Detector measuring distribution of radiation dose will help in cancer treatment

Scientists of the AGH University of Science and Technology are carrying out a research and development programme that can lead to revolutionising the techniques of measuring the distribution of radiation doses in therapeutic treatment, e.g. in cancer – “Reconfigurable detector for the measurement of the spatial distribution of radiation doses for the use in the preparation of individual treatment plans of patients”. Within the framework of the programme TEAM-NET, the Foundation for Polish Science has granted the project PLN 12,125,000. Work is carried out by the consortium “Dose-3D”, which apart from AGH UST, the leader of the project, comprises the Cracow University of Technology (coordinator: professor Zbisław Tabor), and the Krakow Branch of the Centre of Oncology (coordinator: Damian Kabat, MSc). The head of the project is professor Tomasz Szumlak of the Faculty of Physics and Applied Computer Science.  

Cancer is currently one of the main causes of death around the world. The increasing length of lifespan means that it will still be one of the most frequent causes of death in the future. The first line of treatment in such cases, if possible, is to remove the lesion by means of a surgical operation. Other available forms of therapy include chemotherapy, brachytherapy, targeted radioisotope therapy or external beam radiation therapy (teleradiotherapy). Different types of treatment are usually combined. It is estimated that about 50% of patients with cancer are treated with high-energy external beam radiation, which makes teleradiotherapy one of the methods most frequently offered to patients.  

A high-energy photon beam used in treatment is usually obtained by means of linear medical accelerators, where an accelerated electron beam collides with the target material of high atomic number. The result of the collision is electromagnetic braking radiation of the maximum energy of continuous spectrum in the order of megaelectronvolts (usually within the range between 6 and 20 MeV). After the beam generated in this way has been properly shaped, it is aimed at the illness-affected area, also passing through the healthy tissue. In order to minimise damage to the healthy organs as a side effect of the treatment, the absorbed dose prescribed by a radiotherapist is delivered by means of several photon beams directed at the specified area at different angles. 

Caring about the patient’s safety, each step of the therapeutic treatment should be monitored closely. Taking into account the complexity of the entire process, and in the first place, the complexity of highly-specialised treatment plans, an inexact projection of the real distribution of a dose calculated by computerised radiation treatment planning systems, as well as the uncertainties caused by the therapeutic device itself (for example, an imperfect geometry of the accelerator), it is necessary to verify precisely the developed treatment plans before they are used with the participation of the patient. The verification of plans before the beginning of a treatment in teleradiotherapy means checking the accuracy of the calculated 3D distribution of the absorbed dose (ideally in the geometry of the patient) in a way independent of the applied treatment planning system. It can be done by means of measurements, an independent calculation, or their combination. The accuracy, precision, and rate of calculating the 3D distributions of absorbed doses increases alongside the increasing computing power of machines, and mastering algorithms for the simulation of the influence of ionising radiation on matter. However, despite technological advances in simulations, a direct measurement of the distribution of a dose is considered to be the best method of the verification of therapeutic treatment plans. 

The main aim of the project carried out by the consortium “Dose-3D” is the development of a configurable moulage containing a detector that would be capable of a direct measurement of the spatial distribution of a dose deposited by a therapeutic photon beam. It is planned that the active element of the detector would be a liquid scintillator due to its tissue-resembling structure and high radiation resistance. In order for the measurement to be performed with high precision, the detector mount needs to be of high granulation, which the team are planning to achieve by means of 3D printing. Each cell will have an individual read-out. An important part of the project is developing high quality software for the simulation of a dose and monitoring the entire device. Thanks to collaboration with the Centre of Oncology in Krakow, tests of particular prototypes will take place in conditions identical with the ones during a treatment. 

The solution proposed by the researchers encompasses the construction of a 3D measurement matrix filled with a tissue-like scintillator. Thanks to the use of the latest 3D printing techniques, it will be possible to build a measurement mount of required granulation, and developing the required infrastructure (a system for filling cells with a scintillator and the read-out from each cell) will be an integral part of the process of building the detector mount. In the initial part of the project, it will be necessary to obtain large individual cells for the purpose of the analysis of their mechanical properties. Prototype active cells will be used to build and test the complete read-out system made of an optical fibre (for obtaining the signal from an active cell), a silicon photomultiplier, and a system for the digitalisation and analysis of the obtained signal. The initial phase of tests will finish with a calibration and measurement campaign with the use of the infrastructure that belongs to the Krakow Branch of the Centre of Oncology. An integral part of the system will be a simulation platform based on the GEANT4 engine for the modelling of interaction between radiation and matter. An important issue of the entire research process will be obtaining high consistency between the simulated distribution of a dose and the distribution measured during tests, while the maximum acceptable difference between the simulated and experimentally measured values should not exceed 3%.