EPID-based in vivo dosimetry using Dosimetry Check™: Overview and clinical experience in a 5-yr study including breast, lung, prostate, and head and neck cancer patients.

BACKGROUND: Independent verification of the dose delivered by complex radiotherapy can be performed by electronic portal imaging device (EPID) dosimetry. This paper presents 5-yr EPID in vivo dosimetry (IVD) data obtained using the Dosimetry Check (DC) software on a large cohort including breast, lung, prostate, and head and neck (H&N) cancer patients. MATERIAL AND METHODS: The difference between in vivo dose measurements obtained by DC and point doses calculated by the Eclipse treatment planning system was obtained on 3795 radiotherapy patients treated with volumetric modulated arc therapy (VMAT) (n = 842) and three-dimensional conformal radiotherapy (3DCRT) (n = 2953) at 6, 10, and 15 MV. In cases where the dose difference exceeded ±10% further inspection and additional phantom measurements were performed. RESULTS: The mean and standard deviation ( µ ± σ ) of the percentage difference in dose obtained by DC and calculated by Eclipse in VMAT was: 0.19 ± 3.89 % in brain, 1.54 ± 4.87 % in H&N, and 1.23 ± 4.61 % in prostate cancer. In 3DCRT, this was 1.79 ± 3.51 % in brain, - 2.95 ± 5.67 % in breast, - 1.43 ± 4.38 % in bladder, 1.66 ± 4.77 % in H&N, 2.60 ± 5.35% in lung and - 3.62 ± 4.00 % in prostate cancer. A total of 153 plans exceeded the ±10% alert criteria, which included: 88 breast plans accounting for 7.9% of all breast treatments; 28 H&N plans accounting for 4.4% of all H&N treatments; and 12 prostate plans accounting for 3.5% of all prostate treatments. All deviations were found to be as a result of patient-related anatomical deviations and not from procedural errors. CONCLUSIONS: This preliminary data shows that EPID-based IVD with DC may not only be useful in detecting errors but has the potential to be used to establish site-specific dose action levels. The approach is straightforward and has been implemented as a radiographer-led service with no disruption to the patient and no impact on treatment time.

Dose evaluation of Grid Therapy using a 6 MV flattening filter-free (FFF) photon beam: A Monte Carlo study.

PURPOSE: Spatially fractionated radiotherapy is a strategy to overcome the main limitation of radiotherapy, i.e., the restrained normal tissue tolerances. A well-known example is Grid Therapy, which is currently performed at some hospitals using megavoltage photon beams delivered by Linacs. Grid Therapy has been successfully used in the management of bulky abdominal tumors with low toxicity. The aim of this work was to evaluate whether an improvement in therapeutic index in Grid Therapy can be obtained by implementing it in a flattening filter-free (FFF) Linac. The rationale behind is that the removal of the flattening filter shifts the beam energy spectrum towards lower energies and increase the photon fluence. Lower energies result in a reduction of lateral scattering and thus, to higher peak-to-valley dose ratios (PVDR) in normal tissues. In addition, the gain in fluence might allow using smaller beams leading a more efficient exploitation of dose-volume effects, and consequently, a better normal tissue sparing. METHODS: Monte Carlo simulations were used to evaluate realistic dose distributions considering a 6 MV FFF photon beam from a standard medical Linac and a cerrobend mechanical collimator in different configurations: grid sizes of 0.3 × 0.3 cm2 , 0.5 × 0.5 cm2 , and 1 × 1 cm2 and a corresponding center-to-center (ctc) distance of 0.6, 1, and 2 cm, respectively (total field size of 10 × 10 cm2 ). As figure of merit, peak doses in depth, PVDR, output factors (OF), and penumbra values were assessed. RESULTS: Dose at the entrance is slightly higher than in conventional Grid Therapy. However, it is compensated by the large PVDR obtained at the entrance, reaching a maximum of 35 for a grid size of 1 × 1 cm2 . Indeed, this grid size leads to very high PVDR values at all depths (≥ 10), which are much higher than in standard Grid Therapy. This may be beneficial for normal tissues but detrimental for tumor control, where a lower PVDR might be requested. In that case, higher valley doses in the tumor could be achieved by using an interlaced approach and/or adapting the ctc distance. The smallest grid size (0.3 × 0.3 cm2 ) leads to low PVDR at all depths, comparable to standard Grid Therapy. However, the use of very thin beams might increase the normal tissue tolerances with respect to the grid size commonly used (1 × 1 cm2 ). The gain in fluence provided by FFF implies that the important OF reduction (0.6) will not increase treatment time. Finally, the intermediate configuration (0.5 × 0.5 cm2 ) provides high PVDR in the first 5 cm, and comparable PVDR to previous Grid Therapy works at depth. Therefore, this configuration might allow increasing the normal tissue tolerances with respect to Grid Therapy thanks to the higher PVDR and thinner beams, while a similar tumor control could be expected. CONCLUSIONS: The implementation of Grid Therapy in an FFF photon beam from medical Linac might lead to an improvement of the therapeutic index. Among the cases evaluated, a grid size of 0.5 × 0.5 cm2 (1-cm-ctc) is the most advantageous configuration from the physics point of view. Radiobiological experiments are needed to fully explore this new avenue and to confirm our results.

Field correction factors for a PTW-31016 Pinpoint ionization chamber for both flattened and unflattened beams. Study of the main sources of uncertainties.

PURPOSE: The primary aim of this study was to determine correction factors, kQclin,Qmsrfclin,fmsr for a PTW-31016 ionization chamber on field sizes from 0.5 cm × 0.5 cm to 2 cm × 2 cm for both flattened (FF) and flattened filter-free (FFF) beams produced in a TrueBeam clinical accelerator. The secondary objective was the determination of field output factors, ΩQclin,Qmsrfclin,fmsr over this range of field sizes using both Monte Carlo (MC) simulation and measurements. METHODS: kQclin,Qmsrfclin,fmsr for the PTW-31016 chamber were calculated by MC simulation for field sizes of 0.5 cm × 0.5 cm, 1 cm × 1 cm, and 2 cm × 2 cm. MC simulations were performed with the PENELOPE code system for the 10 MV FFF Particle Space File from a TrueBeam linear accelerator (LINAC) provided by the manufacturer (Varian Medical Systems, Inc. Palo Alto, CA, USA). Simulations were repeated taking into account chamber manufacturing tolerances and accelerator jaw positioning in order to assess the uncertainty of the calculated correction factors. Output ratios were measured on square fields ranging from 0.5 cm × 0.5 cm to 10 cm × 10 cm for 6 MV and 10 MV FF and FFF beams produced by a TrueBeam using a PTW-31016 ionization chamber; a Sun Nuclear Edge detector (SunNuclear Corp., Melbourne, FL, USA) and TLD-700R (Harshaw, Thermo Scientific, Waltham, MA, USA). The validity of the proposed correction factors was verified using the calculated correction factors for the determination of ΩQclin,Qmsrfclin,fmsr using a PTW-31016 at the four TrueBeam energies and comparing the results with both TLD-700R measurements and MC simulations. Finally, the proposed correction factors were used to assess the correction factors of the SunNuclear Edge detector. RESULTS: The present work provides a set of MC calculated correction factors for a PTW-31016 chamber used on a TrueBeam FF and FFF mode. For the 0.5 cm × 0.5 cm square field size, kQclin,Qmsrfclin,fmsr is equal to 1.17 with a combined uncertainty of 2% (k = 1). A detailed analysis of the most influential parameters is presented in this work. PTW-31016 corrected measurements were used for the determination of ΩQclin,Qmsrfclin,fmsr for 6 MV and 10 MV FF and FFF and the results were in agreement with values obtained using a TLD-700R detector (differences < 3% for a 0.5 cm square field) for the four energies studied. Uncertainty in field collimation was found to be the main source of influence of ΩQclin,Qmsrfclin,fmsr and caused differences of up to 15% between calculations and measurements for the 0.5 cm × 0.5 cm field. This was also confirmed by repeating the same measurements at two different institutions. CONCLUSIONS: This study confirms the need to introduce correction factors when using a PTW-31016 chamber and the hypothesis of their low energy dependence. MC simulation has been shown to be a useful methodology to determine detector correction factors for small fields and to analyze the main sources of uncertainty. However, due to the influence of the LINAC jaw setup for field sizes below or equal to 1 cm, MC methods are not recommended in this range for field output factor calculations.

[Aetiology of surgical infections in patients undergoing craniotomy]. / Etiología de las infecciones quirúrgicas en pacientes sometidos a craneotomía.

BACKGROUND: Postoperative infections in patients undergoing craniotomy constitute significant complications associated with increased hospital stay and patient morbidity and mortality. Knowing the aetiology of surgical infections after craniotomy may contribute to improving antibiotic prophylaxis and empirical treatment. METHOD: Information relating to surgical infections in patients undergoing craniotomy was obtained from a series of annual surveys on prevalence of infections in Spanish hospitals (EPINE) during the period 1999-2006. The study protocol collected relevant clinical information on patients with infection. Presence of infection was determined according to the Centres for Disease Control infection criteria. RESULTS: During the time period considered, 107 cases of surgical infections in patients undergoing craniotomy were diagnosed. Forty patients were women (37%) and 67 were male (63%). The mean age was 51.7 years (median 55, range 6-86 years). The duration of the intervention was over 180minutes in 49 patients (45.8%).Thirty-eight patients (35.5%) underwent emergency surgery. Seventy-eight patients (73%) received surgical prophylaxis. Thirty-eight patients (35.5%) had superficial infection of the surgical wound, 38 patients (35.5%) had deep wound infection (including bone flap) and 31 patients (29%), postoperative infections of organ or space (meningitis, subdural empyema or brain abscess). The most common aetiology corresponded to staphylococci (50%), mainly S. aureus (one third of them methicillin-resistant), Pseudomonas aeruginosa (11%), Enterobacter spp (10%) and Acinetobacter baumannii (9%). CONCLUSION: Empirical treatment of these infections should include a glycopeptide such as vancomycin and a beta-lactam with coverage against non-fermenting gram-negative bacilli.

[Susceptibility to measles and varicella in healthcare workers in a tertiary hospital in Catalonia]. / Susceptibilidad frente a sarampión y varicela en el personal sanitario de un hospital de tercer nivel en Cataluña.

INTRODUCTION: To estimate the susceptibility to measles and varicella (chickenpox) in healthcare workers in a public tertiary level teaching hospital, in Catalonia. METHODS: A prevalence study was conducted from January 2006 to December 2008 on 2,752 workers who had serology performed for the determination of measles or varicella by ELISA test during a health examination. Data were analysed by, sex, age, professional category and work unit. RESULTS: A total of 153 healthcare workers were susceptible to measles and 187 to varicella. The susceptibility of healthcare workers to measles was 6.04% (95% CI: 5.78 to 6.30), and to varicella it was 7.45% (95% CI: 7.14 to 7.75). The highest susceptibility to measles was in resident physicians with 14% (95% CI: 10.8 to 18.5). In high-risk services, where highly immunocompromised patients are attended, the susceptibility of workers was slightly higher than the rest to measles (6.32% vs 5.93%) and varicella (8.34% vs 7.09%). Healthcare workers born after 1980 were 20 times (95% CI: 11.0 to 37.2) more likely to be susceptible to measles, and 2 times (95% CI: 1.2 to 3.2) more likely to be susceptible to varicella than those those born before 1965. CONCLUSIONS: The susceptibility to measles in healthcare workers in our centre is higher in younger cohorts, with values higher than expected in a community with high vaccination coverage against measles, mumps, rubella vaccine (MMR) in the paediatric population for many years.

[Microbiology of surgical site infections in abdominal tract surgery patients]. / Microbiología de las infecciones del sitio quirúrgico en pacientes intervenidos del tracto digestivo.

INTRODUCTION: Knowledge of the microbiology of surgical infections after abdominal surgery can be of use when prescribing effective empirical antibiotic treatments. METHOD: Analysis of surgical infections after abdominal surgery in patients enrolled in the Prevalence of Infections in Spanish Hospitals (EPINE) corresponding to the years 1999-2006. RESULTS: During the period of the study, 2,280 patients who were subjected to upper or lower abdominal tract surgery were diagnosed with an infection at the surgical site (SSI). Eight hundred and eighty three patients (37%) had an operation of the upper abdominal tract (gastric, hepatobiliary, and pancreatic surgery) and 1,447 patients (63%) lower abdominal tract surgery (appendectomy and colon surgery). A total of 2,617 bacterial species were isolated in the 2,280 patients included in the analysis. The most frequent microorganisms isolated were, Escherichia coli (28%), Enterococcus spp. (15%), Streptococcus spp. (8%), Pseudomonas aeruginosa (7%), and Staphylococcus aureus (5%, resistant to methicillin 2%). In the surgical infections after upper abdominal tract procedures, there were a higher proportion of isolations of staphylococci, Klebsiella pneumoniae, Enterobacter spp., Acinetobacter spp. and Candida albicans and less Escherichia coli, Bacteroides fragilis and Clostridium spp. CONCLUSION: The microbiology of SSI produced after upper abdominal tract surgery did not show any significant differences compared to those of the lower tract. However, more cases of SSI were detected due to staphylococci, Klebsiella pneumoniae, Enterobacter spp., Acinetobacter spp. and Candida albicans and less caused by Escherichia coli, Bacteroides fragilis and Clostridium spp.

[Patient characteristics and health care burden during the influenza A (H1N1) 2009 pandemic in the university Hospital Vall d'Hebron of Barcelona]. / Características de los pacientes y carga asistencial durante la pandemia de gripe A (H1N1) 2009 en el Hospital Universitario Vall d'Hebron de Barcelona.

BACKGROUND AND OBJECTIVE: The influenza A (H1N1) 2009 pandemic initially had a mild impact in Catalonian hospitals, but in the autumn there was an important pandemic wave. We describe the main characteristics of patients seen in the Vall d'Hebron University Hospital in Barcelona (HUVH) during this pandemic, the risk factors associated with hospitalization and the health-care burden generated. MATERIAL AND METHOD: We included all cases of influenza A (H1N1) 2009 with laboratory confirmation seen in the HUVH from July 2, 2009 to January 22, 2010. We performed a descriptive analysis of the cases and a multivariate analysis to identify variables associated with the risk of hospitalization. RESULTS: The diagnosis was confirmed in 741 patients; 56.8% were under 16 years, while only 2.8% were 65 and over. Thirty three per cent of children had no risk factor for complications, whereas in adults it was 45%. One hundred and ninety cases were hospitalized, 26 of them in the intensive care unit (ICU) with 5 deaths. The factors associated with risk of hospitalization were, age less than one year, immunodeficiency, and neuromuscular disease in children; and chronic lung disease in adults. The diagnosis of pneumonia in the emergency department was an important predictor of hospitalization in both children and adults. The maximum caseload was recorded on November 19, with 43 hospital admissions, 6 of them in the ICU. CONCLUSIONS: Between July and September 2009 the pandemic had a low impact on hospital resources, but in autumn there was a marked increase in emergency department visits and hospitalizations. Children had higher rates of confirmed cases, while adults had higher rates of hospitalizations. The risk of hospitalization was higher in patients with certain conditions especially in those with pneumonia. The pandemic wave was a moderate work load for HUVH, since it did not involve any modification of the usual health care programs.

[Epidemiology of influenza A (H1N1) worldwide and in Spain]. / Epidemiología de la gripe A (H1N1) en el mundo y en España.

On June 11, 2009, the World Health Organization declared an established pandemic due to a new influenza virus A (H1N1) of swine origin. Initial cases were detected in Mexico in March and within 6 weeks the virus had spread worldwide. The transmissibility of influenza A (H1NA) is slightly higher than that of the seasonal virus, but its pathogenicity and virulence are low. The main target groups of this new virus have been children and young adults under 30 years old. Mortality has affected mainly persons aged between 20 and 50 years old. In areas with temperate climates, two epidemic waves have occurred. The first one, from mid-April to mid-August, affected Mexico, the United States and, consecutively, Spain, England, Japan, and other countries in the northern hemisphere. A few weeks later, coinciding with the beginning of the influenza season, the H1N1 epidemic started in the southern hemisphere countries, especially Argentina, Chile, Australia and New Zealand; in these countries, the epidemic finished at the end of September or October. The second wave affected the northern hemisphere, starting in the United States and Mexico at the beginning of September, and a few weeks later in European countries. In mid-December, this wave was considered to have ended, although some influenza activity persists. The intensity of this second wave was higher compared to the first one.

Effectiveness of varicella vaccines as postexposure prophylaxis.

BACKGROUND: Although chickenpox is usually a mild disease, it is not always free of complications, especially in adolescents and adults. Previous studies of postexposure prophylaxis conducted with experimental vaccines showed the vaccine to be highly effective if administered in the first 3 to 5 days after exposure. However, studies carried out with commercialized vaccines yielded discordant results. The aim of the present study was to assess the effectiveness of currently available varicella vaccines as postexposure prophylaxis. METHODS: We conducted a prospective cohort study. Patients susceptible to chickenpox consulting at the Preventive Medicine Department of the Vall d'Hebron Hospital after household exposure to a case of chickenpox were included. Postexposure prophylaxis with varicella vaccine was administered within the first 5 days after contact. Subjects were interviewed by telephone between 4 and 8 weeks after vaccination to ascertain whether chickenpox had appeared and, if so, its severity. The effectiveness of the vaccine in preventing and attenuating the disease was calculated with a confidence interval of 95%. RESULTS: Sixty-seven subjects were included in the study. Effectiveness of the varicella vaccine in preventing any type of disease was 62.3% (CI 95%: 47.8-74.9) and 79.4% (CI 95%: 66.4-88.9) in preventing moderate and severe disease. No statistically significant differences were found when effectiveness was compared according to sex, age, or days elapsed since exposure. CONCLUSIONS: Administration of varicella vaccines within the first 5 days postexposure is effective in preventing chickenpox and in attenuating the illness.

[Prevalence of infection by carbapenem-resistant Acinetobacter baumannii in Spain (1999-2005)]. / Prevalencia de infecciones por Acinetobacter baumannii resistente a carbapenemas en España (1999-2005).

INTRODUCTION: This study determines the prevalence of infections by carbapenem-resistant Acinetobacter baumannii (CRAB) in Spain, and identifies trends over time, geographical variations, and factors associated with resistance. METHODS: Yearly prevalence surveys (EPINE, Estudio de Prevalencia de las Infecciones Nosocomiales en España) during 1999 to 2005 were analyzed, including data on the site of infection, culture, and antimicrobial susceptibility, and characteristics of the patients and hospitals. RESULTS: On average, 246 hospitals/year participated in the survey. A total of 1168 A. baumannii isolates were identified, yielding an infection prevalence rate of 3/1,000 hospitalized patients. Fourteen percent of isolates were related to community-onset infections. The most frequent sites of infection were the respiratory tract (42.2%), surgical wound (15.1%), urinary tract (12.9%), and skin (11.7%). Rate of carbapenem resistance was 34.5% (95% CI, 31.8-37.3), and was even higher among ICU patients (43.8%; 95% CI, 38.9%-48.7%). There were considerable differences between Spanish regions, with the highest rates of resistance in central regions. Higher resistance rates were observed in respiratory tract infections (43%) and catheter-related bacteremia (47.6%) than among other sites of infection (P =.003). Main factors associated with CRAB identified by multivariate analysis were surgical or tracheostomy procedures, use of invasive devices such as urinary, nasogastric, or central venous catheters, and mechanical ventilation, as well as male gender and pressure sores. CONCLUSIONS: The prevalence of CRAB in Spain is very high. Differences in resistance rates have been observed according to geographic region and area of hospitalization. Several invasive procedures, as well as male gender and pressure sores, are associated with higher rates of carbapenem resistance.

Nosocomial transmission of hepatitis C virus during contrast-enhanced computed tomography scanning.

We have investigated two cases of acute hepatitis C that occurred in patients who underwent digestive endoscopy and contrast-enhanced computed tomography (CT) scanning at two different centers. Investigations to identify the sources of infection included an on-site review of diagnostic procedures, interview of the involved healthcare staff, serological testing of the patients who underwent the procedures before and after the index cases and a molecular analysis of viral isolates from the patients and from potential viremic sources. In both cases, the epidemiological investigation identified a chronic hepatitis C virus (HCV) carrier who had been subjected to CT-scanning immediately before the index patient. Genetic distance and molecular phylogenetic analyzes of HCV sequences showed a close relationship between the isolates from these carriers and those from the acute-hepatitis patients, strongly suggesting that patient-to-patient transmission had occurred during CT. This is the first report describing two well documented cases of HCV nosocomial patient-to-patient transmission during contrast-enhanced CT scanning.

[Etiology of hospital-acquired infections in Spanish hospitals (EPINE, 1990-1999)]. / Etiología de las infecciones hospitalarias en España (EPINE, 1990-1999).

BACKGROUND: Clinical and demographic characteristics of patients, their interaction with pathogens and antimicrobial therapies are prompting changes in the epidemiology of hospital-acquired infections (HI). The knowledge of the etiology of hospital-acquired infections is valuable for the treatment of infected patients and for the prevention of HI. PATIENTS AND METHOD: We analyzed a series of 10 annual prevalence studies during the period 1990-1999 (EPINE project) in Spanish hospitals. Estimate of prevalence of infection was calculated by means of the percent distribution of every organism regarding overall identified organisms and infections. RESULTS: 40,550 HI were identified among 484,013 patients (HI prevalence = 8.4%; 95% CI, 8.3-8.5%). Gram-positive organism predominated steadily in bloodstream and surgical wound infections, while gram-negative bacilli predominated in respiratory and urinary tract infections. There was an increase in HI infections by Acinetobacter baumannii (from 1.9% in 1990 to 3.6% in 1999; P < 0.001) and Candida albicans (from 2.4 to 3.2%; P < 0.001), as well as an increase in both HI and community-acquired infections by methicillin-resistant Staphylococcus aureus [HI: from 4.7 to 40.2% (P < 0.001); community-acquired: from 2.7 to 15.6% (P < 0.001)]. CONCLUSIONS: We observed some changes in the etiology of infections over the last decade: rates of methicillin-resistant S. aureus hospital-acquired and community-acquired infections increased steadily and their initial rates multiplied by 8 and 6, respectively. Rates of HI caused by yeasts and A. baumannii increased also.

[Antimicrobial use in Spanish hospitals (EPINE, 1990-1999)]. / Utilización de los antimicrobianos en los hospitales españoles (EPINE, 1990-1999).

BACKGROUND: Monitoring of antimicrobial use and knowledge of prescription habits are some of the strategies recommended to contain the resistance to antimicrobials in hospitals. METHOD: We analyzed a series of 10 annual studies of prevalence during the period 1990-1999 (EPINE project) in Spanish hospitals. Estimates of antimicrobial use were calculated as the percent distribution of every antimicrobial related to the overall antimicrobials prescribed. RESULTS: Among 484,013 hospitalized patients, 34 to 36% were receiving antimicrobials (antibiotics > 90%). Amoxicillin-clavulanate use increased from 3.8% in 1990 up to 14.8% in 1999 (P < 0.01). Significant increases were also observed in the use of carbapenems (0.9 to 2.7%; P < 0.01), glycopeptides (1.7 to 3.7%; P < 0.01) and quinolones (8.5 to 11.3%; P < 0.01) though to a lesser degree. Conversely, the use of aminoglycosides decreased over the decade studied (15.8 to 9.4%; P < 0.01). CONCLUSIONS: Even though the use of antimicrobials has increased over the last decade, current figures are within the ranges observed in other countries. The pattern of antibiotics use has changed during this period: while the use of aminoglycosides decreased, that of -lactams plus -lactamase inhibitors, quinolones and carbapenems increased.