ESTRO 2024 - Abstract Book

S5900

RTT - Service evaluation, quality assurance and risk management

ESTRO 2024

Results:

The specific changes in techniques and workflow for each of the key elements identified above are as follows.

1. The department eliminated all planar imaging; instead, daily CBCTs are acquired for all patients. An extensive training programme for radiographers was required to achieve and record competency for soft-tissue matching for all anatomical sites. The increased dose to patients is justified by the improved soft-tissue matches. In addition, Gold fiducial markers for prostate patients were no longer required. 2. A rapid treatment planning process for VMAT and IMRT (2-hour turn-around) was created and implemented (“QVMAT”). Radiographers carry out the process at the time of the patient’s CT scan and standard planning templates were developed for all palliative dose regimens in order to automate the process as far as possible. The optimisation uses dose specifications for the target-volume and a generic ‘normal tissue’ constraint. The resulting dose distributions are far superior to any distribution achievable with simple plain fields. 3. Small skin lesions with treatment diameters less than 3cm are now treated using HDR brachytherapy with Leipzig applicators instead of electrons. Investigations for larger lesions showed convincingly that VMAT with suitable 3D-printed bolus always achieves a better dose distribution than electron beams. 4. Non-coplanar arcs had been used for brain, nasopharynx, and mediastinal treatments. Investigations showed that clinically acceptable plans could always be achieved on a ring-gantry linac with (typically) 4 coplanar VMAT arcs. Although the resulting plans are perhaps not as ‘subjectively good’ as non-coplanar plans, they achieve all clinical goals. 5. We replaced extended distance treatments for long target volumes with a multi-iso-centre technique, covering the target-volume in a sequence of couch positions. Investigations showed that IMRT was better than VMAT for ‘feathering’ one dose distribution into another, reducing any concerns over field junctions. A review of SABR treatments showed that, in addition to the lower dose-rate, more arcs are typically required on the ring-gantry linac. The total beam-on time was longer than a C-arm linac, but not prohibitively so. The most extreme time difference occurred for a vertebra treatment: 5.7 minutes on an Ethos machine (4 VMAT arcs, 4106 MU, max 750 MU/min) compared with 2 minutes on a TrueBeam using 10FFF (2 arcs, 3632 MU, max 2400 MU/min). However, due to the shorter time for CBCT acquisition, the total on-table time was only longer by 2.3 minutes on the Ethos machine when two CBCTs were acquired for each fraction.

Conclusion:

The successful redesign of our clinical processes revealed that no serious limitations are introduced when replacing traditional C-arm linacs with ring-gantry linacs. We conclude that a modern radiotherapy service can indeed be provided using only ring-gantry linacs.

Keywords: ring-gantry, workflow, redesign

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Poster Discussion

AIRPoRT Assessment of Information Required by Patients having radical lung Radiotherapy treatment