# Medical Applications of the GEMPix
## 8 On-Going and Future Developments
### LaGEMPix  
The final goal of the LaGEMPix development is to achieve a large size detector for monitoring the typical clinical field size used in hadron therapy, up to \(20\times 20\) cm\({}^{2}\), allowing for a precise evaluation of the dose distribution with scanned ion beams. Two possible modifications of the LaGEMPix described in Section 7 are under consideration and will be explored in the coming months to improve the current spatial resolution. The first implies slightly modifying the present design, by decreasing the distance between the last GEM and the readout plane to reduce the dispersion of the light before reaching the readout. The second focuses on increasing the light detection efficiency by replacing the current OPD  
Figure 18: A cross-sectional view of the planned vacuum vessel housing the GEMTEQ for sealed and low-pressure applications. The GEMTEQ is located in the centre of the vacuum vessel and the colors show the different materials and components: the aluminum vessel (gray), the FITPix (blue), the PCB (green), the GEM frames (beige) and the Pixelman ASICs (brown). The GEMs are not included in this drawing. active layer by a different one offering a better match between the emitted light and the OPD's quantum efficiency. The other options involve changing the readout technology. Excluding the approach of scaling up the current design by tiling more Timepix ASICs (either Timepix3 or Timepix4) for the reasons mentioned in the previous section, there are two alternatives that may be considered. The first alternative to the current readout system is to eliminate the OPD layer leaving a TFT-only electronic readout. With this approach, the readout would directly measure the secondary electrons produced in the electron avalanche. This TFT-only solution could yield a more compact and more efficient device with a higher signal-to-noise ratio, providing a spatial resolution potentially better than 1 mm, as the electrons are guided by the electric field and their diffusion is much smaller than unfocused light. The spatial resolution of the current LaGEMPix has been compared with that of the standard GEMPix with 40 kV X-rays from an X-Ray irradiator, using the \"edge response\" method [64]. The resolution obtained with the GEMPix is about a factor of 2 better than that of the LaGEMPix, indicating that a better performance can be achieved with the charge readout option. The other option still exploits the light emitted in the GEM holes, but detecting the optical photons using a CCD/CMOS camera or the TpxCam [65,66]. The TpxCam is a fast optical camera based on a silicon pixel sensor combined with the Timepix chip, providing nanosecond scale time resolution and high quantum efficiency for photons with wavelength between 400 and 1050 nm. In this version, the LaGEMPix would not be as compact as the version using a TFT readout, as it will have to include an optical system consisting of mirror and lenses to focus the light. On the other hand, it would offer the possibility to keep the electronics off the beam. Another possible future development is to employ air instead of an argon-based gas mixture. This could be an optimal solution to simplify the present device. High photon fluences, like those used in radiation therapy, produce significant ionization in air and the GEMPix is highly sensitive to detect this ionization. Finally, it is worth mentioning that QA checks are usually performed before patient treatment. Some preliminary attempts have been made to build devices for on-line transit dosimetry: from a measurement of the dose transmitted through the patient during a treatment session, a software would reconstruct the dose released inside the patient. Until now, conventional devices, like matrix array and EPID, have not guaranteed satisfactory and universally accepted results. This is a field where the GEMPix may also bring a contribution. Various persons and groups performed the work described in this review article, please see the text and references for more details.