The aim of this study was to investigate the organ doses of patients undergoing computed tomography (CT) examination using the wide bore General Electric (GE) "Light Speed RT" unit. The head, chest and pelvic regions of the Rando-phantom were scanned with 120 kV, 200 mA, and 2.5 mm slice thickness for helical and axial modes. Thermoluminescent Dosimeter (TLD) pairs were used for the dosimetry of 10 organs. TL-counts were converted to dose by using CTDIcenter dose on CT-phantom. For the calculation of the organ doses, the ImPACT software was utilized by entering CTDIair (100 mAs) in small and large field of view (26.43 and 21.17 mGy respectively). The in-field dose ranges in helical and axial modes were 64.3 -38 mGy and 47.6 -19.7 mGy in head, 48.3 -14.1 mGy and 34.1 -10 mGy in chest, 28.4 -10.2 mGy and 21 -8.5 mGy in pelvic, respectively. The organ doses from software and TLD were compared and tailored as the in-field and the out-field radiation. First results showed that the organ dose was relatively higher in the helical mode on both direct and indirect measurement. The in-field organ dose differences between TLD and software were seen. In helical and axial modes, the dose differences ranged from +1 to +13.3 and −8.3 to +9.6 mGy for head exam, +1.1 to +15.3 and +0.3 to +9.1 mGy for chest, and −21.7 to +1.9 and −15.5 to +1.8 mGy for pelvic. The availability of this program for organ dose calculations by measuring CTDIair value for CT device used in the radiotherapy would be considered valuable.

Purpose: To investigate the organ doses of patients undergoing to General Electric (GE) Light Speed RT computed tomography (CT) device by the measurement and calculation method. Methods: The head, thorax and pelvis regions of Rando phantom scanned with 120kV, 200 mA, and 2.5 mm thickness for helical and axial mode. TLD pairs were used for dose measurements in specified 10 organ locations. Each exam was repeated and the TL counts averaged for organs. TL count conversion to dose was done for each scanning parameters using CTDI dose measurement on CT phantom. On the other hand, for calculation of organ doses at the same scanning process IMPACT software was utilized by using CTDI‐air (100 mAs) that measured by ion chambers in small and large window widths. CTDI‐air (100 mAs) in small and large window widths was 26.43 mGy and 21.17 mGy respectively. The organ doses that obtained from software and those from TLD measurements were compared. Results: In each examination the organ doses were tailored as the in‐field and out‐field radiation. The in‐field organ dose differences between TLD measurements and Impact software calculation by entering CTDI‐air (100 mAs): In helical and axial head exam the dose differences for eye, brain and thyroid were 2.8, 1 and 13.3, and 8.2, −8.3 and 9.6 mGy respectively, in helical and axial chest exam the dose differences for heart, lung, liver and kidney 2.7, 15.3 1.1 and 7.3 and, 9.1, 6.5, 0.3 and 5.2 mGy respectively, in helical and axial pelvic exam the dose differences for bladder, prostate, uterus and testis −3.6, −5.1, 1.9 and −21.7, and −3, −3.2, 1.8 and −15.5 mGy respectively. Conclusion: The availability of this program for organ dose calculations by measuring the CTDI‐air value of the CT device that used in the radiotherapy would be considered valuable.