Swiss clinic’s use of secondary dose check delivers confidence in online adaptive RT
Hôpital Riviera-Chablais physicists employ ThinkQA Secondary Dose Check for Elekta Unity to ensure safe, accurate treatments in their MR-guided online workflow
During MR-guided online adaptive radiotherapy (ART), patients stay on the treatment couch for recontouring of targets and organs-at-risk, therefore time is critical. Medical physicists need a quick way to confirm that the dose to be delivered is as close as possible to the TPS-specified dose. Hôpital Riviera-Chablais (Rennaz, Switzerland) physicists have been using ThinkQA Secondary Dose Check (SDC)* **, a web-based software that helps them verify – in just a few minutes – that the TPS-calculated dose distribution is consistent with plan parameters. The software can be specifically adapted for use with the Elekta Unity MR-Linac.
“We follow international recommendations for checking the TPS calculation to enable us to treat,” says medical physicist Olivier Pisaturo, PhD. “If we do adapt-to-shape or adapt-to-position daily treatment adaptation, it’s always a new plan. So, we need to perform an independent calculation of monitor units and leaf positions for every fraction, so we know the dose is as accurate as possible before irradiation.”
However, when clinicians began treating with Elekta Unity in January 2020, a dedicated SDC solution was unavailable, which required them to use the SDC provided by their non-Elekta treatment planning system. They soon found that it was impractical for use in an online ART workflow, as it involved a complex and manual process of plan exporting and importing, and the use of scripts to arrive at a calculation result.
“In the end it would take 10 minutes to do the job,” he recalls. “We found we couldn’t do that feasibly for all patients and all fractions on Unity; only physicists perform this task at our facility and since we’re a small department we don’t always have a physicist on hand at the system.”
Commissioning of ThinkQA Secondary Dose Check was straightforward
Hôpital Riviera-Chablais was one of three centers to participate in a pilot program for the new ThinkQA SDC solution specifically developed by DOSIsoft for the Monaco-based Elekta Unity workflow. By every relevant metric, the Rennaz team found the software an ideal solution for dose verification in the online adaptive workflow and is now using ThinkQA for all eight to 10 Elekta Unity patients the center treats each day.
Commissioning ThinkQA was exceptionally straightforward, according to Dr. Pisaturo.
“Commissioning was simple and straightforward because the software uses the gold standard beam modeling data for Elekta Unity.”
“Commissioning was simple and straightforward because the software uses the gold standard beam modeling data for Elekta Unity,” he says. “DOSIsoft just asked us for the cryogen level data, which was acquired during the MR-Linac commissioning process following installation. For the actual commissioning, we tested the dosimetry on different localizations on 10 to 15 patients over a two-day period and sent that information to the company, which performed some fine-tuning of the beam model. Then, I and medical physicist Dr. Sarah Ghandour did the validation over a two-day period.”
Speed, accuracy, simplicity
Dr. Pisaturo and his colleagues have found that the key benefits of ThinkQA SDC are speed, accuracy and simplicity.
“Within just a few minutes after exporting the Monaco plan to the software we have the result, so ThinkQA is super-fast.”
“Within a few minutes after exporting the Monaco plan to the software we have the result, so ThinkQA is super-fast and works automatically,” he says. “It’s also very simple to use because it’s a web interface, so you can have ThinkQA on every computer in the department – you don’t need to be close to the workstation. A traffic light system makes it very easy for the RTT to know when to proceed – if the light is green we can treat, if it’s red we can check the details of the calculation by referencing the simple graphics to find out why and then resolve the issue. The ThinkQA graphics show a dose matrix analysis, including automatic volume indicators and DVH, but the parameter we’re most interested in is the gamma passing rate [Figure 1].
“ThinkQA satisfies our criteria of no more than three percent difference between the TPS-specified dose and the result the software provides.”
“In terms of accuracy,” Dr. Pisaturo adds, “ThinkQA satisfies our criteria of no more than three percent difference between the TPS-specified dose and the result the software provides. It was a great surprise when we did our initial accuracy check, because the Collapsed Cone Convolution [CCC] algorithm doesn’t account for the static magnetic field [B0]. It’s a standard CCC with intelligent tuning of the calculation to be as close as possible to the result calculated by Monaco’s Monte Carlo algorithm, which does account for B0.
“The conclusion was that the beam model and software are very accurate,” he says. “The difference we observed was not more than two to two-and-half percent.”
For the center’s online adaptive radiotherapy workflow, ThinkQA SDC has satisfied all key requirements, ensuring a streamlined workflow, safe patient treatments and compliance with AAPM recommendations – contributing significantly to the confidence of Hôpital Riviera-Chablais physicists.
“With Elekta Unity, we’re providing patients with the most advanced, personalized radiotherapy possible,” Dr. Pisaturo says. “Having a secondary dose calculation solution that is precise, fast and easy to use in the Elekta Unity online adaptive workflow has been extremely beneficial for department productivity and for our patients.”
* Product is designed by DOSIsoft S.A. and distributed exclusively by Elekta.
** DOSIsoft QA secondary dose check is U.S. FDA 510(k) pending. Device is not commercially available for sale in U.S. Device is not available in all markets.