Evaluation of the Long-Term Stability for the Cylindrical Ionization Chambers

Purpose: To analyze the long-term stability of Farmer-type cylindrical ionization chambers by calibration factor provided from the KFDA (Korea Food Drug Administration) Materials and Methods: The cylindrical ionization chambers used in this study were the PTW 30001 (30006), 30013, 30002, 30004, 23333, the Capintec PR06C, the NE 2571, the Exradin A12 and the Wellhofer FC65G (IC70). We were analyzed that the N-k and N-D,N-W calibration factor for the cylindrical chambers and compared between the measured N-D,N-W and calculated N-D,N-W calibration factor. Results: We have observed that the long-term stability of the PTW 30013 (30006), the Wellhofer FC65G (IC70) and the NE 2571 has varied within 0.2%. The measured N-D,N-W calibration factor was about 1.0% higher than the calculated N-D,N-W that determined by the N-k calibration factor. Conclusion: The study has evaluated that the long-term stability of the cylindrical chambers through analysis for the N-k and N-D,N-W calibration factor. It has contributed to the improvement of clinical electron dosimetry in radiotherapy centers.