Dosimetry characteristics of GAFCHROMIC EBT film responding to therapeutic electron beams.

For the last 50 years, high-energy electron beams have been used mainly for treatment of superficial targets. Accordingly, two-dimensional (2D) measurements are required to determine the margin between the surface and protected normal tissues in high-dose-gradient regions. As recommended by the AAPM, 2D electron beam dosimetry should be conducted primarily with films because of their high spatial resolution and because of the fact that they produce permanent records. In this work, the dosimetric characteristics of a newly developed radiochromic film, GAFCHROMIC EBT film were used to study treatment parameters for therapeutic electron beams. The dose-response curve was found to be weakly dependent on the electron beam energy (within +/-4%). The effect of fractionation, as well as electron beam dose rate, had small influence on the calibration curve of EBT films (+/-2.5% and 2%, respectively). For the investigated range of depth, dose-response curves are nearly independent of the calibration depth. As for the cone size dependence, we found that it is accurate to calibrate GAFCHROMIC EBT films using a 10 x 10 cm(2) cone and apply this calibration to other cone sizes.     

Problems of dose modification in total body irradiation

Physical treatment planning of total body irradiation (TBI) has the goal to optimize the spatial distribution of dose, taking radiobiological requirements and technical possibilities into account. In order to improve the dose homogeneity in the target volume or to reduce dose and dose rate in organs at risk dose modifications are needed to raise or to lower the local dose. Treatment optimization demands to know possible techniques, the methods of individual planning and calculation as well as the limitations of beam modifying aids.     

In vivo ESR dosimetry in total body irradiation

Total body irradiation (TBI) using high doses (about 10 Gy) with photons in the range between 1 and 10 MV combined with intensive chemotherapy has been used successfully in treatment of acute and chronic leukemia before bone marrow transplantation. One of the principal international guidelines in TBI is to use in vivo dosimetry in order to compare the prescribed dose with that absorbed. The use of in vivo dosimetry is also useful as a retrospective evaluation of any deviation from the prescribed dose greater than +/- 5% for relevant parts of the body, especially in the lung and in other organs at risk. In this paper, Electron Spin Resonance (ESR), using alanine dosimeters, is demonstrated to be a powerful tool for absorbed dose evaluation in TBI by detection of free radicals produced in alanine by ionizing radiation. In this study, we present the results obtained using ESR dosimetry in eleven patients undergoing TBI. The major advantages appear to be: 1. the ESR signal in alanine dosimetry is stable for years without fading: 2. the detection of the ESR signal does not destroy the information and so enables a retrospective judgment of the TBI plan adopted.     

Secondary radiation dose during high-energy total body irradiation

Aim

The goal of this work was to assess the additional dose from secondary neutrons and γ-rays generated during total body irradiation (TBI) using a medical linac X-ray beam.

Background

Nuclear reactions that occur in the accelerator construction during emission of high-energy beams in teleradiotherapy are the source of secondary radiation. Induced activity is dependent on the half-lives of the generated radionuclides, whereas neutron flux accompanies the treatment process only.

Materials and methods

The TBI procedure using a 18 MV beam (Clinac 2100) was considered. Lateral and anterior–posterior/posterior–anterior fractions were investigated during delivery of 2 Gy of therapeutic dose. Neutron and photon flux densities were measured using neutron activation analysis (NAA) and semiconductor spectrometry. The secondary dose was estimated applying the fluence-to-dose conversion coefficients.

Results

The main contribution to the secondary dose is associated with fast neutrons. The main sources of γ-radiation are the following: ⁵⁶Mn in the stainless steel and ¹⁸⁷W of the collimation system as well as positron emitters, activated via (n,γ) and (γ,n) processes, respectively. In addition to 12 Gy of therapeutic dose, the patient could receive 57.43 mSv in the studied conditions, including 4.63 μSv from activated radionuclides.

Conclusion

Neutron dose is mainly influenced by the time of beam emission. However, it is moderated by long source–surface distances (SSD) and application of plexiglass plates covering the patient body during treatment. Secondary radiation gives the whole body a dose, which should be taken into consideration especially when one fraction of irradiation does not cover the whole body at once.     

Benefits of online in vivo dosimetry for single-fraction total body irradiation

Use of a patient test dose before single-fraction total body irradiation (TBI) allows review of in vivo dosimetry and modification of the main treatment setup. However, use of computed tomography (CT) planning and online in vivo dosimetry may reduce the need for this additional step. Patients were treated using a supine CT-planned extended source-to-surface distance (SSD) technique with lead compensators and bolus. In vivo dosimetry was performed using thermoluminescent dosimeters (TLDs) and diodes at 10 representative anatomical locations, for both a 0.1-Gy test dose and the treatment dose. In total, 28 patients were treated between April 2007 and July 2013, with changes made in 10 cases (36%) following test dose results. Overall, 98.1% of measured in vivo treatment doses were within 10% of the prescribed dose, compared with 97.0% of test dose readings. Changes made following the test dose could have been applied during the single-fraction treatment itself, assuming that the dose was delivered in subportions and online in vivo dosimetry was available for all clinically important anatomical sites. This alleviates the need for a test dose, saving considerable time and resources.     

The accuracy of dose determination during total body irradiation

AIM: The aim of this work was to estimate the error in dose calculations, to check the agreement between the measured and calculated doses and to analyse dose discrepancies in the group of patients undergoing total body irradiation. PATIENTS AND METHODS: A combination of lateral and anterior-posterior fields was used in 8 fractions and on 4 consecutive days. Doses were preliminarily calculated and then measured in vivo by thermoluminescent, semiconductor and ionization dosimeters attached to the body in 10 representative transverse cross-sections. Calculations and measurements were carried out for the beam at the body entry and exit. The error in dose calculations was estimated for each reference point. Dose deviations between calculations and measurements were analysed using the Student's t-test. RESULTS: The error in preliminary dose calculations ranged from 3% to 15% (Table 1). Standard deviations of the measurements and percent deviations from the calculations exceeded 10% only for the lung and neck exits (Table 3). Average thermoluminescent readings were 6% higher than the corresponding semiconductor readings. The measured doses fitted the calculated values within the limit of error, except for the lung, head and neck exits for the whole group, depending on the type of fields used (Table 4).     

Lung dose rate and interstitial pneumonitis in total body irradiation for bone marrow transplantation.

The effect of dose rate to the lungs and development of interstitial pneumonitis (IP) was evaluated in 114 bone marrow transplant patients receiving fractionated total body irradiation (TBI) (1200 rads TD in 6 fractions twice daily over 3 days) as part of their pre-conditioning regimen. The tumour dose (TD) was calculated as the mean lung dose as previously described (1). A 6MV linear accelerator at a mid-line dose rate of 7.5 rads/minute was used between March 1981 and June 1985 and a Co-60 source at 5 rads/minute thereafter. This resulted in a range of dose rates to the lung of between 6.9 and 8.9 rads/minute and 2.9 and 6.5 rads/minute respectively. In the majority of patients the aetiology of IP was investigated by lung biopsy with histology and culture. There was no statistically significant difference in the incidence of IP over the two sets of dose rates. Our study suggest that the incidence of IP using fractionated TBI is not influenced by dose rates below 8.9 rads per minute.     

大剂量全身照射比格狗生物效应观察

目的 :为极重度骨髓型急性放射病实验治疗提供依据 ,观察了不同剂量照射比格狗的生物效应。方法 :60 Coγ辐射源分别照射 6 .5 ,5 .5 ,5 .0 ,4.5 ,3.5 ,2 .5Gy ,照射剂量率为 7.2 2 4× 10 _2 C/(kg·min)。观察照射动物的一般临床表现、外周血细胞计数、骨髓细胞培养。结果 :所有比格狗于照射后 0 .5～ 2h均有呕吐。 6 .5Gy照射组动物于照射后第 2天出现腹泻 ,并伴有白色黏液 ,其中 3只动物出现血水样便或咖啡样便。 5 .5Gy组有个别动物出现水样便 ,而 4.5Gy以下剂量照射组动物出现一般稀便。比格狗除 2 .5Gy组有一只动物活存外 ,其余均死亡 ,各组死亡动物平均活存时间依剂量的大小分别为 5 .0 ,8.0 ,9.3,9.5 ,10 .5和 14.1d。照射后 1d骨髓造血祖细胞集落数随照射剂量的增加而明显减少。照射后外周血白细胞和血小板数最低值出现时间随照射剂量的增大而提前 ,且剂量效应关系显著。结论 :对临床症状、外周血白细胞及活存时间的分析结果表明 ,比格狗的极重度骨髓型急性放射病 (偏轻 )模型的全身照射剂量为 4.5～ 5 .0Gy。     

Estimation of the mean effective organ doses for total body irradiation from Rando phantom measurements.

For the total body irradiation (TBI) procedure, it is necessary to compare the mean dose obtained from the tissue or organs and the estimated dose equivalent value from the computer program. Due to the easy-access of the Rando phantom and repeatability of TLDs and its output, the results from the experiment are quite encouraging for the verification of the dose distributions from total body irradiation at the given prescribed monitor units. The estimation of effective dose equivalent particularly across the lung sections was studied by combinations of using arms as the scatter volume to compensate for the inhomogeneity across the breast portion, as well as using the spoiler for skin-sparing purposes. The results were based upon various beam quality such as 4 MV, 6 MV, and 10 MV X rays. One series of experiments performed for this survey to ascertain the dose equivalent of the tissues was conducted. This paper describes the method and procedure for comparison between the measured data and computed data as a reference in the dosimetry of total body irradiation. Comparison of the measured and computed data for the largest collimated field shows that the calculated dose rates do not differ by more than 2% from the measured data. Because uncertainty is inherent in non-patient-like phantoms, the calculated data may be served as a reference for the dosimetry. For the total body irradiation setup, considering the radiation field size and treatment distances commonly employed, we conclude that the best combination of the patient setup will be (1) laying both arms down as compensation for lung inhomogeneity, and (2) the spoiler, which is made of acrylic about 8 mm thick and functions like a bolus, is needed to reduce the skin sparing effects and contribute the uniform dose distribution. The beam spoiler with the frame stands near the patient during the treatment.     

Investigation of dose homogeneity in paediatric anthropomorphic phantoms for a simple total body irradiation technique

The technique for treating total body irradiation patients used at the centre involves no compensation for the inhomogeneity of patient shape. Dose is prescribed to the lung, and monitor units are derived from standard data depending on the external dimensions of the patient at nipple level. Dose measurements were made during standard treatments on three paediatric anthropomorphic phantoms representing children of 5, 10 and 15 years of age. The results confirmed that the measured dose to the lung was within 4% of the prescribed dose, and dose homogeneity was within +/- 5%, excluding the neck, where the higher measured doses were still within tissue tolerance.     

Appropriate treatment planning method for field joint dose in total body irradiation using helical tomotherapy

Total body irradiation (TBI) using helical tomotherapy (HT) has advantages over the standard linear accelerator-based approach to the conditioning regimen for hematopoietic cell transplantation. However, the radiation field has to be divided into two independent irradiation plans to deliver a homogeneous dose to the whole body. A clinical target volume near the skin increases the skin surface dose; therefore, high- or low-dose regions arise depending on the set-up position accuracy because the two radiation fields are somewhat overlapped or separated. We aimed to determine an adequate treatment planning method robust to the set-up accuracy for the field joint dose distribution using HT-TBI. We calculated treatment plans reducing target volumes at the interface between the upper and lower body irradiations and evaluated these joint dose distributions via simulation and experimental studies. Target volumes used for the optimization calculation were reduced by 0, 0.5, 1.0, 2.0, 2.5, and 3.0 cm from the boundary surface on the upper and lower sides. Combined dose distributions with set-up error simulated by modifying coordinate positions were investigated to find the optimal planning method. In the ideal set-up position, the target volume without a gap area caused field junctional doses of up to approximately 200%; therefore, target volumes reduced by 2.0–3.0 cm could suppress the maximum dose to within 150%. However, with set-up error, high-dose areas exceeding 150% and low-dose areas below 100% were found with 2.0 and 3.0 cm target volume reduction. Using the dynamic jaw (DJ) system, dose deviations caused by set-up error reached approximately 20%, which is not suitable for HT-TBI. Moreover, these dose distributions can be easily adjusted when combined with the intensity modulation technique for field boundary regions. The results of a simulation and experimental study using a film dosimetry were almost identical, which indicated that reducing the target volume at the field boundary surface by 2.5 cm produces the most appropriate target definition.     

全身(全淋巴)照射后100例医源性急性放射病的临床分析

在造血干细胞移植治疗肿瘤过程中用全身照射（ＴＢＩ）或全淋巴照射（ＴＬＩ）预处理，研究受照不同剂量患者发生医源性急性放射病严重程度，治疗方法和造血恢复及相关合并症。方法１００例患者（白血病９１例，其他肿瘤９例）接受５００～１０００ｃＧｙＴＢＩ或ＴＬＩ和超大剂量化疗作预处理。结果均发生医源性急性放射病，白细胞降至（０～０．１５）×１０９／Ｌ，骨髓空虚，合并各种感染和出血。经造血干细胞移植，抗感染，应用ＧＭ－ＣＳＦ或Ｇ－ＣＳＦ积极支持治疗及保护隔离措施，９２例造血恢复，８例死于不同感染和出血。结论造血干细胞的移植起主要治疗作用，不同造血因子用于治疗急性放射病，可能是一种有希望的方法     

Physically-based biodosimetry using in vivo EPR of teeth in patients undergoing total body irradiation

Purpose:?The ability to estimate individual exposures to radiation following a large attack or incident has been identified as a necessity for rational and effective emergency medical response. In vivo electron paramagnetic resonance (EPR) spectroscopy of tooth enamel has been developed to meet this need.

Materials and methods:?A novel transportable EPR spectrometer, developed to facilitate tooth dosimetry in an emergency response setting, was used to measure upper incisors in a model system, in unirradiated subjects, and in patients who had received total body doses of 2 Gy.

Results:?A linear dose response was observed in the model system. A statistically significant increase in the intensity of the radiation-induced EPR signal was observed in irradiated versus unirradiated subjects, with an estimated standard error of dose prediction of 0.9?±?0.3 Gy.

Conclusions:?These results demonstrate the current ability of in vivo EPR tooth dosimetry to distinguish between subjects who have not been irradiated and those who have received exposures that place them at risk for acute radiation syndrome. Procedural and technical developments to further increase the precision of dose estimation and ensure reliable operation in the emergency setting are underway. With these developments EPR tooth dosimetry is likely to be a valuable resource for triage following potential radiation exposure of a large population.     

A polymer-alanine film for measurements of radiation dose distributions

A film dosimeter (0.35 mm thick) composed of polyethylene-vinyl acetate and microcrystalline l-α-alanine has been prepared and investigated with respect to dosimetric properties using electron spin resonance spectroscopy. The useful absorbed dose range is ∼ 25 to 10⁵ Gy and no dose-rate dependence of the response is observed between 1 and 10⁷ Gy s⁻¹ within the dose range up to 50 kGy. With irradiation temperature increasing from 25 to 80°C, the response increases at most by 10%. The response is stable, within experimental uncertainty, at least up to 2500 h after irradiation. The suitability of the polymer-alanine film for measurements of ionizing photon and electron dose distributions is demonstrated.     

General and specific aspects of experimental dose measurement in total body irradiation (TBI)

In magna-field irradiation using high energy bremsstrahlung (photons), i.e. total body irradiation, it is desirable to achieve a homogeneous dose distribution or to realize a planned modification in dose deposition within the target volume. In the Department of Radiology, University of Kiel, for this purpose individually constructed compensators are in routine use for about three years. Some physical and dosimetric aspects of this irradiation technique are described briefly and the experimental test procedure for TBI-compensators is highlighted by several details, for example transmission measurements, radiographies of the compensators and determination of actual dose rates in the midplane of the patient.     

Comparison of Kodak EDR2 and Gafchromic EBT film for intensity-modulated radiation therapy dose distribution verification

The quantitative dose validation of intensity-modulated radiation therapy (IMRT) plans require 2-dimensional (2D) high-resolution dosimetry systems with uniform response over its sensitive region. The present work deals with clinical use of commercially available self-developing Radio Chromic Film, Gafchromic EBT film, for IMRT dose verification. Dose response curves were generated for the films using a VXR-16 film scanner. The results obtained with EBT films were compared with the results of Kodak extended dose range 2 (EDR2) films. The EBT film had a linear response between the dose range of 0 to 600 cGy. The dose-related characteristics of the EBT film, such as post irradiation color growth with time, film uniformity, and effect of scanning orientation, were studied. There was up to 8.6% increase in the color density between 2 to 40 hours after irradiation. There was a considerable variation, up to 8.5%, in the film uniformity over its sensitive region. The quantitative differences between calculated and measured dose distributions were analyzed using DTA and Gamma index with the tolerance of 3% dose difference and 3-mm distance agreement. The EDR2 films showed consistent results with the calculated dose distributions, whereas the results obtained using EBT were inconsistent. The variation in the film uniformity limits the use of EBT film for conventional large-field IMRT verification. For IMRT of smaller field sizes (4.5 x 4.5 cm), the results obtained with EBT were comparable with results of EDR2 films.