ESTRO meets Asia 2024 - Abstract Book

S19

Invited Speaker

ESTRO meets Asia 2024

Proton therapy utilises a different set of devices from conventional photon therapy. Proton therapy nozzles are typically larger than photon therapy. For optimal proton beam dosimetry, beam modifying accessories such as range shifters and apertures are affixed to the nozzle, resulting in a tight distance between the machine and patient. Good immobilisation and reproducibility are extremely crucial in proton therapy as they impact depth dose distribution and setup uncertainty. Furthermore, immobilisation accurately determines the target water-equivalent thickness (WET) depth along the beam’s path. Since immobilisation is the key governing factor in proton therapy, pre-treatment procedure is fundamental in preparing patients undergoing treatment. Radiation therapists (RTTs) will need to comprehend the complexity of proton beam arrangements and select the right devices for daily position reproducibility. RTTs are strongly encouraged to huddle on the proton cases and the suitable setup. Every detail including alignment, arms position, head tilt, motion management, fiducial marker gating, surface tracking or even dental clearance is important to discuss prior to simulation. Primarily, tables or inserts used must be proton-compatible, support patients well and allow freedom of beam angles. They have to be metal-free with lesser attenuation material. For example, RTTs must choose suitable devices for brain or head and neck (HN) proton cases; type of head cushion, shell (3-point or 5-point shell) and HN baseplate (small, medium, large). Uniquely for HN proton irradiation, poorly fabricated shell and head cushion cause irregular folds of the cushion and gaps between patient’s HN and device. Irreproducible HN position will significantly impact proton beam’s depth dose distribution. Fabrication of customised immobilisation devices requires highly trained RTTs. During CT simulation, dedicated scanning protocol must be developed to facilitate proton robust planning optimisation. Common CT artefacts such as prosthesis, stent, dental filling or even swallowing or breathing motion are ought to be picked up during CT simulation. Physicists have to be alerted regarding these taboo situations in order for them to rectify the situation. Indexing all immobilisation equipment to the treatment couch is important so that patient is moved relative to the couch. This will help reduce systematic errors arising from pre-treatment. Proper documentation on devices, indexes, tattoos or setup alignments must be done. Additionally, obtaining photos of the devices or placement will also assist patient setup. It is impossible to eliminate all errors for immobilisation because it is highly patient dependent. The most effective way to ensure accurate proton beam delivery is through daily CBCT couch correction where we also check the immobilisation devices and soft tissue. Daily reproducibility in proton therapy is important for accurate proton treatment delivery. A well-designed, simulated patient should be comfortable, stable and reproducible, especially in proton therapy setting. Moving forward, immobilisation will continue to evolve to optimise patient’s comfort while maintaining high accuracy in proton therapy.

496

Imaging protocol optimisation for safety and efficiency

Bartosz Bak

Radiotherapy Department II, Greater Poland Cance Center, Poznan, Poland. Electroradiology Department, University of Medical Science, Poznan, Poland

Abstract