Poster - Thur Eve - 70: Quantification of tumour dose enhancement at kilo-voltage energies due to the presence of gold nanoparticles during radiation therapy: EGSnrcMP Monte Carlo study

One of the greatest challenges in radiation therapy is the ability to deliver a lethal dose of radiation to a tumour while sparing the surrounding normal tissues. In theory, the dose delivered to a tumour during photon-based radiation therapy can be enhanced by loading high atomic number (Z) materials into the tumour, which results in greater photoelectric absorption and hence increased photoelectron fluence within the tumour than in surrounding tissues. The EGSnrcMP Monte Carlo code, together with DOSXYZnrc, a three-dimensional voxel dose calculation module has been used to study the macroscopic dose enhancement factor (MDEF) in a tumour infused with gold nanoparticles at the kilo-voltage energies. We observed that gold nanoparticles infused in a tumour irradiated with kilo-voltage energies has the potential to enhance the tumour dose by a factor ranging from 0.25 to about 5 depending on the mean energy of the beam and the concentration of gold nanoparticles in the tumour. The increase in dose can be attributed to the significant increase in the photoelectron fluence within the tumour loaded with gold particles during the irradiation. Future studies will involve the characterization of the MDEF at megavoltage energies.

The effect of environmental temperature on protein and energy changes following burn injury in the rat

The metabolic response to a standard burn injury in rats (25% of body surface area) was investigated at environmental temperature 20 degrees C and 30 degrees C. With an intake of 15 g diet (20% w/w protein) per day, burned rats at 20 degrees C were found to be in negative energy balance mainly due to increased insensible (evaporative) losses, and they lost weight. Fat was the main endogenous source of energy, although protein was also catabolised from both carcass and pelt. At 30 degrees C, insensible losses of burned rats were still high, but they had lower sensible (mainly radiative) losses leading to a positive energy balance and a gain in weight. This consisted mainly of carcass water, fat and protein. Urine catecholamines were higher in burned rats at 20 degrees C than at 30 degrees C and correlated with heat loss, urine nitrogen and urine 3-methylhistidine, supporting the hypothesis that catecholamines play a central role in mediating the protein and energy changes following burn injury. For the first 4-6 days, urine nitrogen and 3-methylhistidine excretion increased in rats at 30 degrees C, suggesting that this early part of the metabolic response is obligatory. These findings support the use of raised environmental temperatures to reduce the metabolic response to burns.

Normalized data for the estimation of fetal radiation dose from radiotherapy of the breast

There can be several reasons why a pregnant patient may receive a radiological examination. It could have been a planned exposure, or the exposure might have resulted from an emergency when a thorough evaluation of pregnancy was impractical. Sometimes the pregnancy was unsuspected at the time of the examination and, with younger women being diagnosed with breast cancer, the likelihood of this will increase in radiotherapy departments. Whatever the reason, when presented with a pregnant patient who has received a radiological examination involving ionizing radiation, the dose to the fetus should be assessed based on the patient's treatment plan. However, a major source of uncertainty in the estimation of fetal absorbed dose is the influence of fetal size and position as these change with gestational age. Consequently, dose to the fetus is related to gestational age. Various studies of fetal dose during pregnancy have appeared in the literature. Whilst these papers contain many useful data for estimating fetal dose, they usually contain limited data regarding the depth and size of the fetus within the maternal uterus. We have investigated doses to the fetus from radiation therapy of the breast of a pregnant patient using an anthropomorphic phantom. Normalized data for estimating fetal doses that takes into account the fetal size (gestational age: 8-20 weeks post-conception) and depth within the maternal abdomen (4-16 cm) for different treatment techniques have been provided. The data indicate that fetal dose is dependent on both depth within the maternal abdomen and gestational age, and hence these factors should always be considered when estimating fetal dose. The data show that fetal dose can be underestimated up to about 10% or overestimated up to about 30% if the dose to the uterus is assumed instead of the actual fetal dose. It can also be underestimated up to about 23% or overestimated up to about 12% if a mean depth of 9 cm is assumed, instead of using the actual depth of the fetus within the maternal abdomen. Multi-segments sMLC technique showed consistently lower fetal doses compared with all the wedged plans employed.

Randomized clinical assay for hepatic grafts preservation with University of Wisconsin or histidine-tryptophan-ketoglutarate solutions in liver transplantation

University of Wisconsin (UW) solution has been the standard for preservation of liver transplantation grafts since 1989. However, some studies demonstrated that histidine-tryptophan-ketoglutarate (HTK) solution is also effective. The purpose of this study was to compare the efficacy of both solutions in liver transplantation. From January 2003 to August 2004 the livers of deceased donors were randomized into HTK and UW groups. The 102 studied patients included 65 (63.7%) in the UW group and 37 (36.3%) in the HTK group. Sex, race, hemodynamic state, use of adrenergic drugs, and presence of steatosis in the donor were similarly distributed in the two groups (P > .05). The mean age of the donors was 38.1 years (SD +/-14.4) in the UW group and 44.6 years (SD +/-14.2) in the HTK cohort (P = .036). Sex, race, age, etiology of the cirrhosis, retransplant, acute liver failure, portal thrombosis, and Child-Pugh and MELD scores in the recipients were similarly distributed in the two recipient samples (P > .05). Among 89 patients who completed 4 months of follow-up, the HTK group included eight cases (25.8%) of biliary complications versus five cases (8.6%) in the UW group (P = .033; OR = 2.0 95% CI = 1.2-3.5). The incidence of graft dysfunction was 2.8% in the HTK group and 9.4% in the UW group (P = .15). In conclusion, UW and HTK solutions were equally effective for the preservation of the hepatic graft. The routine use of HTK solution can reduce the costs of liver transplantation.

Oxidative stress, hepatocellular integrity, and hepatic function after initial reperfusion in human hepatic transplantation

BACKGROUND

The mechanisms underlying liver graft dysfunction are not completely defined, although much of the injury derives from oxidative stress in organ reperfusion. The antioxidant glutathione in its reduced form (GSH) is an important agent to detoxify oxygen species after reperfusion. However, this effect might be limited by low concentrations at the end of cold storage. The objective of this study was to evaluate GSH and glutathione oxidized (GSSG) hepatic levels pre- and postreperfusion and correlate with hepatocellular injury and liver function in the 5 subsequent days after transplantation.

METHODS

Liver biopsies were taken immediately before implant and 2 hours after venous reperfusion in 34 grafts, determining GSH, GSSG levels, and GSSG/GSH ratio. Aminotransferases (ALT, AST) and PT were measured for 5 days.

RESULTS

There was a strong decrease in GSH concentration (P <.0001), increase of GSSG levels (P <.01), and increase of the GSSG/GSH ratio (P <.0001). No correlations were found between GSH, GSSG, or GSH/GSSH levels and AST, ALT, and PT.

CONCLUSION

Glutathione levels showed significant changes after 2 hours of reperfusion, due to intense oxidative stress. Therapies to replenish GSH should be considered as a protective measure to avoid liver graft dysfunction after transplantation.

A stepwise mapping approach for localization and ablation of ectopic right, left, and septal atrial foci using electroanatomic mapping

AIMS

We describe a new strategic stepwise mapping approach for fast and accurate identification and ablation of ectopic atrial foci using an electroanatomic mapping system.

METHODS AND RESULTS

Mapping procedures started with the acquisition of four points at the superior/septal part of the tricuspid annulus. According to this activation sequence, maps were continued towards the right atrial free wall if relatively early activation was shown at the superior part of the initial map or towards the triangle of Koch and, if necessary, to the left atrium, in cases of relatively early activation at the septum. High density mapping and detailed electrogram analysis only of the target area allowed identification and ablation of 34 foci in 30 of the 32 studied consecutive patients. A small number of mapping points were sufficient within a procedure time of 90 +/- 41 min for right 148 +/- 68 min and for left sided foci and a total fluoroscopy time of 9.6 +/- 7.2 min and 24.8 +/- 16.4 min respectively. Sixteen foci were located at the right free wall, eight at the left free wall, and 10 at the right or left side of the septum.

CONCLUSION

Strategic electroanatomic mapping with fast identification of the area of tachycardia origin and high density mapping only of this target area allowed fast and successful localization and ablation of right and left free wall and septal ectopic atrial foci.

Electromagnetic versus fluoroscopic mapping of the inferior isthmus for ablation of typical atrial flutter: A prospective randomized study

BACKGROUND

Radiofrequency catheter ablation within the tricuspid annulus-inferior caval vein isthmus can cure typical atrial flutter. The target for ablation, nonetheless, is relatively wide, and standard ablation procedures may require significant exposure to radiation.

METHODS AND RESULTS

A total of 50 patients (mean age, 58+/-11 years) with typical atrial flutter were prospectively randomized to receive isthmus ablation using conventional fluoroscopy for catheter navigation (group I, n=24) or electromagnetic mapping (group II, n=26). Complete bidirectional isthmus block was verified with double potential mapping. If complete isthmus block could not be achieved after 20 radiofrequency pulses or 25 minutes of fluoroscopy, the patients were switched to the other group. Eight patients from group I (33%) but only 1 patient from group II (4%) were switched. Overall, complete isthmus block was achieved in 47 of 50 patients (94%). The overall fluoroscopy time, including the placement of the diagnostic catheters, was 22.0+/-6.3 minutes in group I and 3.9+/-1.5 minutes in group II (P:<0.0001). The fluoroscopy time needed for isthmus mapping was 17.7+/-6.5 minutes in group I and 0.2+/-0.3 minutes in group II (P:<0.0001).

CONCLUSIONS

Electromagnetic mapping during the induction of linear lesions for the ablation of atrial flutter permitted a highly significant reduction in exposure to fluoroscopy while maintaining high efficacy, and it allowed the time required for fluoroscopy to be reduced to levels anticipated for diagnostic electrophysiological studies.

Serum albumin distribution in early treated anorexia nervosa

We investigated the effects of malnutrition and refeeding on albumin distribution and metabolism in patients undergoing treatment for anorexia nervosa. Using autologous 125I-labelled albumin, we measured the fractional catabolic rate and calculated the relative sizes of the plasma and extravascular albumin pools in 6 female anorexia nervosa subjects and 6 matched controls. We were unable to demonstrate any differences in either the catabolic rate of albumin (fractional or absolute) or in serum albumin concentration between anorexia nervosa and control subjects. There was a large expansion of the extravascular albumin pool in the anorexia nervosa subjects--36% when expressed in relation to body weight. We conclude that, at the time of study, there were no effects of anorexia nervosa on albumin catabolism in these subjects. However, the condition and its treatment are associated with a significant relative expansion of the extravascular albumin pool. This contrasts to some extent with previous work, which suggested that in protein depletion the plasma albumin pool is maintained at the expense of the extravascular albumin pool. The expansion of the extravascular albumin pool is possibly related to the relative excess of interstitial fluid seen in starvation and in the initial phases of refeeding.

Development of an enzyme-linked immunosorbent assay for human metallothionein-1 in plasma and urine

The development of a sensitive enzyme-linked immunosorbent assay (ELISA) for human metallothionein-1 is reported. Metallothionein was purified from postmortem human liver and used to raise high-titer antibodies in rabbits. The assay was specific for human metallothionein-1 (MT-1), and there was no significant cross-reaction with human metallothionein-2. The detection limit (sensitivity) of the assay was 5 ng/ml, and the added MT-1 could be fully recovered from plasma and urine. The normal reference range for MT-1 was 32 +/- 16 ng/ml in plasma and 10 +/- 6 ng MT-1 per micromole of creatinine in random samples of urine. No significant differences were found between the values for males and females. The concentration of MT-1 was greatly increased between 24 and 48 hours after surgery, indicating that the protein behaves like an acute phase reactant in human subjects.

The effects of experimental malnutrition on albumin metabolism and distribution in rabbits

In order to determine the extent to which the concentration of albumin in plasma is maintained at the expense of the extravascular pool during protein-energy malnutrition, the rates of exchange between albumin in plasma (IA) and the extravascular pool (EA) and consequently the distribution of albumin between intravascular and extravascular pools (expressed as EA:IA) were measured in protein-energy-depleted and control rabbits. The fractional rates of synthesis (FSR) and catabolism (FCR), the concentration of albumin and the plasma volume (PV) were also measured. In animals in which protein-energy intake was reduced by 58% the concentration of albumin in plasma remained unchanged, whereas FCR decreased by 38% and FSR by 30%. No significant changes in EA:IA or PV were found. We conclude that albumin concentration during protein-energy depletion is not maintained at the expense of extravascular albumin, but by parallel changes in the rates of catabolism and synthesis.

Albumin catabolic rate and protein-energy depletion

Severe malnutrition was induced in New Zealand White rabbits by restricting dietary nitrogen and energy to 9.1 and 57.4% of normal intake, respectively. Albumin distribution and metabolism were then determined in these and in control animals. The fractional catabolic rate was reduced by 33.7% in the depleted animals, but there were no changes in the other distribution rate constants. In particular, we were unable to demonstrate a significant change in the relative distribution of albumin between the intravascular and extravascular spaces. In addition, albumin concentration in the depleted group only fell toward the end of the experiment. We conclude that, with acute severe malnutrition, plasma albumin concentration is maintained until late and is therefore not a good nutritional marker. Also, maintenance of intravascular albumin concentration is not at the expense of extravascular albumin.

The regulatory role of external cations on human polymorphonuclear phagocyte chemiluminescence

The effect of the external cations Na+ and Ca2+ on polymorphonuclear chemiluminescence was investigated. Both Ca2+ in the range of 0.2-2 mM and Na+ in the range of 114-143 mM showed a dose dependent increase in polymorphonuclear chemiluminescence, irrespective of the concurrent increase in osmolality. The Na+/H+ antiport inhibitor Amiloride decreased the response significantly. These effects were observed using buffers commonly used for chemiluminescence studies and indicate the importance of defining the Ca2+ and Na+ composition of the buffers used in chemiluminescence assays.

Clinical and nutritional aspects of changes in acute-phase proteins during inflammation

1. When assessing the significance of altered plasma protein concentrations the various physiological factors, including posture and hormones which affect the amount and distribution of fluid in the body and the synthesis and catabolism of plasma proteins, must be kept in mind. 2. Although several cytokines, including IL-1 and TNF, are implicated in the acute-phase response, recent evidence is that the synthesis of the major acute-phase proteins (e.g. CRP) is induced by IL-6. 3. The positive acute-phase plasma proteins are useful non-specific indicators of tissue damage. 4. When there is evidence of an acute-phase response (e.g. increased CRP), decreased concentrations of plasma proteins such as albumin, transferrin, retinol-binding protein and pre-albumin cannot be assumed to reflect malnutrition. 5. Plasma albumin concentration can be a good indicator of prognosis.

Observations on the delay in onset of the acute phase protein response

The early time course of the acute phase protein response (APPR) and mediators involved in its control were investigated in the rat and mouse. After turpentine-induced inflammation in the rat C-reactive protein and fibrinogen increased in concentration peaking at 48 h and 18-24 h, respectively. A 9 h delay prior to elevation of these protein was observed. After injection of endotoxin into mice, a 4-6 h delay was observed prior to any increase in the concentration of the acute phase protein serum amyloid P-component. This delay was shortened to 2 h after injection of leucocytic endogenous mediators (LEM) produced from rabbit peritoneal exudate cells. It is concluded that the delay between the initiating stimulus and the increases in the acute phase proteins is due to some obligatory intermediate steps which lead to the production of the final mediators of the APPR, and that these mediators are present in LEM.

The protein metabolic response to short-term starvation in man

Plasma protein concentrations, in particular the serum albumin concentration, are often quoted as indicators of nutritional state in surgical patients. Injury also affects the circulating concentrations of these proteins. Twenty students were subjected to a 3-day total fast and the concentration of plasma proteins, generally affected by trauma, determined before and after the fast. The only protein to show any negative response was retinal binding protein which fell by 16% during the starvation period (p < 0.001). Albumin, the protein often used as a nutritional index, demonstrated a significant (p < 0.001) increase during this period. This was not related to changes in the hydration state of the subjects.

Pocket computers: a new aid to nutritional support

A program has been written to run on a pocket computer (Sharp PC-1500) that can be used at the bedside to predict the nutritional requirements of patients with a wide range of clinical conditions. The predictions of the program showed good correlation with measured values for energy and nitrogen requirements. The program was used, with good results, in the management of over 100 patients needing nutritional support. The calculation of nutritional requirements for each patient individually facilitates more appropriate treatment and may also produce financial savings when compared with administration of a standard feeding regimen to all patients.

Increased vascular permeability: a major cause of hypoalbuminaemia in disease and injury

The rate of loss of albumin to the tissue spaces (measured as transcapillary escape rate) rose by more than 300% in patients with septic shock, and the average increase within 7 h of cardiac surgery was 100%. The transcapillary escape rate in cachectic cancer patients was twice that of a group of healthy individuals. The rate of loss of albumin to the tissue spaces is normally 5%/h, which is more than 10 times the rates of synthesis and catabolism, and these large rate increases indicate that increased vascular permeability is an important cause of the lowered concentration of albumin commonly seen in acute and chronic disease.

Simplified analytical methods for the measurement of the synthesis rate of plasma proteins in vivo by the [14C]carbonate method

We describe a method for obtaining the specific activity of 14C in urea, essential in the measurement of the synthesis rate of a plasma protein in vivo, which is simpler than the original procedure. The principle is the measurement of 14CO2 and NH4+ separately, after incubation with urease. A simple alteration gives samples of 13CO2 for mass spectrometry. The 'recoveries' of 14C and 13C in urea were invariably between 90 and 96% and the CV was 3%.

Early plasma protein and mineral changes after surgery: a two stage process

Sequential changes in albumin, transferrin, alpha 1-acid glycoprotein, C reactive protein, fibrinogen, copper, iron, and zinc in plasma up to 24 h after hysterectomy were measured. No increases in the concentrations of the acute phase proteins alpha 1-acid glycoprotein, C reactive protein, and fibrinogen were observed until 6 h after the skin incision. These increases were preceded by significant falls at 2-4 h, and this was shown also by albumin, transferrin, iron, zinc, and copper. The ratios of iron and zinc to their binding proteins, transferrin and albumin, did not decrease until 4-6 h and their concentrations remained low for at least 24 h. These patterns suggest that at least two mechanisms operate after trauma. The early fall in the concentrations of the proteins in plasma is consistent with a prompt increase in microvascular permeability. The later decrease in binding of the metals iron and zinc to their transport proteins and the increase in concentrations of the acute phase proteins could be initiated by a common mediator.