In the realm of cancer treatment, proton therapy has emerged as a beacon of precision, offering a targeted approach to destroying tumors while minimizing damage to surrounding healthy tissues. However, a hidden challenge lurks in the shadows of this innovative therapy: the generation of secondary neutrons. These neutrons, born from the nuclear interactions of the therapeutic beam, pose a significant concern as they contribute to out-of-field doses, potentially increasing the risk of secondary cancers. This is where the story of Verónica Morán and her team at Clínica Universidad de Navarra takes center stage, as they embark on a mission to unravel the mysteries of neutron field characterization and develop a practical tool to estimate neutron doses during proton therapy.
Unveiling the Neutron Field
Morán and her colleagues, in their study published in Physics in Medicine & Biology, set out to experimentally characterize the neutron field in a proton therapy treatment room. They employed a Hitachi PROBEAT-CR proton therapy system with pencil-beam scanning, utilizing a diverse array of detectors to measure neutron doses. These included ambient detectors and four types of personal dosimeters: thermoluminescent dosimeters (TLDs), track-etch detectors, bubble detectors (BDs), and electronic personal dosimeters (EPDs).
The team's meticulous measurements revealed a fascinating dependence of out-of-field neutron dose on various beam and room parameters, such as gantry angle, field size, proton energy, and distance to isocentre. At each measurement point, they assessed the neutron ambient dose equivalent and the personal dose equivalent, providing a comprehensive understanding of the radiation field at specific locations.
One intriguing finding was the symmetry of the treatment room. Measurements with ambient detectors indicated that the room was symmetric for certain gantry orientations, reducing the need for extensive measurements and extending the applicability of dose calculation models. Additionally, the team discovered that neutron doses from a single spot field and a 10x10 cm field were similar, while larger fields exhibited up to 22% differences.
A Practical Tool for Neutron Dose Estimation
Building upon their experimental findings, Morán and her team developed a Python-based tool to estimate neutron dose at any point in the treatment room for arbitrary irradiations and detectors. This tool, a first of its kind, requires the radiotherapy plan, detector data, and calculation parameters as inputs, and outputs neutron dose estimates along with associated uncertainties.
The researchers verified the tool's reliability by assessing additional measurement points not used in its development. Comparisons of experimental and calculated dose values demonstrated its effectiveness in providing reliable and useful estimates for ambient detectors and BDs, even in areas with no prior measurements. However, for EPDs, the calculated intervals were often broad, prompting caution in interpreting results.
The Broader Impact and Future Directions
The implications of this work extend far beyond the confines of the treatment room. Morán emphasizes the potential for the tool to support radiation protection studies, workplace dose assessments, research projects, and the evaluation of neutron exposure in various scenarios. Moreover, the methodology behind the tool may be transferable to other clinical centres using comparable technology.
Looking ahead, the team is extending the tool to include paediatric cases, different proton energies, patient sizes, and treatment configurations. They are also investigating the application of these methods to estimate neutron doses received by patients, with the long-term goal of improving the characterization of out-of-field radiation exposure in proton therapy. This work not only advances our understanding of neutron fields but also paves the way for safer and more effective cancer treatments.
In my opinion, this research is a testament to the power of scientific inquiry and innovation. It highlights the importance of characterizing neutron fields in proton therapy to ensure patient safety and improve treatment outcomes. The development of a practical tool for neutron dose estimation is a significant step forward, offering a more comprehensive understanding of the radiation environment in treatment rooms. As we continue to push the boundaries of cancer treatment, it is crucial to address these hidden challenges and ensure that the benefits of proton therapy are realized without compromising patient well-being.
