The U.S. Department of Agriculture‐Agricultural Research Service's (ARS) Experimental Watershed Network grew from Dust Bowl era efforts of the Soil Conservation Service in the mid‐1930s with the ...establishment of small experimental watersheds. In the 1950s, five watershed research centers with intensively instrumented watersheds at the scale of 100 to 700 km2 were established. Primary network research objectives were to quantify on‐site and downstream effects of conservation practices and develop rainfall‐runoff relationships for design of water conservation structures. With passage of the Clean Water Act in 1972, research objectives have evolved to add a variety of observations relevant to the water quality issues. Many of the watersheds within the network have served, and continue to serve, as core validation sites for satellite sensors. As a result of the network's long history and intensive monitoring, coupled with mission‐driven research, a deep knowledge base of watershed processes has been developed. This has led to the extensive development and validation of numerous watershed models that are in widespread use today. The visionary investments in building and maintaining this network and associated scientific investigations for more than half a century have not only resulted in numerous high‐impact research accomplishments but also a wide array of accomplishments that directly benefit society. The ARS Experimental Watersheds formed the core of the Conservation Effects Assessment Project (CEAP) as well as the recently established Long‐Term Agroecosystem Research (LTAR) network. LTAR will expand the mission of the ARS Watersheds Network to include agricultural intensification, maintaining or improving ecosystem services while enhancing rural prosperity.
Plain Language Summary
Understanding how watersheds respond to precipitation, agricultural management, and other land use changes is critical to maintaining clean water, viable food production, and predicting flood hazards and soil loss from erosion. To understand watershed responses and processes, the Soil Conservation Service, followed by the USDA‐Agricultural Research Service, established experimental watersheds across the United States. These watersheds were instrumented with equipment to make detailed measurements of weather and watershed response. Experiments were designed to observe how runoff, erosion, and water quality might change with changing agricultural practices to change agricultural practices and observe how runoff, erosion, and water quality would change. From these experiments, predictive computer models were developed and tested with data from the watersheds. The watershed observations, the process knowledge developed, and associated research and models have resulted in numerous societal benefits. Billions of dollars of conservation measures and drainage infrastructure investment were guided by these models and methods. The ARS Experimental Watersheds formed the core of the recently established Long‐Term Agroecosystem Research (LTAR) network. LTAR will expand the mission of the ARS Watershed Network to include producing more food on the same amout of land, maintaining or improving ecosystem services (clean water and air, healthy soils, etc.) while enhancing rural prosperity.
Key Points
Agricultural Research Service's Experimental Watersheds and associated mission‐driven research have operated for over half a century
High‐resolution watershed observations and experimentation have produced a deep watershed process knowledge and database
The research network has been critical to developing and validating numerous watershed models and management methods, resulting in extensive societal benefits
The objective of this descriptive analysis of a large cohort of patients with Langerhans cell histiocytosis (LCH) was to add to the understanding of the natural history, management, and outcome of ...this disease.
Three hundred fourteen Mayo Clinic patients with histologically proven LCH were categorized into those patients with multisystem disease and those patients with single system disease. Clinical features, treatment, and outcome were determined from the case history notes and tumor registry correspondence. Treatment included chemotherapy, radiotherapy, and surgical excision. The end points were disease free survival, active disease, or death. The median time of follow-up was 4 years (range, 1 month to 47.5 years).
The age of the patients ranged from 2 months to 83 years. Of the 314 patients, there were 28 deaths. Multisystemic LCH was found in 96 patients, 25 of whom had continuing active disease after treatment. Isolated bone LCH lesions were observed in 114 of the 314 patients, 111 of whom (97%) achieved disease free survival after treatment. The most common sites of osseous LCH were the skull and proximal femur. Of the 87 patients with isolated pulmonary involvement, only 3 were nonsmokers. After treatment with corticosteroids (+/- cyclophosphamide or busulphan), 74 patients achieved disease free survival, but 10 patients died. Pituitary-thalamic axis LCH, characterized by diabetes insipidus, was found in 44 patients. After treatment, 30 of these patients had disease free survival, but all required long term hormone replacement with desmopressin acetate. Lymph node involvement was found in 21 patients, and mucocutaneous involvement was found in 77 patients.
Patients with isolated bone LCH lesions have the best prognosis compared with patients with LCH involvement of other systems. By contrast, 20% of patients with multisystem involvement have a progressive disease course despite treatment. The identification of prognostic indicators to facilitate appropriate treatment and long term follow-up surveillance is recommended.
To determine local control (LC) and complication rates for patients with intracranial meningiomas who underwent radiosurgery.
One hundred ninety consecutive patients with 206 meningiomas underwent ...radiosurgery between 1990 and 1998. One hundred forty-seven tumors (77%) involved the cranial base. The median age at the time of radiosurgery was 58 years (range, 20-90 yr). There were 126 female patients (66%). One hundred twelve patients (59%) had undergone one or more previous operations (median, 1; range, 1-5). Twenty-two patients (12%) had either atypical (n = 13) or malignant (n = 9) tumors. The median prescription isodose volume was 8.2 cm(3) (range, 0.5-50.5 cm(3)), and the median tumor margin dose was 16 Gy (range, 12-36 Gy). The median imaging and clinical follow-up periods were 40 and 47 months, respectively.
Overall survival rates for the entire cohort at 5 and 7 years were 82 and 82%, respectively; cause-specific survival rates at 5 and 7 years were 94 and 92%, respectively. The cause-specific survival rates at 5 years for patients with benign, atypical, and malignant tumors were 100, 76, and 0%, respectively (P < 0.0001). The 5-year LC rate was 89%, with 114 tumors (56%) decreasing in size. LC rates were correlated with tumor histological features (P < 0.0001); patients with benign tumors exhibited a 5-year LC rate of 93%, compared with 68 and 0% for patients with atypical or malignant meningiomas, respectively. No correlation was observed between radiation dose and LC rate. Twenty-four patients (13%) experienced treatment-related complications, including cranial nerve deficits (8%), symptomatic parenchymal changes (3%), internal carotid artery stenosis (1%), and symptomatic cyst formation (1%). Only six patients (3%) exhibited decreases in functional status that were directly related to radiosurgery. Tumor volume, tumor margin dose, or previous radiotherapy was not associated with the development of radiation-related complications.
Radiosurgery is an effective management strategy for many patients with meningiomas. Patients with atypical or malignant tumors exhibit high recurrence rates despite the use of radiosurgery, and these patients continue to exhibit worse cause-specific survival rates despite aggressive treatment, including surgery, external-beam radiotherapy, and radiosurgery. Further study is needed to determine the tumor control and complication rates 10 years or more after meningioma radiosurgery.
The use of stereotactic radiosurgery to treat cerebral cavernous malformations (CMs) is controversial. To evaluate the efficacy and safety of CM radiosurgery, the authors reviewed the experience at ...the Mayo Clinic during the past 10 years.
Seventeen patients underwent radiosurgery for high-surgical-risk CMs in the following sites: thalamus/basal ganglia (four patients), brainstem (12 patients), and corpus callosum (one patient). All patients had experienced at least two documented hemorrhages before undergoing radiosurgery. Stereotactic magnetic resonance (MR) imaging was used for target localization in all cases. The median margin radiation dose was 18 Gy and the median maximum dose was 32 Gy. The median length of follow-up review following radiosurgery was 51 months. The annual hemorrhage rate during the 51 months preceding radiosurgery was 40.1%, compared with 8.8% in the first 2 years following radiosurgery and 2.9% thereafter. In 10 patients (59%) new neurological deficits developed that were associated with regions of increased signal on long-repetition time MR imaging performed a median of 8 months (range 5-16 months) after radiosurgery. Three patients recovered, giving the group a permanent radiation-related morbidity rate of 41%. Compared with 31 patients harboring arteriovenous malformations (AVMs) of sizes and in locations similar to those of the aforementioned CMs, who underwent radiosurgery during the same time period, the patients with CMs were more likely to experience radiation-related complications (any complication, 59% compared with 10%; p < 0.001; permanent complication, 41% compared with 10%; p = 0.02).
It is impossible to conclude that radiosurgery protects patients with CMs against future hemorrhage risk based on the available data, although it appears that some reduction in the bleeding rate occurs after a latency interval of several years. The risk of radiation-related complications after radiosurgery to treat CMs is greater than that found after radiosurgery in AVMs, even when adjusting for lesion size and location and for radiation dose.
Purpose: To better understand radiation complications of arteriovenous malformation (AVM) radiosurgery and factors affecting their resolution.
Methods and Materials: AVM patients (102/1255) who ...developed neurological sequelae after radiosurgery were studied. The median AVM marginal dose (D
min) was 19 Gy (range: 10–35). The median volume was 5.7 cc (range: 0.26–143). Median follow-up was 34 months (range: 9–140).
Results: Complications consisted of 80/102 patients with evidence of radiation injury to the brain parenchyma (7 also with cranial nerve deficits, 12 also with seizures, 5 with cyst formation), 12/102 patients with isolated cranial neuropathies, and 10/102 patients with only new or worsened seizures. Severity was classified as minimal in 39 patients, mild in 40, disabling in 21, and fatal in 2 patients. Symptoms resolved completely in 42 patients for an actuarial resolution rate of 54% ± 7% at 3 years post-onset. Multivariate analysis identified significantly greater symptom resolution in patients with no prior history of hemorrhage (
p = 0.01, 66% vs. 41%), and in patients with symptoms of minimal severity: headache or seizure as the only sequelae of radiosurgery (
p < 0.0001, 88% vs. 34%).
Conclusion: Late sequelae of radiosurgery manifest in varied ways. Further long-term studies of these problems are needed that take into account symptom severity and prior hemorrhage history.
To evaluate the risk of clinically significant radiation optic neuropathy (RON) for patients having stereotactic radiosurgery of benign tumors adjacent to the optic apparatus.
We reviewed the dose ...plans and clinical outcomes of 218 gamma knife procedures (215 patients) for tumors of the sellar and parasellar region (meningiomas,
n = 122; pituitary adenomas,
n = 89; craniopharyngiomas,
n = 7 patients). Previous surgery or radiation therapy was performed in 156 (66%) and 24 (11%) patients, respectively. Median follow-up was 40 months (range 4–115).
The median maximum radiation dose to the optic nerve was 10 Gy (range 0.4–16.0). Four patients (1.9%) developed RON at a median of 48 months after radiosurgery. All had prior surgery, and 3 of 4 had external beam radiotherapy (EBRT) in their management either before (
n = 2) or adjuvantly (
n = 1). The risk of developing a clinically significant RON was 1.1% for patients receiving 12 Gy or less. Patients receiving prior or concurrent EBRT had a greater risk of developing RON after radiosurgery (
p = 0.004).
RON occurred in less than 2% of our patients, despite the majority (73%) receiving more than 8 Gy to a short segment of the optic apparatus. Knowledge of the dose tolerance of these structures permits physicians to be more aggressive in treating patients with sellar or parasellar tumors, especially those with hormone-producing pituitary adenomas that appear to require higher doses to achieve biochemical remission.
A prospective phase II study was initiated to assess the response rate, survival, and late effects of treatment in patients with newly diagnosed CNS germ cell tumors (GCT), using etoposide plus ...cisplatin followed by radiation therapy prescribed by extent of disease, histology, and response to chemotherapy.
Seventeen patients aged 8 to 24 years with histologically proven CNS GCT received etoposide (100 mg/m2/d) plus cisplatin (20 mg/m2/d) daily for 5 days every 3 weeks for four cycles, followed by radiation therapy. Nine patients had germinomas; eight had mixed GCT. Four patients (three with germinomas and one with mixed GCT) presented with leptomeningeal dissemination.
Radiographically, 14 of 17 patients were assessable for response; 11 patients experienced complete regression, and three had major partial regression before radiation. Six of seven assessable patients with elevated CSF levels of alpha-fetoprotein or betahuman chorionic gonadotropin had normalization with chemotherapy alone; all normalized with combined chemotherapy and radiation therapy. All 17 patients are alive without evidence of disease (median follow-up, 51 months). One patient developed a relapse in the spinal leptomeninges and was rendered free of disease with spinal radiation more than 5 years ago. One patient developed carotid stenosis requiring surgery. Thus far, only minimal long-term deterioration in neurocognitive function has been detected as a consequence of protocol treatment.
Conventional-dose intravenous chemotherapy with etoposide and cisplatin can effect tumor regression in a high proportion of patients with CNS GCT, including those with leptomeningeal metastases. Acute and long-term toxicities are acceptable. Progression-free survival and overall survival are excellent.
Purpose: This analysis was performed to examine the outcome of patients with histologically confirmed ependymomas of the brain or spinal cord who received postoperative radiotherapy.
Methods and ...Materials: Eighty patients with histologically confirmed ependymomas were evaluated retrospectively. All were treated with various combinations of surgery, radiotherapy (RT), and chemotherapy. Follow-up ranged from 5 to 30 years (median 10.4 years).
Results: The 5- and 10-year survival rates for the entire study group were 79% and 73%, respectively. Patients with low-grade (1 and 2 of 4) tumors had a 5-year survival rate of 87% as compared to 27% for those with high-grade (3 and 4 of 4) tumors (p < 0.0001). Patients with tumors of the spine had a 5-year survival rate of 97% as compared to 68% for those with infratentorial tumors, and 62% for those with supratentorial tumors (p = 0.03). Patients with myxopapillary ependymomas of the spine had a 5-year survival rate of 100% as compared with 76% for patients with other histological subtypes of ependymoma (p = 0.02). Multivariate analysis revealed that the survival rate was independently associated with tumor grade (p = 0.0007) and histological subtype (p = 0.02). Twenty-eight patients (35%) experienced local failure and 10 patients (13%) developed leptomeningeal seeding. The 5-year leptomeningeal failure rate was 10% in patients with low-grade tumors as compared to 41% for patients with high grade tumors (p = 0.01).
Conclusion: Patients with low-grade tumors, especially those with myxopapillary subtypes, have high 5-year survival rates when treated with post-operative radiotherapy. High grade ependymomas are associated with a much poorer outcome. New forms of therapy are required to improve the outcome of patients with high-grade ependymomas.
Purpose: Stereotactic radiosurgery is an effective management strategy for properly selected arteriovenous malformation (AVM) patients. However, the risk of postradiosurgical radiation-related injury ...generally limits this procedure to patients with AVMs of an average diameter of 3 cm or less. Radiosurgery of large AVMs in a planned staged fashion was undertaken to limit the radiation exposure to the surrounding normal brain.
Methods and Materials: Between April 1997 and December 1999, 10 patients with a median AVM volume of 17.4 cm
3 (range, 7.4–53.3 cm
3) underwent staged-volume radiosurgery (23 procedures). At the first radiosurgical procedure, the total volume of the AVM is estimated and a dose plan calculated that covers 10 cm
3–15 cm
3, or one-half the nidus volume if the AVM is critically located (brainstem, thalamus, or basal ganglia). At 6-month intervals thereafter, radiosurgery was repeated to different portions of the AVM with the previous dose plan(s) being re-created utilizing intracranial landmarks to minimize radiation overlap. Radiosurgical procedures were continued until the entire malformation has been irradiated.
Results: The radiation dosimetry of staged-volume AVM radiosurgery was compared to hypothetical single-session procedures for the 10 patients. Staged-volume radiosurgery decreased the 12-Gy volume by an average of 11.1% (range, 4.9–21%) (
p < 0.001). The non-AVM 12-Gy volume was reduced by an average of 27.2% (range, 12.5–51.3%) (
p < 0.001).
Discussion: Staged-volume radiosurgery of large AVMs results in less radiation exposure to the adjacent brain. Further follow-up is needed to determine whether this technique provides a high rate of AVM obliteration while maintaining an acceptable rate of radiation-related complications.
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