[Thirty years of tuberculosis control in Cameroon: alternating "vertical" and "horizontal" health care delivery systems]. / Trente ans de lutte antituberculeuse au Cameroun: une alternance entre systèmes d'offre de soins de santé "vertical" et "horizontal".

BACKGROUND: In sub-Saharan Africa, tuberculosis remains endemic despite reforms of health systems and the tuberculosis control organization carried out in the last decades. METHODS: We conducted a retrospective study of tuberculosis control in Cameroon from the period 2009 back to 1980. Data were collected from documents and activity reports of tuberculosis control, and interviews with managers of the National tuberculosis control program. FINDINGS: The history of tuberculosis control in Cameroon from 2009 back to 1980 can be divided into three main periods. The first period, from 1980 to 1994, corresponded to the implementation of the 'primary health care' policy. At that time, tuberculosis case management was delivered free of charge, but centralized in specialized services with a gradual and mild increase in new cases detected. The second period, from 1995 to 2000, was characterized by the implementation of the 'primary health care reorientation' policy that decentralized tuberculosis care to all health facilities, but introduced cost recovery --which came along with a dramatic drop in the number of tuberculosis cases detected. The National tuberculosis control program, established in 1996, entrusted health facilities--especially hospitals--with the responsibility of tuberculosis diagnosis and treatment, and referred to them as tuberculosis diagnosis and treatment centers. During the third period, from 2001 to 2009, owing to major support from global health initiatives, the number of tuberculosis diagnosis and treatment centers was increased (reaching 216 centers in 2009), with a significant increase of new cases detected that peaked in 2006, from where the situation started declining till 2009. CONCLUSION: Tuberculosis control indicators have never been optimal in Cameroon, despite the generally positive trend from 1980 to 2009. The strategy of tuberculosis diagnosis and treatment centers, which are essentially nested within hospitals, seems to have reached its intrinsic limitations. Better performance in tuberculosis control will henceforth require greater decentralization of tuberculosis detection and treatment to health centers. This careful decentralization will improve access for tuberculosis patients and lead to a comprehensive use of hospital technical expertise for tuberculosis care.

Rheumatic diseases in patients attending a clinic at a referral hospital in Yaounde, Cameroon.

BACKGROUND: The spectrum of rheumatic diseases in sub-Saharan Africa remains poorly defined. OBJECTIVES: To determine the spectrum of rheumatic diseases in Yaounde. DESIGN: Descriptive cross-sectional study. SETTING: Rheumatology clinic at the Yaounde General Hospital, Cameroon. SUBJECTS: Twelve thousand four hundred and ninety four patients were referred to the outpatient department of the Internal Medicine service of the General Hospital of Yaounde over a 12-month period. Of these cases, 536 (9.4%) were diagnosed as belonging to the general class of rheumatic conditions. There were 334 (62.31%) females and 202 (37.69%) males. The mean age was 52.72 +/- 5.3 years. RESULTS: The 536 cases were further classified as follows: degenerative disease of the spine 196 (36.5%), osteoarthritis of the limbs 110 (20.5%), regional musculo-skeletal disorders 83 (15.5%), arthritis associated with infections 50 (9.3%), chronic inflammatory and connective tissue diseases 44 (8.2%), crystalline arthropathies 32 (5.9%) and miscellaneous (unclassified) rheumatic conditions 21 (4.1%). CONCLUSION: From these results, we concluded that degenerative disease of the spine and limbs are the most common forms of rheumatic disease in this region. Gout is the most commnon acute inflammatory arthropathy and rheumatoid arthritis the most prevalent arthropathy due to chronic inflammation.

On the choice of phantom material for the dosimetry of 192Ir sources.

Dosimetric characteristics of polystyrene, solid water, and polymethylmethacrylate were examined and compared to water to determine the suitability of these solid materials for the dosimetry of 192Ir. Ionization charge measured in each of the four media as a function of depth and depth-dose curves calculated by Monte Carlo simulation show that the three solids are equivalent to each other and to water under full scattering conditions. Photon energy spectra generated from the Monte Carlo simulation show little variation for the different media. Mass energy absorption coefficients and exposure-to-dose conversion factors were calculated as a function of depth for these spectra. Measured tissue attenuation factors are in excellent agreement with Meisberger's "selected" values. The radial dose function, which describes the change in dose with distance in phantom exclusive of the inverse square law, was calculated from the tissue attenuation factor and found to be in significant disagreement with Dale's Monte Carlo values. The reason for this discrepancy is discussed.

The effect on dose of kilovoltage x-rays backscattered from lead.

Dose enhancement on the backscatter side of a soft tissue/high Z material interface is known to exist for megavoltage x-ray beams. Caused by an increase in backscattered electron fluence, the enhancement persists for short distances upstream of the interface, equal to the range of these electrons. Since photon interaction cross sections are small, there is little photon backscatter at these energies. Consequently, beyond the range of the backscattered electrons, the dose upstream is unaffected by the presence of the interface. A similar dose enhancement has been reported for kilovoltage beams. In this case, due to the very low energy of the backscattered electrons, the enhancement persists for a very short upstream distance. Since photon interaction cross sections at keV energies are relatively large, there is also a substantial backscattered photon fluence. This experimental work investigates the effect of these photons on dose at distances upstream from a water/lead interface beyond the range of the backscattered electrons. Measurements of ionization charge, as a function of interface distance and field size for 60, 100, and 250 kV beams, were made with a parallel plate chamber at a fixed depth. A significant underdose was found upstream of the interface compared to a homogeneous water medium. For example, with the 100 kV beam and a 15 x 15 cm2 field the measured underdose is 23% at 3 mm and 14% at 1.5 cm upstream of the interface. The effect decreases with field size. In fact, for a 2 x 2 cm2 field the upstream dose in unaffected by the interface. Detailed results for this and the other two beams are presented along with backscatter factor measurements for lead. An explanation for the observed underdose is also presented.

1995 survey of physics teaching efforts in radiation oncology residency programs.

A physics teaching survey was constructed and sent to the 83 radiation oncologist training programs. The survey requested program information regarding size, staffing, curriculum, lab/rotation programs, organization, requirements, instructor makeup, teaching materials, and board certification examination results. The surveys were sent to the physicist responsible for the physics program. Forty-nine (59%) institutions returned completed surveys, of which 43 (88%) were university-associated programs, and 27 (55%) were 4-year programs. On average, there were two residents/year. Most programs (39) taught physics exclusively during the first year (PG2). Some programs taught different subjects (or levels) to different year residents. Radiation dosimetry, treatment planning, and brachytherapy constituted nearly half of the teaching hours. On average the total classroom time expended by physicists was 61.4 h/year with a range of 24-118 h. The mean for laboratory/demonstration time was 27 h/year with 18 programs providing none. Physics orientation/rotations ranged from 1 to 480 h with a mean of 170 h for a physics rotation taking place in year 2 (PG3). Mandatory attendance was 80% for first-year residents and decreased in later years. Homework was assigned in 76% of the programs, and 65% of the programs were graded. The primary instructors averaged 18.2 years of experience, and the majority were ABR/ABMP certified. Khan's textbook was the most prevalent resource for most subjects. No correlation could be made between teaching hours and ABR physics percentile scoring. The survey results reveal enormous differences in national teaching efforts.

The epidemiology of Plasmodium falciparum malaria in two Cameroonian villages: Simbok and Etoa.

In support of ongoing immunologic studies on immunity to Plasmodium falciparum, demographic, entomologic, parasitologic, and clinical studies were conducted in two Cameroonian villages located 3 km apart. Simbok (population = 907) has pools of water present year round that provide breeding sites for Anopheles gambiae, whereas Etoa (population = 485) has swampy areas that dry up annually in which A. funestus breed. Results showed that individuals in Simbok receive an estimated 1.9 and 1.2 infectious bites per night in the wet and dry season, respectively, whereas individuals in Etoa receive 2.4 and 0.4 infectious bites per night, respectively. Although transmission patterns differ, the rate of acquisition of immunity to malaria appears to be similar in both villages. A prevalence of 50-75% was found in children < 10 years old, variable levels in children 11-15 years old, and 31% in adults. Thus, as reported in other parts of Africa, individuals exposed to continuous transmission of P. falciparum slowly acquired significant, but not complete, immunity.

Output factors and dose calculations for blocked x-ray fields.

Output factors for blocked fields have been measured in a polystyrene phantom for four collimator field sizes and two blocking schemes using 6-MV x rays. For all measurements the phantom surface was at the calibration source-surface distance (SSD) because, as is shown, the calculation of dose to any point in a phantom at an arbitrary SSD can be expressed in terms of the output factor for the field size at the calibration distance. It is found that output factors are a function of both the surface field size of the blocked field and the collimator field size. Specifically, the output factor for a blocked field is less than that for the collimator field size used but greater than that for an unblocked field of the same surface field size formed by collimator settings only. A method is proposed for utilizing these data to calculate the output factor for any collimator and blocked field size. The validity of the method is checked by using it to calculate dose to a point in a phantom and comparing this to the measured dose.

Choice of material for HVL measurements in megavoltage x-ray beams.

The relative sensitivity of the half-value layer (HVL) method as a quality index for megavoltage x-ray beams is examined by theoretical calculation and experimental measurements for 4-, 6-, 10-, and 25-MV x-ray beams. It is shown that lower atomic number materials are more sensitive to beam quality changes than higher atomic number materials, and that aluminum is a reasonable choice of material for HVL measurements in megavoltage x-ray beams. Further, it was found that the HVL in aluminum or polystyrene is a more sensitive index of spectral quality than the ionization ratio method, recommended by recent dosimetry protocols.

Determining Pion, the correction factor for recombination losses in an ionization chamber.

The 1983 AAPM protocol for the determination of absorbed dose from high-energy photon and electron beams recommends using Pion (the reciprocal of collection efficiency), as determined by the two-voltage technique, to correct for recombination losses in ionization chambers. Methods and data for the determination of ionization chamber collection efficiencies are scattered throughout the literature. The present work consolidates the available information, rectifies certain omissions, and provides several convenient and readily implemented methods for determining Pion. Computer programs, quadratic approximations, and data tables are presented to facilitate the determination of Pion for continuous, pulsed, and pulsed-swept beams.

The effect of lead, gold, and silver backings on dose near 125I seeds.

Brachytherapy for ocular melanoma uses 125I seeds backed by a gold shield. Conflicting results are reported in the literature on the effect of the gold on dose close to the seeds. In this work, a small lucite jig was constructed such that the seed-to-detector separation remained fixed as high-Z materials of lead, silver, and gold were moved in and out of position behind the seed. The jig was clamped in place in the water filled tank of a beam scanning system. The response of two p-type silicon diodes was measured at several distances from the seed with and without the high-Z backings. The response with the high-Z backing relative to water, found to be the same for each diode and the same for lead and gold, decreased from about 1.01 at 1.5 mm to about 0.92 at 20 mm. It has been suggested in the literature that L-shell fluorescent x rays of approximately 10 keV from the gold backing might contribute significantly to the dose within 7 mm of the seed. To test this, the response with the gold backing relative to water was measured with an aluminum cap of 1-mm wall thickness covering the diode. The cap transmits about 70% of the 125I influence but is essentially infinitely thick to 10-keV photons. The relative response (gold/water) was the same with and without the cap showing that the contribution of 10-keV x rays is negligible. Compared to water, the silver backing was found to enhance the diode response by about 14% between 5 to 10 mm from the seed.

Interseed effects on dose for 125I brachytherapy implants.

Dose calculations in multiseed brachytherapy implants are done by adding the contribution of each individual seed and by assuming that radiation from each seed is unaffected by the presence of the other seeds. To test the validity of this assumption, dose measurements with various configurations of multiseed implants of 125I model 6702 and 125I model 6711 sources were performed. For a linear configuration of three 125I model 6702 seeds at 1-cm separation, with their transverse axes coincident, doses at distances of 3.05 and 5.09 cm from the center along the transverse axis were found to be about 8% lower than the sum of doses from the three individual seeds. However, for three seeds at 1-cm intervals with their longitudinal axes coincident, doses at 3.05 and 5.09 cm distances from the center along the longitudinal axis were found to be about equal to the dose sums from individual seeds. These initial experiments indicated that the magnitude of the interseed effect depends upon the orientation of the seed relative to each other in an implant. To evaluate the importance of this interseed effect for multiseed configurations of 125I model 6702 and 125I model 6711 seeds, dose rates at various distances from a two-plane implant (each plane containing a 3 x 3 array of sources in a 1-cm spacing square grid) were measured in a Solid Water phantom with LiF TLDs. These measurements were carried out in two different planes at different orientations relative to the implant. The average values of the interseed effect at distances ranging from 1 to 7 cm outside the implant were observed to be about the same for 125I model 6702 and model 6711 sources. The mean value of the interseed effect was 6% and the maximum was 12%. On the whole, the interseed effect reduces the dose at the periphery of the iodine implant by 6%.

Dosimetry on transverse axes of 125I and 192Ir interstitial brachytherapy sources.

Dose rates along the transverse axes of 125I model 6702, 125I model 6711 and 192Ir 0.2-mm steel sources for interstitial brachytherapy have been measured in a solid-water phantom for distances up to 10 cm using LiF thermoluminescent dosimeters (TLDs). Specific dose rate constants, the dose rates in water per unit source strength 1 cm along the perpendicular bisector of the source, are determined to be 0.90 +/- 0.03, 0.85 +/- 0.03, and 1.09 +/- 0.03 cGy h-1 U-1 for 125I model 6702, 125I model 6711 and 192Ir 0.2-mm steel sources, respectively (1 U = unit of air kerma strength = 1 microGy m2 h-1 = 1 cGy cm2 h-1). In older and obsolete units of source strength (i.e., mCi apparent), these are 1.14 +/- 0.03, 1.08 +/- 0.03, and 4.59 +/- 0.15 cGy h-1 mCi-1 (apparent). Currently accepted values of specific dose rate constant for 125I sources are up to 20% higher than our measured values which are in good agreement with the results of our Monte Carlo simulations. But for 192Ir there is good agreement between our measured value of the specific dose rate constant and currently accepted values. The radial dose function for 125I model 6702 is found to be consistently larger than that for 125I model 6711, with an increasing difference as the distance from the source increases. Our measured values for the radial dose function for 125I sources are in good agreement with the results of our Monte Carlo simulation as well as the measured values of Schell et al. [Int. J. Radiat. Oncol. Biol. Phys. 13, 795-799 (1987)] for model 6702 and Ling et al.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of solid phantoms with water for dosimetry of 125I brachytherapy sources.

Dosimetry of brachytherapy sources is critically dependent on precise measurement of the source-detector distance. A solid phantom can be precisely machined and hence distances can be accurately determined. In this work LiF thermoluminescent chips are used for absolute dose rate measurements in solid water, polymethylmethacrylate (PMMA), and polystyrene. These media are examined for their suitability in the dosimetry of 125I by comparing depth doses in each phantom. Measurements and Monte Carlo calculations show that solid water is equivalent to water for the dosimetry of 125I seeds, however, polystyrene and PMMA are not equivalent to water. Also, photon energy spectra for several depths in each phantom material have been calculated and are used to determine average photon energy and mass energy absorption coefficients as a function of depth.

Code of practice for brachytherapy physics: report of the AAPM Radiation Therapy Committee Task Group No. 56. American Association of Physicists in Medicine.

Recommendations of the American Association of Physicists in Medicine (AAPM) for the practice of brachytherapy physics are presented. These guidelines were prepared by a task group of the AAPM Radiation Therapy Committee and have been reviewed and approved by the AAPM Science Council.

Collection efficiency of an ionisation chamber in a pulsed swept beam: chamber size effects.

Boag's theory for the collection efficiency of a small ionisation chamber in a pulsed swept beam is generalised by taking chamber size into account. The collection efficiency is given in terms of the chamber radius, the Gaussian scale constant of the stationary beam, and the maximum distance between beam and chamber centres. It is shown that, for cases of practical interest, collection efficiency is independent of chamber size.

Collection efficiency of an ionisation chamber in a pulsed swept beam: collimator scatter effects.

The expressions for calculating the collection efficiency of an ionisation chamber in a pulsed swept beam, as derived by Boag, explicitly assume that the stationary beam has a Gaussian radial intensity distribution and implicitly assumes that this distribution, upon being swept, is unperturbed by extra-phantom scatter. Consequently a hyperbolic pulse-size distribution is expected on the central axis. Measurements of pulse-size distributions at the isocentre of a Sagittaire accelerator for small collimator settings yield hyperbolic distributions in accord with this model. However, measurements of large-field pulse-size distributions yield markedly non-hyperbolic distributions for electron energies from 7 to 32 MeV. It is shown that application of the model in such cases might result in significant errors depending on the inherent collection efficiency of the chamber.

Influence of the variation of energy spectra with depth in the dosimetry of 192Ir using LiF TLD.

Absolute dose measurements around low activity seeds used in brachytherapy are difficult to perform with ionisation chambers. The physical size of the chamber does not allow good resolution close to the seeds and the ionisation current generated is very low. Small thermoluminescent dosimeters (TLDs) overcome these problems but the energy dependence of their response should be considered. In this work, dose in polystyrene was measured at several distances from the high activity 192Ir source (370 GBq) of a remote afterloading device using an ionisation chamber and LiF TLD chips. These data show that over a range of 1-10 cm from the source the sensitivity of LiF varies by up to 8.5%. This is attributed to the higher response of LiF to the lower photon energies, and to the shift of the photon spectrum to lower energies with increasing depth. The sensitivity of LiF to 192Ir was also calculated by weighting the energy-dependent response of LiF by the Monte Carlo calculated photon spectra. The calculations give a similar change in sensitivity with distance from the source.

Maternal health services--the developing world.

Women in developing nations run 100 to 200 times the risk of dying in pregnancy and childbirth compared to women in affluent countries. The vast majority of these deaths are preventable. We examine 3 models of health development for their potential impact on maternal mortality. Although universal primary maternal health care would be ideal, resource limitations render its implementation impractical in many regions. The nonavailability of transport and referral services limits the impact of community-based programs. Selective primary health interventions have some role, but more costly and complex services are required to deal with hemorrhage, the complications of illegal abortion and to provide operative deliveries. Public health workers should focus on intersectoral programs at the community level which mobilize women around health issues. Sustainable development has the greatest potential to produce lasting changes in the risks of childbearing.

Computer applications to radioactive-seed: brain-tumor implants.

Malignant brain tumors, in general, and anaplastic astrocytoma and glioblastoma multiforme in particular, have been highly refractory to conventional treatments including surgery, chemotherapy and external-beam irradiation. Although better local control can be achieved with high-dose, external beam irradiation, necrosis of normal brain tissue reduces the quality of life and survival. In order to localize the radiation dose given to brain tumors, the temporary implantation of 125I and 192Ir seeds is undergoing clinical trials at several medical centers. Computers play a key role in this treatment modality: in addition to being essential for image reconstruction of CT scans, a computer is used to reconstruct a tumor volume from outlined regions on individual cuts; a programable calculator is used in conjunction with a stereotaxic head holder to obtain the coordinates of the radioactive seeds; a radiation-therapy, treatment-planning computer is used to optimize the radioactive-seed positions and strengths, and to generate the corresponding dose distribution.

A simple eye-lens shielding technique compatible with independent jaws of a linear accelerator.

A technique, compatible with accelerators having independent collimators, is presented, which greatly simplifies alignment of pencil eye-lens shields. The patient is placed so that the eye to be shielded is on the central axis of the beam and the accelerator's collimators are adjusted independently to define the field. A divergent lead shield 14 cm long is suspended from a wire that hangs along the central axis from a blocking tray in its usual location. The suspension length is variable and adjusted on the first day so that the shield is about 1 cm above the patient's eye. On subsequent treatment days, the wire is simply put in place on the tray with no further adjustment required. This technique reduces setup time and makes the shield positioning highly reproducible.