The Varian Ethos system allows for online adaptive treatments through the utilization of artificial intelligence (AI) and deformable image registration which automates large parts of the anatomical contouring and plan optimization process. In this study, treatments of intact prostate and prostate bed, with and without nodes, were simulated for 182 online adaptive fractions, and then a further 184 clinical fractions were delivered on the Ethos system. Frequency and magnitude of contour edits were recorded, as well as a range of plan quality metrics. From the fractions analyzed, 11% of AI generated contours, known as influencer contours, required no change, and 81% required minor edits in any given fraction. The frequency of target and noninfluencer organs at risk (OAR) contour editing varied substantially between different targets and noninfluencer OARs, although across all targets 72% of cases required no edits. The adaptive plan was the preference in 95% of fractions. The adaptive plan met more goals than the scheduled plan in 78% of fractions, while in 15% of fractions the number of goals met was the same. The online adaptive recontouring and replanning process was carried out in 19 min on average. Significant improvements in dosimetry are possible with the Ethos online adaptive system in prostate radiotherapy.

This study examines the dosimetric accuracy of Gafchromic EBT2 model radiochromic film for use in radiotherapy quality assurance. In this study, film was scanned using an Epson Perfection V700 flatbed scanner in transmission mode at 75 DPI with the subsequent analysis performed using the red and blue colour channels and ImageJ software. Results of this study suggest that the conversion of film optical density to measured dose should, at present, utilise red channel data only, without application of a blue channel correction to the data. For the batch of film examined here, film uniformity and reproducibility appear to have improved compared with published results using older batches. The orientation of the film on the scanner and the side of the film facing the light source were found to have substantial effects on results. Based on the results of this study, it is possible to recommend the use of EBT2 film in routine quality assurance testing for radiotherapy, in situations where a dose uncertainty of up to 2.8% is acceptable.

To enhance the utility of radiochromic films for high-resolution dosimetry of small and modulated radiotherapy fields, we propose a means to negate the effects of heterogeneities in EBT2 (and other) films. The results of using our simple procedure for evaluating radiation dose in EBT2 film are compared with the results of using the manufacturer's recommended procedure as well as a procedure previously established for evaluating dose in older EBT film. It is shown that Newton's ring-like scanning artefacts can be avoided through the use of a plastic frame, to elevate the film above the scanner's surface. The effects of film heterogeneity can be minimized by evaluating net optical density, pixelwise, as the logarithm of the ratio of the red-channel pixel value in each pixel of each irradiated film to the red-channel pixel value in the same pixel in the same film prior to irradiation. The application of a blue-channel correction was found to result in increased noise. It is recommended that, when using EBT2 film for radiotherapy quality assurance, the films should be scanned before and after irradiation and analysed using the method proposed herein, without the use of the blue-channel correction, in order to produce dose images with minimal film heterogeneity effects.

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Radiochromic film has the potential to provide accurate in vivo dosimetry measurements. However, it is not known whether small film pieces can still provide accurate dosimetric results. The use of small film pieces is of particular interest in regions of interest (ROIs) such as the eye, or where the patient's contour changes rapidly. This study examines the dosimetric accuracy of Gafchromic EBT2 and EBT3 models of radiochromic film and its dependence on film size, ROI size, and height above the scan bed for 6 MV photons and 9 MeV electrons. Films cut to sizes of 5.0 × 5.0, 10.0 × 10.0, 20.0 × 20.0, and 40.0 × 40.0 mm² were tested and it was found that there was no increase in uncertainty of dose when even the smallest film sizes were used. For a film 5.0 × 5.0 mm², ROIs of 1.4 × 1.4, 2.1 × 2.1 and 3.5 × 3.5 mm² were tested and it was found that the ROI size of 2.1 × 2.1 mm² was the most accurate. The standard deviation of the EBT3 placed on the glass (2.1%) was larger than the standard deviation of the EBT3 film raised above the glass (1.2%), therefore it is recommended that film is scanned raised above the scan bed. The general dosimetric performance of EBT3 was comparable to EBT2. We conclude that film pieces as small as 5.0 × 5.0 mm² could be used for the purpose of in vivo dosimetry of radiotherapy treatments.