What is your current clinical environment?

The radiotherapy department at Skåne University Hospital, Lund, annually treats about 6000 cancer patients. For that purpose the department has twelve linear accelerators. Six Varian TrueBeam, three Elekta synergy, one Elekta Precise, one TomoTherapy and one Varian iX. Around 65% of the patients are treated with an intensity modulated technique, in our case TomoTherapy or VMAT. All these patients are verified with a Delta4 measurement. Today we have two Delta44 Phantom +. Additionally we have a HexaMotion 6D motion platform to simulate tumour or patient movement. The HexaMotion is currently not used in the clinical routines.

You are using the Motion Management QA tool Delta4 HexaMotion. For which clinical applications do you use it?

We have used the HexaMotion in two different research projects. In the first project we used it to verify an in-house developed simulation method to investigate breathing motion induced interplay effects. We made simulations in the treatment planning system (Eclipse) and to verify the method the corresponding measurements were carried out using the Delta4PT phantom and HexaMotion platform. The phantom was positioned on the HexaMotion and five VMAT plans were delivered, both static and during motion, using a TrueBeam linear accelerator. Optical surface scanning (Catalyst, C-rad) was used to synchronize the radiation delivery and the motion, i.e. to make sure that the radiation delivery started in the correct breathing phase. The measured and simulated dose distributions were then compared, both static and during motion, in the Delta4 software using gamma analysis. A good agreement was observed for both the static and motion dose distributions, and hence by using HexaMotion we were able to verify our simulation method which could then be used for further simulations.

In the second project the effect of prostate motion during hypo-fractionated radiotherapy was verified. VMAT treatment plans with both Flattened and Flattening Filter Free beams were measured statically and during motion. The static and motion measurements were then compared and we found that the FFF VMAT was less affected by the motion. In this project we used a Delta4 Phantom + with the HexaMotion. We also had to construct the motion patterns using an inhouse developed program.  

During these projects we did discover some limitations in the use of HexaMotion which was not always user-friendly. We had to make our own program to create the motion trajectories in a very specific format to be able to run them with HexaMotion. In the first project, since we used HexaMotion together with the Delta4PT phantom, it was difficult, time-consuming, and required two persons to mount the phantom onto the HexaMotion platform. However, in the second research project we used the Delta4 phantom +, which was much easier to mount onto the HexaMotion, making it possible to use in a clinical environment. In the first project, investigating interplay effects, a very high precision in the motion trajectory was required since simulated and measured dose distributions were compared. The HexaMotion delivered slightly shorter period times than planned, which greatly affected our results. To compensate for this, the period times had to be changed in the simulations to fit the measurement. Another solution could have been to “trick” the HexaMotion into delivering the desired period. Following this, we do not consider the precision in the movement of HexaMotion to be good enough for the purpose of this study. Therefore, we recommend that the HexaMotion performance is verified in detail for every project or routine.

Do you see any new areas where it could be used in the future?

One clinical project that we are currently working on is the evaluation for VMAT and TomoTherapy for moving targets in the lung and thorax. This project is now in the stage of verifying the performance of the HexaMotion as it could be implemented into a clinical routine.

 

References

- Motion-induced interplay effects for VMAT radiotherapy. Anneli Edvardsson et al 2018 Phys. Med. Biol. 63 085012

- The effect of prostate motion during hypofractionated radiotherapy can be reduced by using flattening filter free beams. Benedek, Hunor et al Physics and Imaging in Radiation Oncology , Volume 6 , 66 - 70 -