ESTRO 2025 - Abstract Book

S4067

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

ESTRO 2025

Keywords: database evaluation, Total Marrow Irradiation TMI

References: Lambri N, Antonetti SL, Dei D, Bellu L, Bramanti S, Brioso RC, Carlo-Stella C, Castiglioni I, Clerici E, Crespi L, et al. Impact of the Extremities Positioning on the Set-Up Reproducibility for the Total Marrow Irradiation Treatment. Current Oncology . 2023; 30(4):4067-4077. Doi: 10.3390/curroncol30040309

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Poster Discussion Optimising Proton Head-and-Neck Re-setup Through the Implementation of Updated Quantitative Imaging Protocol Semaya Natalia Chen 1 , Hong Qi Tan 1,2 , Sze Yarn Sin 1 1 Division of Radiation Oncology, National Cancer Centre Singapore, Singapore, Singapore. 2 Oncology Academic Clinical Programme, Duke-NUS Medical School, Singapore, Singapore Purpose/Objective: Precise dose deposition at Bragg peak with no exit dose is the main dosimetric advantage of proton beam. Misalignment of tissue and density variation will affect overall dose deposition. Highly precise patient positioning is hence paramount in proton therapy (PT). Imaging protocol acts as a gatekeeper to provide guidelines for image verification and precise patient setup. Initial head-and-neck (HN) PT imaging tolerance was adopted from departmental photon HN protocol developed from auditing >1000 CBCTs. However, multiple re-setups were observed and preliminary analysis highlighted contour variations in neck-shoulder region as the most common factor. An updated imaging protocol was subsequently developed, factoring in the acceptable range of contour variations for HN PT cases. Here, we discuss the development of updated HN PT imaging protocol and evaluate its impact. Material/Methods: Various re-setup factors were evaluated by HN APRT while the physicist analysed dosimetric differences influenced by varying degrees of skin contour. This was performed by simulating various skin contour thickness on RayStation(v12B) and evaluating the resulting CTV dose coverage. Data from 40 HN patients were collated (20 pre- and 20 post-implementation of updated protocol) and rates of re-setups were examined. Additionally, translational and rotational shifts were audited based on protocol tolerances. Two-tailed paired t -test ( p <0.05) was used for statistical analysis. Results: Common re-setup factors were analysed as mismatch of contour, head-tilt, cord and neck-shoulder position. Skin contour differences of ≤0.7cm were shown to produce acceptable differences in CTV D95% coverage ( Figure 1 ). These findings facilitated development of updated HN PT imaging protocol. Post-implementation, rates of ≥1 re-setup(s) significantly reduced ( p <0.05). Furthermore, additional CBCTs acquired due to re-setups were observed to reduce by 11.9%, from 35.8% to 23.9% ( Table 1 ). Fewer re-setups indicates decreased imaging radiation exposure and overall treatment time. Translational (0.11±0.095cm vs 0.12±0.098cm, p <0.001) and rotational (0.4±0.37° vs 0.5±0.45°, p =0.879) shifts remained within departmental imaging tolerances. Number of patients sent for re-CT due to setup reproducibility issues caused by contour and cord variations reduced by half post-implementation of updated protocol. The updated protocol helps to refine and improve overall workflow while safeguarding patient’s treatment delivery.