ESTRO 2025 - Abstract Book

S4036

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2025

Purpose/Objective: This study investigated the Deep Inspiration Breath Hold (DIBH) thresholds used within our institution to observe what values are recommended for clinical use. DIBH is used as per protocol for all patients who are receiving radiotherapy to the left breast; inclusive of partial breast irradiation (PBI), +/- SCF & Axillary nodes. It is also used for radiotherapy to the right breast when the Internal Mammary Chain (IMC). Material/Methods: This investigation was completed retrospectively, taking into consideration the chestwall distance to cardiac tissue (LD-C) achieved for patients scanned October 2023 – December 2023. The thresholds which are recorded on the Varian RPM system will be assessed to see if there is a correlation between these thresholds and the LD-C achieved. This will allow a predictive model to be built around estimated LD-C based on the thresholds achieved. A one-way ANOVA and linear correlation coefficient measurements were run in SPSS V27. Results: A total of 165 planning scales were reviewed, out of these 111 were successfully scanned DIBH. 54 patients were scanned in free breathing. The DIBH cohort had a larger average LD-C in comparison with the FB cohort (2.4cm and 1.09cm, respectively). There is a linear correlation between the LD-C and the minimum threshold achieved for the left breast only. In those which can achieve a consistent breath-hold the most frequent thresholds achieved are 1.0 1.5cm, however, the modelled system suggests that a minimum threshold of 0.5cm gives an adequate improvement to LD-C in comparison to the free-breathing average (1.7cm and 1.09cm, respectively). The average LD-C for the free-breathing cohort was 1.09cm (Range: 0.0-2.9cm). Of these 51 patients scanned in FB, 41% (21) had an LD-C of <1cm and 27% (14) of these had cardiac tissue adjoining the chest wall, giving an LD-C of 0. The total DIBH patient data was initially analysed against the LD-C, this proved a weak positive correlation between having a minimum gating threshold of 0.5cm+ (figure 1). The data was then split to see if any other potential trends would be observed.

Conclusion: The model demonstrates that any consistent breath-hold regardless of the minimum threshold can give improvement to LD-C when compared to the ‘free-breathing’ technique when applied to a general population.

Keywords: DIBH, Thresholds, Gating