Room: Stars at Night Ballroom 1
Purpose: To perform dosimetric validation for plan adaptation and high definition motion management (HDMM) system of Gamma Knife (GK) Icon in various clinical scenarios with a motor-controlled pitch adjustable phantom.
Methods: First we designed and built an assembly for an anthropomorphic head phantom with its pitch rotation precisely controlled by a stepper motor. Secondly thirteen realistic clinical scenarios were selected for end-to-end testing of the GK Icon workflow. These scenarios included treatments near the limit of various HDMM alarm levels thresholds, multiple plan adaptations due to interrupted treatments, frequent patient motion to simulate coughing, and initial setup with rotation at a large pitch angle. Lastly, dosimetric and positional accuracy were measured with film and compared with measurements acquired without interruption or pitch movement.
Results: While dosimetric variation in the chin-up direction was within 2% near the limit of the 3 mm HDMM alarm level threshold, the result of chin-down direction showed a dramatic dose decrease up to 6-12 % at the superiorly located 4 mm shot near the threshold of 2 and 3 mm HDMM alarm levels without plan adaptation. Multiple adapted plans caused by interrupted treatments showed dose deviations up to 5 % with a 3 mm HDMM alarm level threshold. We also found dosimetric variation to be within 2% for initial setup pitch angles up to 20o. Frequent short excursions simulating coughing motion did not cause significant dosimetric variation. Positional deviation in the coronal plane was within experimental uncertainty (â‰¤ 0.3 mm) in all clinical scenarios.
Conclusion: Our results indicate that the dosimetric accuracy of the GK Icon system is not affected even in the extreme treatment conditions such as a patientâ€™s frequent coughing. However, the user should exercise caution for superiorly located small lesions with an HDMM alarm level threshold more than 2 mm.