بررسی صحیح بودن مقدار اشعه داده شده در پرتودرمانی سرطان پستان با ترمولومینسانس دوزیمتری

In vivo dosimetry seems an appropriate method for quality assurance in radiotherapy with CO-60, which can be considered as a routine program in radiotherapy centers. In this study, entrance and exit dose in tangential fields were measured in phantom for 30 breast cancer patients by using TLD in radiotherapy section of Imam Khomeini Hospital. TLD crystals were calibrated against SSDL (Secondary Standard Dosimetry Laboratory) Farmer chamber of Iran Institute of Atomic Energy. An overall check of basic dosimetry, treatment unit parameter, planning and calculation methods and daily set up of the patients can be determined by combination of entrance and exit dose. Correction factors such as field size, SSD, thickness, angle of incidence and back scattered rays were obtained for difference between reference conditions and clinical situations. Measured dose by in vivo dosimetry was compared with the expected values for entrance, exit and midline points. The obtained mean values for these points were 1.95%, 4.3% and 6.87% with standard deviations of 5%, 11% and 6.5% respectively which showed no significant difference between these points except for entrance and midline points. The more spread of errors in exit point than in entrance point is due to more sources of errors in this point. Analysis of the results, field by field, (medial and lateral tangential fields) showed that this deviation was significant for exit point (P-value=0.01). This is due to calculation algorithms and set up uncertainties. Based on the results of in vivo dosimetry in this work, the sources of uncertainties were due to calculation algorithms, in particularly, around inhomogeneities and patient curvature, set up, mobilization, output and data transfer. The aim of this work was to quantify and determine the uncertainties at the end of treatment stage it is therefore concluded that in vivo dosimetry can be used as a valid tool for quality assurance in radiotherapy centres in order to improve the quality of treatment. Key Words: 1) Radiotherapy 2) Quality Control 3) TLD 4) Breast Tissue