Range shifter contribution to neutron exposure of patients undergoing proton pencil beam scanning

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Romero-Expósito, MaiteThe Skandion Clinic Uppsala Sweden;Oncology Pathology Department Karolinska Institutet Solna Sweden (author)

Range shifter contribution to neutron exposure of patients undergoing proton pencil beam scanning

Article/chapterEnglish2023

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2023
2023
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LIBRIS-ID:oai:DiVA.org:su-225734
https://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-225734URI
https://doi.org/10.1002/mp.16897DOI
http://kipublications.ki.se/Default.aspx?queryparsed=id:154423279URI
https://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-518623URI

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Language:English
Summary in:English

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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.

Subject headings and genre

MEDICIN OCH HÄLSOVETENSKAP Klinisk medicin Radiologi och bildbehandling hsv//swe
MEDICAL AND HEALTH SCIENCES Clinical Medicine Radiology, Nuclear Medicine and Medical Imaging hsv//eng
MEDICIN OCH HÄLSOVETENSKAP Klinisk medicin Cancer och onkologi hsv//swe
MEDICAL AND HEALTH SCIENCES Clinical Medicine Cancer and Oncology hsv//eng
analytical modelling
neutron dose equivalent
out-of-field dose
proton therapy

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Liszka, MalgorzataThe Skandion Clinic Uppsala Sweden (author)
Christou, AthanasiaThe Skandion Clinic Uppsala Sweden (author)
Toma-Daşu, Iuliana,1972-Stockholms universitet,Fysikum,Oncology Pathology Department Karolinska Institutet Solna Sweden;Medical Radiation Physics Stockholm University Stockholm Sweden(Swepub:su)iuda0736 (author)
Dasu, AlexandruThe Skandion Clinic Uppsala Sweden;Medical Radiation Sciences, Department of Immunology, Genetics and Pathology Uppsala University Uppsala Sweden(Swepub:uu)aleda511 (author)
The Skandion Clinic Uppsala Sweden;Oncology Pathology Department Karolinska Institutet Solna SwedenThe Skandion Clinic Uppsala Sweden (creator_code:org_t)

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In:Medical physics (Lancaster)0094-2405
In:Medical physics2473-4209

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