Calculation Of Equivalent Dose Research Articles

Refining target coverage and normal tissue avoidance with helical tomotherapy vs linac-based IMRT for oropharyngeal cancer

The use of intensity modulated radiation therapy (IMRT) in the treatment of head and neck (H&N) cancer is expanding worldwide. As radiation dose to selected normal structures (ie, parotid glands) is reduced, dose to adjacent regions (ie, anterior oral cavity) may be increased. Ultimate H&N cancer outcome and patient quality of life (QOL) is complex and can be influenced by many aspects of the radiation dose profile. This study was carried out to compare the capacity of helical tomotherapy versus linac-based IMRT to achieve target dose conformality and normal tissue sparing in oropharynx cancer patients. Twenty oropharyngeal cancer patients treated with curative intent using 7 field H&N IMRT between 2001–2003 were selected for study. Treatment planning and delivery was performed using the PinnacleTM planning system. In general, doses of 66–70 Gy at 2.1–2.2 Gy per fraction were delivered to primary planning target volume (PTV) targets, with 50–60 Gy to subclinical PTV targets. Dose constraints were employed for various normal H&N tissue structures such as parotid gland (20 Gy mean dose), spinal cord and anterior oral cavity (35 Gy maximum dose). Comprehensive H&N tomotherapy plans were designed for these 20 patients using identical prescription parameters. For conventional IMRT design, a 7 field arrangement of equally spaced beams was employed, whereas for helical tomotherapy, over 1000 projections per treatment were used (51 projections per rotation with a minimum of 20 rotations). Resultant treatment plans were then rigorously compared and contrasted. All 40 oropharynx cancer treatment plans analyzed (20 conventional IMRT and 20 helical tomotherapy) met primary treatment objectives regarding dose specification. Specifically, the resultant Equivalent Uniform Dose (EUD) calculations for high and low dose PTV were ≥the prescription dose. In general, helical tomotherapy plans offered favorable dose distributions over that achieved with 7 field IMRT plans as manifested by increased EUD to PTV targets, as well as reduced mean dose to normal tissue avoidance structures. The EUD analysis revealed that tomotherapy plans provided up to 4% increase to high dose PTV over that achieved with 7 field IMRT plans. Simultaneously, mean dose delivered to normal tissue avoidance structures such as contralateral parotid gland, spinal cord and oral cavity was reduced up to 50% with tomotherapy plans. The daily patient treatment time with helical tomotherapy is essentially identical to that with conventional IMRT. However, to ensure comparable delivery times, a jaw opening of 2.5 cm was chosen which yields a 2-fold increase (from 5 to 10 mm) in the conventional 80–20% penumbra in the cephalo-caudal dimension. The overall analysis of H&N treatment plans identifies several potential advantages for helical tomotherapy over that achieved with conventional IMRT. The improved dose distributions are largely explained by the fact that tomotherapy offers a significantly larger number of projections than available with conventional MLC-based IMRT. Nevertheless, the ultimate clinical significance of these dose distribution refinements remains ill defined. Intuitively, it would seem that higher conformality of dose to specified targets, and dose reduction to normal tissue avoidance structures may be of value. To further evaluation of this question, a prospective clinical trial is underway to examine normal tissue functional outcome and QOL in H&N cancer patients receiving IMRT with conventional and tomotherapy techniques. In addition to direct measurement of salivary, auditory, voice and swallow function, validated health outcome surveys are obtained to assess patient perception regarding voice, swallow, hearing and overall H&N function before and following treatment. These data should provide further insight regarding the potential value of refining dose distribution in H&N cancer patients receiving highly conformal treatment using either conventional IMRT or helical tomotherapy

Electron spin resonance and radiocarbon dating of coral deposited by Holocene tsunami events on Curaçao, Bonaire and Aruba (Netherlands Antilles)

Electron spin resonance (ESR) dating of coral has become an efficient geochronological tool for studying the last 500,000 years. This study presents results of ESR dating of Holocene coral from Curaçao, Bonaire and Aruba, Leeward Netherlands Antilles. The coral accumulated in rubble ridges and ramparts onshore and the depositional process is attributed to a series of tsunami events. In addition to the calculation of equivalent dose ( D E) values, it is crucial for ESR dating to obtain the correct D 0 value for each sample. The annual dose rate ( D 0) estimation of the samples in this study is uncertain as the timing of the tsunami event and the residence time of a component of the dated sediment in different environments (marine versus terrestrial) is difficult to quantify. Assuming that the tsunami event deposited coral shortly after death, the ESR and 14C ages of 22 samples reaching from 3650 to 128 years correspond well with each other. This confirms the idea that the living coral reef was partly destroyed by tsunami events. The ESR dating uncertainties coincide with the variability of 14C ages caused by the marine reservoir effect. The local marine reservoir effect was estimated using four recent samples from 1920 and provided values between 375 and 595 yr BP.

Current challenges in personal dosimetry at the US DOE Hanford site.

An overview is presented of the dosimetry system, dose equivalent calculation methodology, and QA/QC practices used at the US Department of Energy Hanford site. It describes some of the problems encountered in accurately measuring dose equivalent quantities under a broad range of field conditions that do not necessarily correlate with laboratory calibration conditions and the approach taken to solve these problems. Personnel at Hanford are monitored with a combination of Harshaw model 8825 and 8816 thermoluminescence dosemeters and CR-39 etched track dosemeters. Extremities are monitored using the ICN MeasuRing loaded with a Harshaw XD740 chipstrate TLD. All dosemeters employ LiF:Mg,Ti elements that are read on-site with Harshaw model 8800 and 6600 TLD readers. CR-39 dosemeters are electrochemically etched in non-commercial etch chambers and counted with an automated track counting system developed by Pacific Northwest National Laboratory. Problems with over response of the 8825 with respect to Hp(0.07), under-response of the 8825 with respect to Hp(3), and over response of the 8825 with respect to Hp(10) in Hanford's 90Sr/90Y beta radiation fields are discussed. Approaches to measurement of the operational quantities for field conditions and algorithm solutions to the above problems are described. Methods used to calibrate the ring dosemeter for Hanford field conditions together with limitations of the ring dosemeter in measuring Hp(0.07) for extremities, particularly when covered with protective clothing, are also discussed.

A treatment planning comparison of 3D conformal therapy, intensity modulated photon therapy and proton therapy for treatment of advanced head and neck tumours

Background and purpose: In this work, the potential benefits and limitations of different treatment techniques, based on mixed photon-electron beams, 3D conformal therapy, intensity modulated photons (IM) and protons (passively scattered and spot scanned), have been assessed using comparative treatment planning methods in a cohort of patients presenting with advanced head and neck tumours. Material and methods: Plans for five patients were computed for all modalities using CT scans to delineate target volume (PTV) and organs at risk (OAR) and to predict dose distributions. The prescribed dose to the PTV was 54 Gy, whilst the spinal cord was constrained to a maximum dose of 40.5 Gy for all techniques. Dose volume histograms were used for physical and biological evaluation, which included equivalent uniform dose (EUD) calculations. Results: Excluding the mixed photon-electron technique, PTV coverage was within the defined limits for all techniques, with protons providing significantly improved dose homogeneity, resulting in correspondingly higher EUD results. For the spinal cord, protons also provided the best sparing with maximum doses as low as 17 Gy. Whilst the IM plans were demonstrated to be significantly superior to non-modulated photon plans, they were found to be inferior to protons for both criteria. A similar result was found for the parotid glands. Although they are partially included in the treated volume there is a clear indication that protons, and to a lesser extent IM photons, could play an important role in preserving organ functionality with a consequent improvement of the patient's quality of life. Conclusions: For advanced head and neck tumours, we have demonstrated that the use of IM photons or protons both have the potential to reduce the possibility of spinal cord toxicity. In addition, a substantial reduction of dose to the parotid glands through the use of protons enhances the interest for such a treatment modality in cases of advanced head and neck tumours. However, in terms of target coverage, the use of 3D conformal therapy, although somewhat inferior in quality to protons or IM photons, has been shown to be a reasonable alternative to the more advanced techniques. In contrast, the conventional technique of mixed photon and electron fields has been shown to be inferior to all other techniques for both target coverage and OAR involvement.

Optical dating of single sand-sized grains of quartz: sources of variability

Optically stimulated luminescence (OSL) measurements have been made of over 3000 sand-sized grains of quartz. Analysis at this scale highlights the variability in the luminescence sensitivity and the dose saturation characteristics of individual quartz grains. Using a new instrument capable of measuring single grains it is feasible to routinely measure the equivalent dose from many hundreds of grains from each sample. Analysis of such datasets requires assessment of the uncertainties on each equivalent dose since these may vary significantly. This paper assesses the significance of signal intensity, dose saturation characteristics and instrument uncertainty in equivalent dose calculation.

Incorporating heterogeneity in tumor functional/metabolism into the calculation of equivalent uniform dose

Incorporating heterogeneity in tumor functional/metabolism into the calculation of equivalent uniform dose

Calculation of equivalent dose for Auger electron emitting radionuclides distributed in human organs.

Radionuclides that emit Auger electrons can be extremely radiotoxic depending on the subcellular distribution of the radiochemical. Despite this, ICRP 60 provides no guidance in the calculation of equivalent dose H(T) for Auger electrons. The recent report by the American Association of Physicists in Medicine recommends a radiation weighting factor wR of 20 for stochastic effects caused by Auger electrons, along with a method of calculating the equivalent dose that takes into account the subcellular distribution of the radionuclide. In view of these recommendations, it is important to reevaluate equivalent doses from Auger electron emitters. The mean absorbed dose per unit cumulated activity (S-value) from Auger electrons and other radiations is calculated for ninety Auger-electron-emitting radionuclides distributed in human ovaries, testes and liver. Using these S-values, and the formalism given in the recent AAPM report, the dependence of the organ equivalent doses on subcellular distribution of the Auger electron emitters is examined. The results show an increase in the mean equivalent dose for Auger electron emitters when a significant fraction of the organ activity localizes in the DNA.

Sex-specific tissue weighting factors for effective dose equivalent calculations.

The effective dose equivalent was defined in the International Commission on Radiological Protection Publication 26 in 1977 and later adopted by the U.S. Nuclear Regulatory Commission. To calculate organ doses and effective dose equivalent for external exposures using Monte Carlo simulations, sex-specific anthropomorphic phantoms and sex-specific weighting factors are always employed. This paper presents detailed mathematical derivation of a set of sex-specific tissue weighting factors and the conditions which the weighting factors must satisfy. Results of effective dose equivalent calculations using female and male phantoms exposed to monoenergetic photon beams of 0.08, 0.3, and 1.0 MeV are provided and compared with results published by other authors using different sex-specific weighting factors and phantoms. The results indicate that females always receive higher effective dose equivalent than males for the photon energies and geometries considered and that some published data may be wrong due to mistakes in deriving the sex-specific weighting factors.

An analysis of the equivalent dose calculation for the remainder tissues.

In the 1990 Recommendations of the International Commission on Radiological Protection, the risk-weighted quantity "effective dose equivalent" was replaced by a similar quantity, "effective dose." Among other alterations, the selection of the organs and tissues contributing to the risk-weighted quantity and their respective weighting factors were changed, including a modified definition of the so-called "remainder." Close consideration of this latter definition shows that it causes certain ambiguities and unexpected effects which are dealt with in the following. For several geometries of external photon irradiation, the numerical differences of two possible methods of evaluating the remainder dose from the doses to ten single organs, namely as arithmetic mean or as mass weighted average, are assessed. It is shown that deviation from these averaging procedures, as prescribed for those cases where a remainder organ receives a higher dose than an organ with a specified weighting factor, causes discontinuities in the energy dependence of the remainder dose and, consequently, also non-additivity of this quantity. These problems are discussed, and it is shown that, although the numerical consequences for the calculation of the effective dose are small, this unsatisfactory situation needs clarification. One approach might be to abolish some of the ICRP guidance relating to the appropriate tissue weighting factors for the remainder tissues and organs and to make other guidance more precise.

A study of the radiation environment on board the Space Shuttle flight STS-57

A joint NASA-Russian study of the radiation environment inside a SPACEHAB 2 locker on Space Shuttle flight STS-57 was conducted. The Shuttle flew in a nearly circular orbit of 28.5° inclination and 462 km altitude. The locker carried a charged particle spectrometer, a tissue equivalent proportional counter (TEPC), and two area passive detectors consisting of combined NASA plastic nuclear track detectors (PNTDs) and thermoluminescent detectors (TLDs), and Russian nuclear emulsions, PNTDs and TLDs. All the detector systems were shielded by the same Shuttle mass distribution. This makes possible a direct comparison of the various dose measurement techniques. In addition, measurements of the neutron energy spectrum were made using the proton recoil technique. The results show good agreement between the integral LET spectrum of the combined galactic and trapped particles using the tissue equivalent proportional counter and track detectors between about 15 keV/μm and 200 keV/μm. The LET spectrum determined from nuclear emulsions was systematically lower by about 50%, possibly due to emulsion fading. The results show that the TEPC measured an absorbed dose 20% higher than the TLDs, due primarily to an increased TEPC response to neutrons and a low sensitivity of TLDs to high LET particles under normal processing techniques. There is a significant flux of high energy neutrons that is currently not taken into consideration in dose equivalent calculations. The results of the analysis of the spectrometer data will be reported separately.

Dosimetry of Auger-electron-emitting radionuclides: Report No. 3 of AAPM Nuclear Medicine Task Group No. 6

The biological effects of Auger-electron-emitting radionuclides can be as severe as those of alpha particles of high linear energy transfer. A great deal of effort has been expended in exploring the biological effects of Auger electron emitters. Much of this effort has been devoted to improving theoretical and experimental techniques required to calculate absorbed doses and correlate them with the observed biological effects. Given that the main purpose of dosimetry is to obtain a physical descriptor with which to correlate radiation toxicity, then nowhere is this challenge greater than when biological specimens are subject to Auger electron cascades. The dense shower of short-range Auger electrons released by radionuclides, which decay by electron capture or internal conversion, results in biological damage that is highly dependent on the location of the decay site within the cell. In this report, different approaches to Auger electron dosimetry are described and compared. Methods to calculate the absorbed dose from Auger electron emitters at the DNA, cellular, multicellular, and organ levels are described as they relate to the biological effects. The concept of a radiation weighting factor for Auger electrons to be used in the calculation of equivalent dose is reviewed. The importance of subcellular distribution of Auger emitters in determining the biological effects of these radionuclides is emphasized and incorporated into the equivalent dose formalism. The Task Group recommends that a preliminary radiation weighting factor of 10 be used for deterministic effects of Auger electrons, and a value of 20 for stochastic effects.

Time-dose relationship for local tumor control following alternate week concomitant radiation and chemotherapy of advanced head and neck cancer

Purpose : To analyze the time-dose relationship for local control of disease in patients with advanced head and neck neoplasms enrolled in two sequential Phase I dose escalation studies in which concomitant chemotherapy and radiotherapy were delivered on an alternate week schedule (i.e., 1 week of concomitant therapy alternated with 1 week of rest). Methods and Materials : From 1986–1988, 65 patients were enrolled in two Phase I clinical trials. In trial one, 5-fluorouracil and hydroxyurea were administered concomitantly with radiation on an alternate week schedule (39 pts). In trial two, cisplatin was added to 5-fluorouracil and hydroxyurea (26 pts). Fifty-seven patients were evaluable for local control, including 26 patients who had failed prior local therapy and were retreated (group A), and 31 patients who had received no prior local therapy (group B). The median dose of RT and the median duration of therapy were 59.7 Gy and 12 weeks for group A, and 70.2 Gy and 14 weeks for group B, respectively. The biological effective dose of radiation therapy (RT) was calculated using the equation based on the linear quadratic model as proposed by J. Fowler. Univariate and multivariate logistic regression analyses were performed to evaluate prognostic factors for local control. Results : Six of 26 patients in group A and 30 of 31 patients in group B had local control of disease. The 2-year Kaplan-Meier local failure rates were 84% for group A and 4% for group B, respectively. Despite the doubling of treatment duration compared to conventional daily radiotherapy and the low biological equivalent dose calculated (median biological equivalent dose for patients with local control of disease were 50.3 Gy and 48.8 Gy in groups A and B, respectively), local control was achieved in 5/17 patients in group A and 30/31 patients in group B who received RT dose of 59.4 Gy or higher. In multivariate logistic regression analysis, the only significant predictor for local control of disease was RT dose (p = 0.004). Treatment duration, chemotherapy dose intensities, age, and performance status were not significant variables. Decreasing the RT dose by 10 Gy would increase the rate of local failure by 24%. Conclusion : Our data suggest that prolongation of treatment duration to twice the normal duration of conventional once-a-day radiotherapy does not result in loss of local control when aggressive cell-cycle specific chemotherapy is given concomitantly with radiotherapy. The usual time-dose relationship based on RT alone does not appear to be applicable when concomitant chemotherapy is added. The clinical significance of biological equivalent dose calculation based on radiotherapy alone is unclear when chemotherapy is given with radiation.

Simple tools for dose equivalent calculations using the lo model in the daily practice of radiotherapy

Simple tools for dose equivalent calculations using the lo model in the daily practice of radiotherapy

Depth dose distribution for 252Cf source using solid state detectors

LiF (600 and 700) and CR-39 plastic detectors were used for measuring fast and thermal neutrons and γ-ray doses from 252 Cf source in a tissue equivalent phantom. Conversion factors as well as related quality factors were used for absorbed and equivalent dose calculations. Two exposure positions were used: Source at 30 cm and in contact with phantom surface. The contribution of thermal and fast neutrons in both absorbed dose and equivalent dose reaches a maximum value at 3.5 cm while the maximum for γ-ray is at 8.5 cm.

Depth Dose Distribution for 252Cf Source Using Solid State Detectors

LiF (600 and 700) and plastic detector were used for measuring fast and thermal neutrons and γ-ray doses from 252Cf source in tissue equivalent phantom. Conversion factors as well as related quality factors were used for absorbed and equivalent dose calculations. Two exposure positions were used: source at 30 cm and in contact with phatnom surface. The contribution of thermal and fast neutrons in both absorbed dose and equivalent dose reaches a maximum value at 3.5 cm while the maximum for γ-ray is at 8.5 cm. The build up and attenuation in tissue and the corresponding relaxation length were evaluated.

Seasonal variation of indoor Rn at a location in the southwestern United States.

Radon-222 concentrations have been measured in 12 homes typical of a small town in the southwestern United States. Nine of the houses, in which both summer and winter data are available, have an annual mean of 63 +/- 18 Bq m-3 (1.7 +/- 0.5 pCi L-1) and a range of 41 to 96 Bq m-3 (1.1 to 2.6 pCi L-1). These results were obtained with passive Rn dosimeters using polycarbonate nuclear track detector foils. The overall results fall slightly above the middle of the range of values obtained in other studies in the United States. Winter levels clearly exceed summer by a factor of from two to three. This result is attributed primarily to wide use of evaporative air conditioners for daytime cooling in the summer together with the fact that doors and windows are left open frequently during evening and nighttime hours. Both practices enhance the exchange of outdoor air with indoor air contributing to a decrease in the indoor Rn levels during the summer season. Room-to-room differences were evident during the winter season only. Bedrooms and bathrooms were generally higher in Rn than kitchens and living rooms but by only about 25%. The two adobe houses in the group showed higher Rn concentrations during the winter season than did those of frame-stucco, concrete, or cinder block construction. Dose equivalent calculations yielded a mean figure of 0.29 WLM y-1 for typical occupancy patterns in these New Mexico houses.

Thermal dose determination in cancer therapy

With the rapid development of clinical hyperthermia for the treatment of cancer either alone or in conjunction with other modalities, a means of measuring a thermal dose in terms which are clinically relevant to the biological effect is needed. A comparison of published data empirically suggests a basic relationship that may be used to calculate a “thermal dose.” From a knowledge of the temperature during treatment as a function of time combined with a mathematical description of the time-temperature relationship, an estimate of the actual treatment calculated as an exposure time at some reference temperature can be determined. This could be of great benefit in providing a real-time accumulated dose during actual patient treatment. For the purpose of this study, a reference temperature of 43°C has been arbitrarily chosen to convert all thermal exposures to “equivalent-minutes” at this temperature. This dose calculation can be compared to an integrated calculation of the “degree-minutes” to determine its prognostic ability. The time-temperature relationship upon which this equivalent dose calculation is based does not predict, nor does it require, that different tissues have the same sensitivity to heat. A computer program written in FORTRAN is included for performing calculations of both equivalent-minutes (t 43) and degree-minutes (t dm43). Means are provided to alter the reference temperature, the Arrhenius “break” temperature and the time-temperature relationship both above and below the “break” temperature. In addition, the effect of factors such as step-down heating, thermotolerance, and physiological conditions on thermal dose calculations are discussed. The equations and methods described in this report are not intended to represent the only approach for thermal dose estimation; instead, they are intended to provide a simple but effective means for such calculations for clinical use and to stimulate efforts to evaluate data in terms of therapeutically useful thermal units.

Dose fractionation, dose rate and iso-effect relationships for normal tissue responses

An analysis is,,presented of responses of a variety of normal tissues in animals to fractionated irradiations. It is shown that the influence of fractionation can be described on the basis of a simple formula relating the effectiveness for induction of cellular effects to the dose per fraction: F( D) = 1 D + a 2 D 2. The ratio a 1 a 2 is derived as an essential parameter for, the description of fractionation effects. It is concluded that the values of a 1 a 2 for responses of various tissues range widely from 2 to 10 Gy. On the basis of the review of radiobiological data, a formalism is developed for the analysis and prediction of iso-effect relations for tissue tolerance, which can be used as an alternative to the nominal standard dose (NSD) formula of Ellis and its derived equations. An essential characteristic of the formalism is that three groups of tissue responses are distinguished which can be described with respect to fractionation effects by average values of a l a 2 = 10 ; 5 and 2.5 Gy, respectively. These groups comprise a l: a.o. skin and intestine; 2: connective tissue; 3:a.o. lung and vascular system. Dose rate effects can be described by a similar formalism. For the calculation of equivalent total doses to be applied in clinical treatments, a concept denoted Extrapolated Tolerance Dose (ETD) of Extrapolated Response Dose (ERD) is introduced. ETD is the tolerance dose for an infinite number of very small fractions. This concept is shown to be useful for the summation of different fractionated schedules and of low dose rate treatments. A number of examples is presented illustrating similarities and differences in comparison with calculations based on the NSD formula. An important feature of the described formalism is that it is directly based on radiobiological insights and it provides a more logical concept to account for the diversity of tissue responses than the assumption of different exponents of N and T in the NSD formula.