ESTRO 2024 - Abstract Book

S5495

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

ESTRO 2024

777

Proffered Paper

Initial evaluation of real-time gated proton therapy for prostate cancer in Singapore

Nur Atiqah Binte Samsuri 1 , Jason Wei Siang Chan 1 , Calvin Wei Yang Koh 1 , Mei Lian Zheng 1 , Kah Seng Lew 1 , Andrew Wibawa 1 , Adelene Hwee San Boo 1 , Sung Yong Park 1,2 , Hong Qi Tan 1,2 1 National Cancer Centre Singapore, Division of Radiation Oncology, Singapore, Singapore. 2 Duke-NUS Medical School, Oncology Academic Clinical Programme, Singapore, Singapore

Purpose/Objective:

Real-time gated proton therapy (RGPT) is a motion management system that utilizes pulsed fluoroscopy during treatment to track fiducial markers implanted within or near to the tumour. The proton beam is only delivered when the markers lie within the pre-defined tolerances. National Cancer Centre Singapore (NCCS) has just started treating the first proton therapy patient in June 2023 and implemented RGPT for prostate cancer patients in July 2023. This work aims to report our initial experience with RPGT in prostate cancer patients.

Material/Methods:

Prostate cancer patients treated with RGPT from July 2023 to October 2023 using Hitachi ProBeat proton therapy system were selected for this study. Three 0.48 x 10 mm Gold Anchor TM gold fiducial markers together with SpaceOAR TM hydrogels were inserted into each patient prior to CT simulation. The marker was chosen based on the best trade-off between dose perturbation and marker visibility under pulsed fluoroscopy. Intensity modulated proton therapy (IMPT) plans were generated with RayStation 10B (RaySearch, Stockholm, Sweden) using two lateral proton fields. The plans were robustly optimised and evaluated using 3.5% range uncertainty and 5.0 mm setup errors in all the three cardinal directions. The tumour was tracked based on a single fiducial marker chosen to be the one closest to the isocentre and the frequency of pulsed fluoroscopy was chosen to be 1 Hz. The tracking began on the second fraction as the first fraction was used for assessing the marker visibility and detection fidelity. If the triangulated marker position during the treatment exceeds the pre-defined tolerance of 2 mm in any of the three directions, the treatment will be paused, and a 3 degree-of-freedom (DOF) marker match will be carried out to re-align the tracked marker position to planned marker position. The number of interventional marker match throughout the fractions will be reported as one of the measures of the clinical value of intra-fraction monitoring with RGPT. The log files which includes the triangulated position of the markers throughout the treatment, were stored for post-hoc analyses. The systematic and random component of the marker shifts relative to the planned marker positions were calculated for each fraction and reported for all the patients.

Results:

3 prostate cancer patients were treated successfully with RGPT up till October 2023. The systematic and random components of the positional errors are shown in Figure 1. The errors are greatest in the SI and AP directions and the lowest in the LR directions. These observations were consistent with the findings reported in Refs [1-5]. The largest mean systematic error observed across all the three patients was -1.7mm (AP), -1.1mm (LR) and -1.7mm (SI) and