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ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
9319
Poster
Physics
00:00 - 00:00
Validation of a commercial software for in vivo patient Quality Assurance
Cinzia Talamonti, Italy
PO-1353

Abstract

Validation of a commercial software for in vivo patient Quality Assurance
Authors: Chiara Arilli.(Azienda Ospedaliero Universitaria Careggi, SOD Medical Physics, Florence, Italy), Paolo Bastiani.(Azienda Sanitaria USL Toscana Centro, S.C. Radioterapia Firenze, Florence, Italy), Marta Casati.(Azienda Ospedaliero Universitaria Careggi, SOD Medical Physics, Florence, Italy), Marco Esposito.(Azienda Sanitaria USL Toscana Centro, S.C. Fisica Sanitaria Firenze, Florence, Italy), Alessandro Ghirelli.(Azienda Sanitaria USL Toscana Centro, S.C. Fisica Sanitaria Firenze, Florence, Italy), Livia Marrazzo.(Azienda Ospedaliero Universitaria Careggi, SOD Medical Physics, Florence, Italy), Stefania Pallotta.(Azienda Ospedaliero Universitaria Careggi, SOD Medical Physics, Florence, Italy), Stefania Pallotta.(University of Florence, Dip Scienze Biomediche Sperimantali e Cliniche "Mario Serio", Firenze, Italy), Silvia Pini.(Azienda Sanitaria USL Toscana Centro, S.C. Fisica Sanitaria Firenze, Florence, Italy), Serenella Russo.(Azienda Sanitaria USL Toscana Centro, S.C. Fisica Sanitaria Firenze, Florence, Italy), Gabriele Simontacchi.(Azienda Ospedaliero Universitaria Careggi, SOD Radioterapia, Florence, Italy), Cinzia Talamonti.(Azienda Ospedaliero Universitaria Careggi, SOD Medical Physics, Florence, Italy), Cinzia Talamonti.(University of Florence, Dip Scienze Biomediche Sperimantali e Cliniche "Mario Serio", Firenze, Italy), Eleonora Vanzi.(Azienda Ospedaliero Universitaria Senese, S.C. Fisica Sanitaria Siena, Florence, Italy)
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Purpose or Objective

DosimetryCheck (DC) is a patient quality assurance software for in-vivo dose verification using the EPID measured fluence of the treatment fields. Back-projection models are used to reconstruct the 3D dose distribution in the CT planning model of the patient. The aim of this study was to test the accuracy of the two dose calculation algorithms available in DC: the pencil beam (PB) and the collapsed cone convolution (CCC).

Material and Methods

The accuracy of the algorithms was tested on phantom in the steps of entrance fluence estimation and dose calculation. Measured OFs and PDDs were evaluated respect to the ones reconstructed by DC using both algorithms. These tests were performed on IBA “I’m RT” phantom. Its central cubic insert was filled in three different ways: homogeneously with RW3 slabs (phantom H) or replacing the central slabs with air (phantom A) or bone inserts (phantom B).

An anthropomorphic phantom study was also performed. Four VMAT clinical plans (head-neck, CNS, prostate and lung) were calculated using the TPS Monaco 5.11 on the RANDO phantom and delivered by an Elekta Synergy. During the delivery a Gafchromic® EBT3 film was embedded in the Rando at the isocenter plane. Each plan was delivered three times. Films were registered with TPS and DC dose maps. Gamma analysis (3%, 2mm, global) and isocenter dose were used to compare measured dose distribution with respect to DC calculated ones using both algorithms.

Results

In-vivo measurements produced relative differences for the phantom H and B, on OFs ranging between -0.48 and 0.92% (0.34%), and between 0.70 and 0.80% (0.30%) respectively. Much higher differences were found in phantom A owing to the use of PB, especially for small fields where a 64.2% difference was found for the 2.4 cm field size. The differences decrease by increasing the field size: a 2.1% difference was found for 15.2 cm field size. The average difference for phantom A was 16.23%.

For the PDDs the percent difference for H and B phantoms were respectively 1% and 1.5% at all depths excluding build up region. For phantom A, DC with PB overestimates the dose up to 12% and 110% in the air slab for the 10.4 cm and 2.4 cm field size respectively. In fig. 1a are shown the PDDs calculated with DC PB and CCC and Monaco TPS relative to the field 10.4x10.4cm2.

Results on anthropomorphic phantom are reported on fig1b. Except for the lung,  in the other sites there is no difference in the use of the two algorithms. A large sigma value in the brain plan is due to an air cavity near the target. These values are in agreement with the previous results: PB works well in homogenous district while in low density regions CCC must be used.

Conclusion


DC is a promising in vivo tool, and since it is possible to use a CCC algorithm for patients in which low density regions are involved, this system can improve quality assurance, as it provides the added value of the in vivo dosimetry