جستجوی مقالات مرتبط با کلیدواژه "فنتوم" در نشریات گروه "پزشکی"

Radiotherapy plays an important role in treatment of CNS benign and malignant tumors. Radiotherapy in addition to killing cancer cells causes damages to normal healthy tissues. The goal of this study was to determine absorbed dose to chiasma, lens of eye, optic chiasm, retina, parotid, thyroid and submandibular glands in the radiotherapy of brain frontal lobe tumors. A head and neck phantom was constructed using human natural bone and paraffin wax with NaCl as soft tissue substitute. Six cylinders were made using phantom material in which places were embedded to insert TLDs. Treatment planning was done on the phantom and absorbed dose to each organ were obtained using dose volume histograms (DVH). The phantom was irradiated using linac and absorbed dose to each organ was obtained using TLDs, too. In both methods absorbed dose to all organs except one lens was in their tolerance dose levels. In all organs except thyroid and submandibular glands, the differences between calculated and measured doses on the phantom were less than 5%. The obtained results presents an estimation of radiotherapy induced complications in this region of brain. Besides, it is possible to validate treatment planning system using measured doses on the phantom. Discussion & Our results showed differences in the range of 1.1%-5% between treatment planning system and direct measurement in all organs except submandibular glands and thyroid which might be due to their large distance to primary radiation field; TLD response in these regions although small, but differs from lower value obtained from treatment planning system which might be due to scattered radiation which is not well considered by the treatment planning system.

External radiotherapy is one of the treatments of cancer in which the risk of radiation exposure of organs is a continue concern. The goal of present study was to measure surface and depth doses in an anthropomorphic phantom and surface dose in patients suffering upper esophageal cancer undergoing radiotherapy. In this study, surface and depth doses and surface doses was measured in phantom and patients, respectively. The phantom had some places to insert thermoluminescence dosimeters (TLDs) in eye, parotid, submandibular glands, and thyroid, spine, sternum and trachea areas. As this treatment performs in two phases, the dosimetry was done in both phases. In phase I, treatment was performed using parallel opposed (AP-PA) technique with a dose of 2 Gy/ fraction and in phase II, treatment was done with three beam technique (an oblique and AP-PA) with a dose of 1.8 Gy/fraction in 5 fractions. In regions out of treatment field such as parotid and eye, measured doses were in the range of 1.36-7.5 cGy. Thyroid doses differ in two phases; in phase I thyroid was in treatment field and its dose in the phantom was 30.84±0.88 cGy and in phase II it was in the outside of the treatment field and its dose was 5.04±0.11 cGy, whereas in patients in phase I the dose was 107.78±10.84 cGy and in phase II was 6.73±1.17 cGy. In other measurement points, there were no significant differences between measured and calculated values with TLDs and treatment planning system, respectively. Discussion & Comparing calculated doses obtained from treatment planning system and measured doses by TLDs, it was observed that these values have little differences in regions out of the treatment field which is due to scattered radiation. According to our results, given the critical role of thyroid and its high risk of radiation exposure, it is necessary to consider thyroid for defining radiation fields.

One of the main goals of establishment of radiology technology discipline is training students who can imagine high-quality radiographic perspective. For this reason students must study theoretical basis of imaging techniques at first, and then follow this principle in lab and finally apply them on patients. At present, in our country the second stage of this process (taking an image in lab) doesn’t take place because of some restrictions such as radiographic phantoms. This matter causes some problems. The Aim of this study was construction of teaching radiographic phantoms to train students to get radiographic image in lab. After lab training, they enter into radiology departments (real environment). Methods and material: Natural bone from anatomy department was provided and then adjusted with respect to its anatomical position in body and various radiographic positions. Simultaneously from each region a mold was prepared and bones set in correct anatomical and radiographic position into that and then it was filled with melted paraffin. After cooling the phantoms, they were taken took out and colored. Investigation and comparison of results showed that instructed phantoms have very similarity with patient radiographs with regard to physical parameters such as density and contrast. This result showed that construction of radiographic teaching phantoms is possible in our country and according to their quality we can use them in training of students.