การเปรียบเทียบผลการคำนวณปริมาณรังสีโดยโปรแกรมวางแผนรังสีรักษาของเครื่องฉายรังสีตัดขวางแบบเกลียวหมุนระหว่างการใช้ภาพรังสีตัดขวางระดับศักย์ไฟฟ้ากิโลโวลต์กับเมกะโวลต์

Abstract

Helical Tomotherapy (HT) unit can acquire megavoltage computed tomography (MVCT) images for pre-treatment position verification. The MVCT images can also be used for delivered dose calculations. By comparing the delivered dose with treatment plan and evaluating to create adaptive radiotherapy (ART), when the delivery dose to patients are significant deviate from the treatment plan. The calculation of the MVCT and kVCT images data dose calculations use difference image value-to-density table (IVDT). The different tables causes the uncertainty in dose calculation. Purpose of this study, the results between dose calculation on MVCT images by planned adaptive software and dose calculation on kVCT images by the helical tomotherapy planning have been compared to evaluate the accuracy of the dose calculation on MVCT images. Fourteen head and neck cancer cases were included in this study. The planning doses were calculated by planning station on kVCT data sets for PTV70, PTV59.4 and PTV54. The MVCT data sets of patients were acquired by the helical tomotherapy system. The merged image between the kVCT and MVCT images were used for planned adaptive calculation. Then D95 of all PTVs, D50 of parotid glands and D2 of spinal cord were evaluated from the DVH. The dosimetric parameters results were compared using Pearson's correlation. The results were found that the averages D95 of kVCT and MVCT does calculation for PTV70, PTV59.4 and PTV54 were 2.121, 1.799, 1.649 and 2.158, 1.833, 1.629 Gy/fraction respectively. The averages of D50 of kVCT and MVCT dose calculation for right and left parotid glands were 0.896, 0.910 and 0.859, 0.871 Gy/fraction respectively. The averages of D2 of kVCT and MVCT dose calculation for the spinal cord were 0.961 and 0.980 Gy/fraction respectively. From this study the dose calculation on MVCT images with Planned adaptive software were significant correlative to planning dose on kVCT from Planning station. This dosimetric results comparison demonstrated that MVCT calculated dose by planned adaptive can be used to evaluate the patient delivered dose and decide to adapt treatment plans when the patients have anatomy changes.