Program Information
Commissioning of a Novel Commercial Motion System to Investigate Dosimetric Consequences Due to Variability of Respiratory Waveforms
A Cetnar*, J James , B Wang , University of Louisville, Louisville, KY
Presentations
MO-B-BRD-1 (Monday, March 9, 2015) 10:00 AM - 12:00 PM Room: Ballroom D
Purpose:
The purpose of our study was to assess the feasibility of HexaMotion (ScandiDos, Uppsala, Sweden) for clinical use. The motion phantom with six degrees-of-freedom was used to evaluate the dosimetric consequences of respiratory waveform variation.
Methods:
The positional accuracy of the HexaMotion was assessed using an independent optical-guided system and digital level. Dosimetric consequences of waveform variation were investigated using an Internal Target Volume (ITV) approach for planning. A waveform of known amplitude was used by HexaMotion to simulate respiratory motion during a 4DCT. A cylindrical ITV was created to cover the inner diode region of the Delta4 through all 10 phases. The plan was delivered using both the waveform from simulation and a waveform of greater amplitude. The delivery was repeated using gating limits that would terminate the beam if the amplitude of the treatment waveform became greater than the amplitude of the expected waveform from simulation.
Results:
The maximum deviation for translation was 0.3 mm and rotation was 0.5 degrees. The device was able to reproduce a patient waveform with a standard deviation of 0.4 mm. As the amplitude of the waveform increases for treatment delivery, the diodes on the periphery of the target volume receive less than the planned dose. However, by using limits to terminate the beam outside of the original amplitude, the measured dose was similar to the planned dose. The average difference in the ITV region between the planned motion and the larger amplitude was 9.1% less with no gating limits, but only differed 0.1% with the gating limits in place.
Conclusion:
When using the ITV technique for SBRT planning, we recommend the use of gating limits that coincide with the amplitude of the patient waveform at simulation to prevent the potential under-dosing of the ITV due to changes in patient respiration pattern.
Contact Email: