Room: AAPM ePoster Library
Single isocenter stereotactic radiosurgery (SRS) of multiple brain metastases is increasing used clinically due to the delivery efficiency. However, the complex nature of these plans relies on the accuracy of equipment used to image, calculate and treat such plans. We conducted an end-to-end test to determine the localization and dosimetric accuracy of using an Elekta Versa HD linear accelerator with multi-leaf collimators to treat multiple brain lesions in a single isocenter and compare it against an established delivery system.
A CT simulation scan of a previously treated patient was used with five brain lesions ranging from 7-20 mm in diameter within 6 cm of isocenter. Two treatment plans were produced. The first using the RayStation treatment planning software (TPS) (RaySearch Laboratories) for VMAT delivery on the linear accelerator and the second with the Precision TPS for delivery on CyberKnife (Accuray Inc.). 20 Gy to all lesions was prescribed in a single fraction in accordance with our clinical practice. Plans were delivered to a 3D-printed phantom emulating the specific patient’s anatomy while including a gel-dosimetry insert to analyze the dose distribution in 3D.
For the Elekta Versa HD, all targets >7mm had 3D global gamma analysis (3%/2?mm) above 95%. More specifically, the 7mm, 9mm, 12mm, 15mm and 20mm lesions had passing rates of 87.8%, 96.8%, 95.6%, 98.5% and 98.7%, respectively. Corresponding values for CyberKnife were 97.1%, 99.3%, 99.0%, 95.5% and 99.0%. Further, the Versa HD was able to deliver a mean dose to each target matching that of the TPS dose within 2%.
The Versa HD accurately delivered a radiosurgery plan for targets within 6cm of isocenter. Clinically acceptable gamma pass rates were achieved for lesion sizes larger than 9mm diameter. Future work will include repeating the end-to-end tests using the integrated Monaco-Versa HD TPS-linac combination.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by a research grant from Elekta AB E. Pappas, G. Kalaitzakis, E. Zoros and K. Zourari are members of the RTsafe R&D department
Gel Dosimeter, Stereotactic Radiosurgery, Treatment Verification
TH- Radiation Dose Measurement Devices: Phantoms for dosimetric measurement