Organic dairy production systems in Pennsylvania: a case study evaluation.

The current market demand and price for organic milk is encouraging dairy producers, particularly those on smaller farms, to consider organic production as a means for improving the economic viability of their operations. Organic production systems vary widely in scale, in practices, and across agroclimatic settings. Within this context, case studies of 4 actual organic dairy farms were used to characterize existing systems in Pennsylvania. Based on data from these farms, a whole-farm simulation model (Integrated Farm System Model) was used to compare 4 production systems representing organic grass, organic crop, conventional crop with grazing, and conventional confinement production. The performance of each of these systems was simulated over each year of 25 yr of central Pennsylvania weather data. Simulation results indicated that farm level accumulation of soil P and K may be a concern on organic farms that use poultry manure as a primary crop nutrient source, and that erosion and runoff loss of P may be of concern on organic farms producing annual crops because more tillage is required for weed control. Whole-farm budgets with prices that reflect recent conditions showed an economic advantage for organic over conventional production. A sensitivity analysis showed that this economic advantage depended on a higher milk price for producers of organic milk and was influenced by the difference in milk production maintained by herds using organic and conventional systems. Factors found to have little effect on the relative profitability of organic over conventional production included the differences between organic and conventional prices for seed, chemicals, forage, and animals and the overall costs or prices assumed for organic certification, machinery, pasture fencing, fuel, and labor. Thus, at the current organic milk price, relative to other prices, the case study organic production systems seem to provide an option for improving the economic viability of dairy operations of the scale considered in Pennsylvania. To motivate transition to organic systems, the economic advantage found requires the persistence of a substantial difference between conventional and organic raw milk prices.

Evaluation of eye shields made of tungsten and aluminum in high-energy electron beams.

PURPOSE: To protect the lens and cornea of the eye when treating the eyelid with electrons, we designed a tungsten and aluminum eye shield that protected both the lens and cornea, and also limited the amount of backscatter to the overlying eyelid when using electron beam therapy. METHODS AND MATERIALS: Custom curved tungsten eye shields, 2 mm and 3 mm thick, were placed on Kodak XV film on 8 cm polystyrene and irradiated to evaluate the transmission through the shields. To simulate the thickness of the eyelid and to hold the micro-TLDs, an aquaplast mold was made to match the curvature of the eye shields. Backscatter was measured by placing the micro-TLDs on the beam entrance side to check the dose to the underside of the eyelid. Measurements were done with no aluminum, 0.5, and 1.0 mm of aluminum on top of the tungsten eye shields. The measurements were repeated with 2- and 3-mm flat pieces of lead to determine both the transmission and the backscatter dose for this material. RESULTS: Tungsten proved to be superior to lead for shielding the underlying structures and for reducing backscatter. At 6 MeV, a 3-mm flat slab of tungsten plus 0.5 mm of aluminum, resulted in .042 Gy under the shield when 1.00 Gy is delivered to dmax. At 6 MeV for a 3-mm lead plus 0.5-mm aluminum, .046 Gy was measured beneath the shield, a 9.5% decrease with the tungsten. Backscatter was also decreased from 1.17 to 1.13 Gy, a 4% decrease, when using tungsten plus 0.5 mm of aluminum vs. the same thickness of lead. Measurements using 9 MeV were performed in the same manner. With 3 mm tungsten and 0.5 mm of aluminum, at 3 mm depth the dose was .048 Gy compared to .079 Gy with lead and aluminum (39% decrease). Additionally, the backscatter dose was 3% less using tungsten. Simulating the lens dose 3 mm beyond the shield for the 2-mm and 3-mm custom curved tungsten eye shields plus 0.5 mm of aluminum was .030 and .024 Gy, respectively, using 6 MeV (20% decrease). Using 9-MeV electrons, the dose 3 mm beyond the shield was .048 Gy for the 2-mm shield and .029 Gy for the 3-mm shield (40% decrease). Backscatter was not further decreased using thicker tungsten. With a 6-MeV beam, using the 2-mm or 3-mm custom tungsten eye shields plus 0.5 mm of aluminum, the backscattered doses were 1.03 and 1.02 Gy, respectively. The backscatter dose with 9 MeV was 1.06 Gy using the 2-mm custom shield plus 0.5 mm aluminum and 1.05 Gy with a 3-mm custom shield plus 0.5 mm aluminum. There was very little difference in backscatter dosage under the eyelid using 0.5 vs. 1.0 mm of aluminum. Therefore, for patient comfort, we recommend using 0.5 mm of aluminum. CONCLUSIONS: Tungsten is superior to lead as a material for eye shields due to its higher density and lower atomic number (Z). Using 6- and 9-MeV electrons, tungsten provides the necessary protection for the lens and cornea of the eye and decreases the amount of backscatter to the eyelid above the shield.

Evaluation of dose variation during total skin electron irradiation using thermoluminescent dosimeters.

PURPOSE: To determine acceptable dose variation using thermoluminescent dosimeters (TLD) in the treatment of Mycosis Fungoides with total skin electron beam (TSEB) irradiation. METHODS AND MATERIALS: From 1983 to 1993, 22 patients were treated with total skin electron beam therapy in the standing position. A six-field technique was used to deliver 2 Gy in two days, treating 4 days per week, to a total dose of 35 to 40 Gy using a degraded 9 MeV electron beam. Thermoluminescent dosimeters were placed on several locations of the body and the results recorded. The variations in these readings were analyzed to determine normal dose variation for various body locations during TSEB. RESULTS: The dose to flat surfaces of the body was essentially the same as the dose to the prescription point. The dose to tangential surfaces was within +/- 10% of the prescription dose, but the readings showed much more variation (up to 24%). Thin areas of the body showed large deviations from the prescription dose along with a large amount of variation in the readings (up to 22%). Special areas of the body, such as the perineum and eyelid, showed large deviations from the prescription dose with very large (up to 40%) variations in the readings. DISCUSSION: The TLD results of this study will be used as a quality assurance check for all new patients treated with TSEB. The results of the TLDs will be compared with this baseline study to determine if the delivered dose is within acceptable ranges. If the TLD results fall outside the acceptable limits established above, then the patient position can be modified or the technique itself evaluated.

Cardiac dilatation associated with collagen alterations.

There is a complex collagen network in the heart. Various components have been identified and generally on the basis of form and position some functions have been ascribed to one or another of these components. Since the various components all appear to be connected in a hierarchial network of some type assigning function is not difficult but demonstrating a given function is somewhat hazardous. We have demonstrated that two I.V. infusions of disulfide reagents one week apart activates a collagenolytic system that results in near complete loss of the collagen struts that interconnect myocytes, the collagen struts that connect capillaries to all adjacent myocytes and the weave complex that surrounds groups of myocytes. Increases in pre load or afterload result in responses indicating that the disulfide treated animals generate pressure equal to or greater than the control hearts, thus, the treatment has no affect on either myocyte contractility or force delivery to the ventricle. However, static pressure volume measurements in the disulfide treated animals are shifted far to the right indicating marked dilatation of the ventricle and increase in distensibility. This indicates that the weave complex contributes to the initial rectilinear portion of the pressure volume curve.