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PURPOSE: Advanced treatment delivery techniques require more robust treatment planning system (TPS) models for accurate dose planning and computation. As stereotactic body radiation therapy (SBRT) and volumetric-modulated arc therapy (VMAT) treatments become more prevalent, the ability of the TPS to accurately calculate dose delivered from small fields becomes of greater importance. An additional level of complexity in photon beam modeling is added with the inclusion of flattening filter free (FFF) treatment beams, due to steep in field dose gradients and non uniform penumbra regions. The purpose of this work is to examine the ability of ADAC/Pinnacle TPS to accurately model and calculate dose from small field FFF treatment beams. METHODS: Photon beam data was first modeled using Pinnacle v9.0. Flattened and FFF beam models were generated for 6MV and 10MV energies. Models were fine-tuned using a 5×5 cm2 field as the standard field in order to place more emphasis on the accuracy of the model for the small fields. An upgrade to Pinnacle v9.2 allowed for comparison between version 9.0 and version 9.2. RESULTS: Accurately modeling small fields using Pinnacle v9.0 proved difficult, particularly in the lower penumbra region. An asymmetry appeared in the small field models for both the flattened and FFF models. The Pinnacle v9.2 upgrade eliminated the small field asymmetries, and allowed for more accurate penumbra region calculations. Preliminary results have shown that Pinnacle v9.2 is capable of developing accurate beam models when an emphasis is placed on the small fields. In addition, patient specific dosimetric information for version 9.0 and version 9.2 was also calculated and examined for prostate, head & neck, and lung treatments. CONCLUSIONS: Pinnacle v9.2 showed improved accuracy in small field FFF dose modeling over version 9.0. Comparison of patient dosimetric information reflected the improvement in the small field modeling.

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Psychiatric inpatients with dementia (N = 61) or depression (N = 67) in late life were 2.6 times more likely to manifest magnetic resonance imaging abnormalities of the brain than were elderly controls (N = 44). Controlling for the effects of age and gender, demented patients were distinguishable from controls by an increased prevalence of cortical atrophy and infarction, while depressed patients exhibited an increased prevalence of cortical infarctions and leukoencephalopathy. Patients with dementia were distinguishable from those with major depression by an increased prevalence of cortical atrophy. These results indicate that major depression in late life, like dementia, is associated with a remarkable increase in overt pathologic changes in the brain.

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We found increased age (p = 0.001) and history or evidence of stroke (p = 0.016) to be significant independent multivariate predictors of the presence and severity of leukoencephalopathy on magnetic resonance imaging brain scans in a mixed population of 35 elderly psychiatric patients and 25 neurologically healthy elderly volunteers. These results suggest that subcortical ischemia, as well as age-related changes that may not be vascular in origin, contribute to the emergence of periventricular and other deep white matter hyperintensities that are commonly seen on the magnetic resonance imaging brain scans of older adults.

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We prospectively evaluated excretion of Giardia lamblia in children in day care centers in Houston by conducting two prevalence studies of 600 children enrolled in 30 DCC, day care centers, and an 18-month longitudinal study in 82 children in one center. In the two prevalence surveys, Giardia cysts were identified in 72 (21%) and 67 (26%) children, respectively, who provided stool specimens. Trophozoites were found in 15 (4%) and 8 (3%), respectively. There was no correlation between the frequency of recent diarrheal episodes and the finding of Giardia. Stool specimens containing cysts were significantly (P less than 0.0001) more frequent in the 13- to 30-month-old children than in children younger than 12 months. Children attending day care centers for more than 3 months were more likely to be excreting Giardia than those attending for less than 3 months. In the longitudinal study, cysts were detected in stool specimens from 27 (33%) of the 82 children at least once during the survey. Twelve children had Giardia cysts in weekly stool specimens for a mean of 6.2 +/- 1.2 months and trophozoites for 3.3 +/- 1.2 months. The number of enteric symptoms observed in children and the classification of nutritional status based on monthly height and weekly weight measurements did not differ significantly when infected and noninfected children were compared. Asymptomatic Giardia excretion in children younger than 36 months is common and appears to be well tolerated.

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We conducted a double-blind treatment study of 110 adults from the United States who were attending summer classes in Guadalajara, Mexico, and had diarrhea (four or more unformed stools in 24 hours, or three or more unformed stools per eight-hour period plus one or more additional clinical indicators of enteric infection). Thirty-seven patients received trimethoprim/sulfamethoxazole (TMP/SMX) (160 mg of TMP and 800 mg of SMX), 38 were given TMP alone (200 mg), and 35 took a placebo twice daily for five days. By the end of the first 24 hours of treatment, patients taking either TMP/SMX or TMP alone passed fewer unformed stools than did patients given placebo (P = 0.0002 and P = 0.01, respectively). Abdominal pain and nausea were reduced in both treatment groups. The beneficial effect was seen in treatment of Escherichia coli-induced diarrhea, shigellosis, and diarrhea not associated with an enteropathogen. Five per cent of patients given TMP/SMX, 8 per cent of those given TMP, and 49 per cent of those given placebo were considered treatment failures (P less than 0.001 for both active drugs as compared with placebo). Early treatment with TMP/SMX or TMP is an alternative to prophylactic use of drugs for travelers' diarrhea.

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The location of food consumption was recorded daily for 3 wk by 130 United States summer students newly arrived in Guadalajara, Jalisco, Mexico, as part of an assessment of bismuth subsalicylate vs. placebo in the irevention of travelers' diarrhea. Eating at locations other than homes and apartments (P < 0.025), and specifically at restaurants, was associated with an increased occurrence of diarrhea. Less eating at restaurants (P < 0.005), street vendors (P < 0.005), and school cafeterias (P < 0.01) was associated with reduced occurrence of travelers' diarrhea, even among persons taking bismuth subsalicylate as a preventive measure.

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The efficacy of a daily dosage regimen of subsalicylate bismuth in preventing or reducing the severity of diarrhea among young healthy adults was evaluated in a double-blind, randomized, placebo-controlled trial. Diarrhea developed in 14 (23%) of 62 students receiving subsalicylate bismuth compared with 40 (61%) of 66 students taking a placebo. The protective effect of subsalicylate bismuth was apparent within a day or two of the study onset and became more obvious as the number of days at risk increased. The students treated with subsalicylate bismuth experienced fewer intestinal complaints and were less likely to pass soft or watery stools of any number. Once diarrhea occurred, enteropathogens were less commonly identified in stools of students receiving subsalicylate bismuth (33%) compared with placebo (71%). Subsalicylate bismuth was well tolerated by students during the 21-day trial.

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Students attending a Mexican university who developed diarrhea were randomly treated with bismuth subsalicylate or a placebo. One hundred and eleven were given 30 ml each 1/2 hr until eight doses (total dose of active drug 4.2 g) were given and 58 students received twice this dose (8.2 g of active drug) over the 3 1/2-hr treatment period. The number of unformed stools was significantly decreased in both bismuth subsalicylate treatment groups compared to the placebo controls for the period 4 to 24 hr after therapy. A reduction in diarrhea was additionally noted for the duration of the 48-hr surveillance period for the students receiving the higher dose of active drug. Subjective relief within 24 hr of therapy of the symptoms of diarrhea, nausea, and abdominal pain or cramps was reported with a significantly increased frequency in the bismuth subsalicylate group. The most pronounced effect of the treatment occurred in the United States students with diarrhea who had recently arrived in Mexico. This appeared to be related to the favorable effect of bismut subsalicylate on the course of toxigenic Escherichia coli infection. Students with shigellosis did not experience a prolonged illness in either treatment group.

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Daily food histories for one month were obtained in summer, 1975, from students attending a Mexican university to determine the influence of food consumption on the development and etiology of diarrhea. In newly-arrived students from the U.S. who ate half or more of their meals in the school cafeteria and public restaurants there were significant increases in diarrhea (p less than 0.005); shigella infection (p less than 0.05) and toxigenic E. coli infection (p less than 0.025) compared to the students eating a comparable number of meals in private homes. In the summer U.S. students there was also an association of diarrhea and eating from street vendors (p less than 0.05). In full-time U.S. students who had lived in Mexico a year or longer as well as in Latin American students a relationship between location of meals and occurrence of enteric disease was not apparent. High numbers of enteric bacteria were recovered from food from the school's cafeteria, public restaurants, street vendors and small grocery stores. Shigella were isolated from cooked and uncooked hamburger patties from the school cafeteria. Four shigella carriers were found among kitchen personnel at the school. This study demonstrates that food serves as a major vehicle through which travelers' diarrhea occurs.

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A clinic was established at Universidad de las Americas, Cholula, Puebla, Mexico for the study of acute diarrhea rates in newly-arrived students and full-time students. Diarrhea occurred in 22 of 55 newlly-arrived U.S. summer students (40%), compared to 28 of 142 U.S. full-time students (20%), 4 of 29 Venezuelan summer and full-time students (14%) and 7 of 66 Mexican full-time students (11%) (the differences were significant, p less than 0.005). Recurrent episodes of diarrhea during the month of study occurred in 15% of U.S. summer students, 4% of U.S. full-time students, and were non-existent in students from Latin America. As well as the 61 students with diarrhea enrolled in the incidence study, all students who developed diarrhea at the univeristy were encouraged to visit the clinic. This gave a total population of 130 cases of diarrhea. The illness that developed in students form the U.S. varied widely, but it typically consisted of seven to 13 unformed stools during the first 48 hours of illness, with illness persiting three to five days. Illness tended to be more severe in the U.S. students. Fifty per cent of the U.S. students with diarrhea had "severe" illness (greater than or equal to 10 unformed stools in first 48 hours) compared to 23% of the Latin Americans. This study indicates that the agents responsible for diarrhea in Latin America are widespread and that resistance to infection develops after prolonged or repeated exposure.

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