Plastic scintillation dosimeters (PSD) have been a topic of a keen research interest for the past 20 years. Numerous PSD systems have been proposed, most times differentiating from the previous by a slight change in one or more components, such as the photodetector. However, a few major technological and engineering innovations have also been made. Over the past few years PSDs have been evaluated for small field dosimetry, in vivo dose measurements, building of arrays and much more. The present manuscript is intended to present the basic physics and properties of PSDs and its application over the past two decades.
Purpose: Using an array of micro‐lenses coupled with its active sensor, a light‐field camera samples the incoming optical photons in both the spatial and angular domain. This work presents the proof‐of‐concept and experimental validation of a 3D dosimeter based on the reconstruction of the light pattern emitted from a plastic scintillator volume and recorded using a light‐field camera. Using a single, fixed camera device, this technology enables real‐time, multi‐plane experimental measurement of static and dynamic radiotherapy delivery. Method: A Raytrix R5 light‐field camera was used to image a 10×10×10cm 3 EJ‐260 plastic scintillator immersed in a water tank and irradiated with both square field and small MLC segments on a Clinac iX linear accelerator. The 3D light distribution emitted by the scintillator volume was reconstructed at a 5mm resolution in all dimensions by backprojecting the light collected by each pixel of the light‐field camera using a total variation minimization iterative reconstruction algorithm. Results: Signal contamination by Cerenkov emission was evaluated to less than 0.5% of the collected scintillation light for all field investigated, and as such Cerenkov light filtration was deemed unnecessary. Light‐field acquisition rate of at least 1 frame per second was achieved by the camera at a 600MU/min dose rate. The absolute dose difference between the reconstructed 3D dose and the expected dose calculated using the treatment planning software Pinnacle3 was on average below 3% for square fields and 5% for MLC segments in the high dose, low gradient region of each acquired field. Conclusions: Millimeter resolution dosimetry over an entire 3D volume is achievable in real‐time using a single light‐field camera. Because no moving parts are required in the dosimeter, the incident dose distribution can be acquired as a function of time, thus enabling the validation of static and dynamic radiation delivery with photons, electrons and ions.
Intramuscular cell transplantation in humans requires so far meticulous repetitive cell injections. Performed percutaneously with syringes operated manually, the procedure is very time consuming and requires a lot of concentration to deliver the cells exactly in the required region. This becomes impractical and inaccurate for large volumes of muscle. In order to accelerate this task, to render it more precise, and to perform injections more reproducible in large volumes of muscle, we developed a specific semimanual device for intramuscular repetitive cell injections. Our prototype delivers very small quantities of cell suspension, homogeneously throughout several needles, from a container in the device. It was designed in order to deliver the cells as best as possible only in a given subcutaneous region (in our case, skeletal muscles accessible from the surface), avoiding wasting in skin and hypodermis. The device was tested in monkeys by performing intramuscular allotransplantations of β-galactosidase-labeled myoblasts. During transplantations, it was more ergonomic and considerably faster than manually operated syringes, facilitating the cell graft in whole limb muscles. Biopsies of the myoblast-injected muscles 1 month later showed abundant β-galactosidase-positive myofibers with homogeneous distribution through the biopsy sections. This is the first device specifically designed for the needs of intramuscular cell transplantation in a clinical context.
Purpose: Lung SBRT is being used by an increasing number of clinics, including our center which recently treated its first patient. In order to validate this technique, the 3D dose distribution of the SBRT plan was measured using a previously developed 3D detector based on plenoptic camera and plastic scintillator technology. The excellent agreement between the detector measurement and the expected dose from the treatment planning system Pinnacle 3 shows great promise and amply justify the development of the technique. Methods: The SBRT treatment comprised 8 non‐coplanar 6MV photon fields with a mean field size of 12 cm 2 at isocentre and a total prescription dose of 12Gy per fraction for a total of 48Gy. The 3D detector was composed of a 10×10×10 cm 2 EJ‐260 water‐equivalent plastic scintillator embedded inside a truncated cylindrical acrylic phantom of 10cm radius. The scintillation light was recorded using a static R5 light‐field camera and the 3D dose was reconstructed at a 2mm resolution in all 3 dimensions using an iterative backprojection algorithm. Results: The whole 3D dose distribution was recorded at a rate of one acquisition per second. The mean absolute dose difference between the detector and Pinnacle 3 was 1.3% over the region with more than 10% of the maximum dose. 3D gamma tests performed over the same region yield passing rates of 98.8% and 96.6% with criteria of 3%/1mm and 2%/1mm, respectively. Conclusion: Experimental results showed that our beam modeling and treatment planning system calculation was adequate for the safe administration of small field/high dose techniques such as SBRT. Moreover, because of the real‐time capability of the detector, further validation of small field rotational, dynamic or gated technique can be monitored or verified by this system.
Purpose: To develop and validate a novel type of 2D dosimeter based on the tomographic reconstruction of the dose projections obtained using long scintillating fibers. Methods: 50 parallel scintillating fibers (diameter, 1mm; length, 6 to 20cm) were aligned in a 30cm diameter cylindrical masonite phantom with a 90cm source‐to‐surface distance and a 100cm source‐to‐fibers distance. The fibers were disposed so that the effective detection area of the scintillating fibers was a 20cm diameter disk. Both ends of each scintillating fiber were coupled to clear optical fibers to enable light collection by a single CCD camera using an f/2, 50mm focal length lens. 7 IMRT segments and 2 square fields were acquired using 18 projections over a 170 degrees rotation of the device. Dose reconstructions were conducted using a total‐variation minimization reconstruction algorithm. 8 monitoring units were programmed for each projection and the reconstructed dose grid pixel resolution was set to 1×1mm,2,. Results: Using a non‐optimized algorithm on a 2GHz CPU, each reconstruction was performed in less than 6 minutes. 3%/3mm gamma tests conducted between the reconstructed IMRT dose distributions and the dose calculated with the treatment planning system Pinnacle,3, were on average successful for 99.6% of the dose pixels for the region over 10% of the maximum dose. For both square fields and the whole summed IMRT field, 100% of the dose pixels were successful to the gamma test. Conclusions: Using tomographic reconstruction on the projections acquired with rotating scintillating fibers, one is able to perform 2D dosimetry of simple and IMRT fields with great accuracy and resolution using only a limited number of scintillating fibers. The underlying concept of tomographic dosimetry and the small number of fibers needed to reconstruct a given 2D dose distribution offer a world of new dosimetric possibility, both applicable to 2D and 3D dosimetry.
Myoblasts were grown from monkey muscle biopsies and infected in vitro with a defective retroviral vector containing a cytoplasmic beta-galactosidase (beta-gal) gene. These myoblasts were then transplanted to 14 different monkeys, 6 of which were immunosuppressed with FK506. Without immunosuppression, only a few myoblasts and myotubes expressing beta-gal were observed 1 week after the transplantation, but no cells expressing beta-gal were observed after 4 weeks. This result was attributed to immune responses since infiltration by CD4+ or CD8+ lymphocytes was abundant 1 week after transplantation but not after 4 weeks. The expression of interleukin 6 (IL-6), interleukin 2 (IL-2), granulocyte/macrophage colony stimulating factor (GM-CSF), transforming growth factor-beta (TGF-beta) and granzyme B mRNAs was increased in the myoblast-injected muscle indicating that the infiltrating lymphocytes were activated. Moreover, antibodies against the donor myoblasts were detected in 3 out of 6 cases. When the monkeys were immunosuppressed with FK506, muscle fibers expressing beta-galactosidase (beta-gal) were present 1, 4 and 12 weeks after the transplantation. There was neither significant infiltration by CD4 or CD8 lymphocytes, nor antibodies detected. The mRNA expression of most cytokines was significantly reduced as compared to the nonimmunosuppressed monkeys. These results indicate that FK506 is effective in controlling short-term immune reactions following myoblast transplantation in monkeys and suggest that it may prove useful for myoblast transplantation in Duchenne Muscular Dystrophy patients.
Backgrounds. Implantation of normal myoblasts may eventually be a treatment for inherited myopathies such as Duchenne muscular dystrophy. Methods. We report a comparative study of the effectiveness on myoblast implantation: (1) into the muscles of young (2 months) mdx mice nonirradiated and noninjected with notexin (group 1), (2) into muscles of old mdx mice (15 months) nonirradiated and noninjected with notexin (group 2), and (3) into muscles of 5 months mdx mice irradiated 3 months before the transplantation (group 3). Roughly 3 million cells were injected with bFGF in the Tibialis anterior. Results. Although mice of groups 2 and 3 had significantly more (P<0.05) fibrotic tissue in their muscles than those of group 1, the transplantation success was not significantly different among the three groups. Conclusion. Therefore these results demonstrated that myoblast transplantation can be successful even when there is abundant fibrosis.
