ESTRO 2024 - Abstract Book

S5578

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

ESTRO 2024

2373

Digital Poster

The role of RTTs in replanning and immobilization for head&neck cancer patients undergoing VMAT

Giuseppe Spataro 1 , Nicola Lambri 1,2 , Damiano Dei 1,2 , Ciro Franzese 1,2 , Carmela Galdieri 1 , Aurora Zucca 1 , Mariya Boyanova Ilieva 1,2 , Anna bertolini 1,2 , Stefano Tomatis 1 , Pietro Mancosu 1 , Marta Scorsetti 1,2 1 IRCCS Humanitas Research Hospital, Radiotherapy and Radiosurgery Department, Rozzano, Italy. 2 Department of Biomedical Sciences, Humanitas University, Pieve Emanuele, Italy

Purpose/Objective:

Radiotherapy is a cornerstone in the management of head and neck (H&N) cancer. The aim of this study was to assess the displacements of daily cone-beam computed tomography (CBCT) matches in patients with squamous cell carcinoma of the pharynx, larynx, and oral cavity undergoing VMAT. The primary objective was to evaluate the feasibility of treatment replanning and its impact on the patient’s positioning.

Material/Methods:

Thirty-one H&N patients received treatment through a simultaneous integrated boost (SIB) technique, with fractional doses of 2.2 Gy, 2.0 Gy, and 1.8 Gy, in over 30 sessions. All patients underwent an initial CT simulation (sCT) and, after 15 fractions, a second CT acquisition for replanning (rCT), which included the creation of a new immobilization mask. Displacement data from CBCT scans were extracted and statistically compared between the two CT groups using the Mann-Whitney test for unpaired data. Additionally, a qualitative analysis was employed using a five-point scale to assess the agreement between CBCT images and CT scans at the start (sCT_first) and conclusion (sCT_last) of the first treatment phase, and post-replanning (rCT_first). The evaluation consisted of examining bony structures, target regions, parotid glands, and overall image match quality. The Wilcoxon signed-rank test for paired data was applied to compare these evaluations. Median and interquartile ranges (Q1 and Q3) were used to statistically summarize the data.

Results:

A total of 935 CBCT scans were analysed. No significant differences in online CBCT shifts were observed between sCT (3.5 mm, [2.5-4.7] mm) and rCT (3.6 mm, [2.6-4.9] mm). However, a substantial variation was noted between sCT_first and sCT_last (p<0.001) for all the considered evaluations, except for bony structures (see an example in figure 1). The maximum differences were found for target66 (4 [2-4] vs. 5 [5-5]), target54 (4 [3-5] vs. 5 [5-5]), and parotids (4 [2-5] vs. 5 [5-5]). No significant differences were observed between sCT_first and rCT_first (see figure 2). The overall visual analysis revealed that 19% of patients achieved optimal image match quality in the sCT_last, suggesting that rCT scans could be removed in selected cases. Moreover, 29% of patients exhibited an optimal immobilization mask during the final treatment session, suggesting that the creation of a new immobilization system during the rCT acquisition might be unnecessary.