%CI: 92.42-99.84, P<0.000 1). CNFD was negatively correlated with H-Y stage and UPDRS-Ⅲ (r=-0.501 and -0.399, both P<0.05). CNBD was significantly negatively associated with H-Y stage, UPDRS-Ⅲ and UPDRS-Total (r=-0.622, -0.394 and -0.354, respectively, all P<0.05). CNFL was negatively correlated with H-Y stage, UPDRS-Ⅲ and UPDRS-total (r=-0.574, -0.484 and -0.422, respectively, all P<0.05). Conclusion: Small nerve fiber injuries exist in PD patients. Corneal nerve fibers negatively correlates with motor symptoms. CNFD have a good discriminative power to distinguish PD patients from healthy controls and may serve as a marker for PD.

[Functional characterization of SLC12A1 gene variants in 3 patients with Bartter syndrome type â ].

Objective: To clarify the molecular basis of patients with Bartter syndrome type I and explore the therapeutic effect of trafficking-defective variations by chemical chaperone 4-Phenylbutyric acid(4-PBA). Methods: The clinical characteristics, laboratory findings and genetic data of 3 patients diagnosed with Bartter syndrome type I who were admitted to Department of Nephrology, Children's Hospital of Nanjing Medical University from 2017 to 2018 were retrospectively analyzed. Wild type and variant SLC12A1 gene constructs were transiently overexpressed in HEK293 cells. Western blotting was used to detect the expression levels of Na+-K+-2Cl-cotransporter(NKCC2) protein. Immunofluorescent staining was applied to investigate the subcellular localization of NKCC2 protein. In addition, the effect of the chemical chaperone 4-PBA on the expression and localization of the SLC12A1 gene variants was investigated. Unpaired t test was used for statistical analysis of 4-PBA treatment. Results: All the 3 patients (2 males and 1 female), aged 3.0, 4.0 and 1.2 years, respectively. All patients had antenatal onset with polyhydramnios and were born prematurely. After birth, all patients presented with hypochlorine alkalosis accompanied by hypokalemia and hyponatremia. Sequencing analysis revealed that the 3 patients were homozygotes or compound heterozygotes for variants in the SLC12A1 gene. In HEK293 cells, the surface expression of NKCC2 in 3 variants (p.L463S, p.L479V, p.507-510del) are all lower than in wild type (0.718±0.039, 0.287±0.081, 0.025±0.156 vs. 1.001±0.028, t=5.92, 8.35, 30.49, all P<0.01). Moreover, the total protein expression of p.L479V and p.507-510del group were all lower than that in wild type group (0.630±0.032, 0.043±0.003 vs. 1.000±0.111, t=3.21, 8.65, all P<0.05). 4-PBA treatment increased the mature protein expression level of the p.L463S and p. L479V group in 4-PBA treatment group are all higher than the untreated group (0.459±0.018 vs. 1.123±0.024, 0.053±0.012 vs. 1.256±0.037, t=2.75, 18.35, all P<0.05). Cytoplasmic retention of the L479V and 507-510del variants were observed by immunofluorescent staining. 4-PBA treatment could rescue a number of NKCC2 L479V variants to the membrane. Conclusions: The 3 SLC12A1 variants cause expression or subcellular localization defects of the protein. The findings that plasma membrane expression and activity can be rescued by 4PBA might help to develop novel therapeutic strategy for Bartter syndrome type Ⅰ.

Skeletal dosimetry in cone beam computed tomography.

Cone beam computed tomography (CBCT) is a relatively new patient imaging technique that has proved invaluable for treatment target verification and patient positioning during image-guided radiotherapy (IGRT). It has been shown that CBCT results in additional dose to bone that may amount to 10% of the prescribed dose. In this study, voxelized human phantoms, FAX06 (adult female) and MAX06 (adult male), are used together with phase-space data collected from a realistic model of a CBCT imager to calculate dose in the red bone marrow (RBM) and bone surface cells (BSCs), the two organs at risk within the bone spongiosa, during simulated head and neck, chest and pelvis CBCT scans. The FAX06/MAX06 phantoms model spongiosa based on micro-CT images, filling the relevant phantom voxels, which are 0.12 x 0.12 x 0.12 cm3, with 17 x 17 x 17 microm3 microvoxels to form a micromatrix of trabecular bone and bone marrow. FAX06/ MAX06 have already been implemented in an EGSnrc-based Monte Carlo code to simulate radiation transport in the phantoms; however, this study required significant modifications of the code to allow use of phase-space data from a simulated CBCT imager as a source and to allow scoring of total dose, RBM dose and BSC dose on a voxel-by-voxel basis. In simulated CBCT scans, the BSC dose is significantly greater than the dose to other organs at risk. For example, in a simulated head and neck scan, the average BSC dose is 25% higher than the average dose to eye lens (approximately 8.3 cGy), and 80% greater than the average dose to brain (5.7 cGy). Average dose to RBM, on the other hand, is typically only approximately 50% of the average BSC dose and less than the dose to other organs at risk (54% of the dose to eye lens and 76% of dose to brain in a head and neck scan). Thus, elevated dose in bone due to CBCT results in elevated BSC dose. This is potentially of concern when using CBCT in conjunction with radiotherapy treatment.

The association between MIF-173 G>C polymorphism and prostate cancer in southern Chinese.

BACKGROUND AND OBJECTIVES: Accumulating epidemiological and molecular evidence suggests that inflammation is an important component in the etiology of PCa. Macrophage migration inhibitory factor (MIF) plays an important role in the pro- and anti-inflammatory response to infection. This study is aimed at investigating the potential association between MIF-173 G>C polymorphism, Gleason score, clinical stage, and prostate-specific antigen (PSA) value with respect to PCa incidence among the Han nationality in Southern China. METHODS: Genotyping was performed by using tetraprimer polymerase chain reaction (PCR) on 259 PCa patients and 301 cancer-free controls. RESULTS: We found that the MIF-173*C variant allele was significantly associated with an increased risk of PCa [adjusted odd ratio (OR) = 2.99, 95% confident interval (CI): 1.94-4.60] and higher Gleason scores from the PCa subjects (adjusted OR = 10.72, 95% CI: 5.35-21.49). In addition, we noted that the MIF -173*C variant allele was related to higher clinical stages and PSA values in PCa patients (adjusted OR = 15.68, 95% CI: 7.40-33.23; adjusted OR = 4.37, 95% CI: 2.41-7.92, respectively). CONCLUSION: Our data suggest that MIF-173 polymorphisms may be associated with a higher incidence of prostate cancer compared to controls, and appears to be associated with higher Gleason scores, higher clinical stages, and PSA values in those with prostate cancer.

Establishment of TBS reference plots and correlation between TBS and BMD in healthy mainland Chinese women.

UNLABELLED: The trabecular bone score (TBS) was obtained from the gray levels of a dual X-ray absorptiometry (DXA) image to evaluate bone microarchitecture. Here, we established the reference plots of TBS in healthy Chinese women of Nanjing area. The TBS references are similar with French and US Caucasian women but higher than Japanese women. PURPOSE: The aim of the study was to establish the reference plots of the TBS in healthy Chinese women of the Nanjing area. METHODS: A total of 537 healthy Chinese women of the Nanjing area were recruited, and the study was approved by the Ethics Committee of the First Affiliated Hospital with Nanjing Medical University. The TBS of the lumbar spine and the bone mineral density (BMD) of the lumbar spine and femur were measured using dual X-ray absorptiometry. The mean ± standard deviation (SD) of the TBS in women with different age groups was calculated. The correlation of TBS and age and BMD was calculated using regression analysis. RESULTS: The reference plots of the TBS were established in healthy Chinese women of the Nanjing area between the ages of 20 and 89 years. The average TBS for total subjects was 1.32 ± 0.11 and reached the peak at the age of 20-29 years and then decreased with age thereafter. The determinant coefficient between TBS and age was 0.5065 while between TBS and BMD was 0.5191. After adjusting for lumbar total BMD, the TBS significantly correlated with age in whole subjects and only in the subgroup of ages 50-59 years. CONCLUSIONS: This study suggested that TBS decreased with age and correlated positively with BMD. The TBS reference of Chinese women is similar with those of French and US Caucasian women but higher than that of Japanese women. Furthermore, the TBS may be more significantly applied in women in menopause for less than 10 years.

A study on beams passing through hip prosthesis for pelvic radiation treatment.

PURPOSE: To study the dose distributions at the interface due to the presence of a metal implant; to show the dose distributions in combined fields in the presence of hip prostheses; and to demonstrate the capabilities and limitations of a conventional system. METHODS AND MATERIALS: Perturbations in the dose distribution caused by a hip prosthesis can result in unacceptable dose inhomogeneities within the target volume and in regions where tissues interface with implant. The Monte Carlo technique and a conventional treatment planning system are used to calculate the dose distributions. RESULTS: Dose increases of 15% in tissue are seen at the interface between metal implant and tissue. Dose reductions of 5-25% or 10-45% are observed in the shadow of the hip prosthesis made of 0.5-3-cm-thick titanium or steel alloy respectively. We compared predicted dose distribution between the Monte Carlo simulation and a commercial treatment planning system (CADPLAN). We found that CADPLAN underestimated the attenuation of hip prostheses. This has led to overestimation of the target dose by 14% for a typical four-field box technique. CONCLUSIONS: An acceptable dose distribution can be achieved with a proper lateral beam weighting and compensation using an eight-field technique. The beam compensation may be applied to achieve an adequate target dose.

Determination of percentage depth-dose curves for electron beams using different types of detectors.

According to the new AAPM TG-51 dosimetry protocol, reference dosimetry for electron beams is performed at depth of d(ref)=0.6R50-0.1 (cm) instead of d(max) recommended in TG-21. In clinical practice most electron beams are normalized at d(max). Therefore it becomes more important to get an accurate percentage-depth-dose (%dd) curve particularly for higher-energy electron beams in which the depth d(ref) is away from d(max). When ionization chambers are used in determining %dd curves the water-to-air stopping-power ratios and the fluence correction factors are required. The TG-51 recommends that the stopping-power ratios for realistic electron beams be used instead of the monoenergetic stopping-power ratios used in TG-21. This investigation aims to study the effects of those correction factors on the determination of %dd curves. We observed 1% deviations in the value of %dd at d(ref) for 15 and 18 MeV beams between a plane-parallel NACP and a cylindrical IC-10 chamber without considering the fluence correction factors P(fl). We explored a method to derive the fluence correction factors at any depth by using the existing fluence correction data at d(max) and tested its feasibility. We compared %dd curves measured by a diode detector and a NACP chamber with stopping-power ratios recommended by TG-51 and those recommended by TG-21. We found that for 15 and 18 MeV beams the difference in the values of %dd at d(ref) between using those two different stopping-power ratios is about 0.5%. Excellent agreement is found between %dd curves measured by the diode and by the NACP chamber when the stopping-power ratios recommended by TG-51 are used.

Mean energy, energy-range relationships and depth-scaling factors for clinical electron beams.

Using Monte Carlo simulations we have studied the electron mean energy, Eo, and the most probable energy, Eo,p, at the phantom surface and their relationships with half-value depth, R50, and the practical range, Rp, for a variety of beams from five commercial medical accelerators with an energy range of 5-50 MeV. It is difficult to obtain a relation between R50 and Eo for all electrons at the surface because the number of scattered lower-energy electrons varies with the machine design. However, using only direct electrons to calculate Eo, there is a relationship which is in close agreement with that calculated using monoenergetic beams by Rogers and Bielajew [Med. Phys. 13, 687-694 (1986)]. We show that the empirical formula Eo,p = 0.22 + 1.98Rp + 0.0025R2p describes accurately the relationship between Rp and Eo,p for clinical beams of energies from 5 to 50 MeV with an accuracy of 3%. The electron mean energy, Ed, is calculated as a function of depth in water as well as plastic phantoms and is compared both with the relation, Ed = Eo (1-d/Rp), employed in AAPM protocols and with values in the IAEA Code of Practice. The conventional relations generally overestimate Ed over the entire therapeutic depth, e.g., the AAPM and IAEA overestimate Ed at dmax by up to 20% for an 18 MeV beam from a Clinac 2100C. It is also found that at all depths mean energies are 1%-3% higher near the field edges than at the central axis. We calculated depth-scaling factors for plastic phantoms by scaling the depth in plastics to the water-equivalent depth where the mean energies are equal. The depth-scaling factor is constant with depth in a given beam but there is a small variation ( < 1.5%) depending on the incident beam energies. Depth-scaling factors as a function of R50 in plastic or water are presented for clear polystyrene, white polystyrene and PMMA phantom materials. The calculated depth-scaling factor is found to be equal to R50water/R50plastic. This is just the AAPM definition of effective density but there are up to 2% discrepancies between our calculated values and those recommended by the AAPM and the IAEA protocols. We find that the depth-scaling factors obtained by using the ratio of continuous-slowing-down ranges are inaccurate and overestimate our calculated values by 1%-2% in all cases. We also find that for accurate work, it is incorrect to use a simple 1/r2 correction to convert from parallel beam depth-dose curves to point source depth-dose curves, especially for high-energy beams.

Measurements of electron beam peak scatter factors.

We have measured the peak scatter factor (PSF) for electron beams which in analogy to photon beams is defined as the ratio of the absorbed dose to water at the depth of dose maximum in a water phantom to the absorbed dose in free air at the same location for a given incident beam. In this study we have measured the PSFs as a function of the incident electron beam energy and field size. We have used both an RK ionization chamber and a silicon diode as radiation detectors. After applying the water/air stopping power ratio and fluence correction factors to the ionization chamber readings, the values of measured PSFs by using two different detectors are in a good agreement. The results show that the value of PSF increases with the increase of the field size and decreases with the increase of the beam energy. The range of the variation with field size between 2 x 2 and 10 x 10 cm2 is 1.24-1.42, 1.15-1.30, 1.15-1.17 for 6, 11, and 20 MeV beams, respectively.

Measurement of Prepl Pwall factors in electron beams and in a 60Co beam for plane-parallel chambers.

This paper describes a method to measure the product of Prepl Pwall correction factors for ionization chambers and presents our measured values of Prepl Pwall for Markus plane-parallel chambers in electron beams. It is shown that the measured values of Prepl Pwall can be fitted to an equation, Prepl Pwall = c1 + c2 R50 + c3 (R50)2, for Markus chambers at the new reference depth for electron beams (6 MeV < or = nominal energy E < or = 20 MeV). We also present our measured values of Prepl Pwall for NACP and Markus chambers in a water phantom irradiated in a 60Co beam.

A rho-theta technique for treatment verification in radiotherapy and its clinical applications.

A new technique based on a rho-theta coordinate system for determining differences in patient position between portal and simulator images is presented. Unlike the conventional point matching method, which requires the fiducial points to be labeled in pairs before the registration, the rho-theta technique avoids this manual procedure. It accomplishes the treatment verification in two major steps; image alignment and field displacement analysis. For the same number of fiducial points in the simulator and portal images, it first finds the corresponding paired points if the points are not distributed symmetrically about their centroid. This is followed by alignment of these paired points using the least squares matching method to find the optimal two-dimensional rigid body transformation parameters (shift, rotation, and scaling factor). The transformation parameters are then used to transform the portal field edge into the simulator image, so that the portal field can be compared with the prescribed field on the simulator image. A number of parameters were explored to describe the field displacement errors, including treatment field size, under/over irradiated size, the shift in center of gravity of the field, the field edge shift, and rotation of the field. The rho-theta technique as implemented is both fast and accurate. Experiments on the registration of radiological phantom portal images acquired with an on-line portal imaging system mounted on a linear accelerator indicate an accuracy on the order of 1 mm in detecting the shift of the field's center of gravity and approximately 1 degree in detecting the field rotation. The results of a clinical trial are also presented.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical reference dosimetry: comparison between AAPM TG-21 and TG-51 protocols.

We compare the results of absorbed dose determined at reference conditions according to the AAPM TG-21 dose calibration protocol and the new AAPM TG-51 protocol. The AAPM TG-21 protocol for absorbed dose calibration is based on ionization chambers having exposure calibration factors for 60Co gamma rays, N(x). The new AAPM TG-51 dosimetry protocol for absorbed dose calibration is based on ionization chambers having 60Co absorbed dose-to-water calibration factor, N60Co(D,w). This study shows that the dose changes are within 1% for a cobalt beam, 0.5% for photon energies of 6 and 18 MV, and 2%-3% for electron beams with energies of 6 to 20 MeV. The chamber primary calibration factors, Nx and N60Co(D,w), are traceable to the Canadian primary standards laboratory (NRCC). We also present estimated dose changes between the two protocols when calibration factors are traceable to NIST in the United States.

R50 as a beam quality specifier for selecting stopping-power ratios and reference depths for electron dosimetry.

For electron beam reference dosimetry in radiotherapy, it is shown that by choosing the reference depth as dref = 0.6R(50)-0.1 cm, where R50 is the half-value depth in centimeters, the Spencer-Attix water-to-air stopping-power ratio at dref is given by (Llp)airw = 1.2534 - 0.1487 (R50)0.2144. This is derived from data for (Llp)airw obtained from realistic Monte Carlo simulations for 24 clinical beams. The rms deviation of this expression from the Monte Carlo calculations is 0.16%, with a maximum deviation of 0.26%. This approach fully takes into account the spectral differences between real electron beams of the same R50 and allows an absorbed-dose calibration at a standards laboratory to be easily and accurately transferred to a reference clinical beam. Using a single parameter to specify (Llp)airw, rather than the two parameters (R50 and depth) needed when the reference depth is chosen as the depth of dose maximum, has the potential to greatly simplify electron beam dosimetry protocols and allows the use of a similar formalism for photon and electron beam dosimetry. For use in converting a depth-ionization curve into a depth-dose curve, a somewhat less accurate but general expression for (Llp)w(air) as a function of R50 and depth is presented.

Calculation of stopping-power ratios using realistic clinical electron beams.

The Spencer-Attix water/air restricted mass collision stopping-power ratio is calculated in realistic electron beams in the energy range from 5-50 MeV for a variety of clinical accelerators including the Varian Clinac 2100C, the Philips SL75-20, the Siemens KD2, the AECL Therac 20, and the Scanditronix Medical Microtron 50. The realistic clinical beams are obtained from full Monte Carlo simulations of the clinical linear accelerators using the code BEAM. The stopping-power ratios calculated using clinical beams are compared with those determined according to the AAPM and the IAEA protocols which were calculated by using monoenergetic parallel beams. Using the energy-range relationship of Rogers and Bielajew [Med. Phys. 13, 687-694 (1986)] leads to the most consistent picture in which the stopping-power ratios at dmax derived from mono-energetic calculations underestimate the stopping-power ratios calculated with the realistic beam by 0.3% at 5 MeV and up to 1.4% at 20 MeV. The stopping-power ratios at dmax determined according to the AAPM TG-21 protocol (1983) are shown to overestimate the realistic stopping-power ratios by up to 0.6% for a 5-MeV beam and underestimate them by up to 1.2% for a 20-MeV beam. Those determined according to the IAEA (1987) protocol overestimate the realistic stopping-power ratios by up to 0.3% for a 5-MeV beam and underestimate them by up to a 1.1% for a 20-MeV beam at reference depth. The causes of the differences in the stopping-power ratios between the realistic clinical mono-energetic beams are analyzed quantitatively. The changes in the stopping-power ratios at dmax are mainly due to the energy spread of the electron beam and the contaminant photons in the clinical beams. The effect of the angular spread of electrons is rather small except at the surface. Data are presented which give the corrected stopping-power ratios at dmax or reference depth starting from those determined according to protocols for any energy of clinical electron beams with scattering foils. For scanned clinical electron beams the correction to stopping-power ratios determined according to protocols is found to be less than 0.5% at dmax or reference depth for all beam energies studied. We quantify the differences in the stopping-power ratios determined using the depth of 50% ionization level and the depth of 50% dose level. The differences are very small except for very-high-energy beams (50 MeV) where they can be up to 0.8%.

Evaluation of the first commercial Monte Carlo dose calculation engine for electron beam treatment planning.

The purpose of this study is to perform a clinical evaluation of the first commercial (MDS Nordion, now Nucletron) treatment planning system for electron beams incorporating Monte Carlo dose calculation module. This software implements Kawrakow's VMC++ voxel-based Monte Carlo calculation algorithm. The accuracy of the dose distribution calculations is evaluated by direct comparisons with extensive sets of measured data in homogeneous and heterogeneous phantoms at different source-to-surface distances (SSDs) and gantry angles. We also verify the accuracy of the Monte Carlo module for monitor unit calculations in comparison with independent hand calculations for homogeneous water phantom at two different SSDs. All electron beams in the range 6-20 MeV are from a Siemens KD-2 linear accelerator. We used 10,000 or 50,000 histories/cm2 in our Monte Carlo calculations, which led to about 2.5% and 1% relative standard error of the mean of the calculated dose. The dose calculation time depends on the number of histories, the number of voxels used to map the patient anatomy, the field size, and the beam energy. The typical run time of the Monte Carlo calculations (10,000 histories/cm2) is 1.02 min on a 2.2 GHz Pentium 4 Xeon computer for a 9 MeV beam, 10 x 10 cm2 field size, incident on the phantom 15 x 15 x 10 cm3 consisting of 31 CT slices and voxels size of 3 x 3 x 3 mm3 (total of 486,720 voxels). We find good agreement (discrepancies smaller than 5%) for most of the tested dose distributions. We also find excellent agreement (discrepancies of 2.5% or less) for the monitor unit calculations relative to the independent manual calculations. The accuracy of monitor unit calculations does not depend on the SSD used, which allows the use of one virtual machine for each beam energy for all arbitrary SSDs. In some cases the test results are found to be sensitive to the voxel size applied such that bigger systematic errors (>5%) occur when large voxel sizes interfere with the extensions of heterogeneities or dose gradients because of differences between the experimental and calculated geometries. Therefore, user control over voxelization is important for high accuracy electron dose calculations.

Electron fluence correction factors for conversion of dose in plastic to dose in water.

In radiation dosimetry protocols, plastic is allowed as a phantom material for the determination of absorbed dose to water in electron beams. The electron fluence correction factor is needed in conversion of dose measured in plastic to dose in water. There are large discrepancies among recommended values as well as measured values of electron fluence correction factors when polystyrene is used as a phantom material. Using the Monte Carlo technique, we have calculated electron fluence correction factors for incident clinical beam energies between 5 and 50 MeV as a function of depth for clear polystyrene, white polystyrene and PMMA phantom materials and compared the results with those recommended in protocols as well as experimental values from published data. In the Monte Carlo calculations, clinical beams are simulated using the EGS4 user-code BEAM for a variety of medical accelerators. The study shows that our calculated fluence correction factor, phi pw, is a function of depth and incident beam energy Eo with little dependence on other aspects of beam quality. However the phi pw values at dmax are indirectly influenced by the beam quality since they vary with depth and dmax also varies with the beam quality. Calculated phi pw values at dmax are in a range of 1.005-1.045 for a clear polystyrene phantom, 1.005-1.038 for a white polystyrene phantom and 0.996-1.016 for a PMMA phantom. Our values of phi pw are about 1-2% higher than those determined according to the AAPM TG-25 protocol at dmax for clear or white polystyrene. Our calculated values of phi pw also explain some of the variations of measured data because of its depth dependence. A simple formula is derived which gives the electron fluence correction factor phi pw as a function of R50 at dmax or at the depth of 0.6R50-0.1 for any clinical electron beam with energy between 5 and 25 MeV for three plastics: clear polystyrene, white polystyrene and PMMA. The study also makes a careful distinction between phi pw and the corresponding IAEA Code of Practice quantity, hm.

Evaluation of a commercial three-dimensional electron beam treatment planning system.

We evaluated a commercial three-dimensional (3D) electron beam treatment planning system (CADPLAN V.2.7.9) using both experimentally measured and Monte Carlo calculated dose distributions to compare with those predicted by CADPLAN calculations. Tests were carried out at various field sizes and electron beam energies from 6 to 20 MeV. For a homogeneous water phantom the agreement between measured and CADPLAN calculated dose distributions is very good except at the phantom surface. CADPLAN is able to predict hot and cold spots caused by a simple 3D inhomogeneity but unable to predict dose distributions for a more complex geometry where CADPLAN underestimates dose changes caused by inhomogeneity. We discussed possible causes for the inaccuracy in the CADPLAN dose calculations. In addition, we have tested CADPLAN treatment monitor unit and electron cut-out factor calculations and found that CADPLAN predictions generally agree with manual calculations.