Topics covered in this article include:
- Setting Baselines and Tolerances
- Setting Tolerances to TG-142 Defaults
- Setting Baselines from Existing Reports
- Viewing Tolerance History
Setting Baselines and Tolerances
Once a template is scheduled for a machine the baselines and tolerances can be set for the schedule.
To manage baselines and tolerances, navigate to the Manage - Schedule Configurations" page.
The Manage - Schedule Configurations page will appear with each machine and its corresponding schedules. To edit tolerances for an individual schedule hover on the desired schedule and click the baselines button as shown below.
A page will open showing the tolerances for all the tests in the scheduled template.
For each tolerance, you may set:
- Toggle between relative to baseline and absolute measurements. For relative to baseline tolerances, the measurements are compared to the baseline and the difference is then compared to the tolerance to determine whether a measurement exceeds the tolerance.
- If the tolerance is set as a relative tolerance then a baseline must be set when a tolerance is set.
- If the tolerance is set as a relative tolerance the tolerance may be designated as a percentage difference by checking the percentage checkbox that appears at the right end of the tolerance.
- The tolerance limits are intended as optional warning limits. If the tolerance is a baseline tolerance then the lower and upper limits should be entered as positive numbers. The lower limit will be subtracted from the baseline value and the upper limit will be added to the baseline. If the tolerance limit is absolute then the lower limit is required to be less than the upper limit.
- The action limits are intended as limits that should not be exceeded in clinical operations. If the tolerance is a baseline tolerance then the lower and upper limits should be entered as positive numbers. The lower limit will be subtracted from the baseline value and the upper limit will be added to the baseline. If the tolerance limit is absolute then the lower limit is required to be less than the upper limit.
- One-sided tolerances are permitted. Undefined tolerances are defined as positive or negative infinity as appropriate.
Important: After changing tolerances, you must click the Continue button at the bottom of the page to save the tolerances.
Setting Tolerances by Meta Item Value
When setting a tolerance on a test that has meta items, different tolerances can be set based on the value in one or more meta items. To create a new subsection of tolerances set by meta item, click the Add tolerance by meta item button at the top of the desired section:
A popup will appear. Check each meta item for which a tolerance is desired. Click the Apply button to create the new subsections or the Cancel button to abort.
In the newly created section or sections, enter the desired baselines and tolerances:
- Example of Baseline Tolerance with Percentage Checked: We set our baseline to 1, our lower and upper tolerance limit at 2, our lower and upper action limit at 3 and have the percentage box checked. The system will calculate the percent difference from the reading and baseline and the tolerance and action warnings will occur if the percent difference is greater than 2 and 3 percent respectively. Hence a reading of 1.015 will be within specs, a reading of 1.025 will give a tolerance (yellow) warning and readings of 1.031 will give an action (red) warning. Outputs are typically done in this fashion.
- Example of Baseline Tolerance with Percentage Unchecked: We set our baseline to 1, our lower and upper tolerance limits at 2, our lower and upper action limits at 3 and have the percentage box unchecked. The system will calculate the magnitude between the reading and the baseline and the tolerance and action warnings will occur if the magnitude of the readings is greater than 2 or 3 respectively. Hence a reading of 2.1 will be within specs, a reading of 3.1 will give a tolerance (yellow) warning and a reading of 4.1 will give an action (red) warning. Flatness and symmetry are typically done in this fashion.
- Example of Absolute Tolerances: We want our output to be with 2% deviation from 1cGy/Mu for the tolerance warning and 3% deviation for the action limit. Hence our lower and upper tolerance limits would be 0.98 and 1.02. Our lower and upper action limits would be 0.97 and 1.03
- Example of Multiple Measurements: When adding multiple measurements within a single test using the Add measurement button (or preset in QA Settings), only the most recent measurement will be used. In the example below:
Note that if meta items are used in the test that only measurements with exactly the same meta-items will be considered as the same measurement. In the example above the three measurements with the Pitch and Left meta items are considered the same measurement while all others are considered separate measurements.
If multiple measurements are outside of tolerance the test will use the most significant alert for the test completion indicator.
Setting Tolerances to TG-142 Defaults
You may add all the default TG 142 tolerances by clicking the Add default TG142 limits button in the upper right of the interface. Note that you must choose a tolerance type from the dropdown in the upper left corner of the interface as the tolerances are often different for IMRT, non-IMRT, and SRS applications. Adding TG142 tolerances will overwrite any unsaved tolerances. Tolerances that were previously saved will be preserved.
Setting Baselines from Existing Reports
You may use an existing report to quickly set baselines from past measurements. To do this you mist have administrative privileges to set baselines on your account.
Open an existing report that you wish to use to establish baselines values. If you have sufficient privileges you will see a button labeled Select baselines near the top of the report.
After clicking the Select baselines button any eligible measurements in the report will be highlighted in light green. Clicking on an eligible measurement will highlight it. To cancel baseline selection clickCancel baselines. Once you have selected the baselines you wish to establish click the Confirm baselines button.
Once you have confirmed baseline selection the Tolerances and Baselines page for the report's schedule will open with the new baselines filled in. Note that you must click Continue at the bottom of the page to save the change.
Viewing Tolerance History
Navigate to the Manage - Schedule Configurations page. To view tolerances for an individual schedule hover on the desired schedule and click the baselines button as shown below.
Next click the View Tolerance History button:
The date and person making any tolerance changes will be shown. Below is an example:
Note that tolerances can be displayed on a report and the tolerances shown will reflect the tolerances as they were set at the time the report was finalized.