Room: Exhibit Hall | Forum 6
Purpose: In radiation therapy to the left breast, deep breath-hold has attracted attention to reduce the radiation dose to the heart.Our hospital uses a 3D patient surface guidance (VOXELAN) to ensure the state of deep breath-hold and the reproducibility of posture. By using VOXELAN, it is possible to measure Inter-fractional variation and Intra-fractional variation without radiation exposure. In this study, we examined whether VOXELAN is valid by evaluating Inter-fractional variation and Intra-fractional variation of deep breath-hold left breast irradiation.
Methods: 14 patients with left breast cancer who had breast irradiation using VOXELAN were analyzed. Patient 's age is 39 to 49 years old (average age 45 years old), all are female. From the electrical portal imaging device (EPID) image obtained during treatment, the distance from the irradiation field end to the breast skin surface was measured at three points in the upper, middle and lower regions. The inter-fractional variation for 14 times was calculated by finding the error of the distance of three points of the first irradiation and the 2nd ~ 15th times respectively. The distances of three points were obtained for multiple images of the same irradiation field and it was taken as intra-fractional variation. Correlation was obtained by comparing the difference between inter-fractional variation of EPID image and VOXELAN using phantom image and patient image.
Results: Inter-fractional variation is 9.2% for differences of 3 mm or more. Intra-fractional variation is 0.7% for differences of 3 mm or more. The correlation coefficient of the phantom was 0.99.The correlation coefficient for each patient was between 0.62 and 0.99, the average value was 0.79, the P value was 0.031 or less in all cases.
Conclusion: VOXELAN and EPID have consistency in position detection, and it is useful to maintain the reproducibility of breath-hold by using VOXELAN.