Dosimetric characteristics with spatial fractionation using electron grid therapy.

Recently, promising clinical results have been shown in the delivery of palliative treatments using megavoltage photon grid therapy. However, the use of megavoltage photon grid therapy is limited in the treatment of bulky superficial lesions where critical radiosensitive anatomical structures are present beyond tumor volumes. As a result, spatially fractionated electron grid therapy was investigated in this project. Dose distributions of 1.4-cm-thick cerrobend grid blocks were experimentally determined for electron beams ranging from 6 to 20 MeV. These blocks were designed and fabricated at out institution to fit into a 20 x 20-cm(2) electron cone of a commercially available linear accelerator. Beam profiles and percentage depth dose (PDD) curves were measured in Solid Water phantom material using radiographic film, LiF TLD, and ionometric techniques. Open-field PDD curves were compared with those of single holes grid with diameters of 1.5, 2.0, 2.5, 3.0, and 3.5 cm to find the optimum diameter. A 2.5-cm hole diameter was found to be the optimal size for all electron energies between 6 and 20 MeV. The results indicate peak-to-valley ratios decrease with depth and the largest ratio is found at Dmax. Also, the TLD measurements show that the dose under the blocked regions of the grid ranged from 9.7% to 39% of the dose beneath the grid holes, depending on the measurement location and beam energy.

A comparison of different intensity modulation treatment techniques for tangential breast irradiation.

PURPOSE: Several intensity modulation (IM) treatment techniques for tangential breast irradiation were evaluated in terms of dose uniformity in the treated breast volume, contralateral breast dose, and treatment irradiation time. METHODS AND MATERIALS: Contralateral breast dose was measured via TLD chips, and the dose uniformity was calculated on two anthropomorphic phantoms. IM was applied to all beams or to the lateral-medial (LM) beam only. The techniques evaluated include (a) IM via "step & shoot" multileaf collimator (MLC), (b) IM via intensity modulator (compensator), (c) virtual wedge, and (d) physical wedge. A dose optimization algorithm was used for the first two techniques. RESULTS: Collimator-generated IM techniques (MLC-IM and the virtual wedge) produced 50% (average) less contralateral breast dose than the conventional two-wedge technique. When the compensator or the physical wedge was used, contralateral breast dose was reduced 30% (average) by leaving the ML beam open. CONCLUSION: The treatments generated by dose optimization algorithm and delivered via the compensator and MLC techniques offered superior dose uniformity. Single-beam IM techniques in general use less irradiation time without significant degradation of dose uniformity. The MLC-IM technique in this study required the longest treatment irradiation time, while the virtual wedge and compensator IM techniques required the least.

Solution structure of a duplex DNA with an abasic site in a dA tract.

The presence of dA tracts in DNA can lead to stable curvature of the DNA, and this curvature can be important in gene regulation, DNA packaging, and other processes. Since damage to DNA may eliminate this stable curvature, the solution state structure of the duplex of d(CGCAAAAATGCG) paired with d(CGCATTDTTCCG), with D indicating an abasic site, has been determined. The undamaged DNA bends into the major groove both in solution and in the crystal state. The presence of the abasic site in the dA tract region induces changes in the DNA structure up to four base pairs away from the damaged site. The structure of the DNA is dependent on whether the abasic site is in the alpha or beta hemiacetal form. These consequences are quite different from the more localized effects that have been observed for "normal" DNAs containing abasic sites. Thus, there appears to be a strong sequence dependence of the structural effects of abasic sites just as there is for undamaged DNA. Furthermore, these results indicate that the presence of an abasic site can alter DNA bending and hence is likely to have significant long range effects on gene regulation and other properties that are dependent on the stable curvature of DNA.

Measurement of 6-MV X-ray surface dose when topical agents are applied prior to external beam irradiation.

PURPOSE: Radiation therapy patients are typically warned not to apply lotions, deodorants, or powders to the skin within the treatment area because of the possible increase in surface dose due primarily to a bolus effect. This study investigates the effect of 15 products, with and without high atomic number components, on surface dose. METHODS AND MATERIALS: A Markus-type parallel plate ionization chamber in a polystyrene phantom was used to measure surface doses for normal applications of the products for a small (5 x 5-cm2) and a large (25 x 25-cm2) field size. RESULTS: The greatest surface dose increase for any product was 5.4% (21.8-27.2%) of the d(max) dose for the small field and 1.0% (43.6-44.6%) for the large field. Products with high-atomic-number components did not increase the surface dose relative to radiation therapy specialty products. CONCLUSION: No large increase in surface dose was detected with a normal application of the products. However, the possibility exists that an increase in skin reaction may occur owing to chemical irritants in the applied product.

Effect of breakfast cereals on short-term food intake.

We evaluated the effect of high-fiber cereals on short-term food intake. At 0730, 14 subjects ingested one of five cereals, plus milk and orange juice. At 1100 they were presented with a buffet lunch. There was a significant inverse correlation between fiber content of the cereals and energy intake at lunch. In a second study subjects ingested a very-high-fiber (VHF) cereal or a very-low-fiber (VLF) cereal. Fewer kcalories were ingested at lunch after ingestion of the VHF cereal than after ingestion of the VLF cereal. The degree of colonic microbial fermentation of the various cereals was evaluated by breath-hydrogen analysis. The higher-fiber cereals resulted in greater hydrogen production; however, this may not influence energy intake. The results of questionnaires that asked about hunger indicated that food intake can be reduced without the perception of feeling less hungry. Thus, we found that cereals containing relatively large quantities of dietary fiber may decrease short-term food intake.

Ultrasound in the perinatal necropsy.

Although plain and contrast radiology have become a well established part of the perinatal and fetal necropsy, the role of ultrasound has been less comprehensively explored. We have found a variety of ultrasonographic approaches to be of value in diagnosis, quality control, and teaching. Ultrasound is of particular help where consent for formal necropsy has been declined.

The bleaching of the bacteriorhodopsin chromophore by ionizing radiation.

The visible chromophore of bacteriorhodopsin, BR(570), undergoes progressive bleaching when subjected to 60CO gamma-irradiation. The low G-value for bleaching confirms that the site of the chromophore is highly protected. Positive and negative circular dichroic (CD) bands associated with the chromosphone undergo concomitant decrease in a manner which is consistent with two independent chromophores rather than exciton coupling between neighbouring chromophoric site.

Memory recovery after traumatic coma.

Serial memory testings of 108 head injury cases were studied over a two year follow up period. The length of the post-traumatic disorientation period (PTD) was found to be an important factor in the rate of memory recovery. In the first year after injury marked differences were seen in the recovery rates of all four PTD groups, the three short PTD groups (less than one month) finally yielding from 74% to 92% cases (according to the group) with normal memory function, while the long PTD group (more than one month) only produced 45% cases (statistical significance 0.05). During the second year and up to the end of this survey relatively little change in memory status occurred in any of the cases, regardless of their PTD. Any improvement that did occur was at an extremely slow rate. Brain damage was the main cause of memory defect in the long PTD group, while anxiety symptoms had a more important role in the short PTD cases. The shapes of memory recall curves were analysed in recovering patients. Three types of curve were found. The incidence of the shape of the curve also varied according to the PTD time (statistical significance 0.05) between long and short PTD groups. Curve shapes are discussed in terms of memory mechanisms, and a possible prognostic value is suggested. Analysis of test errors indicated not only a defective transfer of material from short term long term memory storage but also in some cases, a more complex mechanism involving inappropriate fixation of attention. Reverberation of memory traces is suggested as being a possible cause of interference in both short and long term memory mechanisms. A marked difference in recall performance between auditory and visual presentation of word lists was found to be a useful lateralising sign.

The blink reflex in coma and after recovery from coma.

Comparative studies of the blink reflex in a series of head injuries through the stages of coma and recovery from coma in a series of miscellaneous hemispheral lesions, and in a normal series, reveals that, although the principal centre for the R1 component of the blink reflex seems to be localised in the upper pons, the seat of the R2 late component is in the reticular system. The reappearance of this late component of the blink reflex in our cases of coma although seeming to depend on the integrity of the mesencephalic formation, correlates with the recovery of the patient's alertness. On the other hand, habituation of this reflex depends on the integrity of global cognitive function, rather than on any localised centre. The roles of the cortex, selective attention, and emotional factors, are discussed. The recovery of the normal habituation of the blink reflex obtained by glabellar tapping was found to be a useful sign in the follow up of patients recovering from concussion and other lesions, such as subdural haematomas and brain tumours, with global mental impairment.