Use of the entire spectrum of irradiated alanine for dosimetry.

Alanine is an amino acid commonly used in ESR dosimetry as a reference detector. The classic approach for the measurement of irradiated samples is to determine the amplitude of the central peak of the first derivative spectrum. It is generally considered that this technique represents the best and most reproducible solution for achieving an accurate proportionality between the concentration of free radicals inside the resonant cavity, characterized by the amplitude, and the dose. It is also accepted that this central peak corresponds to the free radical CH3CHCOO-. The hyperfine structure of this radical in the spectrum shows five main peaks with the approximate ratios 1:4:6:4:1 as regards coupling. This paper presents another approach featuring analysis of the entire spectrum: (i) ratios of identified peaks, (ii) ratio variation vs time with regard to several parameters affecting fading. These variations in the alanine spectrum are probably correlated with the variation of the concentrations of different free radical species. These variations and their positions in the spectrum are very important constraints that increase the uncertainty of this type of measurement.     

One year of experience with alanine dosimetry in radiotherapy

Commercially available alanine dosimeters from different manufacturers were purchased for this study. The response of the detectors was evaluated with ⁶⁰Co gamma radiation in the dose range 0.2–200 Gy, using a small EPR spectrometer dedicated to dosimetry. The batch sensitivity, inter-specimen scattering and background signal for the different selection of dosimeters were evaluated. The usefulness of the alanine dosimetry system for clinical routine is illustrated by in vivo measurements during ¹⁹²Ir brachytherapy of cervix carcinoma.     

Use of a modified natural-rubber phantom for radiotherapy dosimetry measurements

The utility of a phantom material, based on SMR(L) [Standard Malaysian Rubber] grade natural rubber and a formulation used for the proprietary rubber phantom-material, Temex, has been examined for the 1-MeV photon-energy range using γ radiation from a ⁶⁰Co source. Measurement has also been performed with 60-keV photons using the radionuclide ²⁴¹Am. At photon-therapy energy levels the measured response, when compared with tabulated central-axis percentage depth doses for the defined measuring conditions, produces everywhere (in the range 1–19 cm depth) better than 2% deviation. The favourable measured response characteristics combined with the ease of processing and casting the phantom material provide the basis for useful radiotherapy machine calibration and anthropomorphic dosimetry measurements. The measured mass-attenuation coefficient, at 60 keV, of 0.204 cm² g^-1 (±3%) is in close agreement with tabulated values for water (0.2055 cm² g^-1).     

A unique calibration curve for alanine EPR dosimetry systems

The alanine EPR dose-response curve was proposed to follow a saturating exponential function. In this study the characteristic parameter D₃₇3of the exponential function was estimated for two types of dosimeters and different EPR spectrometer configurations. The results suggest that only below about 0.3 mW the alanine EPR signal is not saturated with microwave power. A unique alanine calibration curve is suggested for measurements with non-saturating microwave power.     

Design of a multiblock phantom for radiotherapy dosimetry applications.

This note describes the design of a multiblock semi-anatomic phantom, which lends itself to a variety of radiotherapy dosimetry applications, in particular, the audit of external beam treatment planning and delivery. The basic building blocks of the phantom were formed from a variety of tissue substitute materials and could be assembled in many ways to model different cross-sections through the body.     

Biological intercomparisons of neutron beams used for radiotherapy generated by p(+)-->Be in hospital-based cyclotrons.

The new generation of hospital-based neutron therapy facilities involve cyclotrons using protons on beryllium. The spectrum of neutrons produced includes a large and variable proportion of low-energy neutrons that are poorly penetrating but biologically effective. Cells cultured in vitro were used to compare the three US facilities at Seattle, M.D. Anderson and UCLA, together with the UK facility at Clatterbridge. Cyclotrons were compared within a given experiment on the same day using cells from a common suspension. Among the three US facilities, the relative potency factor at a depth of 25 mm differs by about 11%, with Seattle the least and UCLA the most biologically effective. Clatterbridge was compared directly with M.D. Anderson and found to be less effective by about 5%; it has a slightly lower biological effectiveness than any of the US facilities. There is evidence for an increased biological effectiveness in the build-up region, which reduces the effective skin sparing potential. There is not much difference in build-up between the three US facilities. Using the proton-on-beryllium neutron production process results in a wide spectrum of neutrons with a large but variable low-energy component. The biological effectiveness of the beam depends on target design and thickness as well as the design of the collimating system. Consequently the biological effectiveness of neutron beams generated by this process must be assessed on an individual basis. It cannot be assumed that because cyclotrons have similar accelerating energies that the relative biological effectiveness will be the same.     

术中放疗的吸收剂量测算方法的研究

目的 研究和比较水、固体水及有机玻璃3种模体的术中放疗吸收剂量的测算方法。方法 对于3种模体,使用固定在水模体中的电离室对加速器的电子速术中放疗限光筒进行吸收剂量的测算,首先选定参考限光筒对所有能量的电子束在源皮距SSD=100cm,水模内射束中心轴上特定深度,通过调整加速器使1cGy=1MU,然后使用术中放疗及参考限光筒在相同的辐照条件下进行测量,即测量术中放疗限光筒的输出因数,对于水模体,计算出各限光筒的吸收剂量cGy对应的加速器输出MU数值,并据此计算出固体水模体和有机玻璃模体的各限光筒吸收剂量cGy对应的加速器输出的MU数值,结果 相对于水模体,有机玻璃模体的测量误差为0.27%,固体水为0.45%。结论 对没有专用测量水箱和固体水的医院使用有机玻璃模体进行吸收剂量的测量不失为一种切实可行的方法。     

全中枢神经系统肿瘤放疗技术的剂量学研究

目的 以三维适形放疗技术为参照,探讨中枢神经系统肿瘤简单调强(sIMRT)放疗技术的剂量学特性。方法 选取5名已行全脑全脊髓放疗患者,为每位患者设计3D-CRT计划、3野和5野sIMRT计划。利用剂量分布和剂量体积直方图(DVH),评价不同照射技术的靶区和正常器官的照射剂量、靶区剂量均匀性(HI),通过总的机器跳数(MU)间接比较不同照射技术的治疗时间。结果 3D-CRT在射野衔接处只有处方剂量的70%。计划靶区后缘的正常组织接受的剂量达到处方剂量的140%。3野和5野sIMRT计划的靶区剂量均匀性分别为0.09±0.01和0.08±0.01,优于3D-CRT计划的0.18±0.02 (t=7.80、7.65,P<0.05);心脏V₁₀分别为(8.4±1.9)%和(8.4±2.0)%,低于3D-CRT计划的(36.0±6.0)%(t=13.3、13,0,P<0.05);甲状腺V₂₀分别为(12.4±1.5)%和(12.4±1.6)%,低于3D-CRT计划的(69.4±5.7)%(t=26.3、26.4,P<0.05);喉V₂₀分别为(17.2±1.2)%和(17.9±1.5)%,低于3D-CRT计划的(89.4±7.0)%(t=25.5、26.5,P<0.05);靶区后缘正常组织V₃₀分别为(4.4±1.4)%,(4.9±1.9)%,低于3D-CRT计划的(31.9±6.1)%(t=8.5、10.1,P<0.05);平均机器跳数(MU)分别为1100±106和1160±129,高于3D-CRT计划的640±78。结论 3野和5野sIMRT计划在剂量分布、危及器官(OAR)保护、靶区剂量均匀性等方面均好于3D-CRT计划。     

Electron arc therapy treatment planning verification with alanine/EPR dosimetry.

Alanine/EPR dosimetry was applied to measure dose distributions during electron arc therapy treatments generated by electron beams moving isocentrically over a stated arc. Alanine-polyethylene pellets, prepared at ISS according to the NIST recipe, inserted in a homogeneous cylindrical and anthropomorphic phantoms, were used. Preliminary, alanine response to static electron beams in the (6-20) MeV nominal energy range was studied. Then alanine dosimetry was applied to determine the dose versus the gantry angle at a reference point in a cylindrical homogeneous phantom. Finally, arc therapy treatment planning verification was performed in anthropomorphic phantom.     

Application of an alanine dosimetry system for industrial irradiation and radiation protection

This paper reports the application of alanine dosimetry in radiation processing. Continuous checks of the EPR measuring conditions as well as using high-quality alanine dosimeters and consistent technique for dose determination guarantee an accuracy of about ±3% intermediate dose levels. The alanine dosimetry system was applied for dose mapping measurements during irradiator qualification and performance qualification of different products, routine dosimetry, and special radiation protection application within the gamma irradiator.     

Carotid dosimetry for T1 glottic cancer radiotherapy

Objective:

Radiotherapy for T1 glottic cancer is commonly delivered using a lateral parallel opposed pair of megavoltage photon fields. There is increasing reported evidence of cerebrovascular events due to radiation-induced carotid stenosis. An alternative field arrangement is to use an anterior oblique technique. This study compares the carotid dosimetry between the two techniques and reviews the evidence for the risk of radiation-induced vascular events.

Methods:

The radiotherapy plans of 10 patients with T1 glottic cancer treated with an anterior oblique technique were examined for carotid dose. Alternative plans were then created using a parallel opposed pair of fields and the dose to the carotids compared. All patients received 50 Gy in 16 fractions treating once daily, for 5 days in a week.

Results:

The average of the mean dose to the carotids with the anterior oblique technique was 21 Gy compared with 37 Gy using the lateral parallel opposed pair arrangement (p < 0.0001).

Conclusion:

An anterior oblique field arrangement for the treatment of T1 glottic cancer results in a significantly lower radiation dose to the carotid arteries, which may be clinically important in terms of reducing the risk of cerebrovascular events in long-term survivors.

Advances in knowledge:

Although the anterior oblique technique for treating early glottic cancers is well described, and it is predictable that the dose received by the carotid arteries should be lower with this technique, to our knowledge this is the first study to quantify that reduction in dose with a series of patients.For other than clearly defined vocal cord lesions clear of the anterior commissure, radiotherapy remains the mainstay of curative treatment for T1 glottic cancer.^1,2 The radiotherapy target volume should be confined to the larynx without any attempt to encompass neck nodes. There is increasing reported evidence of late cerebrovascular events such as transient ischaemic attacks and ischaemic strokes due to radiation-induced injury of the carotid artery, e.g. accelerated arteriosclerosis. These vascular events can occur many years after radiotherapy such that their relationship to previous radiotherapy is obscured.Classically, a lateral parallel opposed pair of megavoltage photon fields is used for the treatment of early glottic cancer. An alternative approach is an anterior oblique technique, which we adopted following the introduction of a linear accelerator in our centre in 1955 (Figure 1). We aim to assess the extent of carotid exposure, to compare the carotid dosimetry between anterior oblique and lateral parallel opposed pair techniques and also to review the evidence for the increased risk of vascular events.Open in a separate windowFigure 1.Diagram showing the anterior oblique field arrangement.     

非参考条件下放射治疗剂量的TLD比对结果

目的在北京地区三级甲等医院中,用TLD完成非参考条件下放射治疗剂量比对。方法TLD系统用60Coγ线束校准。TLD读数经能量响应及TLD支架减弱等校正因子的修正。结果高能光子束DEAG/DUSER的平均比值是1.001;高能电子束DEAG/DUSER的平均比值是1.000。结论按照IAEA的要求,医院的TLD剂量比对扩展不确定度（k=2）不大于5%。比对结果表明,参加比对的这些医院的高能光子束的合格率是98%,高能电子束的合格率是100%。     

EC intercomparisons for laboratories monitoring environmental radioactivity.

International measurement comparisons are organised regularly for EU laboratories involved in monitoring radioactivity, with emphasis on meeting routine measurement conditions. Using the recent comparison of 137Cs in air filters as an example, the whole cycle is described: establishment of traceable reference values, spiking of individual filters for the comparison and their quality assurance, treatment and measurement of filters in the participating laboratories and evaluation of comparison results. The treatment of an individual result, deviating widely from the reference value, is discussed. Monte-Carlo simulations allow to estimate the maximum errors possibly made due to a non-suitable measurement geometry.     

An application of film dosimetry for helium ion radiotherapy

Clinical dosimetry of complex dose distribution associated with charged particle radiotherapy requires a rapid and convenient technique with a spatial resolution of 3 mm or better. Radiographic film stacks have been evaluated for three-dimensional dosimetry of charged particle beams. Sheets of Cronex 4 film are placed between lucite spacers in a light-tight box and the beam is directed perpendicularly to the film surface. Optical densities on each sheet are digitized with a video digitizer and corrected for density-dose nonlinearity and LET effects. A three-dimensional matrix of the measured dose is constructed and compared with calculated values. Both transverse and depth dose data recorded by film have been compared with diode measurements and generally shown agreement within 5%. The present technique appears to be an effective method to generate experimentally measured dose distributions.     

K-band EPR dosimetry: small-field beam profile determination with miniature alanine dosimeter.

The use of small-size alanine dosimeters presents a challenge because the signal intensity is less than the spectrometer sensitivity. K-band (24 GHz) EPR spectrometer seems to be a good compromise between size and sensitivity of the sample. Miniature alanine pellets were evaluated for small-field radiation dosimetry. Dosimeters of DL-alanine/PVC with dimensions of 1.5 mm diameter and 2.5 mm length with 5 mg mass were developed. These dosimeters were irradiated with 10 MV X-rays in the dose range 0.05-60 Gy and the first harmonic (1h) spectra were recorded. Microwave power, frequency and amplitude of modulation were optimized to obtain the best signal-to-noise ratio (S/N). For beam profile determination, a group of 25 dosimeters were placed in an acrylic device with dimensions of (7.5 x 2.5 x 1)cm3 and irradiated with a (3 x 3)cm2 10 MV X-rays beam field size. The dose at the central region of the beam was 20 Gy at a depth of 2.2 cm (build up for acrylic). The acrylic device was oriented perpendicular to the beam axis and to the gantry rotation axis. For the purposes of comparison of the spatial resolution, the beam profile was also determined with a radiographic film and 2 mm aperture optical densitometer; in this case the dose was 1 cGy. The results showed a similar spatial resolution for both types of dosimeters. The dispersion in dose reading was larger for alanine in comparison with the film, but alanine dosimeters can be read faster and more directly than film over a wide dose range.     

Measurements with alanine and film dosimeters for industrial 10 MeV electron reference dosimetry

Alanine and radiochromic film dosimeters were irradiated with absorbed doses from 3 to 10 kGy at a 10 MeV electron accelerator under typical radiation processing conditions. The nominal doses were measured by graphite calorimeters and the dosimeters were irradiated in graphite phantoms. The dosimeters were calibrated by irradiation with ⁶⁰Co photons.The ratios of calorimeter to film and alanine dosimeter readings were generally within 0.99 ± 0.01 for 10 mm phantoms, but larger differences were observed for 20 mm phantoms. The discrepancies may be due to uncertainties in irradiation geometry, or in the stopping power ratios applied.     

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.