Organ Dose Measurement and Calculation for Dedicated CT Used In Radiotherapy
E CAKMAK1*, N TUNCEL2, B SINDIR2, M YAVUZ3, (1) AKDENIZ UNIVERSITY SCHOOL OF SCIENCE , Antalya, (2) AKDENIZ UNIVERSITY SCHOOL OF SCIENCE and SCHOOL OF MEDICINE, Antalya, (3) AKDENIZ UNIVERSITY SCHOOL OF MEDICINE, AntalyaSU-E-I-48 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
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.