A practical three-dimensional dosimetry system for radiation therapy (original) (raw)
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A comprehensive evaluation of the PRESAGE/optical-CT 3D dosimetry system
Medical Physics, 2009
This work presents extensive investigations to evaluate the robustness ͑intradosimeter consistency and temporal stability of response͒, reproducibility, precision, and accuracy of a relatively new 3D dosimetry system comprising a leuco-dye doped plastic 3D dosimeter ͑PRESAGE͒ and a commercial optical-CT scanner ͑OCTOPUS 5ϫ scanner from MGS Research, Inc͒. Four identical PRESAGE 3D dosimeters were created such that they were compatible with the Radiologic Physics Center ͑RPC͒ head-and-neck ͑H&N͒ IMRT credentialing phantom. Each dosimeter was irradiated with a rotationally symmetric arrangement of nine identical small fields ͑1 ϫ 3 cm 2 ͒ impinging on the flat circular face of the dosimeter. A repetitious sequence of three dose levels ͑4, 2.88, and 1.28 Gy͒ was delivered. The rotationally symmetric treatment resulted in a dose distribution with high spatial variation in axial planes but only gradual variation with depth along the long axis of the dosimeter. The significance of this treatment was that it facilitated accurate film dosimetry in the axial plane, for independent verification. Also, it enabled rigorous evaluation of robustness, reproducibility and accuracy of response, at the three dose levels. The OCTOPUS 5ϫ commercial scanner was used for dose readout from the dosimeters at daily time intervals. The use of improved optics and acquisition technique yielded substantially improved noise characteristics ͑reduced to ϳ2%͒ than has been achieved previously. Intradosimeter uniformity of radiochromic response was evaluated by calculating a 3D gamma comparison between each dosimeter and axially rotated copies of the same dosimeter. This convenient technique exploits the rotational symmetry of the distribution. All points in the gamma comparison passed a 2% difference, 1 mm distance-toagreement criteria indicating excellent intradosimeter uniformity even at low dose levels. Postirradiation, the dosimeters were all found to exhibit a slight increase in opaqueness with time. However, the relative dose distribution was found to be extremely stable up to 90 h postirradiation indicating excellent temporal stability. Excellent interdosimeter reproducibility was also observed between the four dosimeters. Gamma comparison maps between each dosimeter and the average distribution of all four dosimeters showed full agreement at the 2% difference, 2 mm distance-toagreement level. Dose readout from the 3D dosimetry system was found to agree better with independent film measurement than with treatment planning system calculations in penumbral regions and was generally accurate to within 2% dose difference and 2 mm distance-to-agreement. In conclusion, these studies demonstrate excellent precision, accuracy, robustness, and reproducibility of the PRESAGE/optical-CT system for relative 3D dosimetry and support its potential integration with the RPC H&N credentialing phantom for IMRT verification.
Application of Optical CT Scanning in Three-Dimensional Radiation Dosimetry
CT Scanning - Techniques and Applications, 2011
It has been postulated that gel dosimetry using a bench-top optical CT scanner will be a valuable tool for patient specific treatment dose verification, periodic quality assurance of radiation therapy units, and commissioning of new treatment techniques and machines. The purpose of this paper is to give a brief summary of the challenges that are unique in optical CT-based 3D radiation dosimetry. The structure of the chapter is as follows: section 2 describes the two classes of optical CT scanners that have been developed so far; section 3 addresses the use of refractive index matching liquid for minimizing the multiple reflection and refraction at the boundary of a dosimeter; section 4 discusses the dynamic range problem associated with three-dimensional optical CT; section 5 summaries the effects of light scattering on the reconstructed dose distribution in optical CT; section 6 gives the results from 3D dosimeters irradiated with three representative radiation treatment plans.
An investigation of PRESAGE®3D dosimetry for IMRT and VMAT radiation therapy treatment verification
Physics in Medicine and Biology, 2015
The purpose of this work was to characterize three formulations of PRESAGE ® dosimeters (DEA-1, DEA-2, and DX) and to identify optimal readout timing and procedures for accurate inhouse 3D dosimetry. The optimal formulation and procedure was then applied for the verification of an intensity modulated radiation therapy (IMRT) and a volumetric modulated arc therapy (VMAT) treatment technique. PRESAGE ® formulations were studied for their temporal stability postirradiation, sensitivity, and linearity of dose response. Dosimeters were read out using a high-resolution optical-CT scanner. Small volumes of PRESAGE ® were irradiated to investigate possible differences in sensitivity for large and small volumes ('volume effect'). The optimal formulation and read-out technique was applied to the verification of two patient treatments: an IMRT plan and a VMAT plan. A gradual decrease in post-irradiation optical-density was observed in all formulations with DEA-1 exhibiting the best temporal stability with less than 4% variation between 2-22 h postirradiation. A linear dose response at the 4 h time point was observed for all formulations with an R 2 value >0.99. A large volume effect was observed for DEA-1 with sensitivity of the large dosimeter being ~63% less than the sensitivity of the cuvettes. For the IMRT and VMAT treatments, the 3D gamma passing rates for 3%/3 mm criteria using absolute measured dose were 99.6 and 94.5% for the IMRT and VMAT treatments, respectively. In summary, this work shows that accurate 3D dosimetry is possible with all three PRESAGE ® formulations. The optimal imaging windows post-irradiation were 3-24 h, 2-6 h, and immediately for the DEA-1, DEA-2, and DX formulations, respectively. Because of the large volume effect, small volume cuvettes are not yet a reliable method for calibration of larger dosimeters to absolute dose. Finally, PRESAGE ® is observed to be a useful method of 3D verification when careful consideration is given to the temporal stability and imaging protocols for the specific formulation used.
Quality assurance in 3D dosimetry by optical-CT
Journal of Physics: Conference Series, 2006
A promising new system for 3D dosimetry combines a radiochromic plastic dosimeter, PRESAGE [1-3], with an optical-computed-tomography system (optical-CT) capable of reading the dose recorded in the dosimeter [4,5]. Optical-CT is also the method of choice for reading out the dose recorded in the more established polymer gel dosimetry system, for many applications [6-9]. Achieving accurate dosimetry depends critically on the performance characteristics of the optical-CT imaging system. Several systems have been developed [6,10-12], and two are commercially available at the present time (MGS Research Inc, and Modus Medical Devices Inc). Common issues of quality assurance (QA) become significant for all these systems to ensure correct initial commissioning of optical-CT 3D dosimetry and correct continued functioning. Here we present a QA phantom and procedure designed for efficient evaluation of the basic imaging performance of any optical-CT scanning system. Example results are presented from two optical-CT systems, an inhouse CCD based system and the OCTOPUS™ system from MGS Research.
A New Optical-CT Apparatus for 3-D Radiotherapy Dosimetry: Is Free Space Scanning Feasible?
IEEE Transactions on Medical Imaging, 2010
In this paper, we present a new optical computed tomography (Optical-CT) scanner for the verification of the radiation dose schemes delivered in modern radiotherapy applications. The optical-CT scanner is capable of providing rapid relative 3-D dosimetry with high spatial resolution with the use of normoxic N-Vinylpyrrolidone based polymer gel dosimeter. The scanner employs a diffuse uncollimated light illumination beam, a computer controlled motorized rotation stage and a charge-coupled device (CCD) camera. Various test experiments were performed to determine the performance characteristics of the optical-CT apparatus. Attenuation coefficient () versus dose calibration data were generated from two calibration experiments using gel containers of two different diameters. All irradiations were performed using a 6 MV linear accelerator. A comparison of the reconstructed images between optical-CT scans using refractive index (RI) matching fluid and corresponding scans performed in free space was demonstrated. The dose readout of a test irradiation model was found to be in good agreement with independent readout performed by MR imaging. The findings presented in this study suggest that polymer dosimeters combined with the new optical-CT scanner constitute a potentially feasible method capable of measuring complex 3-D dose distributions with high resolution and in a wide dose range.
A prototype optical-CT system for PRESAGE 3D dosimeter readout
Journal of Physics: Conference Series
This work introduces the Duke Integrated-lens Optical Scanner (DIOS), a prototype optical-CT system designed for convenient and low-cost readout of PRESAGE 3D dosimeters. A key novelty of the DIOS is the incorporation of a multipurpose light-collimating tank (the LC-tank). The LC-tank collimates light from a point source, maintains parallel ray geometry through a dosimeter mounted inside the tank, and refocuses emergent light onto a CCD detector. A second purpose is to dramatically reduce the amount of refractive matched fluid required in prior optical-CT scanners. This is achieved by substituting large quantities of refractive-matched fluid with solid RI-matched polyurethane. The advantages of DIOS include eliminating the need for expensive telecentric lenses, and eliminating the impracticality of large volumes of RI matched fluid. The DIOS is potentially more susceptible to stray-light artifacts. Preliminary phantom testing shows promising agreement between PRESAGE/DIOS readout and prior commissioned optical-CT scanners, as well as with Eclipse dose calculations.
On the feasibility of comprehensive high-resolution 3D remote dosimetry
Medical physics, 2014
This study investigates the feasibility of remote high-resolution 3D dosimetry with the PRESAGE®/Optical-CT system. In remote dosimetry, dosimeters are shipped out from a central base institution to a remote institution for irradiation, then shipped back to the base institution for subsequent readout and analysis. Two nominally identical optical-CT scanners for 3D dosimetry were constructed and placed at the base (Duke University) and remote (Radiological Physics Center) institutions. Two formulations of PRESAGE® (SS1, SS2) radiochromic dosimeters were investigated. Higher sensitivity was expected in SS1, which had higher initiator content (0.25% bromotrichloromethane), while greater temporal stability was expected in SS2. Four unirradiated PRESAGE® dosimeters (two per formulation, cylindrical dimensions 11 cm diameter, 8.5-9.5 cm length) were imaged at the base institution, then shipped to the remote institution for planning and irradiation. Each dosimeter was irradiated with the s...
International Journal of Radiation Oncology*Biology*Physics, 2013
We present preliminary results for a 3-dimensional dose evaluation software system (P DRESS, patient-specific 3-dimensional dose real evaluation system). Scanned computed tomography (CT) images obtained by using dosimetry were transferred to the radiation treatment planning system (ECLIPSE, VARIAN, Palo Alto, CA) where the intensity modulated radiation therapy (IMRT) nasopharynx plan was designed. We used a 10 MV photon beam (CLiX, VARIAN, Palo Alto, CA) to deliver the nasopharynx treatment plan. After irradiation, the TENOMAG dosimeter was scanned using a VISTA T M scanner. The scanned data were reconstructed using VistaRecon software to obtain a 3D dose distribution of the optical density. An optical-CT scanner was used to readout the dose distribution in the gel dosimeter. Moreover, we developed the P DRESS by using Flatform, which were developed by our group, to display the 3D dose distribution by loading the DICOM RT data which are exported from the radiotherapy treatment plan (RTP) and the optical-CT reconstructed VFF file, into the independent P DRESS with an ionization chamber and EBT film was used to compare the dose distribution calculated from the RTP with that measured by using a gel dosimeter. The agreement between the normalized EBT, the gel dosimeter and RTP data was evaluated using both qualitative and quantitative methods, such as the isodose distribution, dose difference, point value, and profile. The profiles showed good agreement between the RTP data and the gel dosimeter data, and the precision of the dose distribution was within ±3%. The results from this study showed significantly discrepancies between the dose distribution calculated from the treatment plan and the dose distribution measured by a TENOMAG gel and by scanning with an optical CT scanner. The 3D dose evaluation software system (P DRESS, patient specific dose real evaluation system), which were developed in this study evaluates the accuracies of the three-dimensional dose distributions. Further applications of the system utility are expected to result from future studies.
Physics in medicine and biology, 2010
Achieving accurate small field dosimetry is challenging. This study investigates the utility of a radiochromic plastic PRESAGE read with optical-CT for the acquisition of radiosurgery field commissioning data from a Novalis Tx system with a high-definition multileaf collimator (HDMLC). Total scatter factors (Sc, p), beam profiles, and penumbrae were measured for five different radiosurgery fields (5, 10, 20, 30 and 40 mm) using a commercially available optical-CT scanner (OCTOPUS, MGS Research). The percent depth dose (PDD), beam profile and penumbra of the 10 mm field were also measured using a higher resolution in-house prototype CCD-based scanner. Gafchromic EBT film was used for independent verification. Measurements of Sc, p made with PRESAGE and film agreed with mini-ion chamber commissioning data to within 4% for every field (range 0.2-3.6% for PRESAGE, and 1.6-3.6% for EBT). PDD, beam profile and penumbra measurements made with the two PRESAGE/optical-CT systems and film sho...