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3D In-Vivo Portal Dosimetry for Hypo-Fractionated Radiotherapy with Flattening-Filter-Free Beams: First Results

A Taborda1 , J Stroom1*, S Nijsten2 , C Greco1 , (1) Champalimaud Foundation, Department of Radiotherapy, Lisbon, Portugal (2) University Hospital of Maastricht, Department of Radiation Oncology (MAASTRO), Maastricht, The Netherlands


(Sunday, 7/29/2018) 4:00 PM - 4:30 PM

Room: Exhibit Hall | Forum 7

Purpose: To investigate if our pre-treatment portal dosimetry can be extended to in-vivo portal dosimetry for hypo-fractionated radiotherapy treatments with high-dose rate flattening-filter-free (FFF) beams.

Methods: A set of hypo-fractionated treatment plans using 6X-FFF and 10X-FFF beams were selected for this study including a wide range of tumor sites. The electronic portal image device (EPID) images were acquired at a Varian Edge LINAC equipped with the aS1200 FFF-compatible EPID. 2D and 3D pre-treatment (open images) and in-phantom portal dosimetry (phantom images) analysis was carried out using the absolute dose software EPICoreMedPhys, which was especially calibrated and further developed to allow for the analysis of images of FFF-beams plans. In-phantom tests were performed using the homogeneous cylindrical ArcCheck phantom. The results were analyzed by global gamma comparisons using a 3%/3mm criteria for pre-treatment and 5%/3mm criteria for in-phantom/vivo.

Results: The 2D pre-treatment overall results show an average gamma-passing-rate of 93.5% and an average mean-gamma of 0.43, while the 3D pre-treatment overall results obtained in the high dose region show an average gamma-passing-rate of 93% and an average mean-gamma of 0.33. Regarding the in-phantom portal dosimetry, the 2D in-phantom/vivo global gamma comparisons between predicted and measured dose showed a 94.4% gamma-passing-rate and, for the 3D in-phantom/vivo analysis, a 97.4% gamma-passing-rate was obtained.

Conclusion: This work shows that 3D in-vivo dosimetry for hypo-fractionated radiotherapy treatments with high-dose rate FFF beams and hypo-fractionation doses is possible. The initial tests using the phantom have yielded satisfactory results, but further fine-tuning of the FFF-model is expected. Then we can begin patient in-vivo portal dosimetry testing and carving the way to its implementation in the clinical practice.

Funding Support, Disclosures, and Conflict of Interest: The author A. Taborda was funded by a Varian Medical Systems research grant.


Portal Imaging, In Vivo Dosimetry, Flattening Filters


TH- External beam- photons: portal dosimetry

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