[Safety and efficacy of ultrafiltration on heart failure patients with reduced ejection fraction and diuretic resistance: results from a single-center randomized controlled trial].

Objective: To investigate the safety and efficacy of ultrafiltration on diuretic sensitivity in heart failure patients with reduced ejection fraction and diuretic resistance. Methods: This was a single-center randomized controlled trial. A total of 148 heart failure patients with reduced ejection fraction admitted to the Hospital of Traditional Chinese Medicine of Xinjiang Uygur Autonomous Region from June 2010 to June 2020 were enrolled in this study, and these patients were randomly divided (ratio 1:1) into the ultrafiltration group (n=74) and the control group (n=74). All patients were treated with diuretics, cardiotonic, vasodilator and other comprehensive drugs according to relevant guidelines. After grouping, the patients in the control group were treated with standard treatment plan, while patients in the ultrafiltration group were treated with ultrafiltration on top of standard therapy. Diuretic drugs were discontinued during ultrafiltration, and intravenously furosemide (40 mg) was given immediately and 24 hours after the end of ultrafiltration. Clinical data including gender, age, complicated diseases, New York Heart Association (NYHA) function classification, etc. were collected. Effectiveness indicators include urine volume (the first 12-hour and 24-hour urine volume and the second 24-hour urine volume after using diuretic), body weight and dyspnea severity score. Safety indicators include systolic blood pressure, serum creatinine, serum Na+ concentration, blood K+ concentration and the number of deaths before and after intervention. Results: Two patients in the control group died due to worsening heart failure after randomization and were excluded in this study, 146 patients were finally analyzed (72 patients in the control group and 74 patients in the ultrafiltration group). There were 93 males, and the age was (68.3±11.2) years. There was no significant difference between patients in the ultrafiltration group and the control group in gender, age, body weight, course of disease, dyspnea severity score, NYHA function classification Ⅲ/Ⅳ, the proportion of patients with severe edema of both lower limbs, the proportion of patients with complicated diseases, and basic medication (all P>0.05). After using diuretics, the urine volume of the first 12-hour and 24-hour and the second 24-hour were significantly higher in the ultrafiltration group than in the control group (all P<0.05). Body weight decreased significantly after ultrafiltration treatment as compared with that before intervention in the ultrafiltration group (P<0.05). Compared with the control group, the dyspnea severity score was significantly improved in the ultrafiltration group (P<0.05). There was no significant difference in systolic blood pressure, serum creatinine, serum Na+ concentration, blood K+ concentration of patients between ultrafiltration group and control group before and after intervention (all P>0.05). During the clinical diagnosis and treatment, 2 male patients in the control group died, and the cause of death was aggravation of basic diseases complicated with acute heart failure and cardiogenic shock. There was no death in the ultrafiltration group, and there were no obvious clinical adverse events during and after ultrafiltration. Conclusion: Ultrafiltration therapy is safe and can improve diuretic sensitivity in heart failure patients with reduced ejection fraction and diuretic resistance.

Key characteristics of basal cell carcinoma with large subclinical extension.

BACKGROUND: Basal cell carcinoma with large subclinical extension (BCC-LSE) is a tumour whose extensive spread becomes apparent during Mohs surgery histopathology review. Not recognizing BCC-LSE preoperatively may result in a greater number of Mohs layers and in larger than anticipated postoperative defects. OBJECTIVE: To evaluate the characteristics of BCC-LSE. METHODS: This retrospective study reviewed BCC treated with Mohs surgery at a single academic surgical centre between March 2007 and February 2012. A total of 2044 cases met the criteria of BCC-LSE, which was defined as a lesion requiring at least three Mohs stages and a final surgical margin (difference between preoperative and postoperative measurements in either vertical or horizontal dimensions) of ≥1 cm. RESULTS: In adjusted multivariable analysis, male sex (P = 0.05), Fitzpatrick skin type I (P = 0.002), history of prior BCC (P = 0.003) and subtypes of basosquamous, metatypical, micronodular, infiltrative, morpheaform and sclerosing (P = 0.005) remained significant BCC-LSE predictors. CONCLUSIONS: Demographic factors, including personal history of BCC, skin type, anatomic location, gender and age, in addition to tumour histologic subtype assessed through incisional biopsy, can help predict occurrence of BCC-LSE and assist physicians in optimizing preoperative assessment of surgical time and complexity.

A Retrospective Study of a Chinese Traditional Medicine YIKEER in the Treatment of Verruca Patients in Liaoning District.

BACKGROUND: There are many possible ways to treat verruca, but no one is the single perfect treatment. YIKEER is a kind of compound preparation of Chinese traditional medicine, which has been used in the treatment of verruca for several years. AIM: To confirm the effects of YIKEER for verruca. METHOD: Patients with verruca vulgaris, verruca plantaris, or verruca plana were instructed to apply YIKEER stock solution or diluent to the lesions once or twice daily for 5-7 days. Then, the YIKEER was ceased for 3-4 days, and sea buckthorn oil was used for wound repairing. The total procession was defined as one session. RESULT: Respective 88.05% verruca vulgaris patients, 86.03% verruca plantaris patients, and 82.42% verruca plana patients achieved complete response. Most patients gained complete or partial responses after 4 treatment sessions. The percentage of patients who achieved at least 50% improvement was 90.34% for verruca vulgaris, 90.60% for verruca plantaris, and 80.91% for verruca plana after 4-session treatment. The efficacy of verruca vulgaris or verruca plantaris was better than that of verruca plana. CONCLUSION: YIKEER is an effective, safe, and well-tolerated agent for treating verruca including verruca vulgaris, verruca plantaris, and verruca plana.

Effect of autophagy on myocardial infarction and its mechanism.

OBJECTIVE: To investigate the effect of autophagy on acute myocardial infarction (AMI), and its mechanism in rats. MATERIALS AND METHODS: A total of 75 Sprague Dawley (SD) rats were randomly divided into three groups (n=25): sham operation (S) group, the AMI group and rapamycin (RAPA) treatment group. The model of AMI was established and the myocardial infarction size was calculated by triphenyltetrazolium chloride (TTC) staining. Morphological changes in myocardium were observed by hematoxylin and eosin (HE) staining. Expression levels of autophagy-related proteins LC3-phosphatidylethanolamine conjugate (LC3-II) and p62 were detected by semi-quantitative polymerase chain reaction (PCR) and Western blot. RESULTS: Compared with the S group, the heart-to-body weight ratio on the 21st day in AMI group was significantly increased. TTC staining results showed that compared with the S group, the size of left ventricular infarction area was significantly increased in the AMI group, and that in the RAPA group was significantly decreased. HE staining results showed that the anterior wall of the left ventricle of rats became thinner, and myocardial cells were degenerated and lost seriously in the AMI group 21 days later. Compared with the S group, the expression level of LC3-II in the infarcted peripheral area was significantly increased and that of p62 was significantly increased in the AMI group. Compared with the AMI group, the expression level of LC3-II in the infarction-peripheral area was significantly increased and that of p62 was significantly decreased after the treatment with RAPA. CONCLUSIONS: Autologous activation could protect myocardium by the left anterior descending (LAD) ligation in rats. Autophagy could reduce the area of myocardial infarction after LAD ligation and improve cardiac function.

[The efficacy and safety of ultrafiltration for patients with heart failure: results from a single-center randomized controlled study].

Objective: To evaluate the efficacy and safety of ultrafiltration in patients with heart failure. Methods: One hundred and thirty four cases of patients with heart failure, who hospitalized in our hospital from June 2010 to June 2016 were enrolled in this study. Random serial number was generated using SPSS 22.0 software, patients were then randomly divided into control group and ultrafiltration group with the proportion of 1∶1 (67 cases in each group). Patients in the control group received standard therapy. Patients in the ultrafiltration group received ultrafiltration therapy for 8 hours. Curative effect was evaluated after 8 hours treatment in the control group and after 12 hours in the ultrafiltration group. Following parameters were compared between the two groups: body weight, dyspnea score and 6 minutes walking distance as well as blood pressure, heart rate, Na(+) , K(+) , Cl(-), pH, HCO(3)(-), Hb, PLT, Cr, BUN levels. Results: (1)Two patients died during run-in process and eventually 132 cases were chosen for final analysis (65 cases in control group and 67 cases in the ultrafiltration group). Gender, age, type of heart failure, dyspnea score, body weight at baseline were similar between the two groups. (2)Post therapy, patients' body weight decreased obviously, while dyspnea score and 6 minutes walking distance increased significantly in the ultrafiltration group compared to baseline(all P<0.05), and the improvement was significantly greater compared to control group(all P<0.05). (3)The safety index comparison of two groups: blood pressure, heart rate, Na(+) , K(+) , Cl(-), pH, HCO(3)(-), Hb, PLT, Cr, and BUN were similar between the two groups at baseline and post therapy. Conclusion: Ultrafiltration therapy is safe and effective to treat patients with heart failure.

[Efficacy and safety of a novel ultrafiltration device for treating patients with refractory heart failure].

OBJECTIVE: To evaluate the efficacy and safety of a new ultrafiltration device for treating refractory heart failure patients. METHODS: A total of 52 patients (37 male, age 29-85(33±44)years) with refractory heart failure were treated using a new ultrafiltration device (FQ-16). Body weight, dyspnea score, oxygen saturation (SatO2), left ventricular ejection fraction(LVEF), BUN, creatinine, electrolytes and blood gas analysis were assessed before and after the treatment. Hypotension event and other main adverse events were recorded. RESULTS: Ultrafiltration duration ranged between 8-22 hours. Total ultrafiltration volume was (4 489±1 548) ml. Compared with baseline, patients' body weight decreased from (75.3±8.74) kg to (69.8±8.39) kg (P<0.01), dyspnea score improved from 2.47±1.55 to 12.87±3.61 (P<0.01) and SatO2 increased from 91.0±6.01 to 96.4±2.52 (P<0.01) and LVEF increased from (30.0±4.1)% to (36.0±4.3)% (P<0.01) after ultrafiltration. Blood creatinine, BUN, electrolytes and blood gas analysis values were similar at baseline and post ultrafiltration. No hypotension event and other main adverse events occurred during the ultrafiltration treatment. CONCLUSIONS: The novel ultrafiltration device adequately relieved hypervolemia and dyspnea in patients with refractory heart failure and the treatment process is safe in this patient cohort.

Monte Carlo dose calculations for high-dose-rate brachytherapy using GPU-accelerated processing.

PURPOSE: Current clinical brachytherapy dose calculations are typically based on the Association of American Physicists in Medicine Task Group report 43 (TG-43) guidelines, which approximate patient geometry as an infinitely large water phantom. This ignores patient and applicator geometries and heterogeneities, causing dosimetric errors. Although Monte Carlo (MC) dose calculation is commonly recognized as the most accurate method, its associated long computational time is a major bottleneck for routine clinical applications. This article presents our recent developments of a fast MC dose calculation package for high-dose-rate (HDR) brachytherapy, gBMC, built on a graphics processing unit (GPU) platform. METHODS AND MATERIALS: gBMC-simulated photon transport in voxelized geometry with physics in (192)Ir HDR brachytherapy energy range considered. A phase-space file was used as a source model. GPU-based parallel computation was used to simultaneously transport multiple photons, one on a GPU thread. We validated gBMC by comparing the dose calculation results in water with that computed TG-43. We also studied heterogeneous phantom cases and a patient case and compared gBMC results with Acuros BV results. RESULTS: Radial dose function in water calculated by gBMC showed <0.6% relative difference from that of the TG-43 data. Difference in anisotropy function was <1%. In two heterogeneous slab phantoms and one shielded cylinder applicator case, average dose discrepancy between gBMC and Acuros BV was <0.87%. For a tandem and ovoid patient case, good agreement between gBMC and Acruos BV results was observed in both isodose lines and dose-volume histograms. In terms of the efficiency, it took ∼47.5 seconds for gBMC to reach 0.15% statistical uncertainty within the 5% isodose line for the patient case. CONCLUSIONS: The accuracy and efficiency of a new GPU-based MC dose calculation package, gBMC, for HDR brachytherapy make it attractive for clinical applications.

Racial disparities in the association between diabetes mellitus-associated polymorphic locus rs4430796 of the HNF1ß gene and prostate cancer: a systematic review and meta-analysis.

Polymorphism 17q12 rs4430796 within HNF1ß is a genetic variant associated with both diabetes mellitus and prostate cancer, but findings on the correlations of rs4430796 with prostate cancer risk specifically are not in agreement, especially among diverse populations. To shed some light on the contradictory findings, therefore, we carried out a meta-analysis by pooling the odds ratios (ORs) with corresponding 95% confidence intervals (CIs) of all currently available case-control studies located within PubMed and Embase databases up to December 2012. A total of 16 studies comprising 30 datasets that collectively involved 25,535 prostate cancer patients and 25,726 controls were ultimately included in this analysis. The meta-analysis of all the studies revealed that the rs4430796 polymorphism was significantly associated with an increased risk of prostate cancer in all contrast models (ORA vs G = 1.25, 95%CI = 1.21-1.30, POR < 0.001; ORAA vs GG = 1.53, 95%CI = 1.45-1.62, POR < 0.001; ORAG vs GG = 1.24, 95%CI = 1.16-1.34, POR < 0.001; ORAA vs AG+GG = 1.36, 95%CI = 1.30-1.42, POR < 0.001; ORAA+AG vs GG = 1.37, 95%CI = 1.30-1.44, POR < 0.001). After subgroup analyses stratified by ethnicity, however, the rs4430796 polymorphism was significantly associated with prostate cancer in both Caucasians and Asians but not in African-Americans. In conclusion, our meta-analysis identified a significant association between the 17q12 rs4430796 polymorphism and prostate cancer risk, although the degree of this association and frequency of the causative allele varied among men of different races.

Genetic diversity analysis of okra (Abelmoschus esculentus L.) by inter-simple sequence repeat (ISSR) markers.

Okra (Abelmoschus esculentus L.) is not only a nutrient-rich vegetable but also an important medicinal herb. Inter-simple sequence repeat (ISSR) markers were employed to investigate the genetic diversity and differentiation of 24 okra genotypes. In this study, the PCR products were separated by electrophoresis on 8% nondenaturing polyacrylamide gel and visualized by silver staining. The 22 ISSR primers produced 289 amplified DNA fragments, and 145 (50%) fragments were polymorphic. The 289 markers were used to construct the dendrogram based on the unweighted pair-group method with arithmetic average (UPGMA) cluster analysis. The dendrogram indicated that 24 okras were clustered into 4 geographically distinct groups. The average polymorphism information content (PIC) was 0.531929, which showed that the majority of primers were informative. The high values of allele frequency, genetic diversity, and heterozygosity showed that primer-sample combinations produced measurable fragments. The mean distances ranged from 0.045455 to 0.454545. The dendrogram indicated that the ISSR markers succeeded in distinguishing most of the 24 varieties in relation to their genetic backgrounds and geographical origins.

Target localization and toxicity in dose-escalated prostate radiotherapy with image-guided approach using daily planar kilovoltage imaging.

Dose escalation with intensity-modulated radiation therapy (IMRT) for carcinoma of the prostate has augmented the need for accurate prostate localization prior to dose delivery. Daily planar kilovoltage (kV) imaging is a low-dose image-guidance technique that is prevalent among radiation oncologists. However, clinical outcomes evaluating the benefit of daily kV imaging are lacking. The purpose of this study was to report our clinical experience, including prostate motion and gastrointestinal (GI) and genitourinary (GU) toxicities, using this modality. A retrospective analysis of 100 patients treated consecutively between December 2005 and March 2008 with definitive external beam IMRT for T1c-T4 disease were included in this analysis. Prescription doses ranged from 74-78 Gy (median, 76) in 2 Gy fractions and were delivered following daily prostate localization using on-board kV imaging (OBI) to localize gold seed fiducial markers within the prostate. Acute and late toxicities were graded as per the NCI CTCAEv3.0. The median follow-up was 22 months. The magnitude and direction of prostate displacement and daily shifts in three axes are reported. Of note, 9.1% and 12.9% of prostate displacements were ≥ 5 mm in the anterior-posterior and superior-inferior directions, respectively. Acute grade 2 GI and GU events occurred in 11% and 39% of patients, respectively, however no grade 3 or higher acute GI or GU events were observed. Regarding late toxicity, 2% and 17% of patients developed grade 2 toxicities, and similarly no grade 3 or higher events had occurred by last follow-up. Thus, kV imaging detected a substantial amount of inter-fractional displacement and may help reduce toxicity profiles, especially high grade events, by improving the accuracy of dose delivery.

Derivation of the tumor position from external respiratory surrogates with periodical updating of the internal/external correlation.

In this work we develop techniques that can derive the tumor position from external respiratory surrogates (abdominal surface motion) through periodically updated internal/external correlation. A simple linear function is used to express the correlation between the tumor and surrogate motion. The function parameters are established during a patient setup session with the tumor and surrogate positions simultaneously measured at a 30 Hz rate. During treatment, the surrogate position, constantly acquired at 30 Hz, is used to derive the tumor position. Occasionally, a pair of radiographic images is acquired to enable the updating of the linear correlation function. Four update methods, two aggressive and two conservative, are investigated: (A1) shift line through the update point; (A2) re-fit line through the update point; (C1) re-fit line with extra weight to the update point; (C2) minimize the distances to the update point and previous line fit point. In the present study of eight lung cancer patients, tumor and external surrogate motion demonstrate a high degree of linear correlation which changes dynamically over time. It was found that occasionally updating the correlation function leads to more accurate predictions than using external surrogates alone. In the case of high imaging rates during treatment (greater than 2 Hz) the aggressive update methods (A1 and A2) are more accurate than the conservative ones (C1 and C2). The opposite is observed in the case of low imaging rates.

Effect of statistical uncertainties on Monte Carlo treatment planning.

This paper reviews the effect of statistical uncertainties on radiotherapy treatment planning using Monte Carlo simulations. We discuss issues related to the statistical analysis of Monte Carlo dose calculations for realistic clinical beams using various variance reduction or time saving techniques. We discuss the effect of statistical uncertainties on dose prescription and monitor unit calculation for conventional treatment and intensity-modulated radiotherapy (IMRT) based on Monte Carlo simulations. We show the effect of statistical uncertainties on beamlet dose calculation and plan optimization for IMRT and other advanced treatment techniques such as modulated electron radiotherapy (MERT). We provide practical guidelines for the clinical implementation of Monte Carlo treatment planning and show realistic examples of Monte Carlo based IMRT and MERT plans.

A quality assurance phantom for IMRT dose verification.

This paper investigates a quality assurance (QA) phantom specially designed to verify the accuracy of dose distributions and monitor units (MU) calculated by clinical treatment planning optimization systems and by the Monte Carlo method for intensity-modulated radiotherapy (IMRT). The QA phantom is a PMMA cylinder of 30 cm diameter and 40 cm length with various bone and lung inserts. A procedure (and formalism) has been developed to measure the absolute dose to water in the PMMA phantom. Another cylindrical phantom of the same dimensions, but made of water, was used to confirm the results obtained with the PMMA phantom. The PMMA phantom was irradiated by 4, 6 and 15 MV photon beams and the dose was measured using an ionization chamber and compared to the results calculated by a commercial inverse planning system (CORVUS, NOMOS, Sewickley, PA) and by the Monte Carlo method. The results show that the dose distributions calculated by both CORVUS and Monte Carlo agreed to within 2% of dose maximum with measured results in the uniform PMMA phantom for both open and intensity-modulated fields. Similar agreement was obtained between Monte Carlo calculations and measured results with the bone and lung heterogeneity inside the PMMA phantom while the CORVUS results were 4% different. The QA phantom has been integrated as a routine QA procedure for the patient's IMRT dose verification at Stanford since 1999.

A Monte Carlo dose calculation tool for radiotherapy treatment planning.

A Monte Carlo user code, MCDOSE, has been developed for radiotherapy treatment planning (RTP) dose calculations. MCDOSE is designed as a dose calculation module suitable for adaptation to host RTP systems. MCDOSE can be used for both conventional photon/electron beam calculation and intensity modulated radiotherapy (IMRT) treatment planning. MCDOSE uses a multiple-source model to reconstruct the treatment beam phase space. Based on Monte Carlo simulated or measured beam data acquired during commissioning, source-model parameters are adjusted through an automated procedure. Beam modifiers such as jaws, physical and dynamic wedges, compensators, blocks, electron cut-outs and bolus are simulated by MCDOSE together with a 3D rectilinear patient geometry model built from CT data. Dose distributions calculated using MCDOSE agreed well with those calculated by the EGS4/DOSXYZ code using different beam set-ups and beam modifiers. Heterogeneity correction factors for layered-lung or layered-bone phantoms as calculated by both codes were consistent with measured data to within 1%. The effect of energy cut-offs for particle transport was investigated. Variance reduction techniques were implemented in MCDOSE to achieve a speedup factor of 10-30 compared to DOSXYZ.

Monte Carlo based treatment planning for modulated electron beam radiation therapy.

A Monte Carlo based treatment planning system for modulated electron radiation therapy (MERT) is presented. This new variation of intensity modulated radiation therapy (IMRT) utilizes an electron multileaf collimator (eMLC) to deliver non-uniform intensity maps at several electron energies. In this way, conformal dose distributions are delivered to irregular targets located a few centimetres below the surface while sparing deeper-lying normal anatomy. Planning for MERT begins with Monte Carlo generation of electron beamlets. Electrons are transported with proper in-air scattering and the dose is tallied in the phantom for each beamlet. An optimized beamlet plan may be calculated using inverse-planning methods. Step-and-shoot leaf sequences are generated for the intensity maps and dose distributions recalculated using Monte Carlo simulations. Here, scatter and leakage from the leaves are properly accounted for by transporting electrons through the eMLC geometry. The weights for the segments of the plan are re-optimized with the leaf positions fixed and bremsstrahlung leakage and electron scatter doses included. This optimization gives the final optimized plan. It is shown that a significant portion of the calculation time is spent transporting particles in the leaves. However, this is necessary since optimizing segment weights based on a model in which leaf transport is ignored results in an improperly optimized plan with overdosing of target and critical structures. A method of rapidly calculating the bremsstrahlung contribution is presented and shown to be an efficient solution to this problem. A homogeneous model target and a 2D breast plan are presented. The potential use of this tool in clinical planning is discussed.

Derivation of electron and photon energy spectra from electron beam central axis depth dose curves.

A method for deriving the electron and photon energy spectra from electron beam central axis percentage depth dose (PDD) curves has been investigated. The PDD curves of 6, 12 and 20 MeV electron beams obtained from the Monte Carlo full phase space simulations of the Varian linear accelerator treatment head have been used to test the method. We have employed a 'random creep' algorithm to determine the energy spectra of electrons and photons in a clinical electron beam. The fitted electron and photon energy spectra have been compared with the corresponding spectra obtained from the Monte Carlo full phase space simulations. Our fitted energy spectra are in good agreement with the Monte Carlo simulated spectra in terms of peak location, peak width, amplitude and smoothness of the spectrum. In addition, the derived depth dose curves of head-generated photons agree well in both shape and amplitude with those calculated using the full phase space data. The central axis depth dose curves and dose profiles at various depths have been compared using an automated electron beam commissioning procedure. The comparison has demonstrated that our method is capable of deriving the energy spectra for the Varian accelerator electron beams investigated. We have implemented this method in the electron beam commissioning procedure for Monte Carlo electron beam dose calculations.

The MLC tongue-and-groove effect on IMRT dose distributions.

We have investigated the tongue-and-groove effect on the IMRT dose distributions for a Varian MLC. We have compared the dose distributions calculated using the intensity maps with and without the tongue-and-groove effect. Our results showed that, for one intensity-modulated treatment field, the maximum tongue-and-groove effect could be up to 10% of the maximum dose in the dose distributions. For an IMRT treatment with multiple gantry angles (> or = 5), the difference between the dose distributions with and without the tongue-and-groove effect was hardly visible, less than 1.6% for the two typical clinical cases studied. After considering the patient setup errors, the dose distributions were smoothed with reduced and insignificant differences between plans with and without the tongue-and-groove effect. Therefore, for a multiple-field IMRT plan (> or = 5), the tongue-and-groove effect on the IMRT dose distributions will be generally clinically insignificant due to the smearing effect of individual fields. The tongue-and-groove effect on an IMRT plan with small number of fields (< 5) will vary depending on the number of fields in a plan (coplanar or non-coplanar), the MLC leaf sequences and the patient setup uncertainty, and may be significant (> 5% of maximum dose) in some cases, especially when the patient setup uncertainty is small (< or = 2 mm).

Monte Carlo simulation of electron beams from an accelerator head using PENELOPE.

The Monte Carlo code PENELOPE has been used to simulate electron beams from a Siemens Mevatron KDS linac with nominal energies of 6, 12 and 18 MeV. Owing to its accuracy, which stems from that of the underlying physical interaction models, PENELOPE is suitable for simulating problems of interest to the medical physics community. It includes a geometry package that allows the definition of complex quadric geometries, such as those of irradiation instruments, in a straightforward manner. Dose distributions in water simulated with PENELOPE agree well with experimental measurements using a silicon detector and a monitoring ionization chamber. Insertion of a lead slab in the incident beam at the surface of the water phantom produces sharp variations in the dose distributions, which are correctly reproduced by the simulation code. Results from PENELOPE are also compared with those of equivalent simulations with the EGS4-based user codes BEAM and DOSXYZ. Angular and energy distributions of electrons and photons in the phase-space plane (at the downstream end of the applicator) obtained from both simulation codes are similar, although significant differences do appear in some cases. These differences, however, are shown to have a negligible effect on the calculated dose distributions. Various practical aspects of the simulations, such as the calculation of statistical uncertainties and the effect of the 'latent' variance in the phase-space file, are discussed in detail.

Modeling the extrafocal radiation and monitor chamber backscatter for photon beam dose calculation.

A simple analytical approach has been developed to model extrafocal radiation and monitor chamber backscatter for clinical photon beams. Model parameters for both the extrafocal source and monitor chamber backscatter are determined simultaneously using conventional measured data, i.e., in-air output factors for square and rectangular fields defined by the photon jaws. The model has been applied to 6 MV and 15 MV photon beams produced by a Varian Clinac 2300C/D accelerator. Contributions to the in-air output factor from the extrafocal radiation and monitor chamber backscatter, as predicted by the model, are in good agreement with the measurements. The model can be used to calculate the in-air output factors analytically, with an accuracy of 0.2% for symmetric or asymmetric rectangular fields defined by jaws when the calculation point is at the isocenter and 0.5% when the calculation point is at an extended SSD. For MLC-defined fields, with the jaws at the recommended positions, calculated in-air output factors agree with the measured data to within 0.3% at the isocenter and 0.7% at off-axis positions. The model has been incorporated into a Monte Carlo dose algorithm to calculate the absolute dose distributions in patients or phantoms. For three MLC-defined irregular fields (triangle shape, C-shape, and L-shape), the calculations agree with the measurements to about 1% even for points at off-axis positions. The model will be particularly useful for IMRT dose calculations because it accurately predicts beam output and penumbra dose.