ESTRO 2025 - Abstract Book

S4136

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

ESTRO 2025

Purpose/Objective: To evaluate whether surface-guided radiotherapy (SGRT) is accurately applicable for patient setup in gynaecological cancer patients during external beam radiotherapy, thereby avoiding skin marks. Material/Methods: Forty patients treated for different gynaecological cancers (cervical, endometrial and vaginal) with involvement of para-aortic lymph nodes at various levels of the lumbar vertebrae were included. The dose prescription, delivered in 20 to 28 treatment fractions, varied per patient. Twenty patients were set up using skin marks and laser alignment; the other twenty using SGRT. For the tattoo group, three tattoos were placed at the site of the femoral head: two laterally and one anterior mid patient. In addition, a cranial directional tattoo was placed. For the SGRT group, a region of interest was drawn with inclusion of the pelvic bone area, excluding the abdominal area that moves through breathing. For both groups, a cone-beam CT (CBCT) was acquired after initial patient setup. After comparison with the planning CT, an online correction was derived. In case of large rotations, the patient was re positioned, followed by a repetition of the imaging procedure. Absolute rotational and translational deviations in all directions were extracted from the clinically accepted match results and compared between both groups, using a Mann-Whitney U test. In addition, for each group, the number of fractions in which the patient had to be repositioned was quantified. Results: A total of 1,014 CBCT matches was analysed (505 tattoos, 509 SGRT). Table 1 shows the average and standard deviations of the absolute match results. Translations - which can be corrected before dose delivery by a couch movement - were significantly smaller with SGRT for lateral direction, and larger in longitudinal direction, compared to tattoos.

Figure 1 shows a cumulative distribution of the observed rotations. Largest rotations were observed in pitch.