## 3 Education and Training for Students and Radiation Oncology Professionals
### VR/AR in Brachytherapy  
Brachytherapy (BT) is an even smaller and lesser-known niche of RT in which seeds, ribbons or capsules that contain a radiation source are placed directly in or near the tumor. The great advantage given by the proximity between the source and target is what makes BT attractive for boosting limited-size target volumes to high doses; however, the success of this therapy is determined by the accuracy of radioactive source placement, which then becomes crucial. Nowadays, three-dimensional (3D) image-guided techniques by computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound (US) are used to guide the surgical placement, which is still largely dependent on the confidence and expertise of the operator. Moreover, it is well known that factors such as unfamiliarity with the target region can result in tension of the operator with the risk of medical negligence. In this context, the use of VR or AR in BT has recently gained momentum, both for training and clinical purposes. For instance, a realistic training VR scenario, able to provide an immersive experience, could help doctors become familiar with the surgery scene and with the location of the source, increasing placement accuracy and the confidence of the operator, and thus the rate of success. A lot of effort has been put into works focused on the development of a virtual training system for BT, often involving head-mounted displays (HMDs) to provide an immersive and entertaining learning experience. In this setting, the use of VR in BT has been reported in a few studies. In a 2021 work by [PERSON] et al. [31], a VR training video of an intracavitary BT was created, involving fourteen resident physicians, with or without previous experience, who were invited to perform an intracavitary BT procedure before and after viewing the simulation on an immersive headset. Both procedures were timed, objective measures of implant quality were recorded, and pre- and post- simulation questionnaires were used to assess, among many other areas, users' self-confidence and the perceived usefulness of the session. After viewing the simulation, the subjects found the VR experience extremely useful, enjoyable and easy to use; moreover, confidence improved, as well as technical skills in the assembly and insertion and the average time of implant, confirming the potentiality of VR. In another work by [PERSON] et al. [32], an interactive training system for BT based on VR dedicated to young and unskilled doctors was developed. The virtual environment is linked directly to the TPS, which provides all the information about patient images, needles and seeds; through this system, users can pre-simulate, both in an immersive environment and with mouse and keyboard, the whole surgery procedure: grabbing and positioning the 3D template on the virtual patients, puncturing the tissue seeing what structures the needles pass through, and implanting seeds into the target. A total of 32 physicians took part in the test, performing a training bot test with the VR system and the traditional training one (a software on a computer); after the training was completed, each participant was required to perform the simulated surgery on a dummy with non-radioactive seeds and verification of the implantation was conducted by re-scanning. This system confirms that VR can improve learnability, and the conformity index improved in all the groups except for the expert one, whose CIs were not expected to increase. Later, the same group developed a system which allows the visualization of planning images, volume rendering of organs and preoperative planning on the patient and the tracking of surgical tools in real-time [33; 34]. This mixed reality system was then validatedboth on phantom and animals as a surgical navigation system to be used as an aid during real surgical procedures. Compared with the traditional image-guided system, the procedure had successful results and reduces the number of CT scans required, allowing doctors to perform surgery based on a visualized plan.