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1.
Health Aff Sch ; 1(3): qxad037, 2023 Sep.
Article in English | MEDLINE | ID: mdl-38756673

ABSTRACT

As cybercrime increasingly targets the health care sector, hospitals face the growing threat of ransomware attacks. Ransomware is a type of malicious software that prevents users from accessing their electronic systems-demanding payment to restore access. In response, momentum is gathering to enact policy that will help hospitals strengthen their cybersecurity defenses. However, to design effective policy, it is crucial to understand the characteristics of hospitals associated with the risk of ransomware attack. In this paper, we compare the characteristics of ransomware-attacked and non-attacked short-term acute care hospitals in the United States. Using data from the American Hospital Association's Annual Survey and the Healthcare Cost Report Information System, we found that ransomware-attacked hospitals were larger, had higher net operating revenue, were more likely to be financially profitable, and more likely to provide trauma, emergency, and obstetric care than non-attacked hospitals. Measures of information technology sophistication did not vary between ransomware-attacked and non-attacked hospitals. These results can be used to tailor policy interventions in order to most effectively respond to and prevent cybercrime in health care.

2.
JAMA Health Forum ; 3(12): e224873, 2022 12 02.
Article in English | MEDLINE | ID: mdl-36580326

ABSTRACT

Importance: Anecdotal evidence suggests that health care delivery organizations face a growing threat from ransomware attacks that are designed to disrupt care delivery and may consequently threaten patient outcomes. Objective: To quantify the frequency and characteristics of ransomware attacks on health care delivery organizations. Design, Setting, and Participants: This cohort study used data from the Tracking Healthcare Ransomware Events and Traits database to examine the number and characteristics of ransomware attacks on health care delivery organizations from 2016 to 2021. Logistic and negative binomial regression quantified changes over time in the characteristics of ransomware attacks that affected health care delivery organizations. Main Outcomes and Measures: Date of ransomware attack, public reporting of ransomware attacks, personal health information (PHI) exposure, status of encrypted/stolen data following the attack, type of health care delivery organization affected, and operational disruption during the ransomware attack. Results: From January 2016 to December 2021, 374 ransomware attacks on US health care delivery organizations exposed the PHI of nearly 42 million patients. From 2016 to 2021, the annual number of ransomware attacks more than doubled from 43 to 91. Almost half (166 [44.4%]) of ransomware attacks disrupted the delivery of health care, with common disruptions including electronic system downtime (156 [41.7%]), cancellations of scheduled care (38 [10.2%]), and ambulance diversion (16 [4.3%]). From 2016 to 2021, ransomware attacks on health care delivery organizations increasingly affected large organizations with multiple facilities (annual marginal effect [ME], 0.08; 95% CI, 0.05-0.10; P < .001), exposed the PHI of more patients (ME, 66 385.8; 95% CI, 3400.5-129 371.2; P = .04), were less likely to be restored from data backups (ME, -0.04; 95% CI, -0.06 to -0.01; P = .002), were more likely to exceed mandatory reporting timelines (ME, 0.06; 95% CI, 0.03-0.08; P < .001), and increasingly were associated with delays or cancellations of scheduled care (ME, 0.02; 95% CI, 0-0.05; P = .02). Conclusions and Relevance: This cohort study of ransomware attacks documented growth in their frequency and sophistication. Ransomware attacks disrupt care delivery and jeopardize information integrity. Current monitoring/reporting efforts provide limited information and could be expanded to potentially yield a more complete view of how this growing form of cybercrime affects the delivery of health care.


Subject(s)
Delivery of Health Care , Hospitals , Humans , Cohort Studies , Health Facilities , Organizations
3.
Health Care Manage Rev ; 47(1): 21-27, 2022.
Article in English | MEDLINE | ID: mdl-33181552

ABSTRACT

BACKGROUND: Access to care is often a challenge for Medicaid beneficiaries due to low practice participation. As demand increases, practices will likely look for ways to see Medicaid patients while keeping costs low. Employing nurse practitioners (NPs) and physician assistants (PAs) is one low-cost and effective means to achieve this. However, there are no longitudinal studies examining the relationship between practice Medicaid acceptance and NP/PA employment. PURPOSE: The purpose of this study was to examine the association of practice Medicaid acceptance with NP/PA employment over time. METHODS: Using SK&A data (2009-2015), we constructed a panel of 102,453 unique physician practices to assess for changes in Medicaid acceptance after newly employing NPs and PAs. We employed practice-level fixed effects linear regressions. RESULTS: Our results showed that, among practices employing both NPs and PAs, there was a roughly 2% increase in the likelihood of Medicaid participation over time. When stratifying our sample by practice size and specialty, the positive correlation localized to small primary care and medical practices. When both NPs and PAs were present, small primary care practices had a 3.3% increase and small medical practices had a 6.9% increase in the likelihood of accepting Medicaid. CONCLUSION: NP and PA employment was positively associated with increases in Medicaid participation. PRACTICE IMPLICATIONS: As more individuals gain coverage under Medicaid, organizations will need to decide how to adapt to greater patient demand. Our results suggest that hiring NPs and PAs may be a potential lower cost strategy to accommodate new Medicaid patients.


Subject(s)
Nurse Practitioners , Physician Assistants , Physicians , Humans , Medicaid , Primary Health Care , United States
5.
Health Aff (Millwood) ; 39(10): 1822-1831, 2020 Oct.
Article in English | MEDLINE | ID: mdl-32757955

ABSTRACT

The recent coronavirus disease 2019 (COVID-19) global pandemic has resulted in unprecedented job losses in the United States, disrupting health insurance coverage for millions of people. Several models have predicted large increases in Medicaid enrollment among those who have lost jobs, yet the number of Americans who have gained coverage since the pandemic began is unknown. We compiled Medicaid enrollment reports covering the period from March 1 through June 1, 2020, for twenty-six states. We found that in these twenty-six states, Medicaid covered more than 1.7 million additional Americans in roughly a three-month period. Relative changes in Medicaid enrollment differed significantly across states, although enrollment growth was not systemically related to job losses. Our results point to the important effects of state policy differences in the response to COVID-19.


Subject(s)
Coronavirus Infections/epidemiology , Eligibility Determination/statistics & numerical data , Employment/statistics & numerical data , Insurance Coverage/statistics & numerical data , Medicaid/statistics & numerical data , Pandemics/statistics & numerical data , Pneumonia, Viral/epidemiology , COVID-19 , Cohort Studies , Coronavirus Infections/prevention & control , Databases, Factual , Eligibility Determination/methods , Employment/economics , Female , Humans , Incidence , Insurance, Health/organization & administration , Male , Medically Uninsured/statistics & numerical data , Needs Assessment , Pandemics/prevention & control , Pneumonia, Viral/prevention & control , Retrospective Studies , Risk Assessment , Time Factors , United States
6.
Health Serv Res ; 55(2): 157-169, 2020 04.
Article in English | MEDLINE | ID: mdl-32187392

ABSTRACT

OBJECTIVE: The 340B program allows safety-net hospitals to acquire discounted outpatient drugs and charge payers full price. We examined whether 340B participation increases safety-net engagement. DATA SOURCES: 340B participation data, Medicare hospital cost reports, American Hospital Association Survey, and Schedule 990 nonprofit hospital tax returns. STUDY DESIGN: Quasi-experimental difference-in-differences design comparing 340B hospitals (the "treatment" group) before and after participating to changes over time to three alternative "control" groups: all other nonprofit and public hospitals, hospitals that are not participating during our study, and hospitals that were not-yet-participating but started after 2015. Outcome measures include a range of safety-net care measures that are alternatives to the standard uncompensated care: charity care, community benefit spending, charity care policies, and low-profit service-line provision. DATA EXTRACTION: We extracted data on all nonprofit and public hospitals from 2011 to 2015. We linked 340B participation data to Medicare hospital cost reports and American Hospital Association data using Medicare hospital identifiers. 990 Data was linked on name and address. PRINCIPAL FINDINGS: New 340B participation was not associated with a change in uncompensated care, but was associated with a 28.9 percent increase in charity care spending (SE = 8.8), or about $880,000 per hospital. However, total community benefit spending (including charity care) did not change. 340B was associated with an increase in the probability of offering discounted care (4.3 percentage points, SE = 1.6) from 84 to 88 percent and an increase in the income eligibility limit for discounted care (18.9 percentage points, SE = 5.6) from 294 to 313 percent. Participation was not associated with the probability of offering low-profit medical care services. CONCLUSIONS: Alternative measures show that newly participating hospitals may increase charity care, potentially through offering more patients discounted care. However, increases appear to be fully offset by reductions in other community benefit programs.


Subject(s)
Health Policy , Hospital Costs/legislation & jurisprudence , Hospital Costs/statistics & numerical data , Medicare/legislation & jurisprudence , Medicare/statistics & numerical data , Safety-net Providers/legislation & jurisprudence , Safety-net Providers/statistics & numerical data , Aged , Aged, 80 and over , Female , Humans , Male , United States
7.
J Am Coll Surg ; 230(1): 130-135.e4, 2020 01.
Article in English | MEDLINE | ID: mdl-31672671

ABSTRACT

BACKGROUND: Vertical integration is increasingly common among surgical specialties in the US; however, the effect of vertical integration on access to care for low-income populations remains poorly understood. We explored the characteristics of surgical practices associated with vertical integration and the effect of integration on surgical access for Medicaid populations. STUDY DESIGN: Using a survey of US office-based physician practices, we examined characteristics of 15 surgical subspecialties from 2007 to 2017, including provider sex and specialty, practice payer mix, surgical volume, and county socioeconomic status. Using multivariable logistic regression and time-series analysis, we evaluated practice and provider characteristics associated with vertical integration-our primary outcome-and practice Medicaid acceptance rates-our secondary outcome. RESULTS: Our analysis included 84,795 unique surgical practices (303,903 practice-years). The rate of vertical integration during the 10-year period was 18.0%, with 72.1% of surgical practices never integrating. Practices that integrated were more likely to accept Medicaid patients than practices that did not (81.0% vs 60.8%, p < 0.001). Accepting Medicaid increased the likelihood of vertical integration relative to practices that did not (odds ratio [OR] 4.20, 95% CI 3.93 to 4.49). Practices that integrated were more likely to accept Medicaid in the future (OR 2.61, 95% CI 2.40 to 2.83), even after adjusting for previous Medicaid acceptance and hospital and time fixed effects. CONCLUSIONS: Surgical practices caring for the underinsured are more likely to join larger health care systems, driven by market characteristics. Vertical integration is associated with future increased rates of Medicaid acceptance among practices, allowing for increased access to surgical care for vulnerable, low-income patients. The potential benefit of increased surgical access for low-income beneficiaries from vertical integration must be balanced with the potential for increased prices.


Subject(s)
Health Services Accessibility/statistics & numerical data , Medicaid , Specialties, Surgical/organization & administration , Surgical Procedures, Operative/statistics & numerical data , Adolescent , Adult , Aged , Female , Health Care Surveys , Humans , Male , Middle Aged , United States , Young Adult
8.
JAMA Netw Open ; 2(10): e1914141, 2019 10 02.
Article in English | MEDLINE | ID: mdl-31664442

ABSTRACT

Importance: The federal 340B program lowers the acquisition cost of prescription drugs and places no limits on what hospitals charge payers. Congress established the program to allow 340B profits (the difference between payments and acquisition costs) to subsidize other safety-net services. Little is known about the magnitude of revenues and profits from the 340B program among participating hospitals. Objective: To report revenues and estimated profits from the 340B program that hospitals collect from Medicare and Medicare beneficiaries for outpatient clinic administration of prescription drugs covered under Medicare Part B. Design, Setting, and Participants: This cross-sectional descriptive study used 100% Medicare outpatient Part B claims from January 1, 2013, to December 31, 2016, from fee-for-service Medicare beneficiaries administered separately payable drugs at general acute care nonprofit or public hospitals without special payment designations. Claims data (N = 11 298 860) were aggregated to the hospital-year level (N = 6000) and linked to hospital finances and 340B participation from Medicare cost reports and the 340B covered entity list. Main Outcomes and Measures: Outcomes studied were revenue and estimated profits, assuming a 50% discount from 340B-discounted drug administrations to Medicare patients, as well as Medicare 340B profits relative to hospital net operating revenue, uncompensated care, and disproportionate share hospital payments. Results: During the study period, hospitals received approximately $2.1 billion in 340B revenue from Medicare in 2013, increasing to $3.7 billion in 2016. Estimated 340B profits from Medicare in 2016 totaled $1.9 billion, and per-hospital estimated 340B profits were $2.5 million but exhibited variability (median, $0.8 million; interquartile range, $0.1 million-$2.8 million). In 2016, median estimated 340B profits from Medicare were 0.3% (interquartile range, 0.1%-0.7%; mean, 0.4%) of hospital operating budgets and 9.4% (interquartile range, 1.8%-26.5%; mean, 16.6%) of hospital uncompensated care costs. Conclusions and Relevance: Estimated profits that hospitals derived from administering 340B-discounted drugs to Medicare patients are small compared with operating budgets yet substantial compared with uncompensated care costs for many hospitals. Revenue and profit estimates from 340B-discounted drugs represent a lower bound because data on revenue from the sale of outpatient retail dispensed drugs by hospital contract pharmacies and commercial insurer claims are not available.


Subject(s)
Drug Costs/legislation & jurisprudence , Economics, Hospital , Medicare/economics , Prescription Drugs/economics , Cross-Sectional Studies , Government Programs/economics , Government Programs/legislation & jurisprudence , Government Regulation , Humans , Models, Economic , United States
9.
Health Aff (Millwood) ; 37(7): 1123-1127, 2018 07.
Article in English | MEDLINE | ID: mdl-29985694

ABSTRACT

Consolidation of physician practices by hospitals, or vertical integration, increased across all practice types in 2007-17. Rates of growth were highest among medical and surgical specialty practices and lowest among primary care practices. There was substantial variation within the specialties, ranging from 4 percentage points in dermatology to 34 percentage points in cardiology and oncology.


Subject(s)
Cardiology/statistics & numerical data , Health Facility Merger/trends , Medical Oncology/statistics & numerical data , Physicians/statistics & numerical data , Cardiology/organization & administration , Health Facility Merger/organization & administration , Hospitals , Humans , Medical Oncology/organization & administration , Physicians/trends , United States
10.
Cancer ; 124(12): 2645-2652, 2018 06 15.
Article in English | MEDLINE | ID: mdl-29663343

ABSTRACT

BACKGROUND: The Patient Protection and Affordable Care Act extends Medicaid coverage to millions of low-income adults, including many survivors of cancer who were unable to purchase affordable health insurance coverage in the individual health insurance market. METHODS: Using data from the 2011 to 2015 Behavioral Risk Factor Surveillance System, the authors compared changes in coverage and health care access measures for low-income cancer survivors in states that did and did not expand Medicaid. RESULTS: The study population of 17,381 individuals included adults aged 18 to 64 years, and was predominantly female, white, and unmarried. The authors found a relative reduction in the uninsured rate of 11.7 percentage points and a relative increase in the probability of having a personal physician of 5.8 percentage points. Stratifying by whether states expanded Medicaid by 2015, the authors found that relative gains in coverage and access were larger among those individuals residing in states with expanded Medicaid compared with those residing in nonexpansion states. CONCLUSIONS: The results of the current study suggest that the Patient Protection and Affordable Care Act Medicaid expansion has improved coverage and access for cancer survivors. Cancer 2018;124:2645-52. © 2018 American Cancer Society.


Subject(s)
Cancer Survivors/statistics & numerical data , Insurance Coverage/trends , Insurance, Health/trends , Medicaid/economics , Neoplasms/economics , Adolescent , Adult , Behavioral Risk Factor Surveillance System , Female , Health Services Accessibility/economics , Health Services Accessibility/statistics & numerical data , Health Services Accessibility/trends , Humans , Insurance Coverage/economics , Insurance Coverage/statistics & numerical data , Insurance, Health/economics , Insurance, Health/standards , Male , Medicaid/statistics & numerical data , Medicaid/trends , Middle Aged , Neoplasms/mortality , Neoplasms/therapy , Patient Protection and Affordable Care Act/economics , Poverty/economics , Poverty/statistics & numerical data , Surveys and Questionnaires/statistics & numerical data , United States , Young Adult
11.
Health Aff (Millwood) ; 37(1): 22-29, 2018 01.
Article in English | MEDLINE | ID: mdl-29309229

ABSTRACT

Increasingly, public and private resources are being dedicated to community-based health improvement programs. But evaluations of these programs typically rely on data about process and a pre-post study design without a comparison community. To better determine the association between the implementation of community-based health improvement programs and county-level health outcomes, we used publicly available data for the period 2002-06 to create a propensity-weighted set of controls for conducting multiple regression analyses. We found that the implementation of community-based health improvement programs was associated with a decrease of less than 0.15 percent in the rate of obesity, an even smaller decrease in the proportion of people reporting being in poor or fair health, and a smaller increase in the rate of smoking. None of these changes was significant. Additionally, program counties tended to have younger residents and higher rates of poverty and unemployment than nonprogram counties. These differences could be driving forces behind program implementation. To better evaluate health improvement programs, funders should provide guidance and expertise in measurement, data collection, and analytic strategies at the beginning of program implementation.


Subject(s)
Community Health Services , Delivery of Health Care/methods , Health Promotion , Quality Improvement/statistics & numerical data , Adolescent , Adult , Aged , Child , Child, Preschool , Humans , Infant , Infant, Newborn , Middle Aged , Young Adult
13.
Health Aff (Millwood) ; 36(2): 297-305, 2017 02 01.
Article in English | MEDLINE | ID: mdl-28167719

ABSTRACT

The introduction of Medicaid expansions and state Marketplaces under the Affordable Care Act (ACA) have reduced the uninsurance rate to historic lows, changing the choices Americans make about coverage. In this article we shed light on these changing dynamics. We drew upon multistate transition models fit to nationally representative longitudinal data to estimate coverage transition probabilities between major insurance types in the years leading up to and including 2014. We found that the ACA's unprecedented coverage changes increased transitions to Medicaid and nongroup coverage among the uninsured, while strengthening the existing employer-sponsored insurance system and improving retention of public coverage. However, our results suggest possible weakness of state Marketplaces, since people gaining nongroup coverage were disproportionately older than other potential enrollees. We identified key opportunities for policy makers and insurers to improve underlying Marketplace risk pools by focusing on people transitioning from employer-sponsored coverage; these people are disproportionately younger and saw almost no change in their likelihood of becoming uninsured in 2014 compared to earlier years.


Subject(s)
Forecasting , Insurance Coverage/statistics & numerical data , Patient Protection and Affordable Care Act/statistics & numerical data , Adult , Female , Health Care Reform , Humans , Insurance Coverage/trends , Insurance, Health/statistics & numerical data , Longitudinal Studies , Male , Medicaid , Middle Aged , Risk Factors , United States
14.
Med Care ; 54(7): 714-8, 2016 07.
Article in English | MEDLINE | ID: mdl-27111749

ABSTRACT

BACKGROUND: Strategic alignment and integration is currently in vogue throughout the health care industry, but its diffusion and pace have not been documented in recent years. The full range of downstream implications from greater alignment between hospitals and physicians has also not been completely explored. OBJECTIVES: We track the organizational landscape among all office-based US physician practices from 2009 to 2015 and document the degree of vertical integration over time. Then, we examine the implications of vertical integration on practices' acceptance of publicly insured patients. RESEARCH DESIGN: We use descriptive trends and linear regression models with practice level fixed effects to capture the relationships between within-office changes in integration behavior and changes in public payer acceptance. RESULTS: Independent (nonintegrated) physician practices are still the most common organizational type, but their share is declining as the share of practices integrated with a health system increases 3-fold between 2009 and 2015. Although >80% of practices that are part of a health system accept Medicaid, <60% of independent practices will see these patients. Vertically integrating with a health system makes it more likely a practice will start seeing Medicaid patients. CONCLUSIONS: Integration-and possibly consolidation-appears to be occurring and may be increasing over time in the United States. However, it also seems to increase the number of physician practices participating in the Medicaid program. This beneficial side effect has not been previously documented and should be kept in mind as policymakers weigh the pros and cons of a more integrated health care system.


Subject(s)
Delivery of Health Care, Integrated/trends , General Practice , Group Practice , Medicaid , Databases, Factual , Humans , Linear Models , Physicians, Primary Care , Surveys and Questionnaires , United States
15.
Womens Health Issues ; 26(2): 176-82, 2016.
Article in English | MEDLINE | ID: mdl-26781749

ABSTRACT

BACKGROUND: Since the 1990s, policymakers have successfully increased cervical cancer screening through federal and state public policies. However, the most dramatic gains in Pap smear use occurred in the 1960's and 70's, during the establishment of federal support for family planning clinics through the War on Poverty and Title X. This study estimated the effect of this support on cervical cancer screening, and quantified its role in dramatic increases in Pap smear use. METHODS: Using a natural experiment in the timing and receipt of federal family planning grants, the screening behavior of women who did and did not have access to a federally funded family planning clinic were analyzed. Cross-sectional probability models of annual and lifetime Pap smear use using the 1970 National Fertility Survey were estimated and linked to administrative data on grant timing and receipt between 1964 and 1973. FINDINGS: Federal support for family planning clinics was associated with a 7-percentage point increase in annual use (p < .01), and a 5-percentage point decrease in never use of the Pap smear (p < .001). Scaled by the fraction of women who used funded clinics, federal support for family planning was associated with a roughly 70% increase in Pap smear use. Estimates suggest that the establishment of federal support could explain as much as 15% of the national increase in Pap smear use between 1966 and 1973. CONCLUSIONS: Federal support for family planning played an important--and previously unacknowledged--role in promoting cervical cancer screening and investments in future health.


Subject(s)
Family Planning Services/statistics & numerical data , Financing, Government , Health Expenditures , Mass Screening/statistics & numerical data , Uterine Cervical Neoplasms/diagnosis , Vaginal Smears/statistics & numerical data , Adult , Cross-Sectional Studies , Early Detection of Cancer/statistics & numerical data , Family Planning Services/legislation & jurisprudence , Family Planning Services/trends , Female , Health Care Rationing , Health Knowledge, Attitudes, Practice , Humans , Mass Screening/trends , Organizational Objectives , Papanicolaou Test/statistics & numerical data , Papanicolaou Test/trends , Public Policy , Surveys and Questionnaires , United States , Uterine Cervical Neoplasms/prevention & control , Vaginal Smears/trends
17.
Rev Med Interne ; 35(9): 595-600, 2014 Sep.
Article in French | MEDLINE | ID: mdl-24797142

ABSTRACT

SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) syndrome is a rare entity characterized by the association of heterogeneous osteoarticular and cutaneous manifestations that have for common denominator an aseptic inflammatory process. The etiopathogeny of this disease is still a matter of debate. Although it has been related to the spondylarthritis family, an infectious origin is suggested. Diagnosis is based on the presence of at least one of the three diagnostic criteria proposed by Kahn. The treatment includes NSAIDs, antibiotics, corticosteroids, methotrexate and more recently the bisphosphonates and the TNFα inhibitors.


Subject(s)
Acquired Hyperostosis Syndrome , Acquired Hyperostosis Syndrome/diagnosis , Acquired Hyperostosis Syndrome/epidemiology , Acquired Hyperostosis Syndrome/etiology , Acquired Hyperostosis Syndrome/therapy , Disease Progression , Humans , Prognosis
18.
Technol Cancer Res Treat ; 9(5): 433-52, 2010 Oct.
Article in English | MEDLINE | ID: mdl-20815415

ABSTRACT

This review provides a complete technical description of the CyberKnife VSI System, the latest addition to the CyberKnife product family, which was released in September 2009. This review updates the previous technical reviews of the original system version published in the late 1990s. Technical developments over the last decade have impacted virtually every aspect of the CyberKnife System. These developments have increased the geometric accuracy of the system and have enhanced the dosimetric accuracy and quality of treatment, with advanced inverse treatment planning algorithms, rapid Monte Carlo dose calculation, and post-processing tools that allow trade-offs between treatment efficiency and dosimetric quality to be explored. This review provides a system overview with detailed descriptions of key subsystems. A detailed review of studies of geometric accuracy is also included, reporting a wide range of experiments involving phantom tests and patient data. Finally, the relationship between technical developments and the greatly increased range of clinical applications they have allowed is reviewed briefly.


Subject(s)
Radiosurgery , Robotics , Algorithms , Humans , Radiation Dosage , Radiosurgery/instrumentation , Radiosurgery/methods , Software
19.
Phys Med Biol ; 54(18): 5359-80, 2009 Sep 21.
Article in English | MEDLINE | ID: mdl-19687567

ABSTRACT

Robotic radiosurgery using more than one circular collimator can improve treatment plan quality and reduce total monitor units (MU). The rationale for an iris collimator that allows the field size to be varied during treatment delivery is to enable the benefits of multiple-field-size treatments to be realized with no increase in treatment time due to collimator exchange or multiple traversals of the robotic manipulator by allowing each beam to be delivered with any desired field size during a single traversal. This paper describes the Iris variable aperture collimator (Accuray Incorporated, Sunnyvale, CA, USA), which incorporates 12 tungsten-copper alloy segments in two banks of six. The banks are rotated by 30 degrees with respect to each other, which limits the radiation leakage between the collimator segments and produces a 12-sided polygonal treatment beam. The beam is approximately circular, with a root-mean-square (rms) deviation in the 50% dose radius of <0.8% (corresponding to <0.25 mm at the 60 mm field size) and an rms variation in the 20-80% penumbra width of about 0.1 mm at the 5 mm field size increasing to about 0.5 mm at 60 mm. The maximum measured collimator leakage dose rate was 0.07%. A commissioning method is described by which the average dose profile can be obtained from four profile measurements at each depth based on the periodicity of the isodose line variations with azimuthal angle. The penumbra of averaged profiles increased with field size and was typically 0.2-0.6 mm larger than that of an equivalent fixed circular collimator. The aperture reproducibility is < or =0.1 mm at the lower bank, diverging to < or =0.2 mm at a nominal treatment distance of 800 mm from the beam focus. Output factors (OFs) and tissue-phantom-ratio data are identical to those used for fixed collimators, except the OFs for the two smallest field sizes (5 and 7.5 mm) are considerably lower for the Iris Collimator. If average collimator profiles are used, the assumption of circular symmetry results in dose calculation errors that are <1 mm or <1% for single beams across the full range of field sizes; errors for multiple non-coplanar beam treatment plans are expected to be smaller. Treatment plans were generated for 19 cases using the Iris Collimator (12 field sizes) and also using one and three fixed collimators. The results of the treatment planning study demonstrate that the use of multiple field sizes achieves multiple plan quality improvements, including reduction of total MU, increase of target volume coverage and improvements in conformality and homogeneity compared with using a single field size for a large proportion of the cases studied. The Iris Collimator offers the potential to greatly increase the clinical application of multiple field sizes for robotic radiosurgery.


Subject(s)
Radiosurgery/methods , Robotics/instrumentation , Surgery, Computer-Assisted/methods , Computer-Aided Design , Equipment Design , Equipment Failure Analysis , Reproducibility of Results , Sensitivity and Specificity
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