Detection and localization of radiotherapy targets by template matching

Radio opaque fiducials are implanted in tumors for the purpose of tracking the target motion using X-ray projections during radiation therapy dose delivery. In this paper we describe and evaluate a novel method based on template matching for detection and localization of arbitrary shaped fiducials. Segmentation methods are not adequate for these fiducials because their appearance in online X-ray projections can vary greatly as a function of imaging angle. The algorithm is based on using the planning CT image to generate templates that correspond to the imaging angles of the online images. We demonstrate successful tracking of complex shape fiducials in clinical images of lung and abdomen. We also validate the algorithm by comparing the results with a segmentation approach for one case in which the fiducials could be tracked by both methods. We also show how by adaptive thresholding of the match scores, we can control the false detection rate.

Determination of critical concentrations of second-line anti-tuberculosis drugs with clinical and microbiological relevance

BACKGROUND

Reliable DST against second-line anti-tuberculosis drugs (SLDs) is crucial for the management of the increasing burden of patients affected by multidrug- and extensively drug-resistant TB.

METHODS

This study utilizes 252 clinical isolates of Mycobacterium tuberculosis from five countries (Hong Kong Special Administrative Region, Korea, Latvia, Peru, Philippines) with documented treatment histories to establish clinically and microbiologically relevant critical concentrations (CCs) of six SLDs for three routine testing methods: the absolute concentration method using Löwenstein-Jensen (LJ) medium, the 1% proportion method using Middlebrook 7H10 agar medium, and the radiometric BACTEC 460 system.

FINDINGS

In LJ medium, CCs of capreomycin, ethionamide, kanamycin, ofloxacin, rho-aminosalicylic acid and cycloserine (CS) were respectively 40.0, 40.0, 30.0, 3.0, 1.0 and 30.0 mg/l. In 7H10 agar medium, the respective CCs for the first five antibiotics (except CS) were 8.0, 2.0-3.0, 3.0-5.0, 1.0-1.5 and 0.5-1.0 mg/l. In BACTEC 460 broth, the respective CCs were 1.5-2.0, 1.0-1.5, 2.0-3.0, 0.5-1.0 and 0.5-1.0 mg/l. Precautions in DST interpretation was also discussed.

INTERPRETATION

By adopting this set of CCs as a global standard to define second-line drug susceptibility and resistance, as well as precautions in result interpretation, the screening, diagnosis and management of patients with drug-resistant TB can be greatly improved.

Validation of a rapid method for detection of M. tuberculosis resistance to isoniazid and rifampin in Lima, Peru

SETTING

Treatment of multidrug-resistant tuberculosis (MDR-TB) is often based on drug susceptibility testing (DST) results; for this reason, rapid, simple DST methods are sought which could be applied in resource-poor countries. One such method is a nitrate reductase colorimetric assay known as the Griess method. In Peru, where the incidence rate of TB is among the highest in South America, the National Institute of Health recently undertook the validation and implementation of the direct Griess method.

OBJECTIVE

To describe the process of validation and implemention of the direct Griess method at the Peruvian National Institute of Health.

DESIGN

Prospective study comparing the sensitivity and specificity of the direct Griess method with the Löwenstein-Jensen proportion method in determining resistance to isoniazid (INH) and rifampin (RMP) among clinical isolates.

RESULTS

Among 192 specimens, the sensitivity and specificity of the Griess method for detection of INH resistance was 99.1% and 100%, respectively. For identification of RMP resistance, the sensitivity and specificity was 93.5% and 100%, respectively.

CONCLUSIONS

In addition to its high sensitivity and specificity and rapid turn around time, the Griess method uses simple, inexpensive reagents and requires minimal laboratory space and technical expertise, thus providing an ideal screening tool for resource-poor settings with high rates of MDR-TB.

Acquisition of drug resistance in multidrug-resistant Mycobacterium tuberculosis during directly observed empiric retreatment with standardized regimens

The risk of acquiring additional drug resistance in strains of multidrug-resistant tuberculosis (MDR-TB) during failure of empiric standardized retreatment regimens is poorly defined. We sought to estimate this risk by comparing drug susceptibility profiles and RFLP patterns of paired MDR-TB isolates collected from 27 patients before and after retreatment failure. Among 23 patients with paired isolates with concordant RFLP patterns, 19 (83%) had become resistant to at least one additional drug after failed retreatment. In this limited group of MDR-TB patients, acquisition of resistance was common during failure of empiric drug regimens. Further study is needed to confirm these findings.

rpoBGene Mutations in Clinical Isolates of Multidrug-ResistantMycobacterium tuberculosisin Northern Lima, Peru

In many developing countries and outside hospital settings, the characteristics of endemic Mycobacterium tuberculosis strains resistant to multiple drugs remain unknown. In a community-based referral and therapy program in northern Lima, Peru, beginning in 1996, patients found to be failures on standard regimens were referred for drug-susceptibility testing of their isolates, and those found to be infected with M. tuberculosis isolates resistant to at least rifampin were treated with individualized regimens based on their infecting strains. Isolates from 42 of these patients were subjected to DNA sequencing of the rpoB gene region responsible for rifampin resistance. We determined the frequency of types of mutations in the rpoB gene among these Peruvian isolates.

Drug resistance profiles of Mycobacterium tuberculosis isolates: five years' experience and insight into treatment strategies for MDR-TB in Lima, Peru

SETTING

Lima, Peru.

OBJECTIVE

To describe drug resistance profiles of TB isolates from patients at risk for multidrug-resistant tuberculosis (MDR-TB), and to consider the implications of these findings for treatment.

DESIGN

Descriptive study of drug susceptibility testing (DST) results for TB isolates from 1680 patients referred for suspicion of MDR-TB between 1996 and 2001.

RESULTS

Of 1680 isolates tested, 1144 (68%) were resistant to at least one anti-tuberculosis drug and 926 (55%) were MDR-TB strains. Of 926 MDR isolates, 50 (5%) were resistant to INH and RMP alone, while 367 (40%) were resistant to at least five first-line drugs. We identified 146 unique drug resistance profiles, the most common of which accounted for 11% of drug-resistant isolates. The annual prevalence of isolates with resistance to at least five first-line drugs rose significantly during the study period, from 29% to 37% (P = 0.00086).

CONCLUSIONS

This is a group of patients with TB disease among whom the prevalence of a broad spectrum of often highly drug-resistant strains appears to be increasing over time. A single standardized retreatment regimen may be inadequate to cure most patients. Capacity for drug sensitivity testing is essential for development of multiple standardized retreatment or individualized treatment regimens and epidemiological surveillance for planning.

New method for detection of Mycobacterium tuberculosis Direct Test inhibitors in clinical specimens

Existing protocols for the detection of Mycobacterium tuberculosis Direct Test (MDT) inhibitors require substantial quantities of specimen and cannot distinguish Mycobacterium tuberculosis complex from other mycobacteria if inhibitors are present. We describe a preliminary evaluation of a simple and practical protocol for MTD inhibitor testing that circumvents these difficulties.

Practical strategies for performance optimization of the enhanced gen-probe amplified mycobacterium tuberculosis direct test

The enhanced Gen-Probe Amplified Mycobacterium Tuberculosis Direct (MTD) test was evaluated using a combined set of 338 acid-fast smear-positive and smear-negative, respiratory and nonrespiratory clinical specimens received by the Massachusetts State Tuberculosis Laboratory from September 1999 through March 2002. Microbiological culture was used as the reference method; therefore, the sensitivity and specificity of the MTD test were calculated for culture-positive specimens only. The initial assessment indicated that the overall sensitivity, specificity, and positive and negative predictive values of the MTD test for all specimens grouped together were 62, 98, 99, and 68%, respectively. A detailed discrepancy analysis revealed that two major factors causing negative MTD results in specimens that were culture positive for M. tuberculosis complex were patient treatment with antituberculosis drugs prior to testing and the presence of inhibitory substances in the specimen. Based on these findings, a protocol for optimizing MTD test performance in this setting is proposed in which (i) specimens from patients taking antituberculosis medications are excluded from testing and (ii) all initially MTD-negative or MTD-equivocal specimens are subjected to testing for inhibitors. If this strategy was followed, the MTD test sensitivity would be at least 91%, a significant improvement over the initial sensitivity of 62%. Accordingly, the negative predictive value would increase from 68 to 91%.

Clinical and programmatic considerations in the treatment of MDR-TB in children: a series of 16 patients from Lima, Peru

SETTING

Since 2000, the directly observed treatment, short-course (DOTS) strategy has been expanded in several countries to include treatment of multidrug-resistant tuberculosis (MDR-TB). This strategy is known as DOTS-Plus. Tuberculosis is a common cause of morbidity and mortality for children throughout the developing world. Children may also be infected with MDR-TB, yet most developing countries do not specifically address pediatric MDR-TB.

OBJECTIVE

To present the intermediate outcomes of the first 16 children enrolled in the Peruvian DOTS-Plus program and to demonstrate the tolerability of second-line anti-tuberculosis drugs.

RESULTS

Three children completed therapy and are cured, one child had bacteriologic and clinical failure after 12 months of therapy and died of respiratory insufficiency, and 12 have intermediate outcomes demonstrating favorable clinical, bacteriologic, and radiographic evidence of improvement after 9-19 months of therapy.

CONCLUSIONS

Of the 16 pediatric DOTS-Plus patients, 15 have tolerated therapy well and have had favorable clinical evolution. However, the diagnosis of pediatric MDR-TB is often extremely delayed due to reliance on the adult case definition and should be changed to prevent progressive, chronic illness in such children. Programmatic changes could facilitate earlier diagnosis and treatment of pediatric MDR-TB in Peru and in other DOTS-Plus programs.

Multicenter evaluation of ethambutol susceptibility testing of mycobacterium tuberculosis by agar proportion and radiometric methods

Reproducibility of ethambutol (EMB) susceptibility test results for Mycobacterium tuberculosis has always been difficult for a variety of reasons, including the narrow range between the critical breakpoint for EMB resistance and the MIC for susceptible strains, borderline results obtained with the BACTEC 460TB method, the presence of microcolonies determined using the agar proportion (AP) method, and a lack of agreement between these two testing methods. To assess the frequency of these problems, M. tuberculosis drug susceptibility data were collected in a multicenter study involving four laboratories. Resistant, borderline, and susceptible isolates were shared among the laboratories to measure interlaboratory test agreement. Half of isolates determined by BACTEC 460TB to be resistant were determined to be susceptible by the AP method. Isolates determined to be resistant to EMB by both BACTEC 460TB and AP methods were almost always resistant to isoniazid. Results from isolates tested by the BACTEC 460TB method with an EMB concentration of 3.75 micro g/ml in addition to the standard 2.5 micro g/ml did not show improved agreement by the AP method. While these results do not indicate that the AP method is more accurate than the BACTEC 460TB method, laboratories should not report EMB monoresistance based on BACTEC 460TB results alone. Monoresistance to EMB should only be reported following confirmation by the AP method. Microcolonies could not be confirmed as resistant by the BACTEC 460TB method or by repeat testing with the AP method and do not appear to be indicative of resistance.

Multicenter evaluation of a nonweekend reading schedule for radiometric pyrazinamide susceptibility testing of Mycobacterium tuberculosis

Pyrazinamide (PZA) is an integral component of the short-course chemotherapy regimen for tuberculosis. The BACTEC 460TB PZA susceptibility test for Mycobacterium tuberculosis with a daily (D) reading schedule has been available for more than 10 years, but weekend laboratory staffing is necessary. A nonweekend (NW) reading schedule has not been validated in a multicenter study. This prospective multicenter study compares the interlaboratory reproducibility of PZA susceptibility results by following both the D and NW schedules. A total of 181 cultures were shared among four laboratories. Isolates were selected based on resistance or borderline resistance to at least one streptomycin-isoniazid-rifampin-ethambutol drug or PZA. One laboratory used a D reading schedule, and three laboratories used a NW schedule. Both reading schedules are based on the standard BACTEC 460TB PZA protocol. With the NW schedule, the growth index (GI) is not available for test interpretation on Saturday, Sunday, and Monday. Of the 181 shared cultures, 154 were found to be susceptible by all laboratories, 19 were found to be resistant, and 8 had discordant results. The overall pairwise interlaboratory agreement was 97.7%. The discrepancies were not associated with the type of reading schedule used. However, the median control GI was significantly higher for the NW schedule (321) than for the D schedule (259) (P < 0.0001) although results were available on average in about 7 days from setup for both schedules. These results show that the NW schedule is a suitable alternative for laboratories that do not read and interpret PZA susceptibility tests on weekends.

Novel mycobacterium related to Mycobacterium triplex as a cause of cervical lymphadenitis

The Mycobacterium avium complex (MAC) is an important cause of cervical lymphadenitis in children, and its incidence appears to be increasing in the United States and elsewhere. In areas where Mycobacterium tuberculosis is not prevalent, M. avium causes the vast majority of cases of mycobacterial lymphadenitis, although several other nontuberculous mycobacterial species have been reported as etiologic agents. This report describes the case of a child with cervical lymphadenitis caused by a nontuberculous mycobacterium that could not be identified using standard methods, including biochemical reactions and genetic probes. Direct 16S ribosomal DNA sequencing showed greater than 99% homology with Mycobacterium triplex, but sequence analysis of the 283-bp 16S-23S internal transcribed spacer (ITS) sequence showed only 95% identity, suggesting that it is a novel species or subspecies within a complex of organisms that includes M. triplex. Mycolic acid high-performance liquid chromatography analysis also identified this isolate as distinct from M. triplex, and differences in susceptibility to streptomycin and rifampin between this strain and M. triplex were also observed. These data support the value of further testing of clinical isolates that test negative with the MAC nucleic acid probes and suggest that standard methods used for the identification of mycobacteria may underestimate the complexity of the genus Mycobacterium. ITS sequence analysis may be useful in this setting because it is easy to perform and is able to distinguish closely related species and subspecies. This level of discrimination may have significant clinical ramifications, as closely related organisms may have different antibiotic susceptibility patterns.

Using treatment failure under effective directly observed short-course chemotherapy programs to identify patients with multidrug-resistant tuberculosis

SETTING

Public ambulatory care centers in three districts of northern metropolitan Lima, Peru.

OBJECTIVE

To document drug resistance patterns of isolates of Mycobacterium tuberculosis from patients identified as treatment failures under a model tuberculosis (TB) control program based on directly observed, short-course chemotherapy (DOT-SCC).

DESIGN

Case series.

RESULTS

In a referred, consecutive sample of 173 patients identified as treatment failures on DOT-SCC, 160 (92.5%) had culture-positive TB. Of those 160, 150 (93.8%) had active, pulmonary multidrug-resistant TB (MDR-TB, resistance to at least isoniazid [INH] and rifampicin [RIF]). Sixty of the 150 (40.0%) had isolates resistant to at least INH, RIF, ethambutol (EMB) and pyrazinamide (PZA), the initial first-line empiric treatment regimen used locally. Forty-four (29.3%) had isolates resistant to at least INH, RIF, EMB, PZA and streptomycin (SM), the first retreatment regimen. This series of patients had isolates resistant to a mean of 4.5 of the ten drugs tested. The local profile of multidrug resistance is very different from that obtained from national data from Peru.

CONCLUSION

In this setting, treatment failure on DOT-SCC is strongly predictive of active MDR-TB. Because of existing local drug resistance patterns in northern Lima, 89.3% of MDR-TB patients identified as treatment failures will receive ineffective therapy with two or fewer secondary TB drugs if they are given the five-drug empiric retreatment regimen endorsed by the World Health Organization. Further short-course chemotherapy for these patients would only serve to amplify ominous existing drug resistance patterns.