1
|
Romero-Expósito M, Liszka M, Christou A, Toma-Dasu I, Dasu A. Range shifter contribution to neutron exposure of patients undergoing proton pencil beam scanning. Med Phys 2024; 51:5099-5108. [PMID: 38112191 DOI: 10.1002/mp.16897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 11/30/2023] [Accepted: 12/03/2023] [Indexed: 12/21/2023] Open
Abstract
BACKGROUND Superficial targets require the use of the lowest energies within the available energy range in proton pencil-beam scanning (PBS) technique. However, the lower efficiency of the energy selection system at these energies and the requirement of a greater number of layers may represent disadvantages for this approach. The alternative is to use a range shifter (RS) at nozzle exit. However, one of the concerns of using this beamline element is that it becomes an additional source of neutrons that could irradiate organs situated far from the target. PURPOSE The purpose of this study is to assess the increase in neutron dose due to the RS in proton PBS technique. Additionally, an analytical model for the neutron production is tested. METHODS Two clinical plans, designed to achieve identical target coverage, were created for an anthropomorphic phantom. These plans consisted of a lateral field delivering an absorbed dose of 60 Gy (RBE) to the target. One of the plans employed the RS. The MCNP code was used to simulate the plans, evaluating the distribution of neutron dose equivalent (Hn) and the equivalent dose in organ. In the plan with the RS plan, neutron production from both the patient and the RS were assessed separately. Hn values were also fitted versus the distance to field edge using a Gaussian function. RESULTS Hn per prescription dose, in the plan using the RS, ranged between 1.4 and 3.7 mSv/Gy at the field edge, whereas doses at 40 cm from the edge ranged from 9.9 to 32 μSv/Gy. These values are 1.2 to 10 times higher compared to those obtained without the RS. Both this factor and the contribution of neutrons originating from the RS increases with the distance from field edge. A triple-Gaussian function was able to reproduce the equivalent dose in organs within a factor of 2, although underestimating the values. CONCLUSIONS The dose deposited in the patient by the neutrons originating from the RS predominantly affects areas away from the target (beyond approximately 25 cm from field edge), resulting in a neutron dose equivalent of the order of mSv. This indicates an overall low neutron contribution from the use of RS in PBS.
Collapse
Affiliation(s)
- Maite Romero-Expósito
- The Skandion Clinic, Uppsala, Sweden
- Oncology Pathology Department, Karolinska Institutet, Solna, Sweden
| | | | | | - Iuliana Toma-Dasu
- Oncology Pathology Department, Karolinska Institutet, Solna, Sweden
- Medical Radiation Physics, Stockholm University, Stockholm, Sweden
| | - Alexandru Dasu
- The Skandion Clinic, Uppsala, Sweden
- Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| |
Collapse
|
2
|
Van Hoey O, Stolarczyk L, Lillhök J, Eliasson L, Mojzeszek N, Liszka M, Alkhiat A, Mares V, Trompier F, Trinkl S, Martínez-Rovira I, Romero-Expósito M, Domingo C, Ploc O, Harrison R, Olko P. Simulation and experimental verification of ambient neutron doses in a pencil beam scanning proton therapy room as a function of treatment plan parameters. Front Oncol 2022; 12:903537. [PMID: 36158693 PMCID: PMC9494550 DOI: 10.3389/fonc.2022.903537] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Accepted: 07/07/2022] [Indexed: 11/23/2022] Open
Abstract
Out-of-field patient doses in proton therapy are dominated by neutrons. Currently, they are not taken into account by treatment planning systems. There is an increasing need to include out-of-field doses in the dose calculation, especially when treating children, pregnant patients, and patients with implants. In response to this demand, this work presents the first steps towards a tool for the prediction of out-of-field neutron doses in pencil beam scanning proton therapy facilities. As a first step, a general Monte Carlo radiation transport model for simulation of out-of-field neutron doses was set up and successfully verified by comparison of simulated and measured ambient neutron dose equivalent and neutron fluence energy spectra around a solid water phantom irradiated with a variation of different treatment plan parameters. Simulations with the verified model enabled a detailed study of the variation of the neutron ambient dose equivalent with field size, range, modulation width, use of a range shifter, and position inside the treatment room. For future work, it is planned to use this verified model to simulate out-of-field neutron doses inside the phantom and to verify the simulation results by comparison with previous in-phantom measurement campaigns. Eventually, these verified simulations will be used to build a library and a corresponding tool to allow assessment of out-of-field neutron doses at pencil beam scanning proton therapy facilities.
Collapse
Affiliation(s)
- Olivier Van Hoey
- Belgian Nuclear Research Center (SCK CEN), Institute for Environment, Health and Safety (EHS), Mol, Belgium
- *Correspondence: Olivier Van Hoey,
| | - Liliana Stolarczyk
- Danish Centre for Particle Therapy, Aarhus University Hospital (AUH), Aarhus, Denmark
- Institute of Nuclear Physics, Polish Academy of Sciences, (IFJ PAN), Krakow, Poland
- The Skandion Clinic, Uppsala, Sweden
| | - Jan Lillhök
- Swedish Radiation Safety Authority, Solna, Sweden
| | - Linda Eliasson
- Department of Physics, Royal Institute of Technology (KTH), Stockholm, Sweden
| | - Natalia Mojzeszek
- Institute of Nuclear Physics, Polish Academy of Sciences, (IFJ PAN), Krakow, Poland
| | - Malgorzata Liszka
- Institute of Nuclear Physics, Polish Academy of Sciences, (IFJ PAN), Krakow, Poland
- The Skandion Clinic, Uppsala, Sweden
| | - Ali Alkhiat
- The Skandion Clinic, Uppsala, Sweden
- Department of Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, Stockholm, Sweden
| | - Vladimir Mares
- Helmholtz Zentrum München, Institute of Radiation Medicine, Neuherberg, Germany
| | - François Trompier
- Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSE-Santé, Fontenay-aux-Roses, France
| | - Sebastian Trinkl
- Helmholtz Zentrum München, Institute of Radiation Medicine, Neuherberg, Germany
- Federal Office for Radiation Protection, Neuherberg, Germany
| | | | | | - Carles Domingo
- Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Ondrej Ploc
- Department of Radiation Dosimetry, Nuclear Physics Institute of the Czech Academy of Sciences (CAS), Prague, Czechia
| | - Roger Harrison
- Faculty of Medical Sciences, University of Newcastle upon Tyne, Newcastle Upon Tyne, United Kingdom
| | - Pawel Olko
- Institute of Nuclear Physics, Polish Academy of Sciences, (IFJ PAN), Krakow, Poland
| |
Collapse
|