Average TCP Research Articles

Prostate Cancer Volumetric Arc Therapy (VMAT) Analysis

Aim: The purpose of this study was to derive radiobiological parameters from the dose volume histogram of patients that undergone prostate cancer radiotherapy via the VMAT technique. Material and Methods: A total of twenty-two cases of prostate cancer of 70.2 and 81 Gy were selected for this study. Radiobiological parameters were evaluated by the Poisson equation for the tumor and LKB model for organs at risk. Results: For prostate tumor, the average TCP was 96.28, 86.45, 68.57 for α/β of 1.2, 3.0, and 10, respectively. The average EUD was 37.98 Gy, 59.23 Gy, 21.19 Gy, 20.65 Gy, 16.32 Gy, and 21.87 Gy for bladder, rectum, right femoral head, left femoral head, small bowel, and large bowel respectively. The average NTCP was 7.6 % for the rectum and negligible for other organs at risk. Conclusion: NTCP for critical organs and TCP for prostate cancer can be determined via dose volume histogram.

Stereotactic body radiotherapy optimization to reduce the risk of carotid blowout syndrome using normal tissue complication probability objectives.

PurposeTo determine the possibility of further improving clinical stereotactic body radiotherapy (SBRT) plans using normal tissue complication probability (NTCP) objectives in order to minimize the risk for carotid blowout syndrome (CBOS).Methods10 patients with inoperable locally recurrent head and neck cancer, who underwent SBRT using CyberKnife were analyzed. For each patient, three treatment plans were examined: (1) cone‐based without delineation of the ipsilateral internal carotid (clinical plan used to treat the patients); (2) cone‐based with the carotid retrospectively delineated and spared; and (3) Iris‐based with carotid sparing. The dose–volume histograms of the target and primary organs at risk were calculated. The three sets of plans were compared based on dosimetric and TCP/NTCP (tumor control and normal tissue complication probabilities) metrics. For the NTCP values of carotid, the relative seriality model was used with the following parameters: D 50 = 40 Gy, γ = 0.75, and s = 1.0.ResultsAcross the 10 patient plans, the average TCP did not significantly change when the plans were re‐optimized to spare the carotid. The estimated risk of CBOS was significantly decreased in the re‐optimized plans, by 14.9% ± 7.4% for the cone‐based plans and 17.7% ± 7.1% for the iris‐based plans (p = 0.002 for both). The iris‐based plans had significant (p = 0.02) reduced CBOS risk and delivery time (20.1% ± 7.4% time reduction, p = 0.002) compared to the cone‐based plans.ConclusionA significant improvement in the quality of the clinical plans could be achieved through the delineation of the internal carotids and the use of more modern treatment delivery modalities. In this way, for the same target coverage, a significant reduction in the risk of CBOS could be achieved. The range of risk reduction varied depending on the proximity of carotid artery to the target.

ОЦЕНКА ЭФФЕКТИВНОСТИ ЛУЧЕВОЙ ТЕРАПИИ РАКА ГОЛОВЫ-ШЕИ НА ОСНОВЕ МОДЕЛИ ЛОКАЛЬНОГО КОНТРОЛЯ ОПУХОЛИ

Purpose: Evaluation of the expected effectiveness of radiation therapy based on models of the local tumor control probability (Tumor Control Probability – TCP) for the head-neck cancer. 
 Material and methods: The study used data from 11 patients with locally advanced head-neck cancer (larynx, oropharynx, and oral cavity). For each patient two dosimetric treatment plans have been prepared: SIB-VMAT (70 Gy per tumor, 50 Gy per lymph nodes, 25 fractions) and SEQ-VMAT (70 Gy per tumor, 50 Gy per lymph nodes, 35 fractions). The developed plans were analyzed using A. Niemierko's TCP model with parameters obtained by B. Maciejewski (TCD50 = 70.26 Gy with a 49-day total treatment time), taking into account the dose–volume histograms and the total treatment time.
 Results: The developed plans ensured a high level of coverage (98–98 %) of the Clinical treatment volume (CTV) in all but one patient. The average TCP SIB-VMAT is 99.9 % due to the very short total treatment time. The average TCP for SEQ-VMAT is 61.0%. For one patient, both SIB-VMAT and SEQ-VMAT showed zero expected efficacy due to 95–95 % CTV coverage.
 Conclusion: The use of TCP model allows analyzing personalized treatment plans for patients and developing adaptive treatment regimens with an increase in the total dose, dose per fraction, and a decrease in the total treatment time.

Biological and dosimetric effect of the number of beams for radiotherapy plans of breast cancer patients. Z. Mansour1, Ehab M. Attalla 2, Ibrahim A. Awad 3 M.I. Abdel Hamid 4 and A. Sarhan 5

Aim: To evaluate the biologic differences in treatment plans, the dosimetric outcome with different number of beams on 3D conformal radiotherapy for breast cancer patients as well as evaluate the outcome of plans with more number of fields compared with less number of fields for irradiation of breast cancer patients then determine the optimum plan through dosimetric and biological parameters. The study included 13 of the female breast cancer patients who were irradiated, after surgery. The tumor and the organs at risk were delineated. Then for every patient two plans of increasing and decreasing the number of beams were done. The DVH of each plan was analyzed based on the calculating the TCP and NTCP by MATLAB and calculating the dosemetrical parameters such as CI and HI. Results: All the results representing the following parameters V105% , V95% ,V110%, D mean , D max CI, HI and D5% are the same in both more and less number of beams . All the results also showed that the average TCP% of PTV of the plans that contains more numbers of beams is 54.27 % while in other plans 54.65%. Mean± SEM of group (a) is 54.27 ± 1.121 while in group b is 54.65 ± 0.9297 N=13. This show that there is no significance in the group (a) (increasing numbers of beams) versus group (b) (less numbers of beam) means that the tumor control by increasing the number of beams is nearly the same as decreasing the number, b value = ( 0.7964). This occurred in the rest of the parametersRadio oncologist and medical physicist must make a decision about treatment though the accurate values of TCP and NTCP and this achieved via testing plans by MATLAP program not by the number of beams.

Dosimetric Impact of Interfractional Variations in Prostate Cancer Radiotherapy-Implications for Imaging Frequency and Treatment Adaptation.

Background and purpose: To analyze deviations of the applied from the planned doses on a voxel-by-voxel basis for definitive prostate cancer radiotherapy depending on anatomic variations and imaging frequency.Materials and methods: Daily in-room CT imaging was performed in treatment position for 10 patients with prostate cancer undergoing intensity-modulated radiotherapy (340 fraction CTs). Applied fraction doses were recalculated on daily images, and voxel-wise dose accumulation was performed using a deformable registration algorithm. For weekly imaging, weekly position correction vectors were derived and used to rigidly register daily scans of that week to the planning CT scan prior to dose accumulation. Applied and prescribed doses were compared in dependence of the imaging frequency, and derived TCP and NTCP values were calculated.Results: Daily CT-based repositioning resulted in non-significant deviations of all analyzed dose-volume, conformity and uniformity parameters to the CTV, bladder and rectum irrespective of anatomic changes. Derived average TCP values were comparable, and NTCP values for the applied doses to the bladder and rectum did not significantly deviate from the planned values. For weekly imaging, the applied D2 to the CTV, rectum and bladder significantly varied from the planned doses, and the CTV conformity index and D98 decreased. While TCP values were comparable, the NTCP for the bladder erroneously appeared reduced for weekly repositioning.Conclusions: Based on daily diagnostic quality CT imaging and voxel-wise dose accumulation, we demonstrated for the first time that daily, but not weekly imaging resulted in only negligible deviations of the applied from the planned doses for prostate intensity-modulated radiotherapy. Therefore, weekly imaging may not be adequately reliable for adaptive treatment delivery techniques for prostate. This work will contribute to devising adaptive re-planning strategies for prostate radiotherapy.

Diagnosing Observed Stratospheric Water Vapor Relationships to the Cold Point Tropical Tropopause

AbstractDehydration at the tropical cold point tropopause primarily controls the entry value of water vapor to the stratosphere, with additional (uncertain) contributions from subtropical monsoonal circulations and extreme deep convection. Here we quantify the links of observed stratospheric water vapor with near‐equatorial cold point temperature (TCP), based on interannual variations of monthly zonal averages over the period 1993–2017. Water vapor observations are from combined Halogen Occultation Experiment and Aura Microwave Limb Sounder satellite measurements, and cold point temperatures are from high quality radiosondes and GPS satellite data. Interannual water vapor anomalies are highly correlated with TCP, and coherent patterns can be traced in space and time away from the tropical tropopause to quantify transport in the Brewer‐Dobson circulation, including diagnosing seasonal changes in circulation. Lagged regressions with TCP are used to reconstruct water vapor variations directly tied to the cold point, and these reconstructions account for a majority of the observed interannual water vapor variability in the lower to middle stratosphere over most of the globe. Small systematic differences from observed water vapor can identify processes not tied to zonal average TCP, and/or possible uncertainties in the satellite measurements.

On the Split-TCP Performance over Real 4G LTE and 3G Wireless Networks

The global mobile traffic is growing exponentially, and currently more than 90 percent of the internet traffic depends on TCP for reliable transmission. However, it is well known that TCP performs quite poorly over unreliable wireless networks, while its dynamic TCP flow control is sensitive to congestion events and tends to underutilize the available network capacity. Despite these known limitations, the industry believes that significant network performance enhancement can be achieved through TCP optimization, and in particular through solutions centered on Split-TCP. In this article we share a sample of TCP throughput performance measurements after implementing Split-TCP on commercial 4G LTE and 3G networks. Experimental results show that Split-TCP provides average TCP throughput gains on the order of 60 percent over a 4G LTE network and on the order of 5 percent over a 3G network. Furthermore, TCP throughput gains superior to 200 percent were measured for individual TCP connections over the 4G LTE network. We expect such throughput gains to be even greater when advanced radio technologies, such as 5G, are deployed. For these reasons, Split-TCP has the potential to be widely deployed in both current and next generation networks.

Cross-layer TCP performance analysis in IEEE 802.11 vehicular environments

In this paper we provide a performance analysis of TCP in IEEE 802.11 vehicular environments for different well-known TCP versions, such as Tahoe, Reno, New Reno, Vegas, and Sack. The parameters of interest from the TCP side are the number of Duplicate Acknowledgements - DupAck, and the number of Delayed Acknowledgements - DelAck, while on the wireless network side the analyzed parameter is the interface queue - IFQ. We have made the analysis for the worst-case distance scenario for single-hop and worst-case multihop vehicular environments. The results show that the number of wireless hops in vehicular environments significantly reduces the TCP throughput. The best average performances considering all scenarios were obtained for TCP Vegas. However, the results show that the interface queue at wireless nodes should be at least five packets or more. On the other side, due to shorter distances in the vehicular wireless network, results show possible flexibility of using different values for the DupAck without degradation of the TCP throughput. On the other side, the introduction of the DelAck parameter provides enhancement in the average TCP throughput for all TCP versions.

SU‐E‐T‐453: PET Image‐Guided Dose Escalation Study for Cervical Cancer Patients Receiving HDR Brachytherapy

Purpose: To study the feasibility and benefit of boosting dose to active regions of cervical cancer identified by positron emission tomography (PET) imaging during brachytherapy. Methods: 5 patients imaged with MRI and PET/CT were retrospectively studied. An experienced physician contoured the GTV and HR‐CTV using the MRI scan alone, and then contoured the region of PET‐hot activity using a PET/CT image. The MRI and PET/CT images where then fused, and a PET‐HR‐CTV volume was constructed from the union of the HR‐CTV and PET‐GTV.Each patient had been treated using a Syed applicator with 4–20 needles. Two new plans were optimized using Oncentra's IPSA package with the following objectives: 1) a “PET‐blindA plan in which the HR‐CTV‐D90 received the prescription dose (Rx), and 2) a plan where the PET‐HR‐CTV D90 received Rx and the PET‐GTV D90 was boosted to 1.5 times Rx. In both cases the EQD2 D2cc dose to the bladder and rectum were kept below the GEC‐ESTRO guidelines of 90 and 75 Gy, including the contribution from external beam therapy. Dose‐volume parameters and TCP biological predictors were calculated for the PET‐target volumes in both plans. Results: Significant differences were seen between the non‐PET and PET‐GTV (average size difference 21.8cc, average overlap 50%). In the unboosted plans, the average percent D90 to the PET‐GTV was 171%, whereas in the boosted plans it increased to 223%. Average TCP, calculated using risk‐scaled parameters for IR‐, HR‐CTV and GTV, increased from 76% to 84% with the boost to the PET positive region. Conclusion: PET imaging modality has the potential to identify residual cervical cancer otherwise not visible on MRI and CT studies. This work has found that MRI target contouring regularly does not include regions of PET activity, and PET‐based planning can lead to improved outcome predictions over plans using MRI alone. Funding support partly provided by a Varian research grant.

다중 경로 라우팅을 지원하는 IEEE 802.11s기반 메쉬 라우터 구현

본 논문에서는 다중 경로 라우팅을 지원하는 IEEE 802.11s기반 메쉬 라우터를 구현하였다. IEEE 802.11s에는 현재 다중 경로 라우팅 알고리즘이 정의되어 있지 않다. 따라서 본 논문에서는 IEEE 802.11s에 정의되어있는 단일 경로 라우팅 알고리즘뿐만 아니라 AOMDV기반 다중 경로 라우팅 알고리즘도 구현하였다. 또한 이 메쉬 라우터는 싱글 채널 싱글인터페이스 사용 시, 홉의 수가 증가함에 따라 송수신 대역폭이 급격히 감소하는 현상을 방지하기 위하여 멀티 채널 멀티 인터페이스를 지원하도록 구현되었다. 우리는 이 메쉬 라우터를 이용하여 테스트베드를 구축하였으며, 이를 통해 이 메쉬 라우터의 대역폭 성능, 실시간 비디오 스트리밍 서비스 성능을 검증하였고, 단일 경로 라우팅과 다중 경로 라우팅의 성능을 비교 검증하였다. 이 메쉬 라우터의 평균 TCP 대역폭은 5홉 기준 23.8Mbps이고, 평균 latency는 2.4ms이다. 이 메쉬 라우터의 평균 지터는 5홉 기준 0.547ms이다. 또한 이 메쉬 라우터는 다중 경로 라우팅을 사용함으로써 평균 12.73%의 경로 복구 시간을 단축하였다. This paper focuses in the implementation of mesh router supporting multi-path routing based on IEEE 802.11s. In HWMP of IEEE 802.11s, the single path routing just was defined. So, in this work, we implemented not only the single path routing defined in IEEE 802.11s, but also a multipath routing based on AOMDV which extended the standard. A multi-channel multi-interface technology that can transmit and receive simultaneously and lower bandwidth reduction caused by interferences than a single-channel single-interface was implemented in our mesh router. We also developed an outdoor test bed with the mesh routers. The bandwidth of the mesh router and a real-time video streaming service were verified using the test bed. And, the single path and multipath routing algorithms are also compared. In this test bed, The average TCP bandwidth was 23.77 Mbps and the latency was 2.4 ms in five hops. The test bed could service real-time streaming with an average jitter of 0.547 ms in five hops. The mesh router that used the multipath routing path reduced the path recovery time by 12.73% on average.

Router Buffer Sizing for TCP Traffic and the Role of the Output/Input Capacity Ratio

The issue of router buffer sizing is still open and significant. Previous work either considers open-loop traffic or only analyzes persistent TCP flows. This paper differs in two ways. First, it considers the more realistic case of nonpersistent TCP flows with heavy-tailed size distribution. Second, instead of only looking at link metrics, it focuses on the impact of buffer sizing on TCP performance. Specifically, our goal is to find the buffer size that maximizes the average per-flow TCP throughput. Through a combination of testbed experiments, simulation, and analysis, we reach the following conclusions. The output/input capacity ratio at a network link largely determines the required buffer size. If that ratio is larger than 1, the loss rate drops exponentially with the buffer size and the optimal buffer size is close to 0. Otherwise, if the output/input capacity ratio is lower than 1, the loss rate follows a power-law reduction with the buffer size and significant buffering is needed, especially with TCP flows that are in congestion avoidance. Smaller transfers, which are mostly in slow-start, require significantly smaller buffers. We conclude by revisiting the ongoing debate on ldquosmall versus largerdquo buffers from a new perspective.

Towards a Bufferless Optical Internet

This paper investigates the relationship between buffer size and long-term average TCP performance in dense wavelength division multiplexing (DWDM) networks. By investigating TCP NewReno, we demonstrate that buffer requirements are related to the number of wavelength channels at a bottleneck. With sufficient wavelengths, high throughput can be obtained with a buffer of one packet per channel; furthermore, there may be situations where an entirely bufferless optical packet switching (OPS) will become feasible. For this study, we develop new evaluation tools. First, we propose a method based on a two-part analytical model, with a new ¿open loop¿ component which approximates packet discarding in a bottleneck DWDM switch, and a ¿closed loop¿ fixed-point which reflects the impact of TCP. This analytical method provides accurate and scalable approximations of throughput and packet loss rate that can be used as part of a tool for DWDM network and switch design. Second, we propose an extrapolation technique to allow simulation of TCP over long ultra-high bit rate links, avoiding the intractable processing and memory requirements of direct simulation. This extrapolation technique enables us to validate the analytical model for arbitrarily high bit rate scenarios.

A MAC/PHY cross-layer design for efficient ARQ protocols

In many wireless data systems, automatic repeat request (ARQ) and hybrid automatic repeat request (HARQ) work independently. In this paper, we introduce a new ARQ feedback scheme called Cross-Layer ARQ (CL-ARQ), where ARQ closely interoperates with HARQ by making use of the acknowledgement of HARQ internally. By doing so, CL-ARQ not only removes the overhead for ARQ acknowledgement messages, but also improves the average delivery delay and TCP throughput. Especially, when the entities in charge of HARQ and ARQ are located far apart geographically, CL-ARQ remarkably outperforms the legacy scheme.

Machine-learnt versus analytical models of TCP throughput

We first study the accuracy of two well-known analytical models of the average throughput of long-term TCP flows, namely the so-called SQRT and PFTK models, and show that these models are far from being accurate in general. Our simulations, based on a large set of long-term TCP sessions, show that 70% of their predictions exceed the boundaries of TCP-Friendliness, thus questioning their use in the design of new TCP-Friendly transport protocols. We then investigate the reasons of this inaccuracy, and show that it is largely due to the lack of discrimination between the two packet loss detection methods used by TCP, namely by triple duplicate acknowledgements or by timeout expirations. We then apply various machine learning techniques to infer new models of the average TCP throughput. We show that they are more accurate than the SQRT and PFTK models, even without the above discrimination, and are further improved when we allow the machine-learnt models to distinguish the two loss detection techniques. Although our models are not analytical formulas, they can be plugged in transport protocols to make them TCP-Friendly. Our results also suggest that analytical models of the TCP throughput should certainly benefit from the incorporation of the timeout loss rate.

SU‐FF‐J‐66: Iso‐NTCP Dose Escalation with Image‐Guided Adaptive Radiation Therapy (IGART) for Localized Carcinoma of the Prostate

Purpose: To evaluate the efficacy of various image‐guided target localization techniques to assist in the safe dose escalation for prostate cancer radiation therapy in the presence of geometric uncertainties. Method and Materials: Five prostate cancer patients were analyzed, retrospectively. All patients were planned with an 18MV six‐field conformal technique with a 10 mm margin and an initial prescription dose of 70 Gy in 35 fractions. For the dose escalation study, the prescription dose was increased from 50 Gy in 2 Gy increments until the rectum normal tissue complication probability (NTCP) reached the level equal to that of the plan NTCP (i.e., iso‐NTCP). The target localization techniques simulated were (1) laser alignment to external tattoo marks, (2) alignment to bony landmarks with daily portal images, and (3) alignment to the clinical target volume (CTV) with daily CT imaging. Techniques (1) and (3) were re‐simulated with a reduced margin of 5 mm to investigate further dose escalation. Results: The selection of the target localization technique was less critical on the treatment outcome when 10 mm margin was used. Reducing the margin size from 10 to 5 mm effectively decreased the NTCP by ∼60 % for all patients. For iso‐NTCP dose escalation, to our surprise, the average dose and TCP gain for the five patients were largest with the external tattoo technique (6.4 Gy and 7.5 %, respectively) followed by the daily CTV and the bony landmarks. The variability in gain across the five patients, however, was also largest with the tattoo registration technique and smallest with the daily CTV technique. Conclusion: Based on these data, the best dose escalation strategy is to combine margin reduction (for increased normal tissue sparing) with the use of the daily CTV technique to localize the target volume (for consistent dosimetric coverage and escalation).

Potential outcomes of modalities and techniques in radiotherapy for patients with hypopharyngeal carcinoma

Background and purpose To determine potential improvements in treatment outcome for patients with hypopharyngeal carcinoma, T4N0M0, using proton and intensity modulated photon radiotherapy (IMRT) compared to a standard 3D conformal radiotherapy treatment (3D-CRT) in terms of local tumour control probability, TCP, and normal tissue complication probability (NTCP) for the spinal cord and the parotid glands using. Patients and methods Using the three-dimensional treatment-planning system, Helax-TMS™, 5 patients were planned with protons, IMRT, and 3D-CRT plans. The prescribed dose used was 30 fractions×2.39 Gy for the protons and IMRT and 35 fractions×2.00 Gy for 3D-CRT. The treatment plans were evaluated using dose volume data and dose response models were used to calculate TCP and NTCP. The target volumes were delineated to spare the parotid glands. A dose escalation was made for protons and IMRT using NTCP constraints to the spinal cord. Results On average, protons and IMRT increase TCP by 17% compared to 3D-CRT. For the spinal cord NTCP values are zero for all methods and patients. Average NTCP values for the parotid glands were >90% for 3D-CRT and significantly lower for protons and IMRT varying from 43–65%. The average parotid gland dose was 33 Gy for the protons, 38 Gy for IMRT and 48 Gy for 3D-CRT. Conclusions Protons and IMRT gave a significant TCP increase compared to 3D-CRT while no significant difference between protons and IMRT was found. Protons generally show lower non-target tissue doses, which indicates a possibility for further dose escalation. Large individual dose differences between protons and IMRT for parotid glands indicate that some patients may benefit more from protons and others from IMRT.

Modeling short-lived TCP connections with open multiclass queuing networks

In this paper we develop an open multiclass queuing network model to describe the behavior of short-lived TCP connections sharing a common IP network. The queuing network model is paired with a simple model of the IP network, and the two models are solved through an iterative procedure. The combined models need as inputs only the primitive network parameters, and they produce estimates of the packet loss probability, the round trip time, the TCP connection throughput, and of the average TCP connection completion time (that is, of the average time necessary to transfer a file with given size over a TCP connection). We derive models for both TCP-Tahoe and TCP-NewReno. The Tahoe model is presented in detail, while the NewReno model is presented describing differences with respect to Tahoe. Results are shown for both models. The analytical performance predictions are validated against detailed simulation experiments in realistic networking scenarios, proving that the proposed modeling approach is accurate.

Neurologic Function among Termiticide Applicators Exposed to Chlorpyrifos

Chlorpyrifos is a moderately toxic organophosphate pesticide. Houses and lawns in the United States receive a total of approximately 20 million annual chlorpyrifos treatments, and 82% of U.S. adults have detectable levels of a chlorpyrifos metabolite (3,5, 6-trichloro-2-pyridinol; TCP) in the urine. The U.S. Environmental Protection Agency has estimated that there are 5,000 yearly reported cases of accidental chlorpyrifos poisoning, and approximately one-fourth of these cases exhibit symptoms. Organophosphates affect the nervous system, but there are few epidemiologic data on chlorpyrifos neurotoxicity. We studied neurologic function in 191 current and former termiticide applicators who had an average of 2.4 years applying chlorpyrifos and 2.5 years applying other pesticides, and we compared them to 189 nonexposed controls. The average urinary TCP level for 65 recently exposed applicators was 629.5 microg/L, as compared to 4.5 microg/L for the general U.S. population. The exposed group did not differ significantly from the nonexposed group for any test in the clinical examination. Few significant differences were found in nerve conduction velocity, arm/hand tremor, vibrotactile sensitivity, vision, smell, visual/motor skills, or neurobehavioral skills. The exposed group did not perform as well as the nonexposed group in pegboard turning tests and some postural sway tests. The exposed subjects also reported significantly more symptoms, including memory problems, emotional states, fatigue, and loss of muscle strength; our more quantitative tests may not have been adequate to detect these symptoms. Eight men who reported past chlorpyrifos poisoning had a pattern of low performance on a number of tests, which is consistent with prior reports of chronic effects of organophosphate poisoning. Overall, the lack of exposure effects on the clinical examination was reassuring. The findings for self-reported symptoms raise some concern, as does the finding of low performance for those reporting prior poisoning. Although this was a relatively large study based on a well-defined target population, the workers we studied may not be representative of all exposed workers, and caution should be exercised in generalizing our results.

Neurologic function among termiticide applicators exposed to chlorpyrifos.

Chlorpyrifos is a moderately toxic organophosphate pesticide. Houses and lawns in the United States receive a total of approximately 20 million annual chlorpyrifos treatments, and 82% of U.S. adults have detectable levels of a chlorpyrifos metabolite (3,5, 6-trichloro-2-pyridinol; TCP) in the urine. The U.S. Environmental Protection Agency has estimated that there are 5,000 yearly reported cases of accidental chlorpyrifos poisoning, and approximately one-fourth of these cases exhibit symptoms. Organophosphates affect the nervous system, but there are few epidemiologic data on chlorpyrifos neurotoxicity. We studied neurologic function in 191 current and former termiticide applicators who had an average of 2.4 years applying chlorpyrifos and 2.5 years applying other pesticides, and we compared them to 189 nonexposed controls. The average urinary TCP level for 65 recently exposed applicators was 629.5 microg/L, as compared to 4.5 microg/L for the general U.S. population. The exposed group did not differ significantly from the nonexposed group for any test in the clinical examination. Few significant differences were found in nerve conduction velocity, arm/hand tremor, vibrotactile sensitivity, vision, smell, visual/motor skills, or neurobehavioral skills. The exposed group did not perform as well as the nonexposed group in pegboard turning tests and some postural sway tests. The exposed subjects also reported significantly more symptoms, including memory problems, emotional states, fatigue, and loss of muscle strength; our more quantitative tests may not have been adequate to detect these symptoms. Eight men who reported past chlorpyrifos poisoning had a pattern of low performance on a number of tests, which is consistent with prior reports of chronic effects of organophosphate poisoning. Overall, the lack of exposure effects on the clinical examination was reassuring. The findings for self-reported symptoms raise some concern, as does the finding of low performance for those reporting prior poisoning. Although this was a relatively large study based on a well-defined target population, the workers we studied may not be representative of all exposed workers, and caution should be exercised in generalizing our results.