Revolutionizing Proton Therapy: A Comprehensive Tool for Neutron Dose Estimation
The world of cancer treatment is witnessing a paradigm shift with the advent of proton therapy, a highly precise method that targets tumors while minimizing damage to surrounding healthy tissues. However, a recent study has shed light on an often-overlooked aspect of this treatment: the generation of secondary neutrons during proton irradiation. These neutrons, produced due to nuclear interactions, pose a potential risk of contributing to secondary cancer risks, particularly in areas outside the treatment field, known as out-of-field doses.
A team of researchers from Clínica Universidad de Navarra in Spain has made a groundbreaking contribution to this field by developing a practical Python-based calculation tool. This tool estimates neutron dose for arbitrary irradiations, providing a fast and accurate initial assessment using information from the treatment plan. The study, published in Physics in Medicine & Biology, offers a comprehensive understanding of neutron fields in proton therapy treatment rooms, utilizing various detectors to measure neutron dose.
The research team, led by medical physicist Verónica Morán, employed a Hitachi PROBEAT-CR proton therapy system with pencil-beam scanning. They measured neutron dose using ambient detectors and four types of personal dosimeters: thermoluminescent dosimeters (TLDs), track-etch detectors, bubble detectors (BDs), and electronic personal dosimeters (EPDs). The ambient detectors proved to be the most reliable, functioning as expected in a synchrotron-based facility, while personal dosimeters showed variations in response.
One of the key findings of the study was the symmetry of the treatment room. The team discovered that the room was largely symmetric for certain gantry orientations, reducing the number of measurements needed and extending the applicability of the dose calculation model. This symmetry also allowed for the interchangeability of single spot fields and 10x10 cm fields, with the latter differing by up to 22% relative to the former.
The researchers also investigated the dependence of neutron doses on proton energy, which followed the expected power law. The ambient detectors provided the best fits, followed by BDs and TLDs. Furthermore, the team delivered a clinical proton treatment to a scattering phantom, examining the linear superposition approach to estimate total neutron dose from individual energy layers. This approach worked well with ambient detectors and BDs but not with EPDs, highlighting the importance of careful interpretation of EPD results.
The Python-based tool developed by the team is a significant advancement in the field. It estimates neutron dose at any point in the treatment room for arbitrary irradiations and detectors, providing reliable and useful estimates for ambient detectors and BDs. However, the tool also acknowledges the limitations of EPDs, suggesting that results should be interpreted with caution due to the broad calculated intervals.
The study's findings have far-reaching implications for the proton therapy community. The tool is the first of its kind to estimate out-of-field neutron dose based on treatment room measurements and is expected to be transferable to other clinical centers using comparable technology. The researchers are now extending the tool to include paediatric cases, different proton energies, patient sizes, and treatment configurations, with the long-term goal of improving the characterization of out-of-field radiation exposure in proton therapy.
In conclusion, this research marks a significant step forward in the field of proton therapy, offering a comprehensive tool for neutron dose estimation. By addressing the challenges posed by out-of-field doses, the study contributes to the development of safer and more effective cancer treatment options, ultimately improving patient outcomes and quality of life.
