Room: AAPM ePoster Library
Purpose: To reduce pre-treatment table position overrides and to assess the accuracy of table height (TH) predictions from the planning CT.
Methods: Automated reports were created to list all treatment table positions for a given patient on a given accelerator and/or over a user-specified date range. The average position and standard deviation in each dimension are then calculated and compared with the positions and accompanying tolerances specified in the approved treatment fields. Fourteen two-week periods were considered in which all overrides on a given machine were tabulated. Position updates were made at the end of week 1 in each two-week period. Next, a script was created to determine the predicted treatment TH by measuring the distance between the plan isocenter and the CT table. Prediction accuracy is assessed by comparing the planned value with the actual TH recorded at the first treatment fraction for 396 treatment courses, delivered on four accelerators, each with a unique table. Differences are evaluated in the context of the prescribed treatment tolerances and different table attachments used on each machine.
Results: Table overrides for patients who were under treatment in both weeks of each evaluation period were reduced by 72% in the second week. Without correcting for differences in table attachments, setups for 24% of treatments evaluated (95/396) required a vertical positional override at initial treatment. Differences of greater than 1 cm from the planned value occurred in 19% of treatments (74/396) while 7% (28/396) were greater than 2 cm. After accounting for table attachments, these percentages dropped to 18% (72/396), 11% (45/396), and 0.5% (2/396), respectively.
Conclusion: This work has highlighted table attachment differences between accelerators and simulators that are now being considered in pre-treatment TH predictions. Review of recorded treatment table positions is an effective way of reducing the need for overrides.