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High-Dose-Rate (192)Ir Brachytherapy Dose Verification: A Phantom Study.

Nikoofar A, Hoseinpour Z, Rabi Mahdavi S, Hasanzadeh H, Rezaei Tavirani M - Iran J Cancer Prev (2015)

Bottom Line: Because of some concerns about adverse effects due to absorbed radiation dose, it is important to estimate absorbed dose in risky organs during this treatment.In closer regions (≤ 16 cm), the absorbed dose might be as high as 113 cGy.Our study showed similar depth and surface doses; in closer regions, the surface and depth doses differed significantly due to the role of primary radiation that had imposed a high-dose gradient and difference between the plan and measurement, which was more severe because of simplifications in tissue inhomogeneity, considered in TPS relative to phantom.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Iran University of Medical Sciences, Tehran, IR Iran.

ABSTRACT

Background: The high-dose-rate (HDR) brachytherapy might be an effective tool for palliation of dysphagia. Because of some concerns about adverse effects due to absorbed radiation dose, it is important to estimate absorbed dose in risky organs during this treatment.

Objectives: This study aimed to measure the absorbed dose in the parotid, thyroid, and submandibular gland, eye, trachea, spinal cord, and manubrium of sternum in brachytherapy in an anthropomorphic phantom.

Materials and methods: To measure radiation dose, eye, parotid, thyroid, and submandibular gland, spine, and sternum, an anthropomorphic phantom was considered with applicators to set thermoluminescence dosimeters (TLDs). A specific target volume of about 23 cm(3) in the upper thoracic esophagus was considered as target, and phantom planned computed tomography (CT) for HDR brachytherapy, then with a micro-Selectron HDR ((192)Ir) remote after-loading unit.

Results: Absorbed doses were measured with calibrated TLDs and were expressed in centi-Gray (cGy). In regions far from target (≥ 16 cm) such as submandibular, parotid and thyroid glands, mean measured dose ranged from 1.65 to 5.5 cGy. In closer regions (≤ 16 cm), the absorbed dose might be as high as 113 cGy.

Conclusions: Our study showed similar depth and surface doses; in closer regions, the surface and depth doses differed significantly due to the role of primary radiation that had imposed a high-dose gradient and difference between the plan and measurement, which was more severe because of simplifications in tissue inhomogeneity, considered in TPS relative to phantom.

No MeSH data available.


Related in: MedlinePlus

Setup of Thermoluminescence Dosimeters Calibration
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A2330FIG2: Setup of Thermoluminescence Dosimeters Calibration

Mentions: The TLDs (LiF-100, 3.1 × 3.1 × 0.9 mm square chips) were selected (19) and annealed before use in order to achieve better stability of their sensitivity and lower fading. The annealing was performed at 400°C for one hour and was followed by fast cooling and subsequent annealing at 80°C for 24 hours (Atash 1200 Exiton Crop, Iran). Subsequently, elemental correction coefficients (ECCi) were calculated by exposure to a dose of 200 cGy with 6 MV photons and were applied to each TLD as ECCi = < R > / Ri where <R> was the mean signal of all dosimeters and Ri was the individual signal of each TLD (Harshaw TLD Reader, model 3500, the United States) (Figure 2). The calibration curve of TLDs was obtained by exposing TLDs to doses ranging from zero to 250 cGy in Plexiglas slab phantom (depth, 3 cm; distance, 97 cm).


High-Dose-Rate (192)Ir Brachytherapy Dose Verification: A Phantom Study.

Nikoofar A, Hoseinpour Z, Rabi Mahdavi S, Hasanzadeh H, Rezaei Tavirani M - Iran J Cancer Prev (2015)

Setup of Thermoluminescence Dosimeters Calibration
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4581367&req=5

A2330FIG2: Setup of Thermoluminescence Dosimeters Calibration
Mentions: The TLDs (LiF-100, 3.1 × 3.1 × 0.9 mm square chips) were selected (19) and annealed before use in order to achieve better stability of their sensitivity and lower fading. The annealing was performed at 400°C for one hour and was followed by fast cooling and subsequent annealing at 80°C for 24 hours (Atash 1200 Exiton Crop, Iran). Subsequently, elemental correction coefficients (ECCi) were calculated by exposure to a dose of 200 cGy with 6 MV photons and were applied to each TLD as ECCi = < R > / Ri where <R> was the mean signal of all dosimeters and Ri was the individual signal of each TLD (Harshaw TLD Reader, model 3500, the United States) (Figure 2). The calibration curve of TLDs was obtained by exposing TLDs to doses ranging from zero to 250 cGy in Plexiglas slab phantom (depth, 3 cm; distance, 97 cm).

Bottom Line: Because of some concerns about adverse effects due to absorbed radiation dose, it is important to estimate absorbed dose in risky organs during this treatment.In closer regions (≤ 16 cm), the absorbed dose might be as high as 113 cGy.Our study showed similar depth and surface doses; in closer regions, the surface and depth doses differed significantly due to the role of primary radiation that had imposed a high-dose gradient and difference between the plan and measurement, which was more severe because of simplifications in tissue inhomogeneity, considered in TPS relative to phantom.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Iran University of Medical Sciences, Tehran, IR Iran.

ABSTRACT

Background: The high-dose-rate (HDR) brachytherapy might be an effective tool for palliation of dysphagia. Because of some concerns about adverse effects due to absorbed radiation dose, it is important to estimate absorbed dose in risky organs during this treatment.

Objectives: This study aimed to measure the absorbed dose in the parotid, thyroid, and submandibular gland, eye, trachea, spinal cord, and manubrium of sternum in brachytherapy in an anthropomorphic phantom.

Materials and methods: To measure radiation dose, eye, parotid, thyroid, and submandibular gland, spine, and sternum, an anthropomorphic phantom was considered with applicators to set thermoluminescence dosimeters (TLDs). A specific target volume of about 23 cm(3) in the upper thoracic esophagus was considered as target, and phantom planned computed tomography (CT) for HDR brachytherapy, then with a micro-Selectron HDR ((192)Ir) remote after-loading unit.

Results: Absorbed doses were measured with calibrated TLDs and were expressed in centi-Gray (cGy). In regions far from target (≥ 16 cm) such as submandibular, parotid and thyroid glands, mean measured dose ranged from 1.65 to 5.5 cGy. In closer regions (≤ 16 cm), the absorbed dose might be as high as 113 cGy.

Conclusions: Our study showed similar depth and surface doses; in closer regions, the surface and depth doses differed significantly due to the role of primary radiation that had imposed a high-dose gradient and difference between the plan and measurement, which was more severe because of simplifications in tissue inhomogeneity, considered in TPS relative to phantom.

No MeSH data available.


Related in: MedlinePlus