Peripheral Organ Dose Evaluation using a Human Body Phantom in Intensity Modulated Radiation Therapy for Lung Cancer with Helical Type Accelerator
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Purpose: Intensity modulated radiation therapy (IMRT) is characterized by a relatively long period for beam exposure and consequently the risk for unnecessary exposure to non-targeted organs, mainly due to the scattered radiation, should be considered. The puposes of this study are to measure the absorbed dose of the peripheral organs during helical IMRT using a fluorescent glass dosimeter. Materials and Methods: In this research, we took lung cancer as a model and measured the absorbed dose of the peripheral organs during helical IMRT using a fluorescent glass dosimeter. The planning target volume (PTV) dose of 95% was set to be 5 Gy in the phantom. Results and Discussion: The highest exposure dose was observed for the breasts, which were on the PTV trajectory, with the left and right breasts receiving doses of 227.94 mGy and 371.90 mGy, respectively. The exposure doses of the left and right lenses were 3.13 mGy for the left lens and 3.22 mGy for the right lens. An exponential dose reduction to the distance from PTV was confirmed. Our data suggest that the doses for peripheral organs were acceptable in lung cancer case based on past literature search. However, the use of custom blocks for the eyes should be considered to prevent possible late occurance of cataract.Radiation doses to tissues and organs were measured using the anthropomorphic phantom as an equivalent to the human body. When high-energy X-rays are externally applied to treat laryngeal cancer, the absorbed dose at the laryngeal lumen is lower than given dose because of air space, which it should pass through, before reaching the lesion. Specially, in case of high-energy X-rays, the loss of dose is considerable. Three-dimensional absorbed dose distributions have been computed for high-energy photon radiation therapy of laryngeal and hypopharyngeal cancers, using a coaxial pair of opposing lateral beams in fixed positions. Treatment plans obtained under various conditions of irradiation. Keywords—3D Treatment Planning, anthropomorphic phantom, larynx cancer, radiotherapy.
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Until recently, conservative radiation therapy of breast cancer using a wedge-filter combined with rectangular tangential irradiation was widely carried out. This method of irradiation creates uniform dose distribution in the target, minimizing the radiation dose to the lung. However, this method of irradiation results in many cases in which the amount of dose in the irradiated area differs as a result of the shape and size of the breast. It is necessary to prevent excessive doses from reaching the lung. IMRT ensures a uniform dose to the target. Therefore, IMRT was examined because of the possibility that the normal tissue dose can be effectively utilized in cases of conservative radiation therapy of breast cancer by providing a minimum dose. To compare the irradiation of each method of rectangular tangential irradiation, an electronic compensator (ELC), and IMRT, which uses Dynamic MLC, we evaluated target dose uniformity, standard deviation, and target differential DVH in 13 examples. We evaluated the lung dose of the irradiated side (V(30), 30 Gy volume) of the lung to the volume of the lung on the irradiated side based on the report of Hernando.(6)) With this method of irradiation, irrespective of the difference in the shape and size of the target, dose uniformity with ELC was very good. IMRT can reduce the lung dose in comparison with the other irradiation methods. However, it is apt to cause a high-dose area in the irradiation field. In addition, it affects the target and the skin-extracting contour, and the dose to the skin surface declines. Although ELC cannot offer lung doses that are as low as those of IMRT, most of the 13 examples planned for cure with ELC showed rates of 22% of V(30) and below. In conservative radiation therapy of breast cancer, ELC is more effective than the rectangular tangential irradiation method and IMRT.
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Collimator
Collimated light
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Tomotherapy
Concomitant
Thorax (insect anatomy)
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With increased use of intensity-modulated radiation therapy (IMRT) for head and neck treatment questions have arisen as to selection of an optimum treatment approach when either superficial sparing or treatment is desired. Other work has pointed out the increased superficial dose resulting from obliquity effects when multiple tangential beams are applied to head and neck treatment, as is the general case in IMRT planning. Helical tomotherapy might be expected to result in even further enhanced superficial dose compared with conventional bilateral field treatment. We have designed a typical right oropharynx target volume in an anthropomorphic head and neck phantom. Three different treatment techniques have been used to optimally treat this target, including bilateral static fields, eight-field IMRT and helical tomotherapy. The phantom was immobilized in a standard treatment position and treated on a Varian 2300cd linear accelerator and on a Hi-Art Helical Tomotherapy unit. 1 mm3 lithium-fluoride thermoluminescent dosimeters (TLDs) were placed on the surface of the phantom at a number of axial test positions. Film strips (Kodak EDR2) were either wrapped around the surface or sandwiched within the phantom. Measured doses at the surface and as a function of depth are compared with the planning system predictions for each treatment technique. The maximum surface doses on the proximal treatment side, averaged from TLDs and films, were measured to be 69–82% of the target dose with the bilateral fields yielding the lowest surface doses (69%), tomotherapy about 2% more than that (71%) and IMRT 13% more (82%). Anterior to the target volume, doses are always low for bilateral treatment. In this case the minimum anterior surface dose (chin area) was 6% of the prescription dose from that technique as compared with 26% and 35% from the IMRT and tomotherapy methods, respectively. The Eclipse and Tomotherapy planning systems both modelled deep and superficial doses well. Surface doses were better modelled by Eclipse at the test points, while the tomotherapy plans consistently overestimated the measured doses by 10% or more. Depth dose measurements, extracted from embedded films, indicated the depth of dose build-up to >99% to be the shallowest for IMRT (2–5 mm) followed by tomotherapy (5–8 mm) and bilateral fields (10–15 mm). The amount of surface dose is clearly technique dependent and should be taken into account in the planning stage.
Tomotherapy
Isocenter
Thermoluminescent Dosimetry
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Multileaf collimator
Bolus (digestion)
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A systematic set of measurements is reported for evaluation of doses to critical organs resulting from cone‐beam CT (CB‐CT) and cone‐beam tomosynthesis (CB‐TS) as applied to breast setup for external beam irradiation. The specific focus of this study was on evaluation of doses from these modalities in a setting of volumetric breast imaging for target localization in radiotherapy treatments with the goal of minimizing radiation to healthy organs. Ion chamber measurements were performed in an anthropomorphic female thorax phantom at the center of each breast and lung and on the phantom surface at one anterior and two lateral locations (seven points total). The measurements were performed for three different isocenters located at the center of the phantom and at offset locations of the right and left breast. The dependence of the dose on angle selection for the CB‐TS arc was also studied. For the most typical situation of centrally located CB‐CT isocenter the measured doses ranged between 3 and , in good agreement with previous reports. Dose measurements were performed for a range of start/stop angles commonly used for CB‐TS and the impact of direct and scatter dose on organs at risk was analyzed. All measured CB‐TS doses were considerably lower than CB‐CT doses, with greater decrease in dose for the organs outside of the beam (up to 98% decrease in dose). Remarkably, offsetting the isocenter towards the ipsilateral breast resulted on average to additional 46% dose reduction to organs at risk. The lowest doses to the contralateral breast and lung were less than when they were measured for the offset isocenter. The biggest reduction in dose was obtained by using CB‐TS beams that completely avoid the critical organ. For points inside the CB‐TS beam, the dose was reduced in a linear relation with distance from the center of the imaging arc. The data indicate that it is possible to reduce substantially radiation doses to the contralateral organs by proper selection of CB‐TS angles and imaging field sizes. Our results provide the first systematic study on CB‐TS doses from setup imaging for external breast irradiation and can be a useful resource for estimating anticipated radiation doses as a function of the conditions chosen for imaging breast setup.
Isocenter
Tomosynthesis
Dose profile
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Image-guided radiation therapy (IGRT) is increasingly being used in modern radiation therapy, and it is now possible to verify a patient’s position using kilo-voltage cone-beam computed tomography (kV-CBCT). However, if kV-CBCT is used frequently, the dose absorbed by the body cannot be disregarded. A number of studies have been made on the absorbed dose of kV-CBCT, in which absorbed dose measurements were made using a computed tomography dose index (CTDI) or a thermoluminescent dosimeter (TLD). Other methods include comparison of the absorbed dose between a kV-CBCT and other modalities. These techniques are now in common use. However, dose distribution within the patient varies with the patient’s size, posture and the part of the body to which radiation therapy is applied. The chief purpose of this study was to evaluate the dose distribution of kV-CBCT by employing a radiotherapy planning system (RTPS); a secondary aim was to examine the influence of a dose of kV-CBCT radiation when used to treat prostate cancer. The beam data of an on-board imager (OBI) was registered in the RTPS, after which modeling was performed. The radiation dosimetry was arranged by the dosimeter in an elliptical phantom. Rotational radiation treatment was used to obtain the dose distribution of the kV-CBCT within the patient, and the patient dose was evaluated based on the simulation of the dose distribution. In radiation therapy for prostate cancer, if kV-CBCT was applied daily, the dose increment within the planning target volume (PTV) and the organ in question was about 1 Gy.
Image-guided radiation therapy
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