Session Item

As radiation planning becomes more sophisticated, there is increased need for accurate and comprehensive dosimetry. The Clearview 3D dosimeter, VistaScan optical CT scanner, and VistaAce software form a new integral 3D dosimetry system that is now commercially available with potential as a powerful dosimetry verification tool with widespread applicability. However, accuracy and clinical significance are yet to be evaluated. In this study we benchmark this 3D dosimetry system and demonstrate clinical applicability.

We utilized ClearView dosimeters which consist of a tetrazolium salt based radiochromic gel for which the transparency changes as a response to irradiation, and which has a dose range of 0-80Gy. Dose readout was performed using the Vista 16 Cone Beam Optical CT Scanner, which uses degassed water as a refractive index matching fluid and a convergent light source to improve accuracy. The image was reconstructed using 1mm isotropic spatial resolution with an iterative reconstruction algorithm. Dosimetry using the VistaScan Optical CT readout was benchmarked against the well-established Duke Large Field of View Telecentric Optical CT Scanner (DLOS) for plans prepared in phantom geometry, including a simple 3-Field 3D plan and the TG-119 IMRT commissioning mock prostate plan. After benchmarking, clinical applicability was further evaluated by measuring dosimetry of patient treatment plans after recalculation on the dosimeter geometry, including Prostate, Head and Neck, spine and Single Isocenter Multi-Target Stereotactic Radio-Surgery (SIMT-SRS). All plans were delivered using a TrueBeam linac and a single fraction dose of 30-50Gy. Analysis including registration, signal to dose conversion, and 3D gamma analysis were all performed using VistaAce, a newly developed and streamlined 3D dosimetry analysis software.

ClearView/VistaScan demonstrated high (>97% for 2%/2mm, >99% for 3%/2mm, 10% dose threshold) 3D gamma pass rates for both benchmarking irradiations, as indicated in Table 1. Agreement was also high for clinical cases, as indicated in Table 1, with mean Gamma Index Pass Rates of 94.2%±3.9% [91.0% 99.0%] and 96.2%±3.2% [92.4% 99.5%] for criteria of 2%/2mm, and 3%/2mm, respectively (10% threshold).  Data acquisition, including the reconstruction process, takes around 10 minutes, while data analysis (registration, best fit calibration, 3D gamma and line profile measurements) requires around 30 minutes.

This work demonstrated that the ClearView/VistaScan/VistaAce 3D dosimetry system can achieve high accuracy and robust measurement and analysis in a clinical scenario.  This uniquely comprehensive 3D dosimetry system has potential wide-spread adoption in the dosimetric verification of clinical complex and advanced radiation therapy treatment plans.