The application of gradient dose segmented analysis of in-vivo EPID images for patients undergoing VMAT in a resource-constrained environment.

The gamma analysis metric is a commonly used metric for VMAT plan evaluation. The major drawback of this is the lack of correlation between gamma passing rates and DVH values. The novel GDSAmean metric was developed by Steers et al. to quantify changes in the PTV mean dose (Dmean ) for VMAT patients. The aim of this work is to apply the GDSA retrospectively on head-and-neck cancer patients treated on the newly acquired Varian Halcyon, to assess changes in GDSAmean , and to evaluate the cause of day-to-day changes in the time-plot series. In-vivo EPID transmission images of head-and-neck cancer patients treated between August 2019 and July 2020 were analyzed retrospectively. The GDSAmean was determined for all patients treated. The changes in patient anatomy and rotational errors were quantified using the daily CBCT images and added to a time-plot with the daily change in GDSAmean . Over 97% of the delivered treatment fractions had a GDSAmean  < 3%. Thirteen of the patients received at least one treatment fraction where the GDSAmean  > 3%. Most of these deviations occurred for the later fractions of radiotherapy treatment. Additionally, 92% of these patients were treated for malignancies involving the larynx and oropharynx. Notable deviations in the effective separation diameters were observed for 62% of the patients where the change in GDSAmean  > 3%. For the other five cases with GDSAmean  < 3%, the mean pitch, roll, and yaw rotational errors were 0.90°, 0.45°, and 0.43°, respectively. A GDSAmean  > 3% was more likely due to a change in separation, whereas a GDSAmean  < 3% was likely caused by rotational errors. Pitch errors were shown to be the most dominant. The GDSAmean is easily implementable and can aid in scheduling new CT scans for patients before significant deviations in dose delivery occur.

Bridging the Radiotherapy Education Gap in Africa: Lessons Learnt from the Cape Town Access to Care Training Programme Over the Past 5 Years (2015-2019).

The role of radiotherapy (RT) in cancer care is well described, with a clear correlation between access to radiotherapy and overall survival. Cancer mortality rates in Africa are substantially higher than those of the rest of the world, which may be partly attributed to lack of RT access and insufficient human resources. The Access to Care (A2C) Cape Town RT training programme was created in 2014 with the aim of supplementing practical RT training in the region, focusing on clinics moving from 2 to 3D conformal radiotherapy (3DCRT). The programme makes use of hybrid teaching methods, including pre-course e-learning followed by 17 on-site days of free-thinking design exercises, didactic learning, hands-on treatment planning computer sessions (39% of total teaching time), virtual simulation training and departmental demonstration sessions. Email support is offered to all teams for 3 months after each course to develop clinical protocols. Thirteen teams (radiation oncologist, medical physicist and radiation therapy technologist) from Africa attended the course between 2015 and 2019, with additional participants from seven South African and four international centres. E-learning done on the LäraNära training platform was only successful once formal progress tracking was introduced in 2019 (34% vs. 76% test completion rate). Delays between course attendance and initial clinical use of equipment proved to be detrimental to knowledge retention, with some centres having to send a second team for training. The course will be modified for remote teaching in 2021, to make provision for the global changes in travel due to Covid-19.

Concrete density estimation of linac bunker walls using impact-echo testing.

PURPOSE: To estimate the concrete density of a newly constructed bunker using impact-echo testing prior to the installation of the linear accelerator. METHODS: A newly constructed bunker showed visible honeycombing after the removal of the construction formwork. Impact-echo testing, which is based on the propagation and reflection of elastic waves in solids, was applied to confirm the bunker shielding integrity. A mechanical impact on the bunker wall generates a stress pulse, which propagates through the wall and is reflected or refracted by voids or changes in material characteristics such as density. Surface displacements caused by the reflected waves are recorded by a transducer, located near the impact point. The resulting displacement-time curves are analysed in the frequency domain for anomalies. The dominant frequencies are related to the depths from which stress waves are reflected within the structure. If the dynamic elastic modulus and Poisson ratio of the concrete are known, then the measured velocity of the so-called P-wave can be related to the concrete density. RESULTS: Validation measurements on a wall with known concrete density gave an estimate within 3% of the true density. Measured velocities on the honeycombed wall ranged from 3750 m/s to 4300 m/s, corresponding to densities of 2894 kg/m3 and 2201 kg/m3 respectively, with the majority of estimated densities ranging from 2307 kg/m3 to 2544 kg/m3. A radiation survey after the installation of the linear accelerator confirmed adequate shielding. CONCLUSION: Impact-echo testing presents a viable solution to confirm bunker shielding integrity before the installation of a linac.