Room: Exhibit Hall | Forum 4
Purpose: Stereotactic radiation therapy (SRT) with helical tomotherapy (HT) for multiple brain metastases could be treated using highly conformal dose distributions; however, rotational set-up errors in the pitch and yaw angles cannot be corrected using this system. Moreover, these errors increase significant dosimetric uncertainties for multi-target, single-isocenter SRT treatments. Here, we developed a new head supporting device that allows for highly-accurate correction of rotational set-up errors during the process of image-guided radiation therapy (IGRT) using the HT system; we also evaluated the correction accuracy and efficacy of the dose distribution in the head SRT treatment.
Methods: To evaluate the correction accuracy, a head phantom with a rotational error of 1.5 degrees was used, and the correction values acquired from the mega-voltage computed tomography (MVCT) were compared with the ideal error values. After correcting these errors using the developed device, the residual correction errors were measured based on the re-IGRT process. Moreover, an SRT plan with a simultaneous integrated boost was created with a prescription of 40 Gy/4 fractions to D99% of two CTVs and 20 Gy/4 fractions to D95% of the entire brain, and the dosimetric efficacy with rotational correction was evaluated using a calculated dose distribution with MVCT after rotational correction using the developed device.
Results: The proposed device had a beneficial impact on the rotational set-up correction and dose distribution. The results showed that the accuracy of this device can be corrected to within 0.5 degrees in the pitch and yaw directions. Moreover, the dose distribution and DVH curves agreed with those of the ideal treatment plan, and the D99% for the CTVs improved by approximately 10% with rotational correction using the developed device.
Conclusion: A rotational set-up correctable device can be used for IGRT in the HT system according to the degree of MVCT correction.
Immobilization, Tomotherapy, Image-guided Therapy