ESTRO 2023 - Abstract Book

S568

Sunday 14 May 2023

ESTRO 2023

Figure 2:

for all individual chambers included in this work, a) Semiflex3D-MR, b) PinPoint3D-MR.

was 1.5

T

Conclusion The dosimetric behavior of two novel MR-conditional ionization chambers was investigated. In case of PTW31024, all chambers showed consistent results, leading to small uncertainties in the observed correction factors. The PTW31025 chambers we used showed larger uncertainties due to one chamber showing deviating results, potentially indicating intra type variations and emphasizing the need to cross-check new ionization chambers.

References: [1] Pojtinger S et al. PMB 2020

MO-0674 Benchmarking and clinical application of the ClearView / VistaScan / VistaAce 3D dosimetry system K. Lakrad 1,2 , M. Oldham 1 , J. Adamson 1 1 Duke University Medical Center, Department of Radiation Oncology, Durham, NC, USA; 2 Hassan II University, Department of Physics, Casablanca, Morocco Purpose or Objective 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. Materials and Methods 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. Results 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.