Creating optically stimulated luminescence 3D printing filament and synthesizing radiosensitive optically stimulate luminescence crystals

Abstract

In radiotherapy, radiation oncologists use Megavoltage (MV) photon beams to deliver dose to target areas of a patient due to the MV's skin-sparing characteristics, but if the target area is near the surface of the patient, material referred to as a bolus is added to the patient's surface to provide dose build up and bring the maximum dose delivered close to the patient surface. Boluses are 3D printed to minimize air gaps between the patient and the bolus to deliver the dose accurately. Optically stimulated dosimeters (OSLD) are passive dosimeters that collect dosimetric information and are read later by using a stimulating laser to stimulate luminescence from the dosimeter, while a photomultiplier tube (PMT) measures the intensity of the luminescing light. We theorized that it was possible to combine 3D printing technology with OSLD crystals to make OSLD 3D printing filament so that an oncologist could 3D print a patient-specific bolus for a patient receiving radiotherapy treatment, and this bolus would function as a patient-specific dosimeter, ensuring precise, accurate, and safe delivery of dose- enhancing the overall quality of radiation therapy treatment. The first chapter of this study explores how we incorporated OSLD crystals, Al2O3:C, which has a robust field of study exploring its radiosensitivity, with NinjaFlex TPU, a filament used to 3D print patient specific boluses, to create an OSLD filament for oncologists to use to 3D print a bolus which would read by a commercially available LANDAUER microSTAR reader, a reader that utilizes Pulsed Optically Stimulated Luminescence (POSL) technology. We did this by cutting LANDAUER nanoDots, whose primary component is alpha carbon-doped aluminum oxide, into 1 mm or smaller pieces and cutting clear NinjaFlex TPU 3D printing filament into small, less than 1 mm pieces, mixing both at a ratio of 1:90, adding the mixture to a Filabot EX2 extruder, and extruding the mixture at low speed at 180 degrees Celsius. Afterward, the extruded filament was cut and re-extruded 2 more times, then warmed on a hot plate, compressed between 2 glass microscope slides, and cut into 8 mm diameter dots to create Filament Dot (FD) dosimeters. The FDs' dosimetric properties were tested and compared to LANDAUER Dot (LD) dosimeters, whose primary component is Al2O3:C crystals, using a Precision small animal irradiator (SAI). We found that the FDs' dosimetric characteristics were mostly similar to those of the LDs. This is the first study of this type, and we conclude that the results warrant further exploration into integrating OSLD material into 3D printing filament to 3D print radiosensitive patient boluses and 3D other radiosensitive models. LANDAUER had recalled all their nanoDot dosimeters while we were conducting the first chapter of this study, so we decided to explore new ways to synthesize radiosensitive carbon-doped aluminum oxide crystals that the LANDAUER microSTAR could still read. We developed two methodologies: the Arc Furnace methodology, which utilizes an arc furnace to melt aluminum oxide (Al2O3) crystals with carbon (C) powder, and the Hot Acid methodology, which involves mixing alpha-phase aluminum oxide crystals with carbon powder in nitric acid and boiling the nitric acid off then firing the remaining powder in a muffle furnace. The Arc Furnace (AF), Hot Acid (HA), and unmodified aluminum oxide samples were exposed to 1940 cGy using the Precision Small Animal Irradiator. When read by the microSTAR, we found that the AF samples had the strongest luminescence compared to the unmodified aluminum oxide, and the HA samples had no significant difference compared to the unmodified aluminum oxide. Then, to assess if the samples were more sensitive to low energy x-rays, we exposed the samples to an unfiltered beam from the SAI, and we found that the AF samples had a stronger-than-expected increase in luminescence strength when read by the microSTAR, indicating that the AF samples are acutely sensitive to low energy x-rays. We conclude that the Arc Furnace and Hot Acid methodologies created radiosensitive crystals by which the dose can be measured with the LANDAUER microSTAR, and we conclude further research should be conducted to refine these methods. The first study chapter has shown that we can incorporate OSLD crystals into 3D printing filament and the second chapter explores two methodologies to synthesize the crystals. We conclude that further research should be conducted into the methods to synthesize the crystals and the method to integrate the OSLD into the 3D printing filament. This will lead to new methods to create OSLD filament, which can be 3D printed to make radiosensitive boluses that will improve patient outcomes and 3D printing of other objects that researchers will use in other radiotherapy research.