Risk and Quality in Brachytherapy From a Technical Perspective.

AIMS: To provide an overview of the history of incidents in brachytherapy and to describe the pillars in place to ensure that medical physicists deliver high-quality brachytherapy. MATERIALS AND METHODS: A review of the literature was carried out to identify reported incidents in brachytherapy, together with an evaluation of the structures and processes in place to ensure that medical physicists deliver high-quality brachytherapy. In particular, the role of education and training, the use of process and technical quality assurance and the role of international guidelines are discussed. RESULTS: There are many human factors in brachytherapy procedures that introduce additional risks into the process. Most of the reported incidents in the literature are related to human factors. Brachytherapy-related education and training initiatives are in place at the societal and departmental level for medical physicists. Additionally, medical physicists have developed process and technical quality assurance procedures, together with international guidelines and protocols. Education and training initiatives, together with quality assurance procedures and international guidelines may reduce the risk of human factors in brachytherapy. CONCLUSION: Through application of the three pillars (education and training; process control and technical quality assurance; international guidelines), medical physicists will continue to minimise risk and deliver high-quality brachytherapy treatments.

Dandy-Walker-Like Malformation in a Free-Ranging Atlantic Harbour Seal Pup (Phoca vitulina concolor).

An 88.5 cm long, 12.9 kg, 3-week-old stranded male Atlantic harbour seal (Phoca vitulina concolor) presented with cerebellar ataxia, delayed postural reactions, hyperaesthesia and nystagmus. The skull was enlarged and domed. Ultrasound through a persistent fontanelle in the frontal bone revealed hydrocephalus. Magnetic resonance imaging showed diffuse enlargement of the ventricular system, an absent cerebellar vermis, hypertrophy of the choroid plexus of the fourth ventricle and enlargement of the caudal fossa. Throughout rehabilitation, the seal failed to achieve milestones critical for successful release or placement in a managed care facility, including the ability to feed independently and haul out. Three months into rehabilitation it began to regurgitate and staff had difficulty administering food to the seal. The seal was euthanized due to a poor prognosis. Post-mortem examination confirmed a) aplasia of the dorsal cerebellar vermis and hypoplasia of the most dorsal portions of the right and left cerebellar hemispheres, b) severe, diffuse, congenital communicating hydrocephalus, and c) aplasia of the interthalamic adhesion and corpus callosum. This case represents the first report of Dandy-Walker-like malformation (DWLM) in a marine mammal and illustrates the importance of advanced imaging and thorough post-mortem examination in free-ranging pinnipeds that strand with evidence of neurological disease.

Accuracy of liver ablation zone prediction in a single 2450MHz 100 Watt generator model microwave ablation system: An in human study.

PURPOSE: To compare manufacturer provided predictions and realized ablation dimensions in the liver using one 2450MHz 100 Watt generator model microwave ablation (MWA) system. MATERIALS AND METHOD: Between 1/1/2015 and 2/1/2018, MWAs were performed in 86 patients who underwent a total of 103 MWAs with a single MWA system. There were 64 men and 22 women with a mean age of 63.9±9.9 (SD) years (range: 30-88 years). Demographic, procedural, and outcomes data was recorded. The manufacturer predicted ablation zone sizes in three dimensions (anterior-posterior [AP], transverse [TR], and cranial caudal [CC]) were recorded and then compared to the actual ablation zone sizes at one month follow-up imaging. RESULTS: MWAs were most commonly performed to treat hepatocellular carcinoma (92/103, 89.3%). Dividing the actual ablation size by the manufacturer prediction in the AP, TR, and CC directions resulted in a mean of 88.3±20.6 (SD) % (range: 33.3-156.4%), 80.2±26.5 (SD) % (range: 29.6-182.9%), and 86.7±25.1 (SD) % (range: 37-186.1%), respectively. The realized AP direction was statistically closer to the manufacturer prediction than the TR (P<0.01). Ablation Watt setting of 100 Watts resulted in more accurate predictions than the 75 or 45 Watt settings in the AP direction (P=0.03). CONCLUSIONS: This 2450MHz 100 Watt generator MWA system manufacturer provided model fairly accurately predicts ablation zone dimensions, but tends to over predict realized dimensions in this mainly hepatocellular carcinoma, and therefore cirrhotic, cohort. The TR is the most inaccurately predicted dimension and manufacturer predictions appear to be best in the 100W setting, important aspects for interventionalists to consider during ablation planning and execution.

Probing microtubules polarity in mitotic spindles in situ using Interferometric Second Harmonic Generation Microscopy.

The polarity of microtubules is thought to be involved in spindle assembly, cytokinesis or active molecular transport. However, its exact role remains poorly understood, mainly because of the challenge to measure microtubule polarity in intact cells. We report here the use of fast Interferometric Second Harmonic Generation microscopy to study the polarity of microtubules forming the mitotic spindles in a zebrafish embryo. This technique provides a powerful tool to study mitotic spindle formation and may be directly transferable for investigating the kinetics and function of microtubule polarity in other aspects of subcellular motility or in native tissues.

Long-term results for Stage IIIB cervical cancer patients receiving external beam radiotherapy combined with either HDR (252)Cf or HDR (60)Co intracavitary brachytherapy.

PURPOSE: The aim of this work was to compare the long-term curative effects and complications of patients diagnosed with cervical cancer International Federation of Gynecology and Obstetrics IIIB (n = 430) as treated with Californium-252 ((252)Cf) or cobalt-60 ((60)Co) intracavitary brachytherapy (ICBT) combined with external beam radiotherapy (EBRT). METHODS AND MATERIALS: Cervical cancer cases with a history of treatment with (252)Cf or (60)Co ICBT combined with EBRT were selected from the Lithuanian National Cancer Institute database. Complications and second primary malignancies were compared in both patients groups. Estimates of the 5-, 10-, and 15-year overall survival and disease-free survival rates were computed with the Kaplan-Meier method and a Cox proportional hazards model applied using STATA software. RESULTS: At 5, 10, and 15 years, the overall survival rates were 46.9%, 39.3%, and 34.6% for the (252)Cf group and 35.4%, 26.9%, and 22.5% for the (60)Co group (p = 0.004), respectively. The disease-free survival rates were 42.1%, 35.0%, and 31.0% for the (252)Cf group and 32.0%, 25.1%, and 21.4% for the (60)Co group (p = 0.009), respectively. Histopathologic type of adenocarcinoma increased the risk of death for the (252)Cf group (hazard ratio 3.62). Histopathologic tumor type (hazard ratio 7.48) and recurrence (hazard ratio 2.83) were factors that statistically and significantly influenced the patient prognosis for the (60)Co group. CONCLUSIONS: Applying (252)Cf ICBT with EBRT was effective for International Federation of Gynecology and Obstetrics IIIB cervical cancer patients. Moreover, long-term followup data demonstrated higher survival rates in patients treated with (252)Cf ICBT than (60)Co ICBT. Complications in patients treated with neutron ICBT were not more frequent or severe than those treated with (60)Co ICBT.

A round-robin gamma stereotactic radiosurgery dosimetry interinstitution comparison of calibration protocols.

PURPOSE: Absorbed dose calibration for gamma stereotactic radiosurgery is challenging due to the unique geometric conditions, dosimetry characteristics, and nonstandard field size of these devices. Members of the American Association of Physicists in Medicine (AAPM) Task Group 178 on Gamma Stereotactic Radiosurgery Dosimetry and Quality Assurance have participated in a round-robin exchange of calibrated measurement instrumentation and phantoms exploring two approved and two proposed calibration protocols or formalisms on ten gamma radiosurgery units. The objectives of this study were to benchmark and compare new formalisms to existing calibration methods, while maintaining traceability to U.S. primary dosimetry calibration laboratory standards. METHODS: Nine institutions made measurements using ten gamma stereotactic radiosurgery units in three different 160 mm diameter spherical phantoms [acrylonitrile butadiene styrene (ABS) plastic, Solid Water, and liquid water] and in air using a positioning jig. Two calibrated miniature ionization chambers and one calibrated electrometer were circulated for all measurements. Reference dose-rates at the phantom center were determined using the well-established AAPM TG-21 or TG-51 dose calibration protocols and using two proposed dose calibration protocols/formalisms: an in-air protocol and a formalism proposed by the International Atomic Energy Agency (IAEA) working group for small and nonstandard radiation fields. Each institution's results were normalized to the dose-rate determined at that institution using the TG-21 protocol in the ABS phantom. RESULTS: Percentages of dose-rates within 1.5% of the reference dose-rate (TG-21+ABS phantom) for the eight chamber-protocol-phantom combinations were the following: 88% for TG-21, 70% for TG-51, 93% for the new IAEA nonstandard-field formalism, and 65% for the new in-air protocol. Averages and standard deviations for dose-rates over all measurements relative to the TG-21+ABS dose-rate were 0.999±0.009 (TG-21), 0.991±0.013 (TG-51), 1.000±0.009 (IAEA), and 1.009±0.012 (in-air). There were no statistically significant differences (i.e., p>0.05) between the two ionization chambers for the TG-21 protocol applied to all dosimetry phantoms. The mean results using the TG-51 protocol were notably lower than those for the other dosimetry protocols, with a standard deviation 2-3 times larger. The in-air protocol was not statistically different from TG-21 for the A16 chamber in the liquid water or ABS phantoms (p=0.300 and p=0.135) but was statistically different from TG-21 for the PTW chamber in all phantoms (p=0.006 for Solid Water, 0.014 for liquid water, and 0.020 for ABS). Results of IAEA formalism were statistically different from TG-21 results only for the combination of the A16 chamber with the liquid water phantom (p=0.017). In the latter case, dose-rates measured with the two protocols differed by only 0.4%. For other phantom-ionization-chamber combinations, the new IAEA formalism was not statistically different from TG-21. CONCLUSIONS: Although further investigation is needed to validate the new protocols for other ionization chambers, these results can serve as a reference to quantitatively compare different calibration protocols and ionization chambers if a particular method is chosen by a professional society to serve as a standardized calibration protocol.

Fetal dose measurements and shielding efficiency assessment in a custom setup of (192)Ir brachytherapy for a pregnant woman with breast cancer.

PURPOSE: To assess the radiation dose to the fetus of a pregnant patient undergoing high-dose-rate (HDR) (192)Ir interstitial breast brachytherapy, and to design a new patient setup and lead shielding technique that minimizes the fetal dose. METHODS: Radiochromic films were placed between the slices of an anthropomorphic phantom modeling the patient. The pregnant woman was seated in a chair with the breast over a table and inside a leaded box. Dose variation as a function of distance from the implant volume as well as dose homogeneity within a representative slice of the fetal position was evaluated without and with shielding. RESULTS: With shielding, the peripheral dose after a complete treatment ranged from 50 cGy at 5 cm from the caudal edge of the breast to <0.1 cGy at 30 cm. The shielding reduces absorbed dose by a factor of two near the breast and more than an order of magnitude beyond 20 cm. The dose is heterogeneous within a given axial plane, with variations from the central region within 50%. Interstitial HDR (192)Ir brachytherapy with breast shielding can be more advantageous than external-beam radiotherapy (EBRT) from a radiation protection point of view, as long as the distance to the uterine fundus is higher than about 10 cm. Furthermore, the weight of the shielding here proposed is notably lower than that needed in EBRT. CONCLUSIONS: Shielded breast brachytherapy may benefit pregnant patients needing localized radiotherapy, especially during the early gestational ages when the fetus is more sensitive to ionizing radiation.

Norms of the Attitudes Toward Intellectual Disability Questionnaire.

BACKGROUND: The Attitudes Toward Intellectual Disability Questionnaire (ATTID) has demonstrated good psychometric qualities for measuring the attitudes of different groups of adults in the general population toward intellectual disability (ID). A significant advantage of the ATTID is that it addresses the concept of attitudes using a three-dimensional model (affective, cognitive and behavioural). To our knowledge, there are no normative data published regarding attitudes toward ID on general population-based samples. METHODS: The sample of 1605 men and women was stratified to be representative of the general adult population of Quebec. The ATTID was administered by phone interview through an independent survey firm. RESULTS: Normative data are presented as percentile scores associated with the raw score of the ATTID by gender and age categories. Analysis of the variance yielded significant differences in attitude by gender and age. The directions and the strength of these associations vary according to each of the five factors used to define attitudes. CONCLUSION: These norms will provide an essential tool to compare different groups and assess the effectiveness of various public campaigns to encourage more positive attitudes towards persons with ID. These norms would also allow international comparisons.

Public attitudes towards intellectual disability: a multidimensional perspective.

BACKGROUND: Public attitudes towards persons with intellectual disabilities (IDs) have a significant effect on potential community integration. A better understanding of these can help target service provision and public awareness programmes. OBJECTIVE: The objective of the present study is threefold: (1) describe public attitudes towards persons with ID along affective, cognitive and behavioural dimensions; (2) compare and contrast attitudes according to sex, age, education and income, as well as frequency and quality of contacts with persons with ID; and (3) ascertain whether the level of functioning has an effect on attitudes. METHODS: The Attitudes Toward Intellectual Disability Questionnaire (ATTID) was administered by phone to 1605 randomly selected adult men and women, stratified by region in the province of Québec, Canada. The ATTID uses a multidimensional perspective of attitudes that reflect affective, cognitive and behavioural dimensions. RESULTS: The results showed that public attitudes were generally positive regarding all three attitudinal dimensions. Public attitudes towards persons with ID are presented in terms of the five factors measured through the ATTID: (1) discomfort; (2) sensibility or tenderness; (3) knowledge of causes; (4) knowledge of capacity and rights; and (5) interaction. Attitude factor scores vary as a function of participant characteristics (sex, age, education and income) and the degree of knowledge about ID, the number of persons with ID known to the participants, as well as the frequency and quality of their contacts with these persons. Men had greater negative attitudes than women as regards the discomfort factor, while women had more negative attitudes regarding the knowledge of capacity and rights factor. More positive attitudes were revealed among younger and more educated participants. Attitudes were generally not associated with income. Public attitudes tended to be more negative towards people with lower functioning ID. CONCLUSION: These results yield useful information to target public awareness and education.

SU-E-T-313: Probe-Type Experimental Dosimetry in Terms of Absorbed Dose to Water in Photon-Brachytherapy a Proposal for a Radiation-Quality Index.

PURPOSE: In photon-brachytherapy (BT), all data for clinical dosimetry (e.g., the dose-rate constant) are not measured in water, but calculated, based on MC-simulation. To enable the measurement of absorbed dose to water, DW, in the vicinity of a source, the complex energy-dependence and other influence quantities must be considered. METHODS: The detectors response, R=M/D, is understood as product of a detector-material dependent 'absorbed dose response', Ren, and Rin, the 'intrinsic response'. Ren is described by the Burlin-theory and because of dissimilarities between the detector-material and water, will have energy dependent correction factors which convert Ren into the clinically relevant DW,Qo=MQo × ND,W,Qo. To characterize BT- source-types, we propose a new 'radiation-quality index' QBT=Dprim(2cm)/Dprim(1cm), the ratio of the primary-dose to water at r=2cm to that at the reference distance r=1cm, similar to external beam dosimetry. Although QBT cannot be measured directly, it can be derived from primary and scatter separated dose-data, published as consensus data e.g., in the Carlton AAPM-TG-43-database. RESULTS: Mean QBT-values are: for nine HDR and four PDR 192Ir-sources: 0.2258±0.5%; one 169Yb- source: 0.2142; and one 125I-source: 0.1544. CONCLUSIONS: The main benefit of this new QBT-concept is that a type of BT-dosimetry-detector needs to be calibrated only for one reference radiation-quality, e.g., for Q0=192Ir. To measure the dose for different source-types, DW can be determined using calculated radiation-quality conversion factors kQ,QoBT, to be included in the AAPM-database and to be provided by the manufacturer for each detector-type. Typical BT-dosimetry-detectors are plastic scintillation detectors, radiochromic film, thermoluminescence detectors, optically stimulated detectors, and small volume ionization chambers. Recently, different DW(1cm)-primary standards have been developed in several European NMIs, enabling to calibrate BT-radiation- sources and BT-dosimetry-detectors and allowing to verify MC-calculated dose-rate constant values. The proposed definition of QBT has to be discussed internationally to find broad consensus.

SU-D-213AB-03: Design Optimization of a HDR Ir-192 Brachytherapy Skin Applicator Using Monte Carlo-Based Dosimetry.

PURPOSE: AccuBoost® applicators are designed to deliver boost dose after whole breast irradiation in substitution for electron boost. By augmenting the current design through adding a wedge inside the applicator and atungsten window above the skin surface, the AccuBoost applicators can be used to treat skin cancer. This study aimed to design a skin applicator that could deliver brachytherapy in a conformai and homogeneous manner to the skin while minimizing OAR dose. METHODS: The 6 cm round AccuBoost applicator served as the foundation for variations of an internal cone, internal wedge, and external window. Monte Carlo (MC) methods (MCNP5)were used for dose characterization and design optimization of these tungsten-alloy components. Specifically, the cone, wedge, and window dimensions were iteratively varied in MC simulations based on HDR Ir-192 dose distributions having (0.5 mm)̂2 voxels in a soft tissue phantom. The design goal was an applicator that can protect tissue > 5 mm while providing lateral dose conformity and a homogeneous dose distribution for tissue < 3 mm. RESULTS: The internal wedge angle governed field size to be irradiated, limiting depth-dose spread into the phantom. Dose conformity was enhanced by the internal cone and collimating window. Window thickness increased required treatment time, where 3 mm was determined to be optimal when considering tradeoff between depth dose and dose rate. With a lesion thickness of 3 mm and setup uncertainty of 1 mm, the optimal design provided better lateral coverage at d = 5mm. Here, the dose was less than 30% of that within the treatment aperture. CONCLUSION: Standardized criteria were established for dose optimization of a skin applicator. Using these criteria and MC methods, an optimized design was obtained. Optimization is underway for other applicator diameters. Clinical evaluation within a 3D treatment planning system and comparison with other brachytherapy skin applicators is ongoing. Prof. Rivard is a stakeholder of Advanced Radiation Therapy, LLC.

SU-E-T-459: Radiobiological Evaluation of Implant Duration and Radionuclide Selection for COMS Eye Plaque Brachytherapy Using an Objective Function.

PURPOSE: The biologically effective dose (BED) of temporary brachytherapy treatments is a function of both chosen radionuclide (R) and implant duration (T). This study endeavored to evaluate BED delivered to the tumor volume and surrounding ocular structures as a function of plaque position (P), prescription dose, R, and T. METHODS: Plaque-heterogeneity- corrected dose distributions were generated with MCNP5 for the range of currently-available COMS plaques using low-energy radionuclides. These physical dose distributions were imported into the Pinnacle3 TPS using the TG-43 hybrid technique and used to generate DVHs for a T=7d implant within a reference eye geometry at eight standard treatment positions. The Dale equation was employed to create biologically effective dose volume histograms (BEDVHs), allowing for BED volumetric analysis of all ROIs. Isobiologically-effective prescription doses were calculated for T=5-0.01d, with BEDVHs subsequently generated for all ROIs using correspondingly reduced prescription doses. Objective functions were created to evaluate the BEDVHs as a function of R and T. RESULTS: Reducing T from 7 to 0.01d for a 10mm plaque produced an average BED benefit of 26%, 20%, and 17% for 103 Pd, 125 I, and 131 Cs, respectively, for all P; 16mm and 22mm plaque results were more position-dependent. 103 Pd produced a 16-35% BED benefit over 125 I, whereas 131 Cs produced a 3-7% BED detriment, independent of P, T, and plaque size. Additionally, corresponding OAR physical doses were lowest using 103 Pd in all circumstances. CONCLUSIONS: Shorter implant durations may correlate with more favorable outcomes vs. 7d implants for small and medium lesions. T may be safely reduced if the prescription dose is appropriately diminished. 103 Pd offers a substantial 16- 35% radiobiological benefit over 125 I and 131 Cs irrespective of P, T, and tumor size. The objective functions used in this study can be applied to temporary or permanent brachytherapy implants for a variety of disease sites.

[Determinants of geographic variations in asthma medication in Quebec]. / Analyse des variations géographiques de l'usage des médicaments de l'asthme au Québec.

BACKGROUND: The study of geographic variations in the use of medication can constitute an interesting and useful option in public health surveillance for the identification of population needs and for the fair partition of resources. Many studies report variations in the use of medication that are not always understood. Considering the importance of medication, particularly for chronic diseases like asthma, it is important to identify factors that can explain geographic differences in the utilization of medications in order to determine optimal prescription practices. METHODS: We used a multilevel analysis to explore determinants of variation among welfare recipients and subscribers covered by the Quebec public drug plan, aged five to 44, who claimed at least one prescription for an asthmatic medication in 2003. The analysis was based on 73 small areas in Quebec's 15 health regions. RESULTS: Prevalence of usage and hospitalization rates are the main predictors of variation in medication intensity. On the other hand, prevalence of usage is related to the area of residence, proportion of welfare recipients and prevalence of smokers. The quality of medication is related to practitioners' specialty. CONCLUSION: Different factors contribute to the understanding of geographic variations in asthma medication but it remains important to control for severity. Small area analysis makes it possible to identify specific areas facing more important problems in the prevalence and use of medication for asthma and thus leads to better understanding of local needs for more targeted interventions.

[Public health surveillance and role of administrative data]. / Importance de la surveillance en santé publique et utilité des données administratives.

BACKGROUND: Public health surveillance constitutes an important activity since it helps in identifying health needs through data collection, and contributes to decision making and actions by analyzing and interpreting data and communicating key results. METHODS: This paper presents a discussion on the concept of public health surveillance, its objectives and its historical evolution. It deals with the importance of surveillance systems while describing their components and challenges. In addition, the authors point out the importance of administrative data as a relevant source for the surveillance of public health problems, particularly chronic diseases and risk factors. RESULTS: This theoretical discussion leads to the proposal of a conceptual model for surveillance systems, which integrates implementation and evaluation. CONCLUSION: This article provides a summary of the concept of public health surveillance and underlines the general aspects to be considered by the managers of surveillance systems. It also discusses the use of administrative data for surveillance.

[Poverty and sociocultural factors in the use of maternal health services in Ivory Coast]. / Pauvreté et déterminants socioculturels de l'utilisation des services de santé maternelle en Côte d'Ivoire.

BACKGROUND: Better health for populations is linked to the adequate access to health services. This is particularly important in developing countries, where a number of economic, social, and geographic barriers exist. Pregnant women are particularly at risk, as they have many health needs and problems. In addition, the use of maternal health services is particularly influenced by economic and socio-cultural factors. Therefore, we intended to appreciate the association between poverty, socio-cultural factors and use of maternal health services in Ivory Coast. METHODS: For this study, our data were from the demographic and health survey in Ivory Coast in 1998. We used the logistic regression models to analyze the relation between poverty, socio-cultural factors and use of services (antenatal care, type of delivery). RESULTS: 62.4% of women used antenatal care adequately and 48.9% delivered in good conditions. Poverty is strongly linked to the use of services whatever the socio-cultural and demographic aspects are, with the poor using less services than the richer. Concerning the impact of socio-cultural characteristics, women living alone or with one adult (OR=1.60; 95% IC=1.06-2.42), those who are Christian (OR=1.83; 95% IC=1.25-2.67) or Akan are more likely to have adequate antenatal care than women living with 5 adults or more, having traditional or no religion, and those who are Senoufo or non Ivorian. Besides, when the number of children increases, they are less likely to consult. Primiparous, Christians (OR=2.45; 95% IC=1.68-3.59) or Muslims (OR=1.73; 95% IC=1.10-2.72) are more likely to deliver in a health center with a qualified assistance. CONCLUSION: Poverty has a negative effect on the use of maternal services but one should also take into account certain socio-cultural characteristics, namely number of adults in the household, parity, ethnicity and religion. While reducing poverty, it appears important to involve family members and religious or ethnic leaders in order to improve this use.

Shielding evaluation of a medical linear accelerator vault in preparation for installing a high-dose rate 252Cf remote afterloader.

In support of the effort to begin high-dose rate 252Cf brachytherapy treatments at Tufts-New England Medical Center, the shielding capabilities of a clinical accelerator vault against the neutron and photon emissions from a 1.124 mg 252Cf source were examined. Outside the clinical accelerator vault, the fast neutron dose equivalent rate was below the lower limit of detection of a CR-39 etched track detector and below 0.14 +/- 0.02 muSv h(-1) with a proportional counter, which is consistent, within the uncertainties, with natural background. The photon dose equivalent rate was also measured to be below background levels (0.1 muSv h(-1)) using an ionisation chamber and an optically stimulated luminescence dosemeter. A Monte Carlo simulation of neutron transport through the accelerator vault was performed to validate measured values and determine the thermal-energy to low-energy neutron component. Monte Carlo results showed that the dose equivalent rate from fast neutrons was reduced by a factor of 100,000 after attenuation through the vault wall, and the thermal-energy neutron dose equivalent rate would be an additional factor of 1000 below that of the fast neutrons. Based on these findings, the shielding installed in this facility is sufficient for the use of at least 5.0 mg of 252Cf.

A formalism for independent checking of Gamma Knife dose calculations.

For stereotactic radiosurgery using the Leksell Gamma Knife system, it is important to perform a pre-treatment verification of the maximum dose calculated with the Leksell GammaPlan (DLGP) stereotactic radiosurgery system. This verification can be incorporated as part of a routine quality assurance (QA) procedure to minimize the chance of a hazardous overdose. To implement this procedure, a formalism has been developed to calculate the dose DCAL(X,Y,Z,dav,t) using the following parameters: average target depth (dav), coordinates (X,Y,Z) of the maximum dose location or any other dose point(s) to be verified, 3-dimensional (3-dim) beam profiles or off-centerratios (OCR) of the four helmets, helmet size i, output factor Oi, plug factor Pi, each shot j coordinates (x,y,z)i,j, and shot treatment time (ti,j). The average depth of the target dav was obtained either from MRI/CT images or ruler measurements of the Gamma Knife Bubble Head Frame. DCAL and DLGP were then compared to evaluate the accuracy of this independent calculation. The proposed calculation for an independent check of DLGP has been demonstrated to be accurate and reliable, and thus serves as a QA tool for Gamma Knife stereotactic radiosurgery.

Monte Carlo calculations of AAPM Task Group Report No. 43 dosimetry parameters for the MED3631-A/M125I source.

Brachytherapy dosimetry parameters for MED3631-A/M 125I sources have been determined in accordance with the AAPM Task Group No. 43 (TG-43) dosimetry protocol. These data were calculated using the *F8 tally from the MCNP4B2 Monte Carlo radiation transport code with the DLC-189 cross-section libraries. Due to motion of the 125I resin beads and gold-copper markers within the capsule, parameters such as the geometry function, radial dose function, dose rate constant, and anisotropy function were examined with the beads and markers having either "realistic" or "ideal" positions; the realistic position was a weighted combination of "vertical" and "diagonal" capsule orientations. The dose rate constants for the realistic and ideal geometries, lambda99std(realistic) and lambda99std(ideal) were 1.066 and 1.067 cGy h(-1) U(-1), respectively, which were within uncertainties of measured values by Wallace and Fan [Med. Phys. 26, 1925-1931 (1999)] and Li et al. [Med. Phys. 27, 1275-1280 (2000)], 1.06 and 1.067 cGy h(-1) U(-1), respectively. The calculated reference dose rate at r0= 1 and theta0= 90 degrees for the realistic source geometry was 0.7% less than for the ideal source geometry. The anisotropy constants, phian(realistic), for the realistic and ideal geometries were 0.948 and 0.965, respectively. phian(realistic) matched that (0.941) measured by Wallace and Fan, and phian(ideal) was significantly different from that (0.948) calculated by Wierzbicki et al. [Med. Phys. 25, 2197-2199 (1998)] for an ideal MED3631-A/S 125I source.

A discretized approach to determining TG-43 brachytherapy dosimetry parameters: case study using Monte Carlo calculations for the MED3633 103Pd source.

It is of interest to discern the energy-dependence of American Association of Physicists in Medicine (AAPM) TG-43 brachytherapy dosimetry parameters. Using Monte Carlo calculation geometry and techniques (MCNP), dependence of these parameters was calculated as a function of photon energy, in general, and for the MED3633 103Pd source using a discretized approach. Results were weighted and summed to determine the total contribution for comparison with the 103Pd source literature. Comprehensive 2-D results are discussed, and the level of agreement with other assessments are presented.