Induction of multiple signaling loops by MuSK during neuromuscular synapse formation.

At the neuromuscular junction, two motor neuron-derived signals have been implicated in the regulation of synaptogenesis. Neuregulin-1 is thought to induce transcription of acetylcholine receptor (AChR) genes in subsynaptic muscle nuclei by activating ErbB receptors. Neural agrin aggregates AChRs by activating the receptor tyrosine kinase MuSK. Here, we show that these two signals act sequentially. Agrin, by activating MuSK, induces the synthesis and aggregation of both MuSK and ErbB receptors. ErbB acts downstream of MuSK in synapse formation. In this way, MuSK activation leads to the establishment of a neuregulin-1-dependent signaling complex that maintains MuSK, ErbB, and AChR expression at the synapse of electrically active muscle fibers.

Characterisation of postnatal growth of the murine heart.

Using a new technique to isolate rod-shaped cardiomyocytes from small tissue pieces we were able to analyse the developmental profile of postnatal cardiomyocyte growth in the mouse. During the first 4 postnatal days the volume of the cardiomyocytes remains relatively constant despite a concomitant increase in heart weight, indicating growth due to cell division of the cardiomyocytes, also called hyperplasia. After postnatal day 5 the volume of the cardiomyocytes increases dramatically until postnatal day 14, when the increment of the volume curve decreases again. The cardiomyocytes reach their adult volume at around 3 months of age. These measurements present the first detailed analysis of the phase of so-called developmental hypertrophy, i.e. normal cardiomyocyte growth in the mouse, and provide an essential base-line for the analysis of growth parameters in mouse models for cardiomyopathies. We used this method to characterise the growth characteristics of cardiomyocytes from MLP (muscle LIM protein) knockout mice, a mouse model for dilated cardiomyopathy. During the first 2 postnatal weeks there is no significant difference in the growth parameters between MLP knockout and wildtype mice. However, in the adult animals cardiomyocytes from MLP knockout mice are not only characterised by a more irregular shape, but also by a high variability in size compared to cardiomyocytes from wildtype animals. This suggests that the alterations in ventricular morphology in the MLP heart are not due to a general elongation of the cardiomyocytes but to myocyte disarray and ventricular wall thinning caused by the heterogeneous volume of the cardiomyocyte population.

Alterations at the intercalated disk associated with the absence of muscle LIM protein.

In this study, we investigated cardiomyocyte cytoarchitecture in a mouse model for dilated cardiomyopathy (DCM), the muscle LIM protein (MLP) knockout mouse and substantiated several observations in a second DCM model, the tropomodulin-overexpressing transgenic (TOT) mouse. Freshly isolated cardiomyocytes from both strains are characterized by a more irregular shape compared with wild-type cells. Alterations are observed at the intercalated disks, the specialized areas of mechanical coupling between cardiomyocytes, whereas the subcellular organization of contractile proteins in the sarcomeres of MLP knockout mice appears unchanged. Distinct parts of the intercalated disks are affected differently. Components from the adherens junctions are upregulated, desmosomal proteins are unchanged, and gap junction proteins are downregulated. In addition, the expression of N-RAP, a LIM domain- containing protein located at the intercalated disks, is upregulated in MLP knockout as well as in TOT mice. Detailed analysis of intercalated disk composition during postnatal development reveals that an upregulation of N-RAP expression might serve as an early marker for the development of DCM. Altered expression levels of cytoskeletal proteins (either the lack of MLP or an increased expression of tropomodulin) apparently lead to impaired function of the myofibrillar apparatus and to physiological stress that ultimately results in DCM and is accompanied by an altered appearance and composition of the intercalated disks.

Short-term small-dose intravenous iron trial to detect functional iron deficiency in dialysis patients.

BACKGROUND/AIM: Management of renal anemia in end-stage renal disease requires careful evaluation of the iron status before and in particular during erythropoietin treatment. However, there is no simple and practical iron index accurately predictive of functional iron deficiency in these patients till now. The purpose of this prospective study, therefore, is to evaluate whether a short course of low-dose intravenous iron challenge can detect functional iron deficiency in hemodialysis patients. METHODS: Twenty-four patients with baseline serum ferritin levels between 100 and 500 ng/ml were treated with intravenous saccharated ferric oxide, 960 mg over 24 hemodialysis treatments, and the hemoglobin level was checked every week. RESULTS: Patients whose hemoglobin value increased at least by 1 g/dl within the 8-week period were classified as having functional iron deficiency or as responders (n = 26; 81.2%). All other subjects were classified as having adequate iron levels or as nonresponders (n = 6; 18.8%). There were no significant differences in age, sex, dialysis years, Kt/V, dialyzers, hemoglobin, and basal and final transferrin saturation and ferritin between responders and nonresponders. In addition, there were no iron indices with acceptable levels of sensitivity and specificity. On the contrary, the cutoff value of increments of hemoglobin of at least 0.2 g/dl after a 2-week intravenous iron trial had a sensitivity of 96.2% and a specificity of 100% in all patients (n = 32) and a sensitivity of 100% and a specificity of 100% after patients with transferrin saturation <20% were excluded (n = 24). These values had the greatest utility of the tests studied in this work. CONCLUSION: A 240-mg intravenous iron challenge during a 2-week period may be a simple, accurate, and straightforward method to detect a functional iron deficiency status in hemodialysis patients undergoing erythropoietin therapy.

Different domains of the M-band protein myomesin are involved in myosin binding and M-band targeting.

Myomesin is a 185-kDa protein located in the M-band of striated muscle where it interacts with myosin and titin, possibly connecting thick filaments with the third filament system. By using expression of epitope-tagged myomesin fragments in cultured cardiomyocytes and biochemical binding assays, we could demonstrate that the M-band targeting activity and the myosin-binding site are located in different domains of the molecule. An N-terminal immunoglobulin-like domain is sufficient for targeting to the M-band, but solid-phase overlay assays between individual N-terminal domains and the thick filament protein myosin revealed that the unique head domain contains the myosin-binding site. When expressed in cardiomyocytes, the head domains of rat and chicken myomesin showed species-specific differences in their incorporation pattern. The head domain of rat myomesin localized to a central area within the A-band, whereas the head domain of chicken myomesin was diffusely distributed in the cytoplasm. We therefore conclude that the head domain of myomesin binds to myosin but that this affinity is not sufficient for the restriction of the domain to the M-band in vivo. Instead, the neighboring immunoglobulin-like domain is essential for the precise incorporation of myomesin into the M-band, possibly because of interaction with a yet unknown protein of the sarcomere.

Aluminum utensils contribute to aluminum accumulation in patients with renal disease.

Presently, aluminum utensils are widely used in the world, especially in the developing countries. However, whether aluminum leaching from such utensils contributes to aluminum accumulation or causes any damage in patients with renal disease remains unknown. We designed a prospective study to evaluate this problem. After excluding patients who were not examined at follow-up or who poorly complied during the study period, the opened randomized study consisted of 42 patients with chronic renal insufficiency (creatinine clearance <60 mL/min and >10 mL/min). All patients had not taken any aluminum-containing agents for 3 months, but used aluminum kitchen utensils for more than 1 year. Twelve patients comprised the control group; the other 30 patients comprised the study group. The aluminum kitchen utensils used by the study group patients were replaced with stainless steel utensils for 3 months, but those used by the control group were not. After 3 months, the decrements of serum aluminum (5.5 +/- 4.6 microg/L v 2.1 +/- 3.5 microg/L; P = 0.012) and daily urine aluminum excretion (14.3 +/- 15.2 microg/d v 2.1 +/- 5.6 microg/d; P = 0.005) in the study group patients were greater than those in the control group patients. The increments of transferrin saturation of the study group patients (1.8% +/- 9.5% v -3.7% +/- 9.5%; P = 0.052) were greater than those of the control group patients. In addition, the increments of iron (r = 0.368, P = 0.035) and transferrin saturation (r = 0.345, P = 0.049) positively correlated with the decrements of daily aluminum excretion in all patients. The study group patients with greater decrements of serum aluminum (>5.5 microg/L) had greater serum iron levels (90.2 +/- 27.7 microg/dL v 71.9 +/- 27.8 microg/dL; P = 0.047) and transferrin saturation (30.5% +/- 11.0% v 23.0% +/- 9.5%; P = 0.046) than those with less decrements of serum aluminum (<5.5 microg/L) after the study. Our study demonstrates that aluminum kitchen utensils may be the important aluminum exposure source for patients with chronic renal insufficiency who are not taking aluminum-containing agents, and hints that the long-term exposure of aluminum leaching from aluminum utensils probably affects iron levels in patients with chronic renal insufficiency. Further studies are clearly needed to confirm this observation.

Endoscopic polypectomy of a large inflammatory fibroid polyp of the stomach: a case report.

Gastric inflammatory fibroid polyp (IFP) is a rare benign submucosal tumor. It consists of mesenchymal and spindle-shaped cell proliferations with inflammatory cell infiltrations. With the widespread use of fiberoptic endoscopy, gastric polypoid lesions are being recognized with increasing frequency. Conventionally, they have been treated using surgical excision, after which accurate pathological diagnosis was obtained. Recently, endoscopic polypectomy has been widely used and has shown good results in both diagnosis and treatment of polypoid lesions of the stomach. We report a case in which a large symptomatic gastric IFP was successfully removed using single-channel endoscopy.

Criteria for the evaluation of treatment planning systems.

Radiation treatment planning systems (RTPS) are evolving on a rapid and continual basis. After the evaluation of several commercial systems, we have developed a list of features we consider desirable in a product. The goal in the compilation of these criteria was a comprehensive worksheet which categorized the characteristics of RTPS into hardware (computer and peripheral devices), 2-D planning tools, 3-D planning tools, irregular field planning tools, and brachytherapy planning. With these distinctions, one can evaluate a system conforming to the specific planning needs, e.g., conformal therapy, dynamic therapy capabilities, or optimized remote afterloading brachytherapy, of a department. The rationales of the special requirements are provided for justification.

Effect of long-term low-dose aluminum-containing agents on hemoglobin synthesis in patients with chronic renal insufficiency.

To investigate the possible toxic effects of long-term low-dose exposure to A1-containing agents in 55 patients with chronic renal insufficiency (CRI), 37 patients received A1(OH)3 1 tablet 3 times per day (about 302 mg/day of elemental A1) for 3 months and another 18 were used as a control group. The hematological, iron status and A1 data were measured before and after the study. CRI patients who had ingested A1-containing agents for 3 months had significant decreases in hematological parameters and increases in serum A1 and daily urinary A1 excretion. Serum ferritin negatively correlated with serum A1 (r = -0.586, p < 0.0005), and hemoglobin (Hb) positively correlated with renal A1 clearance (r = 0.573, p < 0.0005) and logarithmic transformation of serum A1 (r = -0.437, p < 0.01) in these patients, despite no significant correlations between initially basal hematological and A1 parameters. But there were no significant differences between variables of A1 and hematological parameters before and after 3 months of follow-up in the control group. All factors correlating with Hb were measured with stepwise regression analysis; renal A1 clearance, creatinine clearance (Ccr) and serum iron were the most significant correlation factors with Hb. After Ccr and serum iron had been adjusted, Hb (b = 0.069 +/- 0.02; p < 0.05) still positively correlated with renal A1 clearance. Comparing patients who had reduced Hb (at least 0.5 g/dl) and those who did not, the response group had a lower basal (Ccr, a higher serum A1 and a lower renal A1 clearance after A1 loading for 3 months. In conclusion, A1 does play a role in the significant reduction of Hb and hematocrit in CRI patients after A1 loading for 3 months, and patients with a lower Ccr may easily develop A1-induced hematologically toxic effects. A1-containing agents should be used with care in long-term therapies of CRI patients.

Biologically effective dose distribution based on the linear quadratic model and its clinical relevance.

PURPOSE: Radiotherapy plans based on physical dose distributions do not necessarily entirely reflect the biological effects under various fractionation schemes. Over the past decade, the linear-quadratic (LQ) model has emerged as a convenient tool to quantify biological effects for radiotherapy. In this work, we set out to construct a mechanism to display biologically oriented dose distribution based on the LQ model. METHODS AND MATERIALS: A computer program that converts a physical dose distribution calculated by a commercially available treatment planning system to a biologically effective dose (BED) distribution has been developed and verified against theoretical calculations. This software accepts a user's input of biological parameters for each structure of interest (linear and quadratic dose-response and repopulation kinetic parameters), as well as treatment scheme factors (number of fractions, fractional dose, and treatment time). It then presents a two-dimensional BED display in conjunction with anatomical structures. Furthermore, to facilitate clinicians' intuitive comparison with conventional fractionation regimen, a conversion of BED to normalized isoeffective dose (NID) is also allowed. RESULTS: Two sample cases serve to illustrate the application of our tool in clinical practice. (a) For an orthogonal wedged pair of x-ray beams treating a maxillary sinus tumor, the biological effect at the ipsilateral mandible can be quantified, thus illustrates the so-called "double-trouble" effects very well. (b) For a typical four-field, evenly weighted prostate treatment using 10 MV x-rays, physical dosimetry predicts a comparable dose at the femoral necks between an alternate two-fields/day and four-fields/day setups. However, our BED display reveals an approximate 21% higher BED for the two-fields/day scheme. This excessive dose to the femoral necks can be eliminated if the treatment is delivered with a 3:2 (anterio-posterior/posterio-anterior (AP/PA): bilaterally opposed (BLO)) dose weighting. With Co-60 beams, the increase of BED with alternate two-fields/day, 1:1 setup was even more pronounced (26%). CONCLUSION: We have demonstrated the feasibility of constructing a biologically oriented dose distribution for clinical practice of radiotherapy. The discordance between physical dose distributions and the biological counterparts based on the given treatment schemes was quantified. The computerized display of BED at nonprescription points greatly enhanced the versatility of this tool. Although the routine use of this implementation in clinical radiotherapy should be cautiously done, depending largely on the accuracy of the published biological parameters, it may, nevertheless, help the clinicians derive an optimal treatment plan with a particular fractionation scheme or use it as a quantitative tool for outcome analysis in clinical research.

Human recombinant erythropoietin and phlebotomy in the treatment of iron overload in uremic patients.

Six chronic hemodialysis patients suffering from iron overload (serum ferritin ranged between 2053-15704 mu g/L) were treated with human recombinant erythropoietin (EPO) alone for eighteen months. An initial rapid decrease of serum ferritin was observed in all six patients when the loading dose of EPO was given. Three patients (Cases 4, 5, 6) who suffered from chronic blood loss maintained a continuous decline of serum ferritin in the subsequent stage of maintenance dose EPO therapy, however, the decrease of serum ferritin became sluggish under a maintenance dose in the other three patients (Cases 1, 2 and 3). The serum ferritin eventually decreased to a satisfactory level (975-1761 mu g/L) in Cases 4, 5 and 6, whereas it remained high (4232-8196 mu g/L) in Cases 1, 2, and 3 who had higher basal levels of serum ferritin (5641-15704 mu g/L) and a plateau of response under a maintenance dose of EPO. These three patients were then treated with EPO and phlebotomy. Their serum ferritin decreased quickly from 6752 +/- 1264 mu g/L to 2454 +/- 482 mu g/L after six months of phlebotomy therapy; it was a dramatic improvement in contrast to the stagnant response under a maintenance dose of EPO alone. Our experience indicates that EPO therapy alone has its limitations in treating severe iron overload. Although there is an initial rapid decrease of serum ferritin during the period of the loading dose, the response might become stagnant during the period of maintenance dose. Phlebotomy effectively eliminated the excessive iron stores in these refractory cases. Therefore, we suggest that phlebotomy be considered in severe iron overload if a stagnant response is observed under a maintenance dose EPO therapy.

Comparison for four techniques of catheter insertion in patients undergoing continuous ambulatory peritoneal dialysis.

OBJECTIVE: To compare four different ways of implanting catheters for continuous ambulatory peritoneal dialysis (CAPD) in an effort to reduce the incidence of complications. DESIGN: Retrospective study. SETTING: Teaching hospital, Taiwan. SUBJECTS: 166 Patients who had 180 catheters inserted between 1985 and 1993. INTERVENTIONS: 49 Catheters were inserted through midline incisions (in 24 of which the catheter was fixed with an additional suture) and 131 were inserted through paramedian incisions (in 88 of which the catheter was fixed with an additional suture). MAIN OUTCOME MEASURES: Morbidity, particularly the incidence of migration of the catheter and incisional hernia. RESULTS: 8/68 Catheters migrated in patients in whom no additional fixing suture had been used, compared with 2/112 in whom an additional suture had been used (p = 0.007). There were 4 incisional hernias in 49 midline, compared with 0/131 paramedian, incisions (p < 0.0001). Significantly more catheters had to be removed after midline than after paramedian incisions (35/49 compared with 56/131, p = 0.0008); chi square for independence 15.02, df 3, p = 0.0018. CONCLUSION: For the implantation of catheters for CAPD the paramedian incision is associated with significantly fewer complications than the midline incision and the incidence is even lower if the catheter is fixed to the lower peritoneum with an additional suture.

Urologic cancers in uremic patients.

From 1981 through 1990, 21 urologic cancer cases were discovered in 21 uremic patients at our hospital. This constituted 55% (11 of 20) of the total malignancies in nondialyzed uremic patients, 41% (nine of 22) of the total in chronic hemodialysis patients, and 50% (one of two) of those in patients on continuous ambulatory peritoneal dialysis. No cases of urologic cancer were found in kidney transplant recipients. When compared with the general population, the standardized incidence ratio of kidney cancer in chronic hemodialysis patients was found to be 24.1 (P < 0.01) and that of bladder cancer was found to be 16.4 (P < 0.01). Multiple underlying renal diseases contributed to the development of the urologic cancer cases, including four analgesic nephropathy-associated transitional cell carcinoma cases, two acquired cystic kidney disease-associated renal cell carcinoma cases, two chronic pyelonephritis-associated (stone and tuberculosis) squamous cell carcinoma cases, and one xanthogranulomatous pyelonephritis-associated transitional cell carcinoma case. Uremia per se may be an important promoting factor. Hematuria (17 of 21 cases) was the most common presenting feature despite the fact that most of the patients were anuric. The clinical diagnosis of renal parenchymal tumors was based on ultrasonography (five of five cases), whereas most urothelial tumors were detected by cystoscopy or retrograde pyelography (14 of 16 cases). The survival rate of the 17 aggressively treated patients was 82% at 2 years and 45% at 5 years. We conclude that uremic patients are at greater risk of developing urologic cancer.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of body iron status and serum aluminum in chronic renal insufficiency patients not taking any aluminum-containing drugs.

The present study examines the serum aluminum (Al) and daily urine Al excretion in 50 patients with chronic renal insufficiency (CRI) who are not taking any Al-containing agents. The influence of body iron stores and hematological indexes on the above parameters were also studied. Data on a group of 20 healthy subjects not taking any drugs were included for comparisons. The basal Al levels in CRI patients (10.5 +/- 9.7 micrograms/l) were significantly higher than those (3.8 +/- 2.4 micrograms/l) of the normal subjects. In addition, the renal Al clearance (2.98 +/- 0.35 ml/min) in CRI patients was significantly lower than that (4.93 +/- 0.21 ml/min) in normal subjects. Although all serum Al levels of our patients were within the nontoxic range (< 50 micrograms/l), the results of our study showed a negative correlation between serum Al and serum transferrin saturation (r = -0.40, p < 0.005) as well as serum iron (r = -0.406, p < 0.005). There was a negative correlation between daily urine Al excretion and serum ferritin levels (r = -0.305, p = 0.031). The study group is further divided into 2 subgroups, i.e. group A (ferritin < 100 micrograms/l) and group B (ferritin > 300 micrograms/l). The daily urine Al excretion in group A was higher than that in group B. In conclusion, our study first demonstrates that Al tends to be accumulated in patients with CRI, similar to Al in patients with hemodialysis, and the chronic low-level Al exposure in CRI patients may affect body iron status and metabolism, or iron status may play a role in Al absorption and excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocytosis in patients with renal failure on hemodialysis: study of underlying mechanism by in vitro erythroid culture assay.

Five patients with erythrocytosis associated with renal failure on maintenance hemodialysis were investigated for in vitro erythroid progenitor growth and the effect of their uremic sera on normal erythropoiesis. The duration of hemodialysis prior to discovery of erythrocytosis ranged from 1 week to 96 months. None had acquired cystic disease and no other known cause of increased erythropoietin (Epo) production was identified. With the presence of Epo in cultures, all five patients grew erythroid colonies within normal or higher than normal ranges. Three patients formed spontaneous erythroid colonies in the absence of added Epo; all three fulfilled the clinical diagnosis of polycythemia vera (PV). The uremic sera from patients with PV lacked either a stimulating or an inhibiting effect on normal erythropoiesis. The association between renal failure and PV was coincidental. The other two patients without endogenous erythroid colony formation had enhanced erythropoietic activity in their sera, which increasingly stimulated the erythroid colony growth by normal bone marrow cells as the concentration of the uremic serum was increased. The etiology of increased Epo production in these 2 patients remained undefined during long-term follow-up. The present study on five uremic patients with polycythemia showed two different underlying mechanisms of erythrocytosis--characteristic autonomous erythroid proliferation for PV in three patients and inappropriate idiopathic Epo production in two patients.

Surgical implications of juxtaposed atrial appendages and the associated anomalies.

Juxtaposition of the atrial appendages (JAA) is an uncommon anomaly of the heart that is frequently associated with other cardiac abnormalities, such as transposition of the great arteries and tricuspid atresia. We encountered 7 patients with JAA from July 1984 to July 1989 at National Taiwan University Hospital. The JAA was right-sided in 1 patient and left-sided in 6. The patients' ages ranged from 10 months to 12 years. The cardiac anomalies in the patient with right JAA were double-outlet right ventricle and ventricular septal defect, which was repaired with a patch. Of the 6 patients with left JAA, 5 had transposition of the great arteries, and in 3 of them obstructive tricuspid lesions (tricuspid stenosis in 1, tricuspid atresia in 2) were noted. Three patients with left JAA and normal tricuspid valve underwent total correction (one Senning operation and two Rastelli operations). The other 3 patients with tricuspid obstruction underwent total cavopulmonary connection (2) and Fontan operation (1). We concluded that, first, left JAA was more frequently seen and associated with more morbid anatomy than right JAA. Second, if left JAA is discovered in planning biventricular repair for transposition of the great arteries, the tricuspid valve should be inspected carefully to rule out tricuspid obstruction.

Effect of body iron stores on serum aluminum level in hemodialysis patients.

To evaluate the influence of body iron stores on the serum aluminum (Al) level, we studied the correlation between iron status (the serum ferritin, serum iron and transferrin saturation) and serum Al levels in 68 severely anemic hemodialysis patients. Among them, 36 underwent the desferrioxamine (DFO) mobilization test. These 68 patients were divided into three groups according to their serum ferritin level. The basal Al level in the patient group was 41.4 +/- 37.4 micrograms/l (control, 4.1 +/- 2.4 micrograms/l). The serum Al level after DFO infusion of the patient group was 111.1 +/- 86.8 micrograms/l. A significantly higher basal Al and peak Al level after DFO infusion were found in group 1 patients (serum ferritin less than 300 micrograms/l) when compared to group 2 (serum ferritin 300-1,000 micrograms/l) and group 3 (serum ferritin greater than 1,000 micrograms/l) patients. A significant negative correlation between serum ferritin and basal serum Al (r = -0.544, p = 0.0001), as well as peak serum Al after DFO infusion (r = -0.556, p = 0.0001), was noted. Similarly, a negative relationship between serum Al (both basal and peak) and either serum iron or transferrin saturation was noted. However, there was no correlation between the serum Al level and the dosage of aluminum hydroxide. In conclusion, serum ferritin, serum iron and transferrin saturation were inversely correlated with serum Al in our hemodialysis patients. Iron deficiency may probably increase Al accumulation in these patients.

Total cavopulmonary connection: a modified technique without prosthetic material.

An alternative method to create an intraatrial, cavocaval channel without using any prosthetic material in total cavopulmonary connection is described. This new technique avoids possible thrombotic complication, limitation of heart growth by intraatrial prosthetic material, and reduction in secretion of antinaturetic peptide.

Determination of possible doses to the gonads or fetus in pregnant patients during radiation therapy.

Some of the women undergoing radiation therapy may be pregnant and the scatter radiation to the fetus and gonads is a matter of great concern. Quantitative measurement of the scatter dose in polystyrene solid phantoms with a Farmer type chamber and effects of shielding blocks under the collimators were studied. The scatter dose outside of the primary beam was found to be decreasing exponentially with increasing distance from the radiation beam edge. When the distance increased from 10 cm to 60 cm, the scatter dose drops from 1-2% to 0.15% for the Co-60 beam and from 1-2% to 0.02% for the 10 MV X-rays. The collimation system was a major source of scatter radiation because the scatter dose could be substantially reduced by placing shielding blocks under the collimators and the scatter dosed varied with field sizes. The lead apron used in diagnostic radiographic procedures reduced the scatter dose by 5-6% only. The scatter dose distribution in the body outside of the radiation field was also analyzed.