Calculation of effective dose from measurements of secondary neutron spectra and scattered photon dose from dynamic MLC IMRT for , , and  beam energies

Howell, Rebecca M.; Hertel, Nolan E.; Wang, Zhong Lin; Hutchinson, Jesson D.; Fullerton, Gary D.

doi:10.1118/1.2140119

Cited by 143 publications

(118 citation statements)

References 15 publications

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“…Although the target volume is deep, the fact that radiation is entering the patient from all angles, a beam energy of 6 MV is adequate to produce dose coverage without the increased neutron dose that will result from higher energy beams. ( 23 ) …”

Section: Methodsmentioning

confidence: 99%

A RapidArc planning strategy for prostate with simultaneous integrated boost

Jolly

Alahakone

Meyer

2010

J Applied Clin Med Phys

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Since the clinical implementation of novel rotational forms of intensity‐modulated radiotherapy, a variety of planning studies have been published that reinforce the major selling points of the technique. Namely, comparable or even improved dose distributions with a reduction in both monitor units and treatment times, when compared with static gantry intensity‐modulated radiotherapy. Although the data are promising, a rigorous approach to produce these plans has yet to be established. As a result, this study outlines a robust and streamlined planning strategy with a concentration on RapidArc class solutions for prostate with a simultaneous integrated boost. This planning strategy outlines the field setup, recommended starting objectives, required user interactions to be made throughout optimization and post‐optimization adjustments. A comparative planning study, with static gantry IMRT, is then presented as justification for the planning strategy itself. A variety of parameters are evaluated relating to both the planning itself (optimization and calculation time) and the plans that result. Results of this comparative study are in line with previously published data, and the planning process is streamlined to a point where the RapidArc optimization time takes 15±1.3 minutes. Application of this planning strategy reduces the dependence of the produced plan on the experience of the planner, and has the potential to streamline the planning process within radiotherapy departments.PACS numbers: 87.55.x, 87.55.D, 87.55.de, 87.55.dk

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Section: Methodsmentioning

confidence: 99%

A RapidArc planning strategy for prostate with simultaneous integrated boost

Jolly

Alahakone

Meyer

2010

J Applied Clin Med Phys

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“…9 Generally, in an evaluation of the total dose equivalent, these secondary gammas are accounted for through photon measurements carried out using a separate, photon-specific dosimeter. 5,7,8 Because a photon-specific dosimeter does not distinguish between the secondary gammas arising from neutron capture and photons due to head leakage or patient scatter, all photon doses are generally bundled together. For such circumstances, it would be incorrect to bias the quality factor with photons that were already accounted for as part of the photon measurements.…”

Section: Discussionmentioning

confidence: 99%

“…[5][6][7][8][9] Studies have measured or used Monte Carlo to calculate neutron fluence and energy spectrum, but the majority of these studies have evaluated such neutron properties in air or on the patient's surface rather than within a phantom or patient where organs at risk are actually found. [5][6][7][10][11][12][13] This observation is not surprising because measurements within a patient or even a phantom are very difficult due to substantial challenges in neutron detection. In some instances, the neutron dose equivalent has been determined within a phantom through measurements with bubble detectors 14 and using Monte Carlo.…”

Section: Introductionmentioning

confidence: 99%

Neutron spectra and dose equivalents calculated in tissue for high‐energy radiation therapy

et al. 2009

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Neutrons are by-products of high-energy radiation therapy and a source of dose to normal tissues. Thus, the presence of neutrons increases a patient's risk of radiation-induced secondary cancer. Although neutrons have been thoroughly studied in air, little research has been focused on neutrons at depths in the patient where radiosensitive structures may exist, resulting in wide variations in neutron dose equivalents between studies. In this study, we characterized properties of neutrons produced during high-energy radiation therapy as a function of their depth in tissue and for different field sizes and different source-to-surface distances ͑SSD͒. We used a previously developed Monte Carlo model of an accelerator operated at 18 MV to calculate the neutron fluences, energy spectra, quality factors, and dose equivalents in air and in tissue at depths ranging from 0.1 to 25 cm. In conjunction with the sharply decreasing dose equivalent with increased depth in tissue, the authors found that the neutron energy spectrum changed drastically as a function of depth in tissue. The neutron fluence decreased gradually as the depth increased, while the average neutron energy decreased sharply with increasing depth until a depth of approximately 7.5 cm in tissue, after which it remained nearly constant. There was minimal variation in the quality factor as a function of depth. At a given depth in tissue, the neutron dose equivalent increased slightly with increasing field size and decreasing SSD; however, the percentage depth-dose equivalent curve remained constant outside the primary photon field. Because the neutron dose equivalent, fluence, and energy spectrum changed substantially with depth in tissue, we concluded that when the neutron dose equivalent is being determined at a depth within a patient, the spectrum and quality factor used should be appropriate for depth rather than for in-air conditions. Alternately, an appropriate percent depthdose equivalent curve should be used to correct the dose equivalent at the patient surface.

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“…In contrast, the out‐of‐field neutron dose at that energy has previously been determined in a phantom to be in the range of 0.1 – 1 μGy/MU (assuming a radiation weighting factor of 10 for the dose equivalents determined in the literature). ( 1 , 8 , 9 ) The TLD‐100 response to neutrons is not known for the system used at the RPC, nor is there any simple technique for separating the photon and neutron contributions when reading the TLD. This issue is further complicated because most of the neutron dose equivalent is delivered by fast neutrons, but most of the TLD signal originates from thermal neutrons.…”

Section: Resultsmentioning

confidence: 99%

The use of LiF (TLD‐100) as an out‐of‐field dosimeter

Kry

Price

Followill

et al. 2007

J Applied Clin Med Phys

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The commonly used thermoluminescent dosimeter TLD‐100 (Harshaw Chemical Company, Solon, OH) responds not only to photons and electrons, but also to neutrons that are produced during high‐energy therapies. As a result, TLD‐100 measurements outside of the treatment field are suspect when high‐energy radiation is used. Although alternatives such as TLD‐700 do not respond to neutrons, specialty dosimeters of this kind are expensive and are not routinely used in most clinics. In the current study, we examined the accuracy of TLD‐100 in measuring the out‐of‐field photon dose as a function of treatment energy.To determine the accuracy of TLD‐100 as compared with TLD‐700, TLD‐100 was irradiated outside of the treatment field by medical accelerators operated at 6, 10, 15, and 18 MV. In an effort to eliminate the response of TLD‐100 to neutrons, TLD capsules were encased in varying thicknesses of cadmium foil (0.25 – 0.75 mm) before being irradiated at 18 MV. The out‐of‐field TLD‐100 was found to be accurate at 6 MV and 10 MV, but to be substantially over‐responsive at 15 MV and 18 MV (by up to 1063% relative to TLD‐700). By wrapping the TLD‐100 in up to 0.75 mm of cadmium, it was possible to drastically reduce (down to 39% on average) the over‐response of the TLD‐100; however, total removal of the over‐responsiveness was not possible. Although TLD‐100 is well suited for measuring out‐of‐field dose at energies as high as 10 MV, at higher energies (15 MV or greater), this dosimeter over‐responds substantially and should not be used. Although encasing the TLD in cadmium minimized over‐response to a degree, the reduction was not sufficient to make TLD‐100 viable for measuring out‐of‐field dose at high treatment energies.PACS numbers: 87.52.‐g, 87.53.‐j, 87.53.‐Dq

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Calculation of effective dose from measurements of secondary neutron spectra and scattered photon dose from dynamic MLC IMRT for , , and beam energies

Cited by 143 publications

References 15 publications

A RapidArc planning strategy for prostate with simultaneous integrated boost

A RapidArc planning strategy for prostate with simultaneous integrated boost

Neutron spectra and dose equivalents calculated in tissue for high‐energy radiation therapy

The use of LiF (TLD‐100) as an out‐of‐field dosimeter

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