The COMT L allele modifies the association between MAOB polymorphism and PD in Taiwanese

OBJECTIVE

Reports suggest that catechol-O-methyltransferase (COMT(L/L)) (Val(158)/Met) and monoamine oxidase B (MAOB) intron 13 genotype polymorphism is associated with PD. To understand the ethnicity-specific effects of genetic polymorphism, we performed a case-control study of the association between PD susceptibility and polymorphism of MAOB and COMT, both separately and in combination, in Taiwanese.

METHODS

Two hundred twenty-four patients with PD and 197 controls, matched for age, sex, and birthplace, were recruited. MAOB and COMT polymorphism genotyping was performed by using PCR-based restriction fragment length polymorphism (RFLP) analyses. chi(2), OR, and Fisher's exact tests were used to compare differences in allelic frequencies and genotypes.

RESULTS

The MAOB G genotype (G in men and G:/G in women) was associated with a 2.07-fold increased relative risk of PD. COMT polymorphism, considered alone, showed no correlation with PD risk; however, a significant synergistic enhancement was found in PD patients harboring both the COMT(L) and MAOB G genotypes.

CONCLUSIONS

These results suggest that, in Taiwanese, PD risk is associated with MAOB G intron 13 polymorphism, and this association is augmented in the presence of the COMT(L) genotype, indicating an interaction of these two dopamine-metabolizing enzymes in the pathogenesis of sporadic PD. However, the relatively low frequencies of these combined genotypes in our study necessitates confirmation with a larger sample size.

Determination of urine catecholamines by capillary electrophoresis with dual-electrode amperometric detection

Demonstrated in this study is that without pretreatment and preconcentration nanomolar-level catecholamines in human urine samples can be quantitatively determined with ease by utilizing capillary electrophoresis coupled with amperometric detection. The detector employs a parallel-opposed dual-electrode scheme assembled with an on-capillary electrode and a disk electrode and takes advantage of the redox cycling of analytes between the two working electrodes to improve the limit of detection. The matrix effect of urine samples significantly decreases the detection sensitivity from that obtained in standard solutions. Therefore, calibration curves derived from standard solutions cannot be used in quantitative determination of catecholamines. Methods of standard addition and internal standard have been studied. The results suggest that isoproterenol is a good internal standard to facilitate the measurements of dopamine, epinephrine, and norepinephrine in human urine samples.

Diagnosis of bladder cancer using telomerase activity in voided urine

BACKGROUND AND PURPOSE

Telomerase is an essential enzyme for cellular immortality and tumorigenesis. Reactivation of telomerase is associated with many primary cancers. We evaluated the accuracy of a modified immunodiagnostic technique based on the telomeric repeat amplification protocol (TRAP) assay, by semi-quantitative measurement of telomerase activity in exfoliated urothelial cells in voided urine from patients with bladder cancer.

METHODS

Telomerase activity was assayed in centrifuged urine cell pellets from 17 bladder cancer patients and from 32 patients with benign bladder diseases. Each specimen was collected from a 50-mL sample of single voided urine obtained before surgery, and telomerase activity was detected using a telomerase polymerase chain reaction and enzyme-linked immunosorbent assay (PCR-ELISA) protocol. Results of pathologic study, urine cytologic examination, and urine telomerase activity were determined independently.

RESULTS

The cut-off value for relative telomerase activity was set at 0.059, which provided an optimal diagnostic accuracy of 88% (n = 49). At this cut-off value, the sensitivity and specificity for urine telomerase in bladder cancer were 82% (n = 17) and 91% (n = 32), respectively. Telomerase activity was found in 11 low-grade tumors and six high-grade tumors, whereas negative results for telomerase activity were found in urothelial cells of patients with inguinal hernia, urinary stones, acute urinary tract infection, or chronic cystitis. Only five cytology samples from the same patients were positive for bladder cancer. The difference in these two detection rates was significant (p = 0.002).

CONCLUSION

The results of this study indicate that the measurement of telomerase activity from voided urine using our modified semi-quantitative PCR-ELISA technique may help provide earlier diagnosis of bladder cancer and earlier postoperative indication of recurrence.

Six-year follow-up of untreated T1 carcinoma of prostate

INTRODUCTION

The management of T1 carcinoma of prostate remains controversial and the critical role of histopathology is often underestimated.

MATERIALS AND METHODS

A retrospective review was conducted on 27 cases of T1 prostate carcinoma diagnosed between 1980 and 1992, all of which were managed on a surveillance programme. Pathological material of 24 cases was available for re-examination by a single histopathologist without prior knowledge of the originally assigned grade. Gleason's scoring system was used in the current review.

RESULTS

Twenty-two (81.5%) were T1a and 5 (18.5%) T1b. Mean duration of follow-up was 77.3 months (1.0 to 159.0) and median age was 72.0 years (61.0 to 84.0). Twenty-five (92.6%) were originally graded as well differentiated, 1 (3.7%) was moderately differentiated and 1 (3.7%) was poorly differentiated. Three of the well-differentiated tumours were upstaged because of tumour volume. On review, differences in grading were noted in 13 cases (54.2%) and 11 (45.8%) were, as a consequence, upstaged. Progression was recorded in 5 cases (18.5%). Mean disease-free interval was 47.6 months (7.0 to 75.0) and mean serum PSA at progression was 34.2 ug/l (2.3 to 62.5). Four responded to delayed therapy. Mortality was recorded in 13 cases (48.1%) but cancer-specific mortality was only 7.7% (1/13). Mean age at death was 78.1 years.

CONCLUSION

The importance of accurate grading and staging cannot be overemphasized given its pivotal role in subsequent management. The impact of age is also apparent and surveillance appears a reasonable option for those with limited life expectancy after diagnosis.

A histomorphometric observation of flows in cortical bone under dynamic loading

Ferritin was used as a histological marker for interstitial fluid flows in four goats. Two transcortical pins were inserted into each tibia mediolaterally-one at the proximal side and one at the distal side of the diaphysis. For the experimental limb, dynamic loading was applied to the pins on the lateral side. The contralateral limb was used as control. Ferritin was injected into the nutrient arteries feeding the two tibiae. The goat was then euthanized immediately. Undecalcified slides of the tibial cortical bone from both the experimental and the control limbs were studied histologically. Percentages of Haversian systems marked with ferritin halos and the average radial distance of ferritin transudation away from the Haversian canals were assessed. Results for the medial and lateral sides of both the experimental and control tibiae were reported. Significant differences in the ferritin transudation distance were found between the experimental and the control tibia (P < 0.005) and between the medial and the lateral sectors (P < 0.05). The approach documented in this paper could be used to address systematically how external loading might affect the transport phenomena in cortical bone.

Expression of two novel mouse Iroquois homeobox genes during neurogenesis

Members of the Drosophila Iroquois homeobox gene family are implicated in the development of peripheral nervous system and the regionalization of wing and eye imaginal discs. Recent studies suggest that Xenopus Iroquois homeobox (Irx) genes are also involved in neurogenesis. Three mouse Irx genes, Irx1, Irx2 and Irx3, have been previously identified and are expressed with distinct spatio-temporal patterns during neurogenesis. We report here the cloning and expression analysis of two novel mouse Irx genes, Irx5 and Irx6. Although Irx5 and Irx6 proteins are structurally more related to one another, we find that Irx5 displays a developmental expression pattern strikingly similar to that of Irx3, whereas Irx6 expression resembles that of Irx1. Consistent with the notion that Mash1 is a putative target gene of the Irx proteins, all four Irx genes display an overlapping expression pattern with Mash1 in the developing CNS. In contrast, the Irx genes and Mash1 are expressed in complementary domains in the developing eye and olfactory epithelium.

Cystoscopic diagnosis of bladder cancer by intravesical instillation of 5-aminolevulinic acid induced porphyrin fluorescence--the Singapore experience

OBJECTIVES

1) To determine whether fluorescence cystoscopy after intravesical administration of 5-aminolevulinic acid (5-ALA) is more sensitive in detection of dysplasia and bladder cancer when compared with conventional cystoscopy. 2) To determine the safety of using 5-ALA.

MATERIALS AND METHODS

A 3% 5-ALA solution was instilled intravesically before cystoscopy in 41 patients. The 5-ALA-induced porphyrin fluorescence was excited by violet light from a xenon arc lamp (lambda 375-440 mm).

RESULTS

Among the 175 biopsies obtained, the sensitivity of the fluorescence cystoscopy was greater than that of conventional cystoscopy (89.1% versus 65.6%, P < 0.05). Specificity was at 64.8% and 83.8% respectively with P < 0.05. Duration of ALA instillation did not seem to affect the sensitivity and specificity of photodynamic diagnosis. The procedures were well tolerated by all patients with no additional complication.

CONCLUSIONS

Fluorescence-guided biopsies are more sensitive than random biopsies in detecting dysplasia or bladder cancer without additional risk or complication. The duration of ALA instillation did not seem to affect the accuracy of photodynamic diagnosis.

Zinc and nitric oxide synthase inhibitor L-NAME attenuate NPY-induced feeding in mice

The influences of zinc (Zn) and the nitric oxide synthase (NOS) inhibitor L-NAME on peripheral neuropeptide Y (NPY)-induced feeding in mice were investigated. Male mice received NPY (200 ng/d/mouse subcutaneously) and were separated into four groups based on cotreatments (with or without Zn [0.1 mg/mL]) and with or without L-NAME [0.2 mg/mL]) administered in drinking water for 10 d. A control group that received saline injection was also studied. The results showed that NPY, with or without any studied chemicals, did not affect body weight gain or body fat content. However, the mice that were administered NPY alone had increased energy intakes, higher serum triglyceride and free fatty acid, and lower serum glucose than saline-injected controls. NPY-treated mice that were given Zn and L-NAME cotreatments had compatible results of determined variables in comparison with control mice. This study showed that Zn and L-NAME attenuated NPY-mediated feeding and selected serum variables in mice. However, the mechanisms of the interactions among NPY, Zn and NOS, and their effects on appetite regulation, remain to be elucidated.

Breast cancer risk associated with genotype polymorphism of the estrogen-metabolizing genes CYP17, CYP1A1, and COMT: a multigenic study on cancer susceptibility

Estrogen has been proposed to trigger breast cancer development via an initiating mechanism involving its metabolite, catechol estrogen (CE). To examine this hypothesis, we conducted a multigenic case-control study to determine whether polymorphisms of the genes responsible for CE formation via estrogen biosynthesis (CYP17) and hydroxylation (CYP1A1) and CE inactivation (COMT) are associated with an elevated risk for breast cancer in Taiwanese women, and whether the association between genotype and risk may be modified by estrogen exposure. One hundred and fifty breast cancer patients and 150 healthy controls were recruited. PCR-based RFLP assays were used to determine the genotypes of estrogen-metabolizing genes. The breast cancer risk associated with individual susceptibility genotypes varied among the three genes and was highest for COMT, followed by CYP1A1 and CYP17. After simultaneous consideration of all three genes and other well-established risk factors of breast cancer, the COMT genotype remained the most significant determinant for breast cancer development and was associated with a 4-fold increase in risk (95% confidence interval, 1.12-19.08). Furthermore, a trend of increasing risk for developing breast cancer was found in women harboring higher numbers of high-risk genotypes (P = 0.006), including the high activity CYP17 (CYP17 A2/A2), high inducibility CYP1A1 (CYP1A1 MspI vt/vt), and low activity COMT (COMT L/L) genotypes. The association of risk with the number of susceptibility genotypes was stronger in women with prolonged estrogen exposure (indicated by a higher number of estrogen exposure years or a higher number of estrogen exposure years between menarche and first full-term pregnancy), women with higher estrogen levels (implied by early menarche), and women with a higher body mass index (> or = 22.5). On the basis of comprehensive profiles of estrogen metabolism, this study supports the possibility that breast cancer can be initiated by estrogen exposure.

Histomorphological study on pattern of fluid movement in cortical bone in goats

Streaming potential is considered one of the most important mechanisms to moderate the function of osteoblasts and osteocytes in bone growth, remodeling and fracture repair. The present study was designed to demonstrate the fluid flow pattern in the cortical bone matrix in an animal model using undecalcified histological techniques. Immediately after injection of ferritin into the tibia nutrient artery of four adult goats, the animals were euthanized. Undecalcified transverse and longitudinal blocks of cortical bone obtained from the tibial diaphysis were immersed in Perl's reagent and embedded in methyl methacrylate. Sections were cut and ground to 30-50 microm thickness for histomorphological evaluation at different magnifications and focusing levels. A serial grinding technique was used to validate the observations made at different focusing levels. As expected, ferritin was observed in the interstitial compartment in both transverse and longitudinal sections. In osteons sectioned transversely, the pattern of centrifugal movement of ferritin marker was demonstrated as single or multiple halos around the Haversian canal. The most apparent halo in osteons with multiple halos was the one found closest to the Haversian canal. The total number of identifiable single or multiple halos increased or was altered when counting was made with higher magnification or at different focusing levels, respectively. Irregular and incomplete ferritin halos indicated structural complexity of the osteons. Overall, the pattern of ferritin movement was consistent with bulk interstitial fluid flow influenced by both hydrostatic pressure and transudation. This study demonstrated for the first time multiple concentric halos of the fluid flow marker ferritin around Haversian canals in the cortical interstitial compartment. The results suggest that the undecalcified technique might be a useful method for qualitative and quantitative studies on cortical fluid flow.

Treatment plan evaluation using dose-volume histogram (DVH) and spatial dose-volume histogram (zDVH)

OBJECTIVE

The dose-volume histogram (DVH) has been accepted as a tool for treatment-plan evaluation. However, DVH lacks spatial information. A new concept, the z-dependent dose-volume histogram (zDVH), is presented as a supplement to the DVH in three-dimensional (3D) treatment planning to provide the spatial variation, as well as the size and magnitude of the different dose regions within a region of interest.

MATERIALS AND METHODS

Three-dimensional dose calculations were carried out with various plans for three disease sites: lung, breast, and prostate. DVHs were calculated for the entire volume. A zDVH is defined as a differential dose-volume histogram with respect to a computed tomographic (CT) slice position. In this study, zDVHs were calculated for each CT slice in the treatment field. DVHs and zDVHs were compared.

RESULTS

In the irradiation of lung, DVH calculation indicated that the treatment plan satisfied the dose-volume constraint placed on the lung and zDVH of the lung revealed that a sizable fraction of the lung centered about the central axis (CAX) received a significant dose, a situation that warranted a modification of the treatment plan due to the removal of one lung. In the irradiation of breast with tangential fields, the DVH showed that about 7% of the breast volume received at least 110% of the prescribed dose (PD) and about 11% of the breast received less than 98% PD. However, the zDVHs of the breast volume in each of seven planes showed the existence of high-dose regions of 34% and 15%, respectively, of the volume in the two caudal-most planes and cold spots of about 40% in the two cephalic planes. In the treatment planning of prostate, DVHs showed that about 15% of the bladder and 40% of the rectum received 102% PD, whereas about 30% of the bladder and 50% of the rectum received the full dose. Taking into account the hollow structure of both the bladder and the rectum, the dose-surface histograms (DSH) showed larger hot-spot volume, about 37% of the bladder wall and 43% of the rectal wall. The zDVHs of the bladder revealed that the hot-spot region was superior to the central axis. The zDVHs of the rectum showed that the high-dose region was an 8-cm segment mostly superior to the central axis. The serial array-like of the rectum warrants a closer attention with regard to the complication probability of the organ.

CONCLUSIONS

Although DVH provides an averaged dose-volume information, zDVH provides differential dose-volume information with respect to the CT slice position. zDVH is a 2D analog of a 3D DVH and, in some situations, more superior. It provides additional information on plan evaluation that otherwise could not be appreciated. The zDVH may be used along with DVH for plan evaluation and for the correlation of radiation outcome.

Ionization chamber shift correction and surface dose measurements in electron beams

Cylindrical ionization chambers produce perturbations (gradient and fluence) in the medium, and hence the point of measurement is not accurately defined in electron beam dosimetry. The gradient perturbation is often corrected by a shift method depending on the type of ion chamber. The shift is in the range of 0.33-0.85 times the inner radius (r) of the ion chamber, upstream from the centre of the chamber, depending upon the dosimetry protocol. This variation in shift causes the surface dose to be uncertain due to the high dose gradient. An investigation was conducted to estimate the effective point of measurement of cylindrical ion chambers in electron beams. Ionization measurements were taken with the ion chamber in air and in a phantom at source to chamber distances of <100 cm and >100 cm respectively. The data in air and in the phantom were fitted with the inverse square and electron depth dose functions, respectively. The intersection of the two functions provides an accurate estimate of the ion chamber shift and the surface dose. Our results show that the shift correction for an ion chamber is energy dependent. The measured shifts vary from 0.9r to 0.5r between 6 MeV and 20 MeV beams respectively. The surface dose measured with the ion chambers and mathematically determined values are in agreement to within 3%. The method presented in this report is unambiguous, fast and reliable for the estimation of surface dose and the shift needed in electron beam dosimetry.

Dose profiles in the region of abutting photon and electron fields in the irradiation of head and neck tumors

In the treatment of head and neck tumors, after excluding the spinal cord from the primary photon beam, en face electron fields are employed to boost the dose to the tissues overlying the spinal cord. The electron fields are "hot-matched" on skin with the posterior edges of the photon fields irradiating the primary tumor. The purpose of this study is to measure the dose distribution in the "hot" matched region between the photon and the en face electron fields. Using film dosimetry, we measured the dose distributions at depths of 1 cm and 3 cm in the junction of the abutting photon (4 MV) and electron (9 MeV) fields for a hot-match setup. Two photon field setups were studied: (1) laterally opposed and, (2) shallow (5 degrees) right and left anterior oblique fields, a configuration sometimes used to avoid treating through the shoulders. To investigate the changes in dose distributions due to setup uncertainties, we also measured dose profiles at the same two depths using a 2 mm overlap and a 2 mm gap between the electron and photon fields. For a perfect hot-match, the dose profile across the junction at 1 cm depth consists of "hot-spots" on both sides of the junction. The minimum and maximum doses across the junction are 15% and 58%, respectively, above the prescribed dose for a parallel opposed setup and 35% and 54%, respectively, for the angled setup. At 3 cm depth, a 10% "cold spot" is observed in the electron field proximal to the junction while a 50% 'hot spot' is observed in the photon field for the opposed lateral setup. With the lateral fields angled 5 degrees anteriorly, hot spots are observed on both sides of the junction. The minimum and maximum doses are 23% and 54%, respectively, above the prescribed dose. With the right and left anterior oblique fields, a 2 mm overlap of the en face electron field with the ipsilateral photon field resulted in a 72% and 65% hot spot at 1 cm and 3 cm depths, respectively, in the photon field adjacent to the junction. A 2 mm gap still resulted in about a 45% hot spot in the same region at both depths. Clinically, if dose to the overlying tissue of the spinal cord is of primary concern, our measurements suggest that 80% normalization in the electron boost, together with a slight angulation of the photon fields would ensure adequate dose to the overlying tissues. If dose inhomogeneity to the superficial tissues is critical in the electron irradiation, 90% dose normalization in the electron boost, together with laterally opposed photon fields would be preferred. The clinical decision can only be made on a patient-by-patient basis.

Patterns of dose variability in radiation prescription of breast cancer

PURPOSE

Comparison of radiation outcome of various treatment protocols is difficult due to the variability of dose prescription. A retrospective analysis of the pattern and intercomparison of dose prescriptions is presented for the treatment of breast cancer.

MATERIALS AND METHODS

To represent the clinical practice for breast irradiation with tangential fields, commonly used prescription points were chosen that lie on the perpendicular bisector of the chest wall separation (s) that represents the breast apex height (h). These points are located at 1.5 cm from the posterior beam edge, at the chest wall-lung interface (2-3 cm), at distances of h/3 and h/2, and at the isocenter. One hundred consecutive patients treated with intact breast following excisional biopsy were used in this study. For analysis, treatment planning was carried out without lung correction with a 6 MV beam for all patients, even though some of the patients were treated with high energy beams for dose uniformity. Dose distributions were optimized with wedges and beam weights to provide a symmetrical dose distribution on the central axis plane. The statistical analyses of the different parameters, s, h, maximum dose, and doses at various prescription points were carried out.

RESULTS

The maximum dose (hot spot) in breast varied from +5% to +27% above the prescribed dose among the patient population. The hot spot was directly related to s, and appeared to be independent of h and the ratio h/s. Among 55%, 40%, and 5% of the patients, the magnitude of the hot spot was 5-10%, 10-15%, and >15%, respectively. Except for the magnitude of the hot spot, the doses at various prescription points were independent of the breast size. For a prescription point at h/3 or at the lung-chest wall interface, the dose variation within +/- 1% is observed for 90% of the patient population. On the other hand, the average dose variation is about +/- 3% among other protocols with dose prescription point varying up to the h/2 point. With the prescription point at the isocenter, an average and maximum variation of 4-5% and 11% were observed, respectively. The maximum dose inhomogeneity for some patients was significantly higher, i.e. up to +27% even without the lung correction.

CONCLUSIONS

A wide variation in prescription dose is observed among the different treatment protocols commonly used in breast treatment. For a total dose of 46-50 Gy delivered at 2 Gy/fraction to the breast, the prescribed dose may vary between 50 and 55 Gy and the hot spot dose per fraction may range between 2.3 and 2.5 Gy depending on the protocol and breast size. Thus dose normalization at hot spot and the isocenter should be discouraged unless the total dose to the breast is modified. A uniform definition of dose prescription for breast treatment is greatly required for intercomparison of clinical data.

Dosimetric comparison of treatment planning systems in irradiation of breast with tangential fields

PURPOSE

The objectives of this study are: (1) to investigate the dosimetric differences of the different treatment planning systems (TPS) in breast irradiation with tangential fields, and (2) to study the effect of beam characteristics on dose distributions in tangential breast irradiation with 6 MV linear accelerators from different manufacturers.

METHODS AND MATERIALS

Nine commercial and two university-based TPS are evaluated in this study. The computed tomographic scan of three representative patients, labeled as "small", "medium" and "large" based on their respective chest wall separations in the central axis plane (CAX) were used. For each patient, the tangential fields were set up in each TPS. The CAX distribution was optimized separately with lung correction, for each TPS based on the same set of optimization conditions. The isodose distributions in two other off-axis planes, one 6 cm cephalic and the other 6 cm caudal to the CAX plane were also computed. To investigate the effect of beam characteristics on dose distributions, a three-dimensional TPS was used to calculate the isodose distributions for three different linear accelerators, the Varian Clinac 6/100, the Siemens MD2 and the Philips SL/7 for the three patients. In addition, dose distributions obtained with 6 MV X-rays from two different accelerators, the Varian Clinac 6/100 and the Varian 2100C, were compared.

RESULTS

For all TPS, the dose distributions in all three planes agreed qualitatively to within +/- 5% for the "small" and the "medium" patients. For the "large" patient, all TPS agreed to within +/- 4% on the CAX plane. The isodose distributions in the caudal plane differed by +/- 5% among all TPS. In the cephalic plane in which the patient separation is much larger than that in the CAX plane, six TPS correctly calculated the dose distribution showing a cold spot in the center of the breast contour. The other five TPS showed that the center of the breast received adequate dose. Isodose distributions for 6 MV X-rays from three different accelerators differed by about +/- 3% for the "small" patient and more than +/- 5% for the "large" patient. For two different 6 MV machines of the same manufacturer, the isodose distribution agreed to within +/- 2% for all three planes for the "large" patient.

CONCLUSION

The differences observed among the various TPS in this study were within +/- 5% for both the "small" and the "medium" patients while doses at the hot spot exhibit a larger variation. The large discrepancy observed in the off-axis plane for the "large" patient is largely due to the inability of most TPS to incorporate the collimator angles in the dose calculation. Only six systems involved agreed to within +/- 5% for all three patients in all calculation planes. The difference in dose distributions obtained with three accelerators from different manufacturers is probably due to the difference in beam profiles. On the other hand, the 6 MV X-rays from two different models of linear accelerators from the same manufacturer have similar beam characteristics and the dose distributions are within +/- 2% of each other throughout the breast volume. In general, multi-institutional breast treatment data can be compared within a +/- 5% accuracy.

Dose estimation to critical organs from vertex field treatment of brain tumors

PURPOSE

Radiation management of intracranial tumors may require a noncoplanar vertex field that often irradiates the entire length of the body. In view of radiation related risks to the normal tissues dose estimation to the extracranial organs such as the thyroid gland, spinal cord, heart, and genitalia is performed for a vertex field.

METHODS AND MATERIALS

A vertex field used clinically was reproduced on an anthropomorphic Rando phantom to measure radiation dose to various organs in the primary beam. Three photon beams (4, 6, and 10 MV), and two high energy electron beams (16 and 20 MeV) were used. Dosimetry was performed with an ion chamber sandwiched between phantom slices at the appropriate positions. All doses were normalized to the target dose at a depth of 5 cm. The effect of the head position was studied by rotating the gantry angle up to +/-20 degrees to mimic the extension and flexion of the head. Theoretical calculation was performed using an exponential best fit to the depth dose table to estimate the dose to various points and compare with the measured dose.

RESULTS

The measured normalized dose to the cervical cord, thyroid, heart, and female and male gonads are 60, 36, 16, 2.5, and 1.6%, respectively, for a 6 MV photon beam. The dose from 4 MV and 10 MV are slightly lower and higher, respectively. Doses from electron beams are about a factor of 4-10 lower than those of the photon beams. The measured gonadal dose from the primary beam is <5% of the target dose for all energies used in the study. The actual value, however, is dependent on the body structure, length, and the posture of the patient. A +5 degree head flexion had little effect on the dose to the various parts of the body. The head rotations greater than +/-10 degrees produced relatively lower doses by a factor of 10(-2) to the organs at distances greater than 40 cm from the prescription point. The radiation doses to the different critical organs estimated from the fitted curves are lower than the measured doses up to 35%.

CONCLUSIONS

When a vertex field is used for the treatment of the brain tumors, the entire axial length of the body is irradiated which adds to the integral dose. Unlike the scattered and leakage radiation, the primary dose to extracranial critical organs is greater for higher energies. For a 10 MV beam the ovary and testis at a distance of 80 cm and 90 cm may receive a dose of 4.2 and 3%, respectively, of the target dose. The gonadal dose could be quite significant if the entire treatment is delivered using a vertex field. For pediatric and smaller patients, dose to the critical organs at known distances could be estimated from the empirical equation obtained from the measured data. While the risk-benefit ratio is often evaluated and acceptable for treating malignant tumors, the long-term complications need thorough assessment in younger and curable patients. In view of radiation carcinogenesis and genetic burden, dose reduction to critical organs should be considered using a 3D planning system to arrange beams in other nonaxial planes and by considering electron beams for the vertex field.

Dosimetry of high energy photon and electron beams with CEA films

With all the advantages of film dosimetry in the megavoltage energy range, the use of film as a dosimeter is still limited due to the various difficulties associated with films such as energy dependence, film orientation, and sensitometric nonlinearity. Recently, therapy verification and localization films (CEA TVS and TLF films) from a Swedish manufacturer have become available in vacuum-sealed water-proof packaging in the US. The packaging renders the CEA films useful in a water phantom and ideal for photon and electron dosimetry. A systematic study has been carried out to investigate the potential of dosimetric application of the new films for high energy photon and electron beams. For the TVS films, the characteristic curve is generally energy independent but appears to be dependent on the source of the radiation, i.e., whether it is gamma rays or bremsstrahlung x rays. Compared to Kodak Readypack XV films, the CEA TVS film is linear in optical density over a much larger range of radiation dose. The inter- and intra-variation of the TVS films is less than 2%. For electrons, the characteristic curve is linear over a similar density range as photons but exhibit a slight energy dependence. TVS film is slightly directional dependent on the incident radiation for both photons and electrons. The perpendicular orientation results in higher optical density than the parallel orientation. The differences are within +/- 2% except in the buildup region for photons and in the exponential fall-off region of the electron beams where differences up to 4% are noted. For the CEA TLF film which is about three times faster than the TVS film, the characteristic curve is reasonably linear over the dose range of 0-15 cGy and energy independent within the experimental uncertainty (+/- 5%). Percent depth dose and isodose measurements with the TVS films are in good agreement with ion chamber results.

Unexplained septicaemia and pneumoperitoneum in Vietnamese boat people: a self-inflicted condition?

BACKGROUND

Ten Vietnamese boat people with septicaemic shock or pneumoperitoneum were admitted between April and July 1993.

METHODS

In order to investigate the cause of unexplained septicaemic shock and spontaneous pneumoperitoneum in Vietnamese boat people, an audit was carried out. Attention was paid to the mode of presentation, abnormal physical signs, presence of injection marks, radiological signs, subsequent progress outcome.

RESULTS

The clinical and radiological findings were all in favour of self-inflicted conditions. A retrospective review from the hospital record revealed that the emergency admission rate and disappearance rate of the Vietnamese boat people was higher than those of other patients (P<0.001).

CONCLUSION

It is concluded that self-inflicted conditions are a serious problem among the Vietnamese boat people, who may use a hospital admission to avoid the detention centre.

Electron-beam characteristics at extended treatment distances

A uniform dose to the target site is required with a knowledge of delivered dose, central axis depth dose, and beam flatness for successful electron treatment at an extended source to surface distance (SSD). The central axis depth dose is shown to be nearly independent of moderate changes in the treatment distance. The delivered dose at a point could be calculated with the concept of virtual source position and an inverse square correction. In an extended SSD treatment, underdosage of the lateral tissue may occur due to reduced beam flatness. To study the changes in beam characteristics, the depth dose and beam flatness were measured at different SSDs for clinically used field sizes [(3 x 3)-(15 x 15) cm2] and beam energies ranging from 6 to 20 MeV. Our results indicate that the changes in depth dose are minimal except in the buildup region for most energies. In general, the surface dose is decreased (< or = 10%) as the SSD is increased moderately. Beam flatness was measured in terms of target coverage factor (TCF) defined as the ratio of the width of a specified isodose line to the geometrical field width. It was observed that the loss in beam flatness is significant for smaller fields, higher isodose lines, and lower energies. Variations in SSD have a minimal effect on the relative changes in beam flatness for field sizes greater than 8 x 8 cm2. The lateral loss of beam uniformity could be estimated by various parameters, such as the full width at half maximum, the homogeneity index, the uniformity index, and the TCF; however, TCF is a simpler parameter to use clinically. The beam characteristics (depth dose and TCF) at extended treatment distances are presented for electron beams.

The spectrum and angular distribution of x rays scattered from a water phantom

To calculate the response of an image receptor to the x rays emerging from a scattering medium, it is necessary to know the x-ray spectrum and intensity as a function of the angle of incidence on the receptor. To permit this calculation for any x-ray spectrum incident on a medium, these functions must be known for monoenergetic x rays. For monoenergetic x rays in the range 20-70 keV we have measured with a high-purity germanium detector the spectrum and intensity of x rays emitted from a water phantom at angles of 0 degree-50 degrees to the direction of the primary beam. The spectrum and intensity of emitted x rays have also been calculated by the Monte Carlo method. At small exit angles, most of the x rays have energies close to the incident energy. As the exit angle increases, the fraction of multiply scattered x rays increases. At very large exit angles, the dominant feature of the spectrum is the peak due to these multiply scattered x rays. For small scattering angles the Monte Carlo calculations are in good agreement with the measurements over the range of energies. For large scattering angeles the scattered photon fluence predicted by Monte Carlo modeling is consistently lower than the measurement in the region just below the full energy peak. The cause of the discrepancies is not fully understood, but cannot be accounted for by Compton broadening alone. An alternate approach to model incoherent scattering is proposed.

The use of gold foil wrapping for radiation protection of the spinal cord for recurrent tumor therapy

PURPOSE

The development of a technique to provide sufficient radiation protection to previously irradiated spinal cord in such a manner that interstitial brachytherapy can be conducted after resection of a recurrent tumor and decompression of the cord.

METHODS AND MATERIALS

A technique was developed that uses multiple layers of gold foil that are applied around the thecal sac and nerve root sleeves to produce an enveloping radiation shield after resection of recurrent tumor. Once the layers of gold foil are in place, interstitial I125 seeds are permanently placed in the bed of the tumor resection to prevent any recurrence from microcellular disease. The technique is described and its application in the case of a 28-year-old with a third recurrence of chondrosarcoma after external fractionated radiation therapy at the second to the fourth thoracic segments is reviewed.

RESULTS

This technique has been used in this first patient. An additional tumor dose of 120.0 Gy was delivered to the tumor bed while the spinal cord was calculated to receive only 1% of the dose over the life span of the implant. To date, this dose of radiation has prevented tumor recurrence for more than 18 months of follow-up.

CONCLUSION

This technique of multiple layers of gold foil shielding over the spinal cord and nerve roots has the potential to be a useful tool for the shielding of a previously irradiated spinal cord in the setting of resection of recurrent tumor. It may also have a wider application to a number of other radiosensitive tumors where interstitial brachytherapy may be useful to provide additional treatment after external fractionated radiation therapy.