Abstract
Purpose:A multi‐centre quality assurance program was developed to enable quality improvement by coupling measurement of intensity modulated radiotherapy (IMRT) planning and delivery performance for site‐specific planning exercises with diagnostic testing. The third year of the program specifically assessed the quality of spine stereotactic body radiotherapy (SBRT) planning and delivery amongst the participating centres.Methods:A spine SBRT planning exercise (24 Gy in 2 fractions) was created and completed by participants prior to an on‐site visit. The delivery portion of the on‐site visit included spine SBRT plan delivery and diagnostic testing, which included portal image acquisition for quantification of phantom positioning error and multi‐leaf collimator (MLC) calibration accuracy. The measured dose was compared to that calculated in the treatment planning system (TPS) using 3%/2mm composite analysis and 3%/3mm gamma analysis.Results:Fourteen institutions participated, creating 17 spine SBRT plans (15 VMAT and 2 IMRT). Three different TPS, two beam energies (6 MV and 6 MV FFF), and four MLC designs from two linac vendors were tested. Large variation in total monitor units (MU) per plan (2494–6462 MU) and dose‐volume parameters was observed. The maximum point dose in the plans ranged from 116–149% and was dependent upon the TPS used. Pass rates for measured to planned dose comparison ranged from 89.4–100% and 97.3–100% for 3%/2mm and 3%/3mm criteria respectively. The largest measured MLC error did Result in one of the poorer pass rates. No direct correlation between phantom positioning error and pass rates overall.Conclusion:Significant differences were observed in the planning exercise for some plan and dose‐volume parameters based on the TPS used. Standard evaluation criteria showed good agreement between planned and measured dose for all participants, however on an individual plan basis, diagnostic tests were able to identify contributing factors for poorer results, when using more stringent evaluation criteria.Funding from Cancer Care Ontario is acknowledged.
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