Purpose: To establish baseline gamma passing rates using statistical control process (SPC) for IMRT/SBRT delivery modes on a novel radiotherapy system designed for biology-guided radiotherapy (BgRT).
Methods: SPC is an analytical tool which makes use of statistics to identify random and systematic variations in a process. In this study, the process under investigation was the patient QA gamma passing rates for IMRT/SBRT delivery. A commercially available diode array was used to QA treatment plans for a variety of different sites. The first 20 QA measurements were used to establish action and control limits. Subsequent measurements were then compared against these limits and out of control measurements were identified. A 3%/2mm gamma criteria with 10% dose threshold and global normalization was used to evaluate the delivery of 55 plans.
Results: Out of a total of 55 plans, head and neck plans were the most frequent (51%), followed by Pelvis (22%) and Lung (9%). The mean gamma passing rate for the first 20 plans and the subsequent 35 plans were 96.8 +/- 2.3% and 97.56 +/- 3.57%. respectively. Action and control limits generated from the first 20 plans were 87.8% and 89.5%, respectively. For the subsequent measurements, one measurement (84.3%) was found to be outside tolerance and action limits; the treatment was not pursed on the BgRT system.
Conclusion: The use of SPC to establish action and tolerance limits is beneficial for new treatment modalities as universal limits might not be applicable. Additionally, any QA results outside the action limit can likely be assigned to systematic errors; these measurement can then provide users insight into limitation of this novel system. Process based action limits for BgRT delivery mode needs to be further evaluated following regulatory clearance.
Funding Support, Disclosures, and Conflict of Interest: Stanford receives research grants from Reflexion Medical Systems not related to this study.