MODELING OF THE CHEMICAL STAGE OF RADIOBIOLOGICAL MECHANISM USING PETRI NETS

The biological effect of ionizing particles is caused mainly by water radicals being formed by densely ionizing ends of primary or secondary charged particles during physical stage; only greater radical clusters being efficient in DNA molecule damaging. The given clusters diffuse after their formation and the radical concentration changes also by reactions running mutually or with other substances being present in corresponding clusters. The damage effect depends then on radical concentrations at a time when the cluster meets a DNA molecule. The influence of oxygen may be important (mainly in the case of low-LET radiation) because oxygen is always present in living cells. Oxygen may act then in two different directions: at small concentrations the interaction with hydrogen radicals prevails and final biological effect diminishes while at higher concentrations additional efficient oxygen radicals may be formed. The time evolution of changing radical concentrations during cluster diffusion may be modeled and analyzed well with the help of Continuous Petri nets

An expert consensus definition of failure of a treatment to provide adequate relief (F-PAR) for chronic constipation \u2013 an international Delphi survey

Background: As treatments for constipation become increasingly available, it is important to know when to progress along the treatment algorithm if the patient is not better. Aim: To establish the definition of failure of a treatment to provide adequate relief (F-PAR) to support this management and referral process in patients with chronic constipation. Methods: We conducted an international Delphi Survey among gastroenterologists and general practitioners with a special interest in chronic constipation. An initial questionnaire based on recognised rating scales was developed following a focus group. Data were collected from two subsequent rounds of questionnaires completed by all authors. Likert scales were used to establish a consensus on a shorter list of more severe symptoms. Results: The initial focus group yielded a first round questionnaire with 84 statements. There was good consensus on symptom severity and a clear severity response curve, allowing 67 of the symptom-severity pairings to be eliminated. Subsequently, a clear consensus was established on further reduction to eight symptom statements in the final definition, condensed by the steering committee into five diagnostic statements (after replicate statements had been removed). Conclusions: We present an international consensus on chronic constipation, of five symptoms and their severities, any of which would be sufficient to provide clinical evidence of treatment failure. We also provide data representing an expert calibration of commonly used rating scales, thus allowing results of clinical trials expressed in terms of those scales to be converted into estimates of rates of provision of adequate relief