Departmental audit on immobilisation in a small cohort of patients with lower limb sarcoma

The aim of this piece of work was to audit the immobilisation and Genital Displacement Device (GDD) setup for patients with limb sarcoma.

Ten male and ten female patients treated between 2022 and 2023 had their translational shifts retrospectively reviewed. Position of external genitalia was assessed on CBCTs against the outlined structure on the planning scan and categorised according to a traffic light system.

581 images were reviewed in which 81.2 % of translational shifts were within tolerance. One patient had all shifts below 5 mm. However, three patients had 33.3 %, 44 % and 60 % of shifts out of tolerance. Overall, only 2.6 % of translational shifts were above 1 cm. The highest number of re-setups during a course of treatment was 3. PTV length, treatment site and number of shells were identified as impactful factors for large shifts. The GDDs performed well, with 92 % of CBCTs falling in the green or amber category, meaning that the genitals were not encroaching on the PTV. Only 3 CBCT's were categorised as red, with one patient requiring a re-setup due to position of external genitalia.

The shifts may be skewed due to 2 patients with large shifts. These patients could have benefited from systematic shift corrections as the magnitude and direction of the shifts were consistent. However, the immobilisation system is effective in the majority of patients. The GDDs were successful in limiting mobility of external genitalia in most cases.

The clinical implementation of the traffic light system developed in this audit may be beneficial to standardise the analysis of the displacement of the genitals away from the PTV.