Purpose: Quality assurance (QA) of dose homogeneity in total skin electron therapy (TSET) is challenging since each patient is positioned in six standing poses with two beam angles. Our study tested the feasibility of a unique approach for TSET QA through computational display of the cumulative dose, constructed and synthesized by computer animation methods.
Approach: Dose distributions from Cherenkov emission images were projected onto a scanned 3D body model. Topographically mapped surfaces of the patient were recorded in each of six different delivery positions, while a Cherenkov camera acquired images. Computer animation methods allowed a fitted 3D human body model of the patient to be created with deformation of the limbs and torso to each position. A two-dimensional skin map was extracted from the 3D model of the full surface of the patient. This allowed the dose mapping to be additively accumulated independent of body position, with the total dose summed in a 2D map and reinterpreted on the 3D body display.
Results: For the body model, the mean Hausdorff error distance was below 2 cm, setting the spatial accuracy limit. The dose distribution over the patient’s 3D model generally matched the Cherenkov/dose images. The dose distribution mapping was estimated to be near 1.5 cm accuracy based upon a phantom study. The body model must most closely match at the edges of the mesh to ensure that high dose gradients are not projected onto the wrong location. Otherwise 2 to 3 cm level errors in positioning in the mesh do not appear to cause larger than 5% dose errors. The cumulative dose images showed regions of overlap laterally and regions of low intensity in the posterior arms.
Conclusions: The proposed modeling and animation can be used to visualize and analyze the accumulated dose in TSET via display of the summed dose/Cherenkov images on a single body surface.
It has been reported and discussed that electrical current can be produced when an insulating material interacts with ionizing radiation. We have found that high-resolution images can be obtained from insulating materials if this current is guided by an electric field to the pixels of a TFT array. The charge production efficiency of insulators is much smaller than that of photoconductor materials such as selenium, silicon, or other conventional semiconductors. Nevertheless, when the intensity of the ionizing radiation is sufficiently high, a charge sensitive TFT imaging array with only dielectric material can produce high MTF images with contrast resolution proportional to the intensity of the radiation. The function of the dielectric in this new detector may be similar to that of an ionization chamber. Without the semiconductor charge generating material, the dielectric imaging detector does not exhibit charge generation fatigue or charge generation saturation. Prototype detectors have been tested using diagnostic x-ray beams with energy ranging from 25 kVp to 150 kVp, and therapeutic 2.5MV, 6MV, 10MV, and 15MV photon beams (with and without an electron built-up layer), electron beams, broad area proton beams, and proton pencil beams in the energy range of 150 MeV. High spatial resolution images up to the Nyquist frequency have been demonstrated. The physics, structure, and the imaging properties as well as the potential application of this detector will be presented and discussed.
Total Skin Electron Therapy (TSET) utilizes high-energy electrons to treat cancers on the entire body surface. The otherwise invisible radiation beam can be observed via the optical Cherenkov photons emitted from interaction between the high-energy electron beam and tissue. Cherenkov emission is used to evaluate the dose uniformity on the surface of the patient in real-time. We have utilized a structured light sensor to determine the surface contour of each patient. Each patient was also monitored during TSET via in-vivo detectors (IVD) and/or scintillating discs in nine locations. The Cherenkov image is converted to dose distribution after a two-dimensional perspective geometry correction and the IVD measured dose at umbilicus. Cumulative dose on patient surface is obtained by projecting the two-dimensional dose distribution onto a cylindrical geometry representing the patient anatomic geometry. Patients undergoing TSET in various conditions (whole body and half body) were imaged and analysed, and the cumulative dose based on Cherenkov imaging was evaluated on various patients.
Total Skin Electron Therapy (TSET) utilizes high-energy electrons to treat cancers on the entire body surface. The otherwise invisible radiation beam can be observed via the optical Cherenkov photons emitted from interaction between the high-energy electron beam and tissue. Using a specialized camera-system, the Cherenkov emission can thus be used to evaluate the dose uniformity on the surface of the patient in real-time. Each patient was also monitored during TSET via in-vivo detectors (IVD) in nine locations. Patients undergoing TSET in various conditions (whole body and half body) were imaged and analyzed, and the viability of the system to provide clinical feedback was established.