X-ray detectors for dosimetry 

Modern radiotherapy of cancer includes dynamic dose delivery while the beam projection changes during delivery, VMAT (Volumetric Modulated Arc Therapy). Traditional 2D integrating measurement devices are not sufficient to handle this, 4D (volume and time resolved) measurement devices being required instead. The demands on detector technology, electronics and application software increases dramatically and much more sophisticated solutions are required than in the past. Important for measuring MV x-rays accurately are traditionally dose linearity, dose per pulse linearity, no or small signal dependence on temperature change, long term stability (radiation hard), energy independent signal etc.

Scandidos AB manufactures instruments for threedimensional X-ray and gamma radiation dosimetry. Their dosimetry system is composed of a cylinder shaped body phantom made of PMMA (plexi glass), which is a material that interacts with X-ray radiation similarly to biological tissue. Two orthogonally intersecting printed circuit boards carrying a large number of discrete X-ray detectors are mounted in the phantom. Employing the two orthogonal detector matrices, a three-dimensional image of the radiation dose within the phantom can be constructed.

To produce a better quality dose calibration using the ScandiDos system, a need was identified for component development together with novel solutions for detector assembly. The development concerned simulation of device parameters, component design, fabrication process, electrical characterization of devices on wafer level, post-process treatment of devices and mounting on printed circuit boards. An additional activity involved modification of the assembly process with the aim to improve spatial resolution in X-ray dose measurements. Components were fabricated by Acreo in the Electrum Laboratory in Kista, electrically characterized, and then mounted in the ScandiDos system for full characterization as X-ray detectors in clinical environment. The new component design was found to improve the electrical characteristics of the device, and the modified assembly process was shown to enable better spatial resolution of the X-ray dose measurements. An additional advantage was that the modified assembly process showed greater stability. Based on these studies, the optimized device design and process was used to produce a new standard component, which is now in commercial use in the ScandiDos system Delta⁴.

ScandiDos AB

The core competence of ScandiDos, founded in 2002, is the extensive experience in dosimetry and radiotherapy. It includes the design and development of radiation detectors, electrometers and application software, as well as clinical experience in medical physics and radiation measurements. With a firm foundation in the clinical world, ScandiDos focuses on developing innovative Quality Assurance (QA) solutions to meet new advanced application demands. ScandiDos product Delta⁴ uniquely offers a fast and accurate verification of complex radiotherapy treatment modalities. It allows verifying the dose in 3D, instantly analyzing and approving treatment plans, analyzing the clinical significance of deviations, and finding the causes of deviations. Delta⁴ is the QA solution for Rotational Therapy providing isotropic and accurate dose verification, independent gantry angle verification and synchronized measurements. Measured data can be analyzed and compared with the plan for the whole fraction and even in gantry angle increments. Another application is the verification of TomoTherapy dose delivery. In just one single measurement the dose distributions in the sagittal and coronal planes are simultaneously acquired. Collected data can be then accessed for refine analysis. Delta⁴ provides the unique tools for QA in 4D-RT. It measures both when and where the dose was delivered and the data can be correlated with the respiration cycle