ESTRO 2024 - Abstract Book

S5549

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

ESTRO 2024

1689

Digital Poster

Double Shell Positioning System versus Thermoplastic Shell For Brain Radiotherapy

Kristina Caruana 1 , Alessandro Gagus 2 , Susan Mercieca 2

1 Sir Anthony Mamo Oncology Hospital, Radiotherapy, Msida, Malta. 2 University of Malta, Radiography, Msida, Malta

Purpose/Objective:

Accurate treatment delivery is becoming increasingly important in the era of stereotactic radiotherapy (SRS). The accuracy of treatment delivery for patients undergoing radiotherapy to the brain depends on good positioning and immobilization of the head. The three-point thermoplastic shell (TPS) is a widely used immobilization device in radiotherapy. However, the headrest used by this TPS is not custom-made to fit the specific anatomical shape of the patient, potentially leading to positioning inaccuracies and patient discomfort [1]. Moreover, the foam of the headrests tends to deform over time, thus further increasing the set-up errors. In order to address these issues, MacroMedics® developed The Double Shell Positioning System (DSPS)[2]. This system makes use of a custom-made posterior shell to immobilize the head and neck. Since this system eliminates the need for a foam headrest, it has the potential to improve patient comfort, reduce set-up errors, and decrease the attenuation of the beam, thus facilitating the delivery of SRS. Therefore, in 2022, the Oncology department in Malta replaced the TPS with DSPS as part of the introduction of SRS. In this study, we aimed to compare the set-up errors of the 3-point TPS and DSPS immobilization systems. In addition, we also made use of a questionnaire to assess the radiographers’ perspectives on the accuracy and other practical aspects (e.g., ease of production and positioning, durability, shrinkage, cleaning and storage) of the 2 systems. Adult patients (> 18 years) treated with radical radiotherapy for a primary brain tumor between June 2019 and May 2023 at the local oncology hospital were enrolled in this study. All patients were immobilized using either the Orfit® TPS [3] or the MacroMedics®DSP[2], and the number of fractions ranged from 6 to 33 (Figure 1). The daily translational (left to right (X), craniocaudal (Y), anteroposterior (Z)) and rotational (Roll (Rx), Pitch (Ry), Yaw (Rz) set-up errors for each treatment fraction were measured using kilovoltage cone-beam computed tomography (kV CBCT). All radiographers (n=29) employed at the local oncology department were invited to complete an online questionnaire. In the questionnaire, radiographers were requested to assess their level of agreement regarding the precision, robustness, durability, ease of use, and storage convenience of the 2 immobilization system, using a Likert scale that ranged from 1 (strongly disagree) to 5 (strongly agree). The set-up errors were illustrated through the use of box plots. The percentage number of translation and rotational set-up errors within the set-up threshold of +/-1mm or +/-1° were calculated. Since the data was not normally distributed, the median root mean square (RMS) set-up variations and the radiographers’ ratings between the 2 devices were compared using the Mann-Whitney Test. A p-value below 0.05 was deemed statistically significant. Material/Methods: