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.

Uptake of breast screening and associated factors among Hong Kong women aged ≥50 years: a population-based survey.

OBJECTIVE: To examine the uptake of breast screening and its associated factors among Hong Kong Chinese women aged ≥50 years. STUDY DESIGN: Cross-sectional population-based survey. METHODS: A sample of Hong Kong Chinese women was recruited through telephone random-digit dialling. The survey consisted of six sections: perceived health status, use of complementary medicine, uptake of breast screening, perceived susceptibility to cancer, family history of cancer and demographic data. The factors associated with uptake of breast screening were analysed using logistic regression analysis. RESULTS: In total, 1002 women completed the (anonymous) telephone survey. The mean age was 63.5 (standard deviation 10.6) years. The uptake rate of breast screening among Hong Kong Chinese women aged ≥50 years was 34%. The primary reasons for undertaking breast screening were as part of a regular medical check-up (74%), prompted by local signs and symptoms (11%) and a physician's recommendation (7%). Higher educational level, married or cohabiting, family history of cancer, frequent use of complementary therapies, regular visits to a doctor or Chinese herbalist, and the recommendation of a health professional were all independently and significantly associated with increased odds of having had a mammogram. CONCLUSIONS: This study provides community-based evidence of the need for public health policy to promote broader use of mammography services among this target population, with emphasis on the active involvement of health care professionals, through the development and implementation of appropriate evidence-based and resource-sensitive strategies.

Psychometric properties of the Chinese version of Sexual Function After Gynecologic Illness Scale (SFAGIS).

PURPOSE: This study aims to develop the Chinese version of the Sexual Function after Gynecologic Illness Scale (SFAGIS) and to establish its psychometric properties in Hong Kong Chinese patients with gynecological cancer. METHODS: A Chinese version of SFAGIS was developed using the Brislin model of translation and guidelines for cross-cultural adaptation of scales. The content validity and semantic equivalence were assessed by an expert panel. The translated version of SFAGIS was administered to 150 Hong Kong Chinese women with gynecological cancer to test the scale's psychometric properties and to assess its feasibility. The convergent validity of the Chinese scale was tested by correlating it with the Chinese version of the sex relations subscale of the Psychosocial Adjustment to Illness Scale Self-Report (PAIS-SR). RESULTS: The average completion time for the Chinese SFAGIS was 16.2 ± 6.6 min. The internal consistency of the Chinese SFAGIS was 0.93. Test-retest reliability was also high with an interclass correlation coefficient 0.76. A Pearson product-moment correlation found strong correlations among the Chinese SFAGIS and the Chinese version of the sex relations subscale of the PAIS-SR, indicating that both scales measure the same as or has a similar construct. CONCLUSIONS: The Chinese version of SFAGIS is a reliable and valid instrument which can be used in clinical practice and research for assessing sexual function problems in Chinese patients with gynecological cancer and to identify those in need of attention.

SU-E-T-188: Evaluation of a 3D Patient Relevant Dose QA Tool: Multiple Institutional Studies.

PURPOSE: To evaluate 3DVHTM as a patient dose-verification and analysis tool through multiple institutional studies. Virtual patient doses were measured and compared among different vendors' treatment planning systems (TPS) and delivered by different vendors' LINACS so that we better understand the uncertainty of entire process within a patient undergone radiotherapy. METHODS: One head-and-neck (H&N) and one lung patient were selected in this study. The DICOM images/RT structures along with clinical protocols including prescription doses (59.4Gy for H&N and 70.2Gy for lung) and normal‐tissues tolerances were distributed to six institutions. Based on the same criteria, each institution generated their IMRT plans for the patients. Four different TPS and six different LINACS were used. The conventional per‐beam IMRT QA using MapCHECK was performed by all participants. All the measured and calculated data were sent back to one institution for 3DVH analysis. Through the use of planned-dose-perturbation (PDP)TM algorithm (Sun Nuclear Corp.), the 'actual-DVHs' were generated and then compared to the 'reference-DVHs' from plans. Their differences represented errors induced from the combination of TPS dose-calculation algorithm and beam-delivery systems. RESULTS: All plans in the study have met the clinical criteria. The 3D matching rates for 3%global/3mm (DD/DTA) ranged from 95.8-99.9% for H&N and 93.5-100% for lung. The dose-difference-histogram for PTV had a mean of 0.67% [0-2%] for H&N cases and 1% [0.6-2.8%] for lung cases. The QA tool was able to spot the doses outside 3%/3mm criteria for critical structures much easier than conventional planar QA methods. In addition, the hot/cold spots at the boundaries of collimators are attributed to the uncertainty of collimator-positioning greater than 1-mm. CONCLUSIONS: The analysis of IMRT plans in this study has shown that 3DVH is a vital QA tool for assessing clinically relevant doses as well as diagnosing potential systematic errors from both TPS and delivery systems.

Colorectal cancer screening behaviour and associated factors among Chinese aged 50 and above in Hong Kong - a population-based survey.

PURPOSE: This study reports the uptake rate of colorectal cancer screening among Chinese people aged 50 or above and the identified factors associated with the likelihood of undergoing such screening. METHODS: A cross-sectional population-based telephone survey was conducted in Hong Kong during the period 2 to 28 May 2007. The survey covered demographics, perceived health status and susceptibility to cancer, utilisation of complementary medicine, family history of cancer and cancer screening behaviour. RESULTS: The survey was completed by 2004 Hong Kong Chinese residents aged 50 or older (response rate = 66.6%). The uptake rate of a fecal occult blood test and a colonoscopy was 12% and 19% respectively. Factors associated with colorectal cancer screening behaviour included: male participants, ex-smokers, with cancer or other serious disease, a family history of cancer, perceived health status fair or poor, regular visits to a doctor to look after health, and utilisation of complementary medicine. CONCLUSIONS: The uptake rate of this study population was low though an increasing trend did appear. Heath education and promotion programmes may focus on these identified factors to facilitate colorectal cancer screening in a Chinese population.

An integrated treatment delivery system for CSRS and CSRT and clinical applications.

An integrated treatment delivery system for conformal stereotactic radiosurgery (CSRS) and radiotherapy (CSRT) has been developed through a collaboration involving Siemens Medical Systems, Inc., Tyco/Radionics, Inc., and The University of Texas M. D. Anderson Cancer Center. The system consists of a 6-MV linear accelerator (LINAC) equipped with a Tyco/Radionics miniature multileaf collimator (mMLC). For the conventional SRS treatment, the circular collimator housing can be attached to the opening window of the mMLC. The treatment delivery system is integrated with a radiotherapy treatment planning system and a record-and-verify system. The purpose of this study is to report the characteristics, performance, benefits, and the clinical applications of this delivery system. The technical specifications of the LINAC and mMLC were tested, and all the specifications were met. The 80% to 20% penumbral width for each mMLC leaf is approximately 3 mm and is nearly independent of the off-axis positions of a leaf. The maximum interleaf leakage is 1.4% (1.1% on average) and the maximum intra-leaf leakage is 1.0% (0.9% on average). The leaf position precision is better than 0.5 mm for all the leaves. The integration of the SRS/SRT treatment planning system, mMLC, and LINAC has been evaluated successfully for transferring the patient treatment data file through radiotherapy treatment planning system to the patient information and treatment record-and-verify server and the mMLC controller. Subsequently, the auto-sequential treatment delivery for SRS, CSRS/CSRT, and the step-and-shoot intensity-modulated radiotherapy has also been tested successfully. The accuracy of dose delivery was evaluated for a 2-cm spherical target in a Radiological Physics Center SRS head phantom with GAFChromic films and TLD. Five non-coplanar arcs, using a 2-cm diameter circular collimator, were used for this simulation treatment. The accuracy to aim the center of the spherical target was within 0.5 mm and the deviation of dose delivery to the isocenter of the target was within 2% of the calculated dose. For the irregularly shaped tumor, a tissue-equivalent head phantom was used to evaluate the accuracy of dose delivery for using either geometric conformal treatment or IMRT. The accuracy of dose delivery to the isocenter was within 2% and 3% of the calculated dose, respectively. From October 26, 1999 to September 30, 2002, we treated over 400 SRS patients and 70 SRT patients. Four representative cases are presented to illustrate the capabilities of this dedicated unit in performing conventional SRS, CSRS, and CSRT. For all the cases, the geometric conformal-plan dose distributions showed a high degree of conformity to the target shape. The degree of conformity can be evaluated using the target-volume-ratio (TVR). Our preferred TVR values for highly conformed dose distributions range from 1.6 to 2.0. The patient setup reproducibility for the Gill-Thomas-Cosman (GTC) noninvasive head frame ranges from 0.5 to 1 mm, and the head and neck noninvasive frame is within 2 mm. The integrated treatment delivery system offers excellent conformation for complicated planning target volumes with the stereotactic setup approach, ensuring that dose delivery can be achieved within the specified accuracy. In addition, the treatment time is comparable with that of single isocenter multiple-arc treatments.

Women's knowledge about cervical cancer and cervical screening practice: a pilot study of Hong Kong Chinese women.

Cervical cancer is the seventh leading cause of death and the fourth most common type of cancer among Hong Kong Chinese women. Despite the provision of cervical screening programs, women's attendance for screening remains low at 59%. Evidence suggests that women's knowledge about cervical cancer and preventive strategies are significant to their screening practice. A preliminary pilot study consisting of a two-phase descriptive design using quantitative and qualitative methods of data collection was undertaken to investigate the level of knowledge about cervical cancer and cervical screening among a population of Hong Kong Chinese women. From a total sample of 467 women, 242 (52%) responded to a confidential questionnaire, 18 of whom, aged between 30 and 54 years, volunteered to participate in a semistructured interview. A total of 135 (57%) women had attended screening, with those who were married with children significantly more likely to attend. Although no significant difference was found between the overall level of knowledge of attenders and nonattenders, individual items such as women's knowledge of risk factors were significant. The need for further knowledge about the preventive nature of cervical screening and regular screening was demonstrated. Other factors influencing Chinese women's attendance patterns included advice from practitioners and the significance of children to women's propensity for self-care. The implications of these findings to women's attendance patterns for screening are considered, particularly the need for culturally sensitive health promotion and intervention strategies.

Evaluating psychosocial nursing interventions for cardiac clients and their caregivers: a case study of the community rehabilitation network in Hong Kong.

AIM OF THE STUDY: The purpose of this exploratory study was to describe the type and nature of psychosocial nursing interventions provided for cardiac clients in Hong Kong's Community Rehabilitation Centres (CRNs). DESIGN/METHODS: Using a two-phase case study design data were collected from nurses, cardiac clients and their caregivers. The initial phase focused on identifying the types of psychosocial interventions provided. These data were obtained by observing nursing activities and the keeping of daily journals by the nurses. The second phase acquired data from structured telephone interviews, that reviewed clients' perceptions of the psychosocial interventions provided by the nurses and face-to-face interviews with clients and their caregivers. FINDINGS: These findings revealed that the nurses' interpersonal skills of information giving, social support and counselling were highly valued by cardiac clients and their caregivers. Both clients and caregivers outlined a concern about the lack of individual care and this was reflected in the focus of the CRN on group processes. CONCLUSION: Recommendations for psychosocial cardiac care are made for public health nurses and nurses working in community settings.

A measured data set for evaluating electron-beam dose algorithms.

The purpose of this work was to develop an electron-beam dose algorithm verification data set of high precision and accuracy. Phantom geometries and treatment-beam configurations used in this study were similar to those in a subset of the verification data set produced by the Electron Collaborative Working Group (ECWG). Measurement techniques and quality-control measures were utilized in developing the data set to minimize systematic errors inherent in the ECWG data set. All measurements were made in water with p-type diode detectors and using a Wellhöfer dosimetry system. The 9 and 20 MeV, 15 x 15 cm2 beams from a single linear accelerator composed the treatment beams. Measurements were made in water at 100 and 110 cm source-to-surface distances. Irregular surface measurements included a "stepped surface" and a "nose-shaped surface." Internal heterogeneity measurements were made for bone and air cavities in differing orientations. Confidence in the accuracy of the measured data set was reinforced by a comparison with Monte Carlo (MC)-calculated dose distributions. The MC-calculated dose distributions were generated using the OMEGA/BEAM code to explicitly model the accelerator and phantom geometries of the measured data set. The precision of the measured data, estimated from multiple measurements, was better than 0.5% in regions of low-dose gradients. In general, the agreement between the measured data and the MC-calculated data was within 2%. The quality of the data set was superior to that of the ECWG data set, and should allow for a more accurate evaluation of an electron beam dose algorithm. The data set will be made publicly available from the Department of Radiation Physics at The University of Texas M. D. Anderson Cancer Center.

Fear of hypoglycaemia among insulin-treated Hong Kong Chinese patients: implications for diabetes patient education.

This study investigated fear of hypoglycaemia among insulin-treated Chinese patients in Hong Kong. The study employed a cross-sectional descriptive design. Using structured-interviews, the authors collected data from 120 insulin-treated adults attending a diabetes centre. Results showed that although hypoglycaemic attacks were generally mild, they were common amongst one-third of patients. Fear was predominantly low, however 15% of respondents reported high fear. In addition, fear correlated positively with time since insulin-treatment, frequency of hospitalization due to hypoglycaemia, and frequency of hypoglycaemia affecting working life. Results also showed that although all respondents were insulin-treated, 40% had undesirable metabolic control. No statistically significant differences were found between the respondents' rating of adequacy of their diabetes knowledge among three groups of respondents who had completed, defaulted or were attending an education programme. Implications for diabetes patient education and further study are discussed.

Stereotactic radiosurgery for brain metastases: results and prognostic factors.

This study was conducted to determine prognostic factors for tumor response and patient survival after stereotactic radiosurgery (SRS) for brain metastasis. Eighty-four patients with brain metastasis underwent SRS at a single institution. After fixation of the head with a stereotactic frame, computed tomography treatment planning was performed. The metastatic lesion was treated with multiple arcs to a median dose of 19 Gy. Forty-seven patients (56%) had a solitary brain lesion. Fifty-nine patients (70%) had evidence of extracranial disease at the time of SRS. The median survival duration from SRS was 7 months. Sixty-three percent of the patients had an objective radiographic response to SRS, which in turn was associated with superior central nervous system control. Age, collimator size, number of arcs, tumor location, and histology did not influence objective response rates. Patients who had a solitary lesion or who received treatment within 2 weeks after diagnosis were more likely to have an objective response than were those who did not (P < 0.05). Progressive brain disease accounted for 37% of the deaths. Nineteen patients (23%) had an in-field relapse. Four severe complications were attributed to SRS. This study confirms the role of SRS as an acceptable treatment option for patients with solitary or limited brain metastases. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 157-162 (2000).

The part-time student role: implications for the emotional experience of managing multiple roles amongst Hong Kong public health nurses.

The study investigated the contribution of the added part-time student role on the emotional experience of managing multiple roles of Hong Kong public health nurses (PHNs) who have children by comparing PHNs with and without the part-time student role. The research design employed the experience sampling method. Convenience sampling was used to recruit 20 subjects of which nine were undertaking part-time degree programmes. A watch was worn that gave a signal at six random times each day for 7 days to complete an experience sampling diary. PHNs on average responded to 34 signals (80%) and therefore completed 34 diaries, which collected data on work, college-work and family juggling and their effects on mood states. Results indicate that PHNs with an added part-time student role, although having fewer juggling occasions and higher emotional spouse support, had fewer family-related activities as well as a lower positive effect and a higher negative effect than PHNs without this role. These results suggest that taking up an added part-time student role creates additional role strain to nurses with children, and lend support to the argument that the stress of managing multiple roles is greatest and benefits least when work and non-work role responsibilities are both heavy.

Work and family role juggling and mood states of Hong Kong public health nurses with children.

This study aims to investigate the daily mood states of public health nurses (PHNs) in managerial roles with children in Hong Kong, as a result of multiple role juggling (i.e. simultaneously attending to demands of different roles) using the experience sampling method. Convenience sampling was used to recruit 20 subjects. A watch was worn that beeped at six random times each day for 7 days as a signal to complete an experience sampling diary. PHNs on average responded to 34 signals (80%) to complete the experience sampling diaries. Two major findings provide the focus of this paper. First, results show that PHNs had minimal inter-role juggling between work and family as compared with previous studies in the United States. Cultural factors, sequentially dealing with family and work issues, having a domestic maid or a relative to see to household chores as well as strong spouse support are suggested as the reasons. These results have implications for nursing management and nursing practice. Second, the results also reveal PHNs as having an overall flat affect. It is suggested that PHNs may be using a 'calm and detached' coping style for occupational stress. This coping style has implications on the PHNs' emotional health as well as nurse-client relationships.

The significance of sense of coherence for the perceptions of task characteristics and stress during interruptions amongst a sample of public health nurses in Hong Kong: implications for nursing management.

The study aimed to investigate the significance of sense of coherence (SOC) for the perceptions of task characteristics and for stress perceptions during interruptions of public health nurses (PHNs) with children in Hong Kong. The research design employed the experience sampling method. Convenience sampling was used to recruit 20 subjects. During stage one of the study a watch was worn that gave a signal at six random times each day for seven days to complete an experience sampling diary. PHNs on average responded to 34 signals (80%) to complete the diaries which collected data on work and family juggling, task characteristics, and their effects on mood states. At stage two respondents completed the SOC scale which measured confidence in life as comprehensible, manageable, and meaningful. Two major findings provide the focus for this paper. First, results indicate that there was positive correlation between SOC and perceived task characteristics. Second, results reveal that when interruptions occurred, PHNs with high SOC had higher positive affect and lower negative affect than PHNs with low SOC. These results suggest that SOC as a salutogenic model helps PHNs to cope with the family and work juggling as well as the occupational stress. Implications for nursing management on strengthening SOC of PHNs are discussed.

A pencil-beam photon dose algorithm for stereotactic radiosurgery using a miniature multileaf collimator.

A computer-controlled miniature multileaf collimator (MMLC) with 4 mm leaf width and a maximum field size of 6 cm X 6 cm has been designed as a tertiary beam-shaping device for linac-based stereotactic radiosurgery. The purpose of this study is to develop an accurate and efficient dose calculation model for use with the MMLC. A pencil-beam based algorithm using a sum of three Gaussian kernels was developed to model the off-axis ratio of MMLC fields. Because the kernel integration over a rectangular field can be solved in closed form, dose to any point from an arbitrary MMLC field can be calculated efficiently by summing dose contribution from a set of rectangular apertures and transmission blocks that model individual leaf openings or leaf transmissions. The model uses an effective rectangular field and equivalent square method for determination of depth dose and dose output. Results showed that the calculated percentage depth dose was within 1% and output factor was within 1.5% of measured data. The parameters of the pencil beam kernels were extracted by fitting measured off-axis profiles for a few field sizes at a few depths. The accuracy of the calculated off-axis ratio was tested by comparison with measured data for a number of MMLC fields. The algorithm was shown to be accurate to within 1.5% or 1 mm for off-axis ratios. The algorithm computes at a speed of 34,600 data points per second on a DEC Alpha server model 2000/433 (Digital Equipment Corp., Maynard, MA), which is about 15 times faster than a Clarkson-type summation method.

Comparison of miniature multileaf collimation (MMLC) with circular collimation for stereotactic treatment.

PURPOSE: A prototype Miniature Multi-Leaf Collimator (MMLC) designed specifically for radiosurgery and small field radiotherapy has been fabricated and evaluated at the University of Texas M. D. Anderson Cancer Center (UTMDACC). This work demonstrates the advantages of a computer-controlled MMLC vs. conventional circular collimation for the treatment of an irregularly shaped target volume in the brain. METHODS AND MATERIALS: Two patient treatments were selected for this comparison from 38 intracranial tumors treated with radiosurgery at UTMDACC from 8/6/91 to 5/10/94. Target contours and critical structures defined for one of the patients was used to create a simulated target volume and critical structures in a spherical head phantom. Computer simulations were performed using traditional single isocenter treatment with a circular collimator for a set of six arcs. The same arc paths were used to compute the dose distribution for the MMLC and conformed beam geometries were defined using a three-dimensional (3D) treatment planning system with beam's eye view capabilities. Then, the calculated dose distribution for a single isocenter, conformal treatment was delivered to the spherical head phantom under static conditions by shaping the MMLC to conform the target volume shape projected as a function of couch rotation and gantry angle. Planar dose distributions through the target volume were measured using therapy verification film located in the phantom. The measurements were used to verify that the 3D treatment planning system was capable of simulating the MMLC technique. For the second patient with a peanut-shaped tumor, the 3D treatment planning calculations were used to compare dose distributions for the MMLC and for traditional single and multiple isocenter treatments using circular collimators. The resulting integral dose-volume histograms (DVHs) for the target volume, normal brain, and critical structures for the three treatment techniques were compared. RESULTS: (a) Analysis of the film dosimetry data exemplified the degree of conformation of the high-dose region to the target shape that is possible with a computer-controlled MMLC. (b) Comparison of measured and calculated dose distributions indicates that the 3D treatment planning system can simulate the MMLC treatment. (c) Comparison of DVHs from the single isocenter MMLC and circular collimator treatments shows similar coverage of the target volume with increased dose to the brain for circular collimation (4). Comparison of DVHs from the single isocenter MMLC with the multiple isocenter circular collimator treatment approach shows a more inhomogeneous dose distribution through the target volume and increased dose to the brain for the latter. CONCLUSION: Dosimetry data for single isocenter treatments using computer-controlled field shaping with a MMLC demonstrate the ability to conform the dose distribution to an irregularly shaped target volume. DVHs validated that the single isocenter MMLC treatment is preferable to both single and multiple isocenter, circular collimator treatment because it provides a more uniform dose distribution to an irregularly shaped target volume and reduces the dose to surrounding brain tissue for the example cases.

Verification of radiosurgery target point alignment with an electronic portal imaging device (EPID).

A procedure has been developed using an electronic portal imaging device (EPID) to verify that the center of a patient's lesion is aligned with the center of a treatment cone prior to treatment in a linac-based stereotactic radiosurgery procedure. The coordinates of the lesion center are set on the Brown-Roberts-Wells phantom base using a target simulator. A 3 mm tungsten ball, mounted on the target simulator, is used as the reference point for the planned isocenter. The target simulator is then attached to an adapter mounted on the linac couch, and an EPID image of the simulated target is acquired. The center of the circular-shaped radiation field is calculated from the centroid of the segmented EPID image, and the center of the tungsten ball is identified by an automated computer search algorithm. A summation filter is used to find the position of the lowest radiation intensity coincident with the center of the ball. The alignment error is defined as the difference between the center of the radiation field and the center of the ball. The accuracy of this method was tested and found to be within 0.2 mm. The advantage of the EPID-based procedure is that it can give quantitative offset values quickly for immediate readjustment. We have found that the method is also a convenient tool for testing room laser alignment and the accuracy of the treatment cones.

An evaluation of the effectiveness of public health nursing: a case study of the maternal and child health centres in Hong Kong.

The aim of this study was to evaluate the effectiveness of public health nursing in Hong Kong using the maternal and child health centres as a case study. The case study design, employing both qualitative and quantitative methods of data collection, focused on clients' and nurses' perceptions of the effectiveness of care. The data analysis identified three important factors influencing the effectiveness of care: the need for a health needs data base, the organisation of care and service provision. From these findings the authors suggest that a health needs data base plays an essential role in measuring the effectiveness of care in public health nursing.