Evaluation of the Adsorbed Radiation Dose to Critical Regions of Head and Neck During Radiotherapy of Brain Frontal Lobe

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.