Simulated measurement of doses from kilovoltage cone beam CT based on a 5 years old pediatric anthropomorphic phantom

Abstract

Objective To use thermoluminescense dosimeters (TLDs) to evaluate the radiation doses to various critical organs in the computerized imaging reference systems (CIRS) 5 years old pediatric anthropomorphic phantom result ing from Varian kilovoltage cone beam CT (kV-CBCT) system based on the standard scanning protocols. Effective dose were also calculated based on dose measurement. Methods A batch of TLDs with consistency no larger than 2% were selected and annealed. First, the doses in an anthropomorphic pelvic phantom were measured using a CT chamber and TLDs, respectively, based on the standard pelvic protocols. The ratio of the both measurements is the TLD conversion coefficient. Other TLDs from the same batch were placed between two tissue-equivalent inserts and placed into the pre-drilled organ cavities of the pediatric phantom. By using standard protocols, the organs dose were measured, based on which the corresponding effective doses were calculated. Results The TLD conversion coefficient was 3.91 mGy/per reading. By using the standard head, low-dose thorax, pelvis protocol, the whole body effective dose was 0.63, 6.85 and 19.3 mSv, respectively. Conclusions It is feasible for using the CT chamber-calibrated TLDs to measure the radiation doses from kV-CBCT to pediatric anthropomorphic phantom. The effective dose in pelvic protocol was higher than in thorax and head protocol, indicating that the pelvic protocol has a penitential to lead to larger radiation damage and higher risk of secondary cancer. Key words: Thermoluminescent dosimeter(TLD); Pediatric; Kilo-voltage cone beam CT; Image-guided radiotherapy