"Strong Teeth": an early-phase study to assess the feasibility of an oral health intervention delivered by dental teams to parents of young children.

BACKGROUND: Tooth decay (caries) is a significant health burden in young children. There is strong evidence for the benefits of establishing appropriate home-based oral health behaviours in early childhood. Dental teams are well placed to provide this information and there is clear advice on what oral health information should be given to parents. However, research has shown that there is limited guidance, training and resources on how dental teams should deliver this advice. "Strong Teeth" is a complex oral health intervention, using evidence-based resources and training underpinned by behaviour change psychology, to support behaviour change conversations in dental practice. This early phase evaluation aims to assess the feasibility of this intervention, prior to a full-scale trial. METHODS: The study recruited 15 parents of children aged 0-2-years-old and 21 parents of children aged 3-5 years old, from five NHS dental practices across West Yorkshire. Participant demographics, self-reported brushing behaviours, dietary habits, a dental examination and three objective measures of toothbrushing were collected in a home-setting at baseline, then at 2-weeks and 2-months post-intervention. Recruitment, retention and intervention delivery were analysed as key process outcomes. Brushing habits were compared to national toothbrushing guidelines - the Delivering Better Oral Health toolkit (Public Health England). RESULTS: Strong Teeth was feasible to deliver in a General Dental Practice setting in 94% of cases. Feasibility of recruitment (37%) exceeded progression criterion, however retention of participants (75%) was below the progression criterion for the 0-2 age group. More than half of children recruited aged 3-5-years had caries experience (52%). Total compliance to toothbrushing guidance at baseline was low (28%) and increased after the intervention (52%), an improvement that was statistically significant. Dietary habits remained largely unchanged. Plaque scores significantly decreased in the 3-5-year-olds and toothbrushing duration increased in all age groups. CONCLUSION: "Strong Teeth" intervention delivery and data collection in the home setting was feasible. There was a positive indication of impact on reported toothbrushing behaviours. Some amendments to study design, particularly relating to the inclusion of the 0-2-year-old group, should be considered before progression to a full trial. Trial registration ISRCTN Register: ISRCTN10709150. Registered retrospectively 24/7/2019.

Demographic and mortality analysis of hospitalized children at a referral hospital in Addis Ababa, Ethiopia.

BACKGROUND: Global childhood mortality rates remain high. Millennium Development Goal 4 focused efforts on reducing rates by two-thirds between 1990 and 2015. In Ethiopia, child mortality rates dropped 71 % from 1990 to 2015, however it is estimated that 184,000 Ethiopian children die each year. There is limited information about pediatric hospital admissions in Ethiopia. Our aims were to examine the temporal relationship of mortality to admission, describe the demographics, and identify cause mortality of children admitted to the Zewditu Memorial Hospital (ZMH). METHODS: A four-year retrospective review of pediatric admissions was conducted at the pediatric emergency room and pediatric hospital ward at ZMH in Addis Ababa, Ethiopia. Admission entries from 2011-2014 of children age 29 days-14 years were reviewed. Age, gender, admission date, disease classification, discharge status and date were obtained. Patient gender was compared using Chi-square analysis. A descriptive analysis was used for age and cause mortality. RESULTS: A total of 6866 patient entries were reviewed. The proportion of admissions younger than age 5 was 0.747 (95 % CI 0.736-0.757). Overall mortality was 0.042 (95 % CI, 0.037-0.047). The proportion of recorded deaths occurring within 2 days of admission was 0.437 (95 % CI 0.380-0.494). The proportion of male admissions was significantly higher than female admissions in all age groups (male 0.575, p < 0.0001, 95 % CI 0.562-0.586). The main causes of mortality were pneumonia (0.253, 95 % CI, 0.203-0.303), severe acute malnutrition (0.222, 95 % CI 0.174-0.27), HIV/AIDS-related complications (0.056, 95 % CI 0.029-0.083), spina bifida (0.049, 95 % CI 0.024-0.074), and hydrocephalus (0.045, 95 % CI 0.021-0.069). CONCLUSIONS: Our study revealed a lower mortality rate than previously reported in Ethiopia. Despite this, 44 % of pediatric hospital mortality occurred early during hospitalization, higher than reported at other Ethiopian hospitals. This adds further evidence that systematic efforts should be dedicated to improve pediatric emergency care. Admissions included 58 % male patients, similar to other reports in Ethiopia implying that this may be a nation-wide phenomenon. The observed disparity may be due to societal factors regarding care-seeking behaviors or male predilection for respiratory illness warranting further investigation. Cause mortality patterns were similar to reports in analogous settings.

Helical tomotherapy with simultaneous integrated boost dose painting for the treatment of synchronous primary cancers involving the head and neck.

OBJECTIVE: To demonstrate the feasibility of helical tomotherapy (HT)-based intensity-modulated radiotherapy (IMRT) for the treatment of synchronous primary cancers arising from the head and neck. METHODS: 14 consecutive patients with histologically proven squamous cell carcinoma of the head and neck were determined to have a second primary cancer in the upper aerodigestive tract on further evaluation and were treated with HT using simultaneous integrated boost IMRT. Megavoltage CT scans were acquired daily as part of an image-guided registration protocol. Concurrent platinum-based systemic therapy was given to nine patients (64%). RESULTS: HT resulted in durable local control in 21 of the 28 primary disease sites irradiated, including a complete clinical and radiographic response initially observed at 17 of the 20 sites with gross tumour. The mean displacements to account for interfraction motion were 2.44 ± 1.25, 2.92 ± 1.09 and 2.31 ± 1.70 mm for the medial-lateral (ML), superior-inferior (SI) and anteroposterior (AP) directions, respectively. Table shifts of >3 mm occurred in 19%, 20% and 22% of the ML, SI and AP directions, respectively. The 2-year estimates of overall survival, local-regional control and progression-free survival were 58%, 73% and 60%, respectively. CONCLUSION: The effectiveness of HT for the treatment of synchronous primary cancers of the head and neck was demonstrated. ADVANCES IN KNOWLEDGE: HT is a feasible option for synchronous primary cancers of the head and neck and can result in long-term disease control with acceptable toxicity in appropriately selected patients.

Decreased sensitivity to long-distance dependencies in children with a history of specific language impairment: electrophysiological evidence.

PURPOSE: One possible source of tense and agreement limitations in children with specific language impairment (SLI) is a weakness in appreciating structural dependencies that occur in many sentences in the input. This possibility was tested in the present study. METHOD: Children with a history of SLI (H-SLI; n = 12; M = 9;7 [years;months]) and typically developing same-age peers (TD; n = 12; M = 9;7) listened to and made grammaticality judgments about grammatical and ungrammatical sentences involving either a local agreement error (e.g., "Every night they talks on the phone") or a long-distance finiteness error (e.g., "He makes the quiet boy talks a little louder"). Electrophysiological (ERP) and behavioral (accuracy) measures were obtained. RESULTS: Local agreement errors elicited the expected anterior negativity and P600 components in both groups of children. However, relative to the TD group, the P600 effect for the long-distance finiteness errors was delayed, reduced in amplitude, and shorter in duration for the H-SLI group. The children's grammaticality judgments were consistent with the ERP findings. CONCLUSION: Children with H-SLI seem to be relatively insensitive to the finiteness constraints that matrix verbs place on subject-verb clauses that appear later in the sentence.

Evaluation of hippocampus dose for patients undergoing intensity-modulated radiotherapy for nasopharyngeal carcinoma.

OBJECTIVE: To evaluate the dose received by the hippocampus among patients undergoing intensity-modulated radiotherapy (IMRT) for nasopharyngeal cancer. METHODS: 10 patients with biopsy-proven, locally advanced nasopharyngeal cancer constituted the study population. The total prescribed dose to the planning target volume (PTV) was 70 Gy (D95%) delivered in 2.12-Gy daily fractions using IMRT. Using established anatomical guidelines, MRI co-registration and the assistance of a board-certified neuroradiologist, the right and left hippocampi were delineated on axial imaging from the CT scan obtained at simulation for each patient beginning at the most anterior portion of the lateral ventricle. IMRT treatment plans were generated without dose-volume constraints to the hippocampus. A range of dose-volume statistics was calculated. RESULTS: The mean hippocampus volume was 6.01 ± 2.61 cm(3). The mean V20 was 72.2%; V40 was 22.0%; V50 was 10.2%; and V60 was 5.5%. The average mean, minimum and maximum hippocampus doses were 30.27 Gy (range, 19.08-47.99 Gy); 17.54 Gy (range, 11.66-33.17 Gy); and 54.95 Gy (range, 35.59-75.57 Gy), respectively. The hippocampus received a maximum dose exceeding 70 Gy in 30% of cases. CONCLUSION: Our dosimetric analysis suggests that, for patients undergoing IMRT for nasopharyngeal cancer, the hippocampus routinely receives significantly high doses. ADVANCES IN KNOWLEDGE: The hippocampus receives a fair amount of incidental radiation during treatment for nasopharyngeal cancer. Given the importance of this structure with respect to memory and neurocognitive function, consideration should be given to identifying the hippocampus as a critical organ at risk in the IMRT optimization process.

Clinical-dosimetric relationship between lacrimal gland dose and ocular toxicity after intensity-modulated radiotherapy for sinonasal tumours.

OBJECTIVE: To characterise the relationship between lacrimal gland dose and ocular toxicity among patients treated by intensity-modulated radiotherapy (IMRT) for sinonasal tumours. METHODS: 40 patients with cancers involving the nasal cavity and paranasal sinuses were treated with IMRT to a median dose of 66.0 Gy. Toxicity was scored using the Radiation Therapy Oncology Group morbidity criteria based on conjunctivitis, corneal ulceration and keratitis. The paired lacrimal glands were contoured as organs at risk, and the mean dose, maximum dose, V10, V20 and V30 were determined. Statistical analysis was performed using logistic regression and the Akaike information criterion (AIC). RESULTS: The maximum and mean dose to the ipsilateral lacrimal gland were 19.2 Gy (range, 1.4-75.4 Gy) and 14.5 Gy (range, 11.1-67.8 Gy), respectively. The mean V10, V20 and V30 values were 50%, 25% and 17%, respectively. The incidence of acute and late Grade 3+ toxicities was 23% and 19%, respectively. Based on logistic regression and AIC, the maximum dose to the ipsilateral lacrimal gland was identified as a more significant predictor of acute toxicity (AIC, 53.89) and late toxicity (AIC, 32.94) than the mean dose (AIC, 56.13 and 33.83, respectively). The V20 was identified as the most significant predictor of late toxicity (AIC, 26.81). CONCLUSION: A dose-response relationship between maximum dose to the lacrimal gland and ocular toxicity was established. Our data suggesting a threshold relationship may be useful in establishing dosimetric guidelines for IMRT planning that may decrease the risk of acute and late lacrimal toxicities in the future. ADVANCES IN KNOWLEDGE: A threshold relationship between radiation dose to the lacrimal gland and ocular toxicity was demonstrated, which may aid in treatment planning and reducing the morbidity of radiotherapy for sinonasal tumours.

Serotype prevalence and antibiotic resistance in Streptococcus pneumoniae clinical isolates among global populations.

Streptococcus pneumoniae remains a leading cause of disease in children and adults. Serotypes differ in invasiveness, virulence, and antibiotic resistance; therefore, serotype surveillance is necessary to monitor the burden of pneumococcal disease, especially in the setting of pneumococcal vaccination programs. The Tigecycline Evaluation Surveillance Trial, (TEST), is an on-going global antibiotic susceptibility surveillance program. Serotypes and antibiotic susceptibilities of 2173 invasive S. pneumoniae in this existing database during 2004-2008 were evaluated. Worldwide, serotypes 19A (28%), 19F (10%) and 14 (9%) were the most common in children under 5 years. In adults over 16 years, 19A (13%), 3, 6A and 7F (all 7%) were most common. Serotypes 19A, 6A, 19F, 6B, 15A, 9V, and 14 exhibited significantly higher levels of erythromycin resistance (P<0.05), while 19A, 19F, 35B, 6A, 6B, 23A, 9V, 15A, and 14 demonstrated higher rates of penicillin resistance (P<0.05). This analysis of an existing pathogen database provides a snapshot of global serotype data and describes the consequential issue of antibiotic resistance in specific serotypes, many of which are increasingly common causes of invasive pneumococcal disease.

Interactive binocular treatment (I-BiT) for amblyopia: results of a pilot study of 3D shutter glasses system.

PURPOSE: A computer-based interactive binocular treatment system (I-BiT) for amblyopia has been developed, which utilises commercially available 3D 'shutter glasses'. The purpose of this pilot study was to report the effect of treatment on visual acuity (VA) in children with amblyopia. METHODS: Thirty minutes of I-BiT treatment was given once weekly for 6 weeks. Treatment sessions consisted of playing a computer game and watching a DVD through the I-BiT system. VA was assessed at baseline, mid-treatment, at the end of treatment, and at 4 weeks post treatment. Standard summary statistics and an exploratory one-way analysis of variance (ANOVA) were performed. RESULTS: Ten patients were enrolled with strabismic, anisometropic, or mixed amblyopia. The mean age was 5.4 years. Nine patients (90%) completed the full course of I-BiT treatment with a mean improvement of 0.18 (SD=0.143). Six out of nine patients (67%) who completed the treatment showed a clinically significant improvement of 0.125 LogMAR units or more at follow-up. The exploratory one-way ANOVA showed an overall effect over time (F=7.95, P=0.01). No adverse effects were reported. CONCLUSION: This small, uncontrolled study has shown VA gains with 3 hours of I-BiT treatment. Although it is recognised that this pilot study had significant limitations-it was unblinded, uncontrolled, and too small to permit formal statistical analysis-these results suggest that further investigation of I-BiT treatment is worthwhile.

Intensity-modulated radiotherapy for nasopharyngeal carcinoma: improvement of the therapeutic ratio with helical tomotherapy vs segmental multileaf collimator-based techniques.

OBJECTIVES: The aim of the study was to compare differences in dosimetric, clinical and quality-of-life end points among patients treated with helical tomotherapy (HT) and segmental multileaf collimator (SMLC)-based intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma. METHODS: From June 2005 to August 2009, 30 consecutive patients were treated with IMRT for nasopharyngeal carcinoma to a dose of 70 Gy. 14 patients (47%) were treated using HT and 16 (53%) were treated using SMLC-based IMRT. 28 patients (93%) received concurrent chemotherapy. The patients were evenly balanced between the two radiotherapy groups with respect to clinical and pathological characteristics. Median follow-up was 30 months (range, 6-62 months). RESULTS: The 2-year estimates of overall survival, local-regional control and progression-free survival were 81%, 87% and 82%, respectively. There were no significant differences in any of these end points with respect to IMRT technique (p>0.05 for all). Dosimetric analysis revealed that patients treated by HT had significantly improved salivary sparing with respect to mean dose (27.3 vs 34.1 Gy, p=0.03) and volume receiving greater than or equal to 30 Gy (31.7% vs 47.3%, p=0.01) to the contralateral (spared) parotid gland. The incidence of Grade 3+ late xerostomia was 13 and 7% among patients treated with SMLC-based IMRT and HT, respectively (p=0.62). The corresponding proportion of patients who subjectively reported "too little" or "no" saliva at final follow-up was 38% and 7%, respectively (p=0.04). CONCLUSION: The superior dosimetric outcome observed with HT appeared to translate into moderately improved clinical outcomes with respect to salivary sparing. Prospective trials are needed to validate this gain in the therapeutic ratio.

Metabolomics in drug target discovery.

Most diseases result in metabolic changes. In many cases, these changes play a causative role in disease progression. By identifying pathological metabolic changes, metabolomics can point to potential new sites for therapeutic intervention. Particularly promising enzymatic targets are those that carry increased flux in the disease state. Definitive assessment of flux requires the use of isotope tracers. Here we present techniques for finding new drug targets using metabolomics and isotope tracers. The utility of these methods is exemplified in the study of three different viral pathogens. For influenza A and herpes simplex virus, metabolomic analysis of infected versus mock-infected cells revealed dramatic concentration changes around the current antiviral target enzymes. Similar analysis of human-cytomegalovirus-infected cells, however, found the greatest changes in a region of metabolism unrelated to the current antiviral target. Instead, it pointed to the tricarboxylic acid (TCA) cycle and its efflux to feed fatty acid biosynthesis as a potential preferred target. Isotope tracer studies revealed that cytomegalovirus greatly increases flux through the key fatty acid metabolic enzyme acetyl-coenzyme A carboxylase. Inhibition of this enzyme blocks human cytomegalovirus replication. Examples where metabolomics has contributed to identification of anticancer drug targets are also discussed. Eventual proof of the value of metabolomics as a drug target discovery strategy will be successful clinical development of therapeutics hitting these new targets.

Changes in position and volume of lung cancer target volumes during stereotactic body radiotherapy (SBRT): is image guidance necessary?

The purpose of this study was to analyze inter- and intra-fractional changes in tumor volume with respect to both spatial and volumetric parameters among patients treated by SBRT for lung cancer. Twelve patients (13 tumors) were treated by SBRT with abdominal compression in 3-5 fractions over a 2 week period to a median dose of 60 Gy (range, 48 to 60 Gy). Kilovoltage cone-beam CT (CBCT) was obtained prior to the delivery of each fraction as well as intra-fractionally yielding a total of 55 CBCT scans. All CBCT scans were registered with the planning CT for target alignment and shifts were recorded and analyzed. Retrospectively, gross tumor volume (GTV) was contoured on all CBCT images and compared to initial planning volumes; positional differences were evaluated utilizing directional and vector analysis. Shifts greater than 5 mm were applied inter-fractionally in 6.8% (lateral), 29.5% (longitudinal), and 6.8% (vertical) of all delivered treatments. Using a 10 mm threshold, the corresponding percentages were 2.3%, 13.6%, and 2.3%, respectively. Across all fractions, the calculated inter-fractional shift vectors ranged from 0 to 31.2 mm, with 40.9%, 15.9%, and 11.4% of all fractions having shift vectors≥5 mm, ≥10 mm, and ≥20 mm, respectively. Intra-fractional shifts were also evaluated and found negligible in a small portion of patients evaluated. The mean overall reduction in GTV was 21.1% during SBRT. Significant changes in both position and volume occur during SBRT for lung cancer. Shifts (particularly in the superior-inferior axis) may exceed applied margins and compromise target coverage. Due to the extreme hypofractionation associated with SBRT, inter-fractional image guidance is necessary.

Comparison of IMRT techniques in the radiotherapeutic management of head and neck cancer: is tomotherapy "better" than step-and-shoot IMRT?

Currently, the most common method of delivering intensity-modulated radiotherapy (IMRT) is through step-and-shoot, segmental multi-leaf collimator (SMLC)-based techniques. Although rotational delivery methods such as helical tomotherapy (HT) have been proposed as offering advantages in the treatment of head and neck cancer, a lack of clinical data exists on its potential utility. This study compared dosimetric, clinical, and quality-of-life endpoints among 149 patients treated by HT and SMLC-IMRT for head and neck cancer. Dosimetric analysis revealed that the use of HT resulted in significant improvements with respect to mean dose (23.5 versus 27.9 Gy, p = 0.03) and V30 (30.1 versus 43.9 Gy, p = 0.01) to the contralateral (spared) parotid gland. However, the incidence of grade 3+ xerostomia in the late setting was 10% and 8% among patients treated by HT and SMLC-IMRT, respectively (p = 0.46). There were no significant differences in any of the quality of life endpoints among patients treated by HT and SMLC-IMRT (p > 0.05, for all). Acknowledging the biases inherent in this retrospective analysis, we found that the dosimetric advantages observed with HT compared to SMLC-IMRT failed to translate into significant improvements in clinical outcome. Prospective studies are needed to further evaluate how HT may affect the therapeutic ratio.

Intensity-modulated radiotherapy increases dose to the brachial plexus compared with conventional radiotherapy for head and neck cancer.

OBJECTIVE: The preferential use of intensity-modulated radiotherapy (IMRT) over conventional radiotherapy (CRT) in the treatment of head and neck cancer has raised concerns regarding dose to non-target tissue. The purpose of this study was to compare dose-volume characteristics with the brachial plexus between treatment plans generated by IMRT and CRT using several common treatment scenarios. METHOD: The brachial plexus was delineated on radiation treatment planning CT scans from 10 patients undergoing IMRT for locally advanced head and neck cancer using a Radiation Therapy Oncology Group-endorsed atlas. No brachial plexus constraint was used. For each patient, a conventional three-field shrinking-field plan was generated and the dose-volume histogram (DVH) for the brachial plexus was compared with that of the IMRT plan. RESULTS: The mean irradiated volumes of the brachial plexus using the IMRT vs the CRT plan, respectively, were as follows: V50 (18±5 ml) vs (11±6 ml), p = 0.01; V60 (6±4 ml) vs (3±3 ml), p = 0.02; V66 (3±1 ml) vs (1±1 ml), p = 0.04, V70 (0±1 ml) vs (0±1 ml), p = 0.68. The maximum point dose to the brachial plexus was 68.9 Gy (range 62.3-78.7 Gy) and 66.1 Gy (range 60.2-75.6 Gy) for the IMRT and CRT plans, respectively (p = 0.01). CONCLUSION: Dose to the brachial plexus is significantly increased among patients undergoing IMRT compared with CRT for head and neck cancer. Preliminary studies on brachial plexus-sparing IMRT are in progress.

A compact linac for intensity modulated proton therapy based on a dielectric wall accelerator.

A novel compact CT-guided intensity modulated proton radiotherapy (IMPT) system is described. The system is being designed to deliver fast IMPT so that larger target volumes and motion management can be accomplished. The system will be ideal for large and complex target volumes in young patients. The basis of the design is the dielectric wall accelerator (DWA) system being developed at the Lawrence Livermore National Laboratory (LLNL). The DWA uses fast switched high voltage transmission lines to generate pulsed electric fields on the inside of a high gradient insulating (HGI) acceleration tube. High electric field gradients are achieved by the use of alternating insulators and conductors and short pulse times. The system will produce individual pulses that can be varied in intensity, energy and spot width. The IMPT planning system will optimize delivery characteristics. The system will be capable of being sited in a conventional linac vault and provide intensity modulated rotational therapy. Feasibility tests of an optimization system for selecting the position, energy, intensity and spot size for a collection of spots comprising the treatment are underway. A prototype is being designed and concept designs of the envelope and environmental needs of the unit are beginning. The status of the developmental new technologies that make the compact system possible will be reviewed. These include, high gradient vacuum insulators, solid dielectric materials, SiC photoconductive switches and compact proton sources.

Multimodality image registration quality assurance for conformal three-dimensional treatment planning.

PURPOSE: We present a quality assurance methodology to determine the accuracy of multimodality image registration and fusion for the purpose of conformal three-dimensional and intensity-modulated radiation therapy treatment planning. Registration and fusion accuracy between any combination of computed tomography (CT), magnetic resonance (MR), and positron emission computed tomography (PET) imaging studies can be evaluated. METHODS AND MATERIALS: A commercial anthropomorphic head phantom filled with water and containing CT, MR, and PET visible targets was modified to evaluate the accuracy of multimodality image registration and fusion software. For MR and PET imaging, the water inside the phantom was doped with CuNO(3) and 18F-fluorodeoxyglucose (18F-FDG), respectively. Targets consisting of plastic spheres and pins were distributed throughout the cranium section of the phantom. Each target sphere had a conical-shaped bore with its apex at the center of the sphere. The pins had a conical extension or indentation at the free end. The contours of the spheres, sphere centers, and pin tips were used as anatomic landmark models for image registration, which was performed using affine coordinate-transformation tools provided in a commercial multimodality image registration/fusion software package. Four sets of phantom image studies were obtained: primary CT, secondary CT with different phantom immobilization, MR, and PET study. A novel CT, MR, and PET external fiducial marking system was also tested. RESULTS: The registration of CT/CT, CT/MR, and CT/PET images allowed correlation of anatomic landmarks to within 2 mm, verifying the accuracy of the registration software and spatial fidelity of the four multimodality image sets. CONCLUSIONS: This straightforward phantom-based quality assurance of the image registration and fusion process can be used in a routine clinical setting or for providing a working image set for development of the image registration and fusion process and new software.

Abutment dosimetry for serial tomotherapy.

The dose distributions at the abutment region for serial tomotherapy are reviewed. While tomotherapy provides unparalleled dose distributions, precise couch motion and good patient immobilization are required because the dose in the abutment region changes by 25% for each millimeter of misalignment. The process of delivering intensity-modulated radiation therapy using sequentially delivered modulated arcs yields hot spots below and cold spots above the machine isocenter when arc angles of less than 360 degrees are used. The magnitude of the hot and cold spots increases significantly as the arc angle is reduced 180 degrees such as when limited by couch clearance restrictions. Placement of isocenter also significantly affects the dose heterogeneity in the abutment region, with the hot and cold spots increasing nearly linearly with off-axis distance in the vertical direction. Reduction of the magnitude of the abutment region dose heterogeneities is possible if helical delivery is provided by moving the couch during arc delivery. The dose heterogeneity can also be reduced by creating 2 treatment plans, each with slightly different abutment region positions, or by using multiple couch angles.

Angular measurement of the cobalt-60 emitted radiation spectrum from a radiosurgery irradiator.

The photon energy spectrum emanating from a Leksell Gamma Knife, Model 23004B, was measured between 0.250 and 3.5 MeV with the sources exposed. Measurements were made using a 2x2 inch NaI detector enclosed in a lead-shielded apparatus having a 1/4 inch diameter measurement aperture, which reduced the amount of radiation received by the crystal. All measurements were made one meter above the floor within a quadrant toward one side of the Gamma Knife couch. The measured spectra displayed the expected 60Co doublet of photon peaks at energies of 1.17 and 1.33 MeV. These peaks appeared in spectra beginning at approximately 50 degrees, as one proceeds from a point directly lateral to the source enclosure (0 degrees) toward the foot of the couch (90 degrees). The average photon energy of the spectrum shifts to lower values as the doublet decreases in magnitude with increasing angle until almost vanishing at an angle equal to 90 degrees. Inserting a 16 cm diameter plastic sphere phantom, provided with the Gamma Knife, into the radiation beams increases the low energy photon emissions appearing in the spectrum, especially for measurements at the foot of the couch. Implications for the design of shielding a treatment room containing the Gamma Knife, Model B, and estimation of the radiation exposure to personnel during an emergency procedure in the treatment room with the sources exposed are discussed.