Measurement of surface dose in external radiotherapy of brain frontal lobe: A study on patient and phantom

Radiotherapy plays an important role in the treatment of most malignant and also benign primary CNS tumors. Radiotherapy affects both tumor cells and normal cells. The aim of this study was to determine the absorbed dose of radiation by the skin surfacing organs at risk (lens, parotid, thyroid and submandibular gland) during radiotherapy of tumors at the frontal lobe of the brain via direct measurement in patients and phantom. There are two conventional techniques for external radiotherapy of patients with tumors of the right frontal lobe. These techniques were used to estimate the amount of surface dose absorption by organs at risk (lens of eye, parotid, thyroid, submandibular glands). Technique 1 was performed for 10 patients who referred to Reza Radiation Oncology Center. Technique 1 is the radiation of frontal field with an extension to the lateral field portion. Technique I and 2, which included radiation of one frontal field along with a bilateral field were performed for a phantom model with an anthropomorphic head and neck constructed from natural human bone with paraffin wax and NaCl as surrounding soft tissues. The surface dose for each organ was measured using TLD chips. The measured radiation dose within all organs was within the safe limits in phantom and most patients, however, the surface dose were higher in patients in compare to phantom. In some patients, the right lens was not protected and therefore there would be some risk for cataracts. The findings provide estimation for probable complications along with frontal lobe radiotherapy. Our findings showed that regarding these two techniques, technique I impose less harm to normal tissue, since the right lobe of brain is only irradiated. Besides, the higher values of surface dose in patients compared to phantom might be due to larger tumor field in patients, because the tumor dimensions in phantom was considered 4 cm, while in some patients it was larger