Exploring immunomodulation by endocrine changes in Lady Windermere syndrome.

Lung disease due to nontuberculous mycobacteria (NTM) occurs with disproportionate frequency in postmenopausal women with a unique phenotype and without clinically apparent predisposing factors. Dubbed 'Lady Windermere syndrome', the phenotype includes low body mass index (BMI), tall stature and higher than normal prevalence of scoliosis, pectus excavatum and mitral valve prolapse. Although the pathomechanism for susceptibility to NTM lung disease in these patients remains uncertain, it is likely to be multi-factorial. A role for the immunomodulatory consequences of oestrogen deficiency and altered adipokine production has been postulated. Altered levels of adipokines and dehydroepiandrosterone have been demonstrated in patients with NTM lung disease. Case reports of NTM lung disease in patients with hypopituitarism support the possibility that altered endocrine function influences disease susceptibility. This paper catalogues the evidence for immunomodulatory consequences of predicted endocrine changes in Lady Windermere syndrome, with emphasis on the immune response to NTM. Collectively, the data warrant further exploration of an endocrine link to disease susceptibility in Lady Windermere syndrome.

Heterogeneity of clinical and environmental isolates of Mycobacterium fortuitum using repetitive element sequence-based PCR: municipal water an unlikely source of community-acquired infections.

M. fortuitum is a rapidly growing mycobacterium associated with community-acquired and nosocomial wound, soft tissue, and pulmonary infections. It has been postulated that water has been the source of infection especially in the hospital setting. The aim of this study was to determine if municipal water may be the source of community-acquired or nosocomial infections in the Brisbane area. Between 2007 and 2009, 20 strains of M. fortuitum were recovered from municipal water and 53 patients' isolates were submitted to the reference laboratory. A wide variation in strain types was identified using repetitive element sequence-based PCR, with 13 clusters of ⩾2 indistinguishable isolates, and 28 patterns consisting of individual isolates. The clusters could be grouped into seven similar groups (>95% similarity). Municipal water and clinical isolates collected during the same time period and from the same geographical area consisted of different strain types, making municipal water an unlikely source of sporadic human infection.

Quantifying the effectiveness of ultraviolet-C light at inactivating airborne Mycobacterium abscessus.

BACKGROUND: Mycobacterium abscessus (MABS) group are environmental organisms that can cause infection in people with cystic fibrosis (CF) and other suppurative lung diseases. There is potential for person-to-person airborne transmission of MABS among people with CF attending the same care centre. Ultraviolet light (band C, UV-C) is used for Mycobacterium tuberculosis control indoors; however, no studies have assessed UV-C for airborne MABS. AIM: To determine whether a range of UV-C doses increased the inactivation of airborne MABS, compared with no-UVC conditions. METHODS: MABS was generated by a vibrating mesh nebulizer located within a 400 L rotating drum sampler, and then exposed to an array of 265 nm UV-C light-emitting diodes (LED). A six-stage Andersen Cascade Impactor was used to collect aerosols. Standard microbiological protocols were used for enumerating MABS, and these quantified the effectiveness of UV-C doses (in triplicate). UV-C effectiveness was estimated using the difference between inactivation with and without UV-C. FINDINGS: Sixteen tests were performed, with UV-C doses ranging from 276 to 1104 µW s/cm2. Mean (±SD) UV-C effectiveness ranged from 47.1% (±13.4) to 83.6% (±3.3). UV-C led to significantly greater inactivation of MABS (all P-values ≤0.045) than natural decay at all doses assessed. Using an indoor model of the hospital environment, it was estimated that UV-C doses in the range studied here could be safely delivered in clinical settings where patients and staff are present. CONCLUSION: This study provides empirical in-vitro evidence that nebulized MABS are susceptible to UV-C inactivation.

Model-based dose calculations for (125)I lung brachytherapy.

PURPOSE: Model-baseddose calculations (MBDCs) are performed using patient computed tomography (CT) data for patients treated with intraoperative (125)I lung brachytherapy at the Mayo Clinic Rochester. Various metallic artifact correction and tissue assignment schemes are considered and their effects on dose distributions are studied. Dose distributions are compared to those calculated under TG-43 assumptions. METHODS: Dose distributions for six patients are calculated using phantoms derived from patient CT data and the EGSnrc user-code BrachyDose. (125)I (GE Healthcare/Oncura model 6711) seeds are fully modeled. Four metallic artifact correction schemes are applied to the CT data phantoms: (1) no correction, (2) a filtered back-projection on a modified virtual sinogram, (3) the reassignment of CT numbers above a threshold in the vicinity of the seeds, and (4) a combination of (2) and (3). Tissue assignment is based on voxel CT number and mass density is assigned using a CT number to mass density calibration. Three tissue assignment schemes with varying levels of detail (20, 11, and 5 tissues) are applied to metallic artifact corrected phantoms. Simulations are also performed under TG-43 assumptions, i.e., seeds in homogeneous water with no interseed attenuation. RESULTS: Significant dose differences (up to 40% for D(90)) are observed between uncorrected and metallic artifact corrected phantoms. For phantoms created with metallic artifact correction schemes (3) and (4), dose volume metrics are generally in good agreement (less than 2% differences for all patients) although there are significant local dose differences. The application of the three tissue assignment schemes results in differences of up to 8% for D(90); these differences vary between patients. Significant dose differences are seen between fully modeled and TG-43 calculations with TG-43 underestimating the dose (up to 36% in D(90)) for larger volumes containing higher proportions of healthy lung tissue. CONCLUSIONS: Metallic artifact correction is necessary for accurate application of MBDCs for lung brachytherapy; simpler threshold replacement methods may be sufficient for early adopters concerned with clinical dose metrics. Rigorous determination of voxel tissue parameters and tissue assignment is required for accurate dose calculations as different tissue assignment schemes can result in significantly different dose distributions. Significant differences are seen between MBDCs and TG-43 dose distributions with TG-43 underestimating dose in volumes containing healthy lung tissue.

Changes in dose with segmentation of breast tissues in Monte Carlo calculations for low-energy brachytherapy.

PURPOSE: To investigate the use of various breast tissue segmentation models in Monte Carlo dose calculations for low-energy brachytherapy. METHODS: The EGSnrc user-code BrachyDose is used to perform Monte Carlo simulations of a breast brachytherapy treatment using TheraSeed Pd-103 seeds with various breast tissue segmentation models. Models used include a phantom where voxels are randomly assigned to be gland or adipose (randomly segmented), a phantom where a single tissue of averaged gland and adipose is present (averaged tissue), and a realistically segmented phantom created from previously published numerical phantoms. Radiation transport in averaged tissue while scoring in gland along with other combinations is investigated. The inclusion of calcifications in the breast is also studied in averaged tissue and randomly segmented phantoms. RESULTS: In randomly segmented and averaged tissue phantoms, the photon energy fluence is approximately the same; however, differences occur in the dose volume histograms (DVHs) as a result of scoring in the different tissues (gland and adipose versus averaged tissue), whose mass energy absorption coefficients differ by 30%. A realistically segmented phantom is shown to significantly change the photon energy fluence compared to that in averaged tissue or randomly segmented phantoms. Despite this, resulting DVHs for the entire treatment volume agree reasonably because fluence differences are compensated by dose scoring differences. DVHs for the dose to only the gland voxels in a realistically segmented phantom do not agree with those for dose to gland in an averaged tissue phantom. Calcifications affect photon energy fluence to such a degree that the differences in fluence are not compensated for (as they are in the no calcification case) by dose scoring in averaged tissue phantoms. CONCLUSIONS: For low-energy brachytherapy, if photon transport and dose scoring both occur in an averaged tissue, the resulting DVH for the entire treatment volume is reasonably accurate because inaccuracies in photon energy fluence are compensated for by inaccuracies in localized dose scoring. If dose to fibroglandular tissue in the breast is of interest, then the inaccurate photon energy fluence calculated in an averaged tissue phantom will result in inaccurate DVHs and average doses for those tissues. Including calcifications necessitates the use of proper tissue segmentation.

Validating the Asher-McDade score to assess facial aesthetic outcomes in 22 consecutive complete bilateral cleft lip repairs.

Most scoring systems used to assess facial aesthetics in cleft patients tend to lack consistency, and the absence of an internationally agreed system makes comparison challenging. The most widely used and validated tool is the five-point Asher-McDade index. We note that there are currently no reports (to our knowledge) of its use for scoring outcomes after bilateral cleft lip repair. To validate it for this use, the aim was to describe the outcomes of 22 consecutive bilateral cleft lip repairs assessed using this scale. A retrospective review was undertaken of 22 consecutive patients with bilateral cleft lip repairs performed at our centre. Each patient underwent bilateral advancement rotation repair with a vomer flap on one side at three months followed by repair of the remaining hard palate and an intravelar veloplasty three months later. Standardised photographs were taken five years after repair and were cropped to isolate the nasolabial component. Eleven members of the cleft multidisciplinary team were asked to rate each image on a five-point Likert scale. Statistical analysis was performed using a two-way ANOVA test and intraclass correlation coefficient to interrogate intraobserver and interobserver variance. A total of 22 consecutive patients with complete bilateral cleft lips were photographed. The overall mean (range) score for the repairs was 3.2 (4.3 - 1.8). Two-way ANOVA demonstrated that inter-rater variability accounted for just over 10% (11.23% of the total variance, p < 0.0001). As predicted, the single biggest factor affecting score variability was the patient's appearance, which accounted for 44.51% of the total variance between scores (p < 0.0001). Intraobserver variance was not found to be significant, accounting for 0.33% of the total variance (p = 0.0006). We demonstrate that the Asher-McDade scoring system is a valid tool to use when assessing bilateral cleft lip repairs. Variance in the patient's score was significantly related to a true difference in appearance, with only a small percentage of differences being due to intraobserver and interobserver variation.

Nasolabial appearance of bilateral cleft lip repair at five years of age. Comparing techniques of modified advancement-rotation (Delaire) with Manchester repair: a retrospective cohort study.

The techniques used to repair bilateral cleft lip have evolved over time, yet little data exist to compare outcomes using the various techniques. The aim of this study was to retrospectively evaluate and compare the aesthetic outcomes of two types of complete bilateral cleft repair: advancement rotation and a historic cohort repaired with the Manchester technique. A total of 32 consecutive patients who had complete repair of bilateral cleft lips were identified retrospectively from our centre using inpatient records. The first 16 (born between 1994 and 2005) underwent the Manchester repair, the second 16 (born between 2006 and 2010) a Delaire modified advancement rotation technique. Standardised photographs were taken at five years post repair and cropped to isolate the nasolabial component. Appearance outcomes were assessed by 20 members of the cleft and plastic surgery team, who were each asked to rate all 32 images using the Asher-McDade five-point scale. A chi squared test was used to determine whether there was a statistically significant difference in cleft scores between the two approaches. There was a mean (SD) of 2.8 (1.02) in the advancement rotation group and a mean (SD) of 3.1 (1.07) in the Manchester group. There was a statistically significant difference in the distribution of scores in the advancement rotation group compared with the Manchester group, with lower scores (better results) in the advancement rotation group (p=0.003). This study demonstrates that the advancement rotation technique for the repair of bilateral cleft lip defects resulted in a superior nasolabial appearance when directly compared with the Manchester repair at 5 years of age.

Monte Carlo dosimetry for 125I and 103Pd eye plaque brachytherapy with various seed models.

PURPOSE: Dose distributions are calculated for various models of 125I and 103Pd seeds in the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). The sensitivity to seed model of dose distributions and dose distributions relative to TG-43 are investigated. METHODS: Monte Carlo simulations are carried out with the EGSnrc user-code BrachyDose. Brachytherapy seeds and eye plaques are fully modeled. Simulations of one seed in the central slot of a 20 mm Modulay (gold alloy) plaque backing with and without the Silastic (silicone polymer) insert and of a 16 mm fully loaded Modulay/Silastic plaque are performed. Dose distributions are compared to those calculated under TG-43 assumptions, i.e., ignoring the effects of the plaque backing and insert and interseed attenuation. Three-dimensional dose distributions for different 125I and 103Pd seed models are compared via depth-dose curves, isodose contours, and tabulation of doses at points of interest in the eye. Results are compared to those of our recent BrachyDose study for COMS plaques containing model 6711 (125I) or 200 (103Pd) seeds [R. M. Thomson et al., Med. Phys. 35, 5530-5543 (2008)]. RESULTS: Along the central axis of a plaque containing one seed, variations of less than 1% are seen in the effect of the Modulay backing alone for different seed models; for the Modulay/Silastic combination, variations are 2%. For a 16 mm plaque fully loaded with 125I (103Pd) seeds, dose decreases relative to TG-43 doses are 11%-12% (19%-20%) and 14%-15% (20%) at distances of 0.5 and 1 cm from the inner sclera along the plaque's central axis, respectively. For the same prescription dose, doses at points of interest vary by up to 8% with seed model. Doses to critical normal structures are lower for all 103Pd seed models than for 125I with the possible exception of the sclera adjacent to the plaque; scleral doses vary with seed model and are not always higher for 103Pd than for 125I. CONCLUSIONS: Dose decreases relative to doses calculated under TG-43 assumptions vary slightly with seed model (for each radionuclide). Dose distributions are sensitive to seed model; however, variations are generally no larger than the magnitudes of other systematic uncertainties in eye plaque therapy.

Monte Carlo dosimetry for 125I and 103Pd eye plaque brachytherapy.

A Monte Carlo study of dosimetry for eye plaque brachytherapy is performed. BrachyDose, an EGSnrc user code which makes use of Yegin's multi-geometry package, is used to fully model 125I (model 6711) and 103Pd (model 200) brachytherapy seeds and the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). Three-dimensional dose distributions in the eye region are obtained. In general, dose to water is scored; however, the implications of replacing water with eye tissues are explored. The effect of the gold alloy (Modulay) backing is investigated and the dose is found to be sensitive to the elemental composition of the backing. The presence of the silicone polymer (Silastic) seed carrier results in substantial dose decreases relative to water, particularly for 103Pd. For a 20 mm plaque with a Modulay backing and Silastic insert, fully loaded with 24 seeds, the dose decrease relative to water is of the order of 14% for 125I and 20% for 103Pd at a distance of 1 cm from the inner sclera along the plaque's central axis. For the configurations of seeds used in COMS plaques, interseed attenuation is a small effect within the eye region. The introduction of an air interface results in a dose reduction in its vicinity which depends on the plaque's position within the eye and the radionuclide. Introducing bone in the eye's vicinity also causes dose reductions. The dose distributions in the eye for the two different radionuclides are compared and, for the same prescription dose, 103Pd generally offers a lower dose to critical normal structures. BrachyDose is sufficiently fast to allow full Monte Carlo dose calculations for routine clinical treatment planning.

Feeding practices and the use of supplements for dogs kept by owners in different socioeconomic groups.

The prevalence of feeding practices and supplements for dogs used in private practice (pp) and the non-profit-making People's Dispensary for Sick Animals (pdsa) was evaluated. Questionnaires were completed by 400 pp clients and 400 pdsa clients, of which 27.2 per cent and 29.8 per cent, respectively, gave supplements to their dogs. Fatty acids/oils were given by 10.3 per cent of pp clients and 11.5 per cent of pdsa clients, glucosamine and/or chondroitin by 10.5 per cent and 5.8 per cent, and vitamins by 6.8 per cent and 19.3 per cent, respectively. The supplements were provided daily by 17.8 per cent of the pp clients and 14.3 per cent of the pdsa clients, and the pdsa clients were 50 per cent more likely to provide the supplements only weekly or monthly than the pp clients. A commercially available maintenance or dietetic diet was fed by 98.8 per cent of the pp clients and 94.2 per cent of the pdsa clients.

Patient-specific Monte Carlo dose calculations for (103)Pd breast brachytherapy.

This work retrospectively investigates patient-specific Monte Carlo (MC) dose calculations for (103)Pd permanent implant breast brachytherapy, exploring various necessary assumptions for deriving virtual patient models: post-implant CT image metallic artifact reduction (MAR), tissue assignment schemes (TAS), and elemental tissue compositions. Three MAR methods (thresholding, 3D median filter, virtual sinogram) are applied to CT images; resulting images are compared to each other and to uncorrected images. Virtual patient models are then derived by application of different TAS ranging from TG-186 basic recommendations (mixed adipose and gland tissue at uniform literature-derived density) to detailed schemes (segmented adipose and gland with CT-derived densities). For detailed schemes, alternate mass density segmentation thresholds between adipose and gland are considered. Several literature-derived elemental compositions for adipose, gland and skin are compared. MC models derived from uncorrected CT images can yield large errors in dose calculations especially when used with detailed TAS. Differences in MAR method result in large differences in local doses when variations in CT number cause differences in tissue assignment. Between different MAR models (same TAS), PTV [Formula: see text] and skin [Formula: see text] each vary by up to 6%. Basic TAS (mixed adipose/gland tissue) generally yield higher dose metrics than detailed segmented schemes: PTV [Formula: see text] and skin [Formula: see text] are higher by up to 13% and 9% respectively. Employing alternate adipose, gland and skin elemental compositions can cause variations in PTV [Formula: see text] of up to 11% and skin [Formula: see text] of up to 30%. Overall, AAPM TG-43 overestimates dose to the PTV ([Formula: see text] on average 10% and up to 27%) and underestimates dose to the skin ([Formula: see text] on average 29% and up to 48%) compared to the various MC models derived using the post-MAR CT images studied herein. The considerable differences between TG-43 and MC models underline the importance of patient-specific MC dose calculations for permanent implant breast brachytherapy. Further, the sensitivity of these MC dose calculations due to necessary assumptions illustrates the importance of developing a consensus modelling approach.

Development of virtual patient models for permanent implant brachytherapy Monte Carlo dose calculations: interdependence of CT image artifact mitigation and tissue assignment.

This work investigates and compares CT image metallic artifact reduction (MAR) methods and tissue assignment schemes (TAS) for the development of virtual patient models for permanent implant brachytherapy Monte Carlo (MC) dose calculations. Four MAR techniques are investigated to mitigate seed artifacts from post-implant CT images of a homogeneous phantom and eight prostate patients: a raw sinogram approach using the original CT scanner data and three methods (simple threshold replacement (STR), 3D median filter, and virtual sinogram) requiring only the reconstructed CT image. Virtual patient models are developed using six TAS ranging from the AAPM-ESTRO-ABG TG-186 basic approach of assigning uniform density tissues (resulting in a model not dependent on MAR) to more complex models assigning prostate, calcification, and mixtures of prostate and calcification using CT-derived densities. The EGSnrc user-code BrachyDose is employed to calculate dose distributions. All four MAR methods eliminate bright seed spot artifacts, and the image-based methods provide comparable mitigation of artifacts compared with the raw sinogram approach. However, each MAR technique has limitations: STR is unable to mitigate low CT number artifacts, the median filter blurs the image which challenges the preservation of tissue heterogeneities, and both sinogram approaches introduce new streaks. Large local dose differences are generally due to differences in voxel tissue-type rather than mass density. The largest differences in target dose metrics (D90, V100, V150), over 50% lower compared to the other models, are when uncorrected CT images are used with TAS that consider calcifications. Metrics found using models which include calcifications are generally a few percent lower than prostate-only models. Generally, metrics from any MAR method and any TAS which considers calcifications agree within 6%. Overall, the studied MAR methods and TAS show promise for further retrospective MC dose calculation studies for various permanent implant brachytherapy treatments.

Lysosomal thyroid hormone 5'-deiodinase.

Lysosomes prepared from rat liver and kidney after loading with the detergent Triton WR-1339 show membrane-bound 5'-deiodinase activity with marked specificity for 3,3',5'-triiodothyronine (reverse T3), lesser activity with respect to thyroxine (T4) and almost none towards 3,3',5'-triiodothyronine (T3). The enzyme is thiol dependent and shows maximal catalysis at pH 7.2. As many of the states known to alter thyroid hormone levels also affect lysosomal function, inhibition of the lysosomal 5'-deiodinase leading to an increase in intracellular reverse T3 may be an initiating mechanism for thyroid hormone change.

Cytomegalovirus retinitis, human immunodeficiency virus antibody positivity and normal T helper cell numbers.

We describe a 46-year-old man in whom retinitis was diagnosed as his initial HIV and AIDS defining illness. A diagnosis of CMV infection was made based on the clinical appearance of the fundus and confirmed by DNA polymerase chain reaction (PCR) on his vitreous biopsy. His CD4+ T lymphocyte count at the time was 580 x 10(6)/l (16%) with a CD4:CD8 ration of 0.28. He had a splenectomy following trauma more than 20 years earlier. He responded very well to intravenous and oral ganciclovir and remains recurrence-free almost 2 years later. This case and others highlight two issues: (i) CMV retinitis in HIV positive is not confined to those with very low CD4+ T lymphocyte counts; (ii) previous splenectomy may have an impact on CD4+ cell numbers and function.

Sinoatrial disorders, the "sick sinus" syndrome. Experience with implanted cardiac pacemakers.

The long term results of permanent pacemaker implantation in patients with disorders of the sinoatrial node and atrial conduction pathways were studied. In a consecutive series of 300 patients treated by pacemaker implantation, 68 ((22.3%) had sinoatrial disorders. Mean age of the group was 54 years (33-82 years); 37 were male, 31 female. Diagnosis was confirmed by serial electrocardiography with overdrive suppression of sinoatrial node function as indicated. Twenty-two patients presented with sinus bradycardia alone (Type I disorder) and 46 with bradycardia-tachycardia syndrome (Type II disorder) were completely controlled. of the 46 Type II patients, in 30 (65.2%) tachyarrhythmias were controlled by pacing alone and in 14 (30.4%) by pacing and antiarrhythmic drug therapy. Congestive cardiac failure was relieved in 80% and anginal pain in 70% of patients with rate control alone. Systemic embolisation did not recur after pacemaker implantation. The average duration of pacemaker therapy was 52 months (12-96 months). In this series, long term ventricular demand pacing proved beneficial in both types of sinoatrial disorders.

Early systemic hypertension after surgical closure of atrial septal defect.

The systemic haemodynamic changes occurring in the immediate post-operative period were examined in a series of patients undergoing closure of atrial septal defect (A.S.D.) and in a consecutive series of all patients undergoing open-heart surgery in this Unit. Significant systemic hypertension was observed in 47.5% of patients in the A.S.D. series. In an attempt to explain this finding, several other haemodynamic variables were examined in relation to the systemic blood pressure. There was no correlation between central venous pressure or blood loss and systemic blood pressure. However, there was an inverse correlation between blood balance and systolic and diastolic blood pressure at 4 hours after operation. The explantation of this finding is unclear but it may be due to the effects on atrial receptors of lower right atrial and pulmonary artery pressures following closure of the A.S.D. Although the post-operative systemic hypertension was transient in most cases, it may produce adverse effects in the early post-operative period and therefore treatment with hypotensive agents should be considered in severe cases.

Hypernatraemic dehydration following tricuspid valve replacement.

The development of abnormally high plasma sodium and plasma osmolality levels is described in 5 patients following open-heart surgery involving prosthetic replacement of the tricuspid valve. These biochemical abnormalities developed in the early post-operative period and were associated with an excessive diuresis during the first 3 to 4 days after operation. Biochemical correction required a prolonged, high volume intravenous water load, and was paralleled by progressive clinical improvement, notably in peripheral circulation, tissue turgor and cerebral function. Plasma sodium and osmolality levels and observed fluid balance in 20 patients undergoing similar surgical procedures for tricuspid valve lesions fail to show this hypernatraemic, hyperosmolar state, and indicate that the majority of such patients have a markedly positive observed fluid balance in the early post-operative period. These differences are statistically highly significant (p less than 0.001). Consideration of urine/plasma osmolality levels reveals a transient but highly significant impairment of renal concentration in the hypernatraemic patients (p less than 0.001).

Model-based dose calculations for COMS eye plaque brachytherapy using an anatomically realistic eye phantom.

PURPOSE: To investigate the effects of the composition and geometry of ocular media and tissues surrounding the eye on dose distributions for COMS eye plaque brachytherapy with(125)I, (103)Pd, or (131)Cs seeds, and to investigate doses to ocular structures. METHODS: An anatomically and compositionally realistic voxelized eye model with a medial tumor is developed based on a literature review. Mass energy absorption and attenuation coefficients for ocular media are calculated. Radiation transport and dose deposition are simulated using the EGSnrc Monte Carlo user-code BrachyDose for a fully loaded COMS eye plaque within a water phantom and our full eye model for the three radionuclides. A TG-43 simulation with the same seed configuration in a water phantom neglecting the plaque and interseed effects is also performed. The impact on dose distributions of varying tumor position, as well as tumor and surrounding tissue media is investigated. Each simulation and radionuclide is compared using isodose contours, dose volume histograms for the lens and tumor, maximum, minimum, and average doses to structures of interest, and doses to voxels of interest within the eye. RESULTS: Mass energy absorption and attenuation coefficients of the ocular media differ from those of water by as much as 12% within the 20-30 keV photon energy range. For all radionuclides studied, average doses to the tumor and lens regions in the full eye model differ from those for the plaque in water by 8%-10% and 13%-14%, respectively; the average doses to the tumor and lens regions differ between the full eye model and the TG-43 simulation by 2%-17% and 29%-34%, respectively. Replacing the surrounding tissues in the eye model with water increases the maximum and average doses to the lens by 2% and 3%, respectively. Substituting the tumor medium in the eye model for water, soft tissue, or an alternate melanoma composition affects tumor dose compared to the default eye model simulation by up to 16%. In the full eye model simulations, the average dose to the lens is larger by 7%-9% than the dose to the center of the lens, and the maximum dose to the optic nerve is 17%-22% higher than the dose to the optic disk for all radionuclides. In general, when normalized to the same prescription dose at the tumor apex, doses delivered to all structures of interest in the full eye model are lowest for(103)Pd and highest for (131)Cs, except for the tumor where the average dose is highest for (103)Pd and lowest for (131)Cs. CONCLUSIONS: The eye is not radiologically water-equivalent, as doses from simulations of the plaque in the full eye model differ considerably from doses for the plaque in a water phantom and from simulated TG-43 calculated doses. This demonstrates the importance of model-based dose calculations for eye plaque brachytherapy, for which accurate elemental compositions of ocular media are necessary.

Monte Carlo dosimetry for 103Pd, 125I, and 131Cs ocular brachytherapy with various plaque models using an eye phantom.

PURPOSE: To investigate dosimetry for ocular brachytherapy for a range of eye plaque models containing(103)Pd, (125)I, or (131)Cs seeds with model-based dose calculations. METHODS: Five representative plaque models are developed based on a literature review and are compared to the standardized COMS plaque, including plaques consisting of a stainless steel backing and acrylic insert, and gold alloy backings with: short collimating lips and acrylic insert, no lips and silicone polymer insert, no lips and a thin acrylic layer, and individual collimating slots for each seed within the backing and no insert. Monte Carlo simulations are performed using the EGSnrc user-code BrachyDose for single and multiple seed configurations for the plaques in water and within an eye model (including nonwater media). Simulations under TG-43 assumptions are also performed, i.e., with the same seed configurations in water, neglecting interseed and plaque effects. Maximum and average doses to ocular structures as well as isodose contours are compared for simulations of each radionuclide within the plaque models. RESULTS: The presence of the plaque affects the dose distribution substantially along the plaque axis for both single seed and multiseed simulations of each plaque design in water. Of all the plaque models, the COMS plaque generally has the largest effect on the dose distribution in water along the plaque axis. Differences between doses for single and multiple seed configurations vary between plaque models and radionuclides. Collimation is most substantial for the plaque with individual collimating slots. For plaques in the full eye model, average dose in the tumor region differs from those for the TG-43 simulations by up to 10% for(125)I and (131)Cs, and up to 17% for (103)Pd, and in the lens region by up to 29% for (125)I, 34% for (103)Pd, and 28% for (131)Cs. For the same prescription dose to the tumor apex, the lowest doses to critical ocular structures are generally delivered with plaques containing (103)Pd seeds. CONCLUSIONS: The combined effects of ocular and plaque media on dose are significant and vary with plaque model and radionuclide, suggesting the importance of model-based dose calculations employing accurate ocular and plaque media and geometries for eye plaque brachytherapy.

Metallic artifact mitigation and organ-constrained tissue assignment for Monte Carlo calculations of permanent implant lung brachytherapy.

PURPOSE: To investigate methods of generating accurate patient-specific computational phantoms for the Monte Carlo calculation of lung brachytherapy patient dose distributions. METHODS: Four metallic artifact mitigation methods are applied to six lung brachytherapy patient computed tomography (CT) images: simple threshold replacement (STR) identifies high CT values in the vicinity of the seeds and replaces them with estimated true values; fan beam virtual sinogram replaces artifact-affected values in a virtual sinogram and performs a filtered back-projection to generate a corrected image; 3D median filter replaces voxel values that differ from the median value in a region of interest surrounding the voxel and then applies a second filter to reduce noise; and a combination of fan beam virtual sinogram and STR. Computational phantoms are generated from artifact-corrected and uncorrected images using several tissue assignment schemes: both lung-contour constrained and unconstrained global schemes are considered. Voxel mass densities are assigned based on voxel CT number or using the nominal tissue mass densities. Dose distributions are calculated using the EGSnrc user-code BrachyDose for (125)I, (103)Pd, and (131)Cs seeds and are compared directly as well as through dose volume histograms and dose metrics for target volumes surrounding surgical sutures. RESULTS: Metallic artifact mitigation techniques vary in ability to reduce artifacts while preserving tissue detail. Notably, images corrected with the fan beam virtual sinogram have reduced artifacts but residual artifacts near sources remain requiring additional use of STR; the 3D median filter removes artifacts but simultaneously removes detail in lung and bone. Doses vary considerably between computational phantoms with the largest differences arising from artifact-affected voxels assigned to bone in the vicinity of the seeds. Consequently, when metallic artifact reduction and constrained tissue assignment within lung contours are employed in generated phantoms, this erroneous assignment is reduced, generally resulting in higher doses. Lung-constrained tissue assignment also results in increased doses in regions of interest due to a reduction in the erroneous assignment of adipose to voxels within lung contours. Differences in dose metrics calculated for different computational phantoms are sensitive to radionuclide photon spectra with the largest differences for (103)Pd seeds and smallest but still considerable differences for (131)Cs seeds. CONCLUSIONS: Despite producing differences in CT images, dose metrics calculated using the STR, fan beam + STR, and 3D median filter techniques produce similar dose metrics. Results suggest that the accuracy of dose distributions for permanent implant lung brachytherapy is improved by applying lung-constrained tissue assignment schemes to metallic artifact corrected images.