ESTRO 2024 - Abstract Book

S3321

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

2290

Mini-Oral

Radiation exposure to a parent in the treatment room during pediatric proton therapy

Johannes Tjelta 1,2 , Kristian Smeland Ytre-Hauge 2 , Helge Henjum 2 , Erlend Lyngholm 2 , Andreas Havsgård Handeland 1,2 , Camilla Hanquist Stokkevåg 1,2 1 Haukeland University Hospital, Medical physics, Bergen, Norway. 2 University of Bergen, Institute of physics and technology, Bergen, Norway

Purpose/Objective:

Radiation protection regulations prohibit parents from remaining near their children during radiotherapy treatment. However, new treatment modalities such as pencil beam scanning proton therapy (PT) may open new possibilities due to significantly reduced radiation exposure in the treatment room compared to conventional photon-based radiotherapy and passively scattered PT. This study aims to examine the scenario of a parent in the treatment room during pencil beam scanning PT, wherein we quantify the potential dose exposure and estimate the associated risks.

Material/Methods:

A model of the PT treatment room and gantry under construction at our PT facility was implemented in the FLUKA Monte Carlo (MC) code from the technical drawings, including bending magnet, patient treatment area, gantry cylinder and nozzle. A whole-body CT of a male representing a parent located in the treatment room was positioned at variable distances from a 10-year-old pediatric patient on the treatment couch. The parent was situated at distances 1 m, 3 m 45 o - and 3 m perpendicular to the gantry (Figure 1: position A, B and C respectively). Two treatment scenarios were simulated for the pediatric patient: i) 2 field treatment of a low-grade glioma brain tumor (volume 4.4 cc) with dose prescription 54 Gy (RBE), and extremal energies of 70 MeV and 122 MeV; and ii) 5 field craniospinal irradiation (CSI) (1444 cc) with dose prescription 23.4 Gy (RBE) and extremal energies of 87 MeV and 182 MeV. All fields for the CSI patient included 57 mm water equivalent thickness range shifters. The treatment plans were optimized in the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, California, USA), and further recalculated in the FLUKA MC code to obtain the neutron and photon fluence and energy spectra (collected at the black line, Figure 1) in the treatment room. A phase space (position, direction, energy and particle type) was sampled for neutrons and photons in a vertical plane between the parent and patient (black line, Figure 1) for 10 9 primaries. The phase space was utilized as a source for each position of the parent for calculation efficiency. The radiation exposure and estimated equivalent doses to the parent were subsequently obtained at the different positions. The ICRP 103 weighting was applied for equivalent doses of neutrons. The lifetime attributable risk (LAR) of radiation induced cancer was estimated according to the ICRP assuming the parent age at exposure equal to 40 years.

Results:

For both the CSI and the brain tumor treatment, the mean body dose to the parent for the whole treatment was well below 1 mSv in all the considered positions. The CSI parent received 24.2 µSv, 14.4 µSv and 5.7 µSv in positions A, B and C, respectively (Figure 2). During the simulated treatment of the brain tumor patient, the total parent mean body