Abstract. The therapeutic effect from molecular radiation therapy (MRT), on both tumour and normal tissue, is determined by the radiation absorbed dose. Recent research indicates that as a consequence of biological variation across patients the absorbed dose can vary, for the same administered activity, by as much as two orders of magnitude. The international collaborative EURAMET-EMRP project ಯMetrology for molecular radiotherapy (MetroMRT)ರ is addressing this problem. The overall aim of the project is to develop methods of calibrating and verifying clinical dosimetry in MRT. In the present paper an overview of the metrological issues in molecular radiotherapy is provided. Introducing the problem of molecular radiation therapyMolecular radiation therapy (MRT), also known as targeted radionuclide therapy, is a unique form of radiotherapy where a high radiation dose is delivered internally, ideally to a specific target. The therapeutic agent may be administrated in several ways: ingestion, intravenous infusion, injection to a body cavity or pathological space (locoregional therapy) or direct injection into a solid tumour.Molecular radiotherapy is routinely prescribed on the basis of administered activity of the therapeutic agent. However, uptake and retention differ from patient to patient and therefore the individual dose to the target can vary between patients given the same administered activity. Recent research indicates the range of variation can be up to two orders of magnitude, which is particularly alarming from the point of view of radiation protection [1,2]. At the low extreme, the patient might gain negligible therapeutic benefit. At the high extreme, the patient might receive more radiation than is needed to treat the tumour. Both cases technically constitute maladministrations.Recent research and new technology developments have permitted estimates of radiation dose in individual patients to target tissues and critical normal tissues at risk to be obtained. However, there has been almost no adoption of these methodologies in routine clinical MRT practice. The reasons are many, but, mainly because the methodology is difficult, there is no standardization of procedures, and there is no objective means of predicting the effect of individual patient dosimetry on treatment outcomes.In fact, when compared with conventional external beam radiotherapy, in which individual patient dosimetry is mandatory and strictly controlled according to agreed protocols, there is full traceability to primary standards, and there are even legal requirements for accuracy (within 5 % of a reference value), it is clear that MRT is urgently in need of metrological support in order to bring dosimetry practice to an acceptable and comparable standard.The new international collaborative EURAMET-EMRP project ಯMetrology for molecular radiotherapyರ (MetroMRT) is addressing this problem. The project is developing the background metrology to support routine individual MRT patient dosimetry, and together with a programme of disseminatio...
An analog of Fano's theorem for ionization in cavities is shown to hold for the stepwise representation of electron paths used in Monte Carlo computer models of electron transport. This brings to light an error in the distribution of electron paths and hence energy deposition which is induced by interrupting steps which cross the interface between media of different densities. The magnitude of the error depends on the shape of the cavity and its size relative to the electron path length in the cavity gas. In a typical calculation of a cylindrical chamber exposed to 60Co radiation, if the electron step size is taken as 10% of the remaining path, then a 3% energy deficit in the cavity results. An algorithm for crossing an interface is described which does not produce this error.
the relative incidence rates of second cancers of the thyroid, salivary gland and breast following paediatric radiotherapy (conventional radiotherapy for photons and proton therapy for neutrons) are investigated in a pilot single-institution study, exploring the possible design of a multi-institution prospective study comparing the long-term out-of-field and in-field effects of scanned and scattered protons. The results will be used to validate an RBE-based risk model developed by the project, and validate the corresponding RBE values.
As radical radiotherapy treatments become more effective, more and more cancer patients are becoming cured of their disease and surviving for decades. Damage to exposed healthy tissues that becomes manifest in the medium-to-long-term is becoming a more significant factor in the choice of individual treatment plans and treatment modality. However, currently there are no reliable objective methods for predicting in an individual patient the occurrence of normal tissue complications, or second cancers caused by radiation. This is especially needed as new competing techniques and modalities become available, such as IMRT, protons, carbon ions, etc., all advancing the ability to focus the radiation dose on the target while sparing normal tissue. ALLEGRO is a Euratom-funded project that is currently investigating the current state of knowledge, and attempting to define the priority research areas. Preliminary considerations of the problems to be solved and research priorities are presented.
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