Room: AAPM ePoster Library
Purpose: evaluate intra-fractional dose variations of high risk clinical target volume(HR-CTV) and applicator shift during irradiation, and to analyze correlation with the dose evaluation indices of HR-CTV during High-dose-rate(HDR) computed tomography (CT)-guided brachytherapy (BT) for cervical cancer.
Methods: patients (53 HDR fractions in which CT images could be taken both of before and after irradiation) received CT-based BT for cervical cancer. For all cases, treatment plans (Original Plan) were generated with CT-images (Original CT) after applicator insertion. Additional CT-images (After CT) were acquired immediately after HDR BT fraction. The dose variations of the dose evaluation indices (D100, D98, D90) of HR-CTV was analyzed by comparing the Original plan with After plan. In addition, Original CT and After CT images were matched by pelvic structures. For both of tip and base of the tandem, the difference in coordinate position between the two images was calculated on three axes (anterior-posterior / left-right / cranio-caudal directions) as "applicator shift"
Results: dose differences (mean ± SD) of D100, D98, and D90 for were 0.50±0.68 Gy, -0.41±0.69 Gy and -0.31±0.51 Gy, respectively. Significant difference was observed for all dose evaluation indices (p < 0.05).The average shift of the tip is 1.7mm (0 to 7.8), 1.5mm (0 to 6.5), 1.9mm (0 to 10.0), and the average shift of the base is 1.2mm (0 to 4.3), 0.9mm (0 to 4.1) and 1.4mm (0 to 10.0), for anterior-posterior / left-right / cranio-caudal direction, respectively. In the correlation analysis of applicator shift and HR-CTV dose variation, weak correlation was observed between D98, D100 and the anterior-posterior and cranio-caudal shift of the tip.
Conclusion: the CT-based BT, significant differences were found in the HR-CTV dose evaluation indices before and after treatment. The cranio-caudal applicator shift was the largest at both the tip and base of the tandem