Comparison of kilovoltage x-ray and electron beam dose distributions for radiotherapy of the sternum.

The dose distributions for a patient with cancer involving the sternum were calculated for both a kilovoltage x-ray beam and a megavoltage electron beam. The minimum target dose and dose uniformity over the target volume were significantly better using electrons (90%-101%) than kilovoltage x-rays (68%-119%). The calculated lung dose and integral patient dose were also less for electrons than kilovoltage x-rays. For treating cancers of the sternum with radical intent, megavoltage electrons are recommended as the treatment mode of choice rather than kilovoltage x-rays.     

电子线放疗患者屏蔽防护实验研究

目的 探讨1~4层铅围裙（LA,0.5 mm铅当量/层）和自有专利防护装置（BSD,1~2 mm铅当量）对6~15 MeV电子线放疗时野外辐射剂量的屏蔽效果。方法 利用JR1152-B氟化锂热释光剂量片（TLD）,测量不同能量、不同限光筒大小、不同距离处,经不同层数铅围裙和不同厚度BSD屏蔽前、后的野外辐射剂量,计算出铅围裙和BSD对野外辐射的遮挡率,对比分析两种方法的屏蔽效果。结果 当限光筒不变时（10 cm×10 cm）,遮挡率随测量点的距离增加而增大（r=0.717,P < 0.05）,随电子线能量的增大而减小（r=-0.678,P < 0.05）;当能量不变时,遮挡率与限光筒的尺寸大小无相关性（P > 0.05）;对于6和9 MeV的较低能量电子线,1 mm Pb-BSD的遮挡率略高于2层铅围裙（t=2.519、2.662,P < 0.05）, 其变化范围分别为81.5%~95.3%和55.4%~84.6%;对于12和15 MeV的较高能量电子线,2 mm Pb-BSD的遮挡率略高于4层铅围裙（t=3.768、7.934,P < 0.05）,其变化范围分别为64.6%~93.4%和51.1%~92.4%。结论 铅围裙或BSD都能大幅减小野外辐射剂量,可望降低患者野外辐射二次致癌的风险,与铅围裙相比,BSD具有更明显的优势。     

An analytic dosimetry study for the use of radionuclide-liposome conjugates in internal radiotherapy.

A dosimetric analysis has been performed to evaluate the potential of liposome systems as carriers of radionuclides in internal radiotherapy. METHODS: Pharmacokinetic data for a variety of liposome constructs (multilamellar vesicles [MLV]; small unilamellar vesicles [SUV]; and sterically stabilized liposomes, monosialoganglioside [G(M1)]-coated) were used to obtain tumor and normal-organ absorbed dose estimates for (67)Cu, (188)Re, (90)Y, and (131)I. Dosimetry was performed for two tumor models: subcutaneous Ehrlich ascites tumor, growing intramuscularly, and C26 colon carcinoma, growing intrahepatically. Dose estimates were obtained using the MIRD schema. Tumor doses were obtained assuming local deposition of electron energy; photon contributions were incorporated assuming spheric tumor geometry. With the conservative assumption that intravenously administered liposomes achieve rapid equilibration with the red marrow extracellular fluid volume, red marrow absorbed dose estimates were obtained from blood kinetics. RESULTS: For intramuscular tumors, absorbed dose ratios for tumor to red marrow ranged from 0.93 ((131)I-MLV) to 13.9 ((90)Y-SUV). Tumor-to-liver ratios ranged from 0.08 ((188)Re-MLV) to 0.92 ((188)Re-SUV); corresponding values for tumor to spleen were 0.13 ((90)Y-MLV) and 0.54 ((188)Re-G(M1)). The optimal combination of radionuclide and liposome system was obtained with (90)Y-SUV. Tumor-to-liver ratios for the G(M1)-coated construct were greatest when the tumor was intrahepatic (1.13 for (90)Y). For a given liposome system, absorbed dose ratios for tumor to normal tissue exhibited up to a twofold variation depending on the radionuclide selected. CONCLUSION: This study provides a dosimetric evaluation for the use of some liposome systems as carriers in targeted radionuclide therapy. Although much further work must be undertaken before any clinical application is considered, these results suggest that radionuclide targeting using liposomes is feasible and may have the advantage of reduced red marrow absorbed dose.     

An on-line electronic portal imaging system for external beam radiotherapy

A digital imaging system has been constructed to obtain the treatment portal image of a patient during external beam radiotherapy. A DEC LSI-11/23 microcomputer controls a stepper motor, which moves a linear array of 256 silicon diodes to scan the radiation transmitted through the patient. The computer also processes the collected data to generate an image for displaying on a video monitor. The quality of the digital image is comparable to that of the conventional verification radiographs. Major advantages of the system include the speed and simplicity in data storage and retrieval and in its capability of direct comparison with simulation radiographs.     

A comparison of the performance characteristics of four film dosimeters in a 10-MeV electron beam.

Performance characteristics of four routine film dosimeters (CTA, B-3, PVC and LiF (Sunna)) in a 10-MeV electron beam were investigated. Dose response curves for the range 5-40kGy are presented. The dose response curve is linear for the CTA film, supralinear for the LiF (Sunna) film and sublinear for the B-3 and PVC films. The low sensitivity of the CTA film to ionizing radiation restricts its use to high doses, while the supralinear response curve of the LiF (Sunna) dosimeter allows this film to be used only in measurements of low doses. The optical absorption temperature coefficients for the CTA, B-3 and LiF (Sunna) films were found to be at the level of +/-0.1%/( composite function)C. The temperature coefficient for the PVC film decreased from +0.35%/( composite function)C immediately after irradiation to +0.04%/( composite function)C three months later. Because of the significant time dependence of the PVC film signal, a careful standardization of the heating regimen and of the time between the irradiations and measurements is necessary.     

Wall-scattering effects in electron beam collimation.

This report describes now a set of applicators, convering fields with dimensions of 4 to 20 cm, for the 6 to 20 MeV electron beams of a MEL SL75-20 linear accelerator was developed. The electron scatter contribution of the applicator walls to the treatment field was investigated, varying the applicator entrance opening and the scattering foil, with the aim of optimizing the resulting field flatness, with a minimum loss of depth dose. Experiments with field defining end frames and additional perspex scatterers for large field sizes are also reported.     

A comparison of protocols for external beam radiotherapy beam calibrations

A number of codes of practice (CoP) for electron and photon radiotherapy beam dosimetry are currently in use. Comparison is made of the more widely used of these, specifically those of the International Atomic Energy Agency (IAEA TRS-398), the American Association of Physicists in Medicine (AAPM TG-51) and the Institute of Physics and Engineering in Medicine (IPEM 2003). All are based on calibration of ionization chambers in terms of absorbed dose to water, each seeking to reduce uncertainty in delivered dose, providing an even stronger system of primary standards than previous air-kerma based approaches. They also provide a firm, traceable and straight-forward formalism (Radiology, 1996). Included in making dose assessments for the three CoP are calibration coefficients for a range of beam quality indices. Measurements have been performed using clinical photon and electron beams, the absorbed dose to water being obtained following the recommendations given by each code. Electron beam comparisons have been carried out using measurements for electron beams of nominal energies 6, 9, 12, 16 and 20 MeV. Comparisons were also carried out for photon beams of nominal energies 6 and 18 MV. For photon beams use was made of NE2571 cylindrical graphite walled ionization chambers, cross-calibrated against an NE2611 Secondary Standard; for electron beams, PTW Markus and NACP-02 plane-parallel chambers were used. Irradiations were made using Varian 600C/2100C linacs, supported by water tanks and Virtual Water? phantoms. The absorbed doses for photon and electron beams obtained following these CoP are all in good agreement, with deviations of less than 2%. A number of studies have been carried out by different groups in different countries to examine the consistency of dosimetry codes of practice or protocols. The aim of these studies is to confirm that the goal of those codes is met, namely uniformity in establishment of dosimetry of all radiation beam types used in cancer therapy in the world, and this is one of the studies.     

Modified Blalock-Taussig shunt patency for pulmonary atresia: assessment with electron beam CT

PURPOSE: The purpose of this work was to evaluate electron beam CT (EBCT) for the noninvasive assessment of modified Blalock-Taussig (BT) shunt patency in patients with pulmonary atresia. METHOD: Five infants and children with pulmonary atresia and modified BT shunts underwent contrast-enhanced EBCT. Modified BT shunts from the subclavian artery to the pulmonary artery were performed to improve the pulmonary blood flow. Electrocardiogram (ECG)-triggered EBCT was obtained with a 100 ms exposure, 3 mm section thickness, and 2 mm table feed after intravenous administration of contrast material. Three-dimensional (3D) or maximum intensity projection (MIP) EBCT images were compared with conventional angiography. The visibility of modified BT shunts was graded and recorded with use of a four-point scale. RESULTS: Satisfactory visualization was achieved in both 3D and MIP EBCT images to evaluate modified BT shunt patency. CONCLUSION: Contrast-enhanced 3D or MIP EBCT imaging with ECG trigger may be used as an effective substitute to evaluate modified BT shunts with low radiation dose exposure.     

Fast neutron beam radiotherapy of glioblastoma multiforme.

Twenty-one patients with glioblastoma multiforme were treated with fast neutron beam irradiation of the whole brain. Therapy was well tolerated up to calculated doses of 1.850 radn+y in 12-18 increments over 6 weeks. The survival rate 6 month after initiation of treatment was 62%, not significantly different from conventional photon therapy; average posttreatment survival appears to be shortened compared to photon therapy. No improvement or prolonged maintenance of existing neurologic function was observed. Autopsy findings in seven patients showed replacement of tumor by coagulative necrosis persisting at least 16 months posttreatment, paucity of tumor cells with infrequent mitosis, and suppression of macrophage response. These findings differ from those in conventionally irradiated patients. No treatment-related changes were documented by conventional gross and histologic studies of the irradiated brains distant from the tumors. Thus the deaths of patients in this study appear to be related to unexplained causes other than progressive growth of tumor.     

Characterization and use of a commercial n-type diode system.

The characteristics of n-type diodes (linearity, temperature, dose rate, radiation damage response, directional dependence, output factors, wedge factors and percentage depth dose determinations) were investigated. Subsequently, the diodes were used clinically for in vivo dose verification during external megavoltage photon beam therapy. It has been shown that n-type diodes are easy to use and the results obtained are comparable to those reported for p-type diodes. On most occasions, n-type diodes can be used without any additional correction factors apart from regular monthly calibration. There is good agreement between the uncertainty limits estimated from the diodes' characteristics and those obtained on the basis of 2261 patient measurements.     

An assessment of radionuclidic impurities of (210)Po produced via neutron irradiation of (209)Bi for use in targeted alpha-particle radiotherapy.

Radionuclidic impurities of (210)Po prepared by neutron irradiation of (209)Bi via the (209)Bi(n,gamma)(210)Bi reaction were investigated. Following irradiation and ingrowth, a pure (210)Po solution was obtained by sublimation and dissolution. Results were obtained by liquid scintillation (LS) counting, isotope dilution alpha (alpha)-spectrometry, and high-purity germanium gamma-ray spectrometry. No alpha-emitting (3-10MeV) or gamma-emitting (30-3600keV) impurities were detected, with calculated lower limits of detection for impurities of approximately 0.01% (210)Po activity. LS spectra revealed no identifiable beta-emitting impurity. LS sources prepared using Opti-Phase 'Hi Safe' III and Opti-Fluor LS cocktails were stable over a 4-day multi-cycle counting period for (210)Po dissolved in 0.1% trifluoracetic acid (pH approximately 2, water fraction approximately 2%). The radioactivity concentration determined by LS counting was verified by isotope dilution alpha spectrometry. These results suggest that neutron irradiation of (209)Bi (followed by sublimation) can produce (210)Po in a highly pure form that is suitable for radiopharmaceutical preparations.     

Monitoring of prostate-specific antigen during external beam radiotherapy for carcinoma of the prostate.

In 35 patients with histologically confirmed carcinoma of the prostate confined to the pelvis, the value of prostate-specific antigen (PSA) was evaluated during external beam radiotherapy to the prostate and draining pelvic lymph nodes. In eleven patients initial prostate-specific antigen levels were more than 10 ng/ml and in twelve patients between 4 and 10 ng/ml. In the remaining twelve, initial prostate-specific antigen levels were less than 4 ng/ml. In the course of radiotherapy we could see a significant decrease of the prostate-specific antigen, even in those with levels between 4 and 10 ng/ml. This decrease seems to follow a logarithmic course but, because only three measurements during radiotherapy were made, this needs further study. With higher levels (more than 20 ng/ml), we rarely saw a value of less than 10 ng/ml at the end of radiotherapy but had to wait for several months for lower values to be reached. In several cases prostate-specific antigen decrease took up to three months after the end of the radiation course. Our results indicate that prostate-specific antigen values actually start decreasing during the radiation course itself and may, therefore, be useful for monitoring response to radiotherapy.     

Elective irradiation with the electron beam after mastectomy for breast cancer.

From 1963 to 1970, 380 patients have received elective treatment with the electron beam after radical mastectomy for breast cancer. One hundred and twenty-nine patients received treatment to the supraclavicular and internal mammary lymph node areas only, and 251 patients received treatment to the chest wall as well as to the areas of peripheral lymphatic drainage. Analysis of the results shows the value of elective irradiation of occult deposits of disease since the incidence of local recurrences is significantly less than would be anticipated in this group of patients.