The alanine detector in BNCT dosimetry: dose response in thermal and epithermal neutron fields.

PURPOSE: The response of alanine solid state dosimeters to ionizing radiation strongly depends on particle type and energy. Due to nuclear interactions, neutron fields usually also consist of secondary particles such as photons and protons of diverse energies. Various experiments have been carried out in three different neutron beams to explore the alanine dose response behavior and to validate model predictions. Additionally, application in medical neutron fields for boron neutron capture therapy is discussed. METHODS: Alanine detectors have been irradiated in the thermal neutron field of the research reactor TRIGA Mainz, Germany, in five experimental conditions, generating different secondary particle spectra. Further irradiations have been made in the epithermal neutron beams at the research reactors FiR 1 in Helsinki, Finland, and Tsing Hua open pool reactor in HsinChu, Taiwan ROC. Readout has been performed with electron spin resonance spectrometry with reference to an absorbed dose standard in a (60)Co gamma ray beam. Absorbed doses and dose components have been calculated using the Monte Carlo codes fluka and mcnp. The relative effectiveness (RE), linking absorbed dose and detector response, has been calculated using the Hansen & Olsen alanine response model. RESULTS: The measured dose response of the alanine detector in the different experiments has been evaluated and compared to model predictions. Therefore, a relative effectiveness has been calculated for each dose component, accounting for its dependence on particle type and energy. Agreement within 5% between model and measurement has been achieved for most irradiated detectors. Significant differences have been observed in response behavior between thermal and epithermal neutron fields, especially regarding dose composition and depth dose curves. The calculated dose components could be verified with the experimental results in the different primary and secondary particle fields. CONCLUSIONS: The alanine detector can be used without difficulty in neutron fields. The response has been understood with the model used which includes the relative effectiveness. Results and the corresponding discussion lead to the conclusion that application in neutron fields for medical purpose is limited by its sensitivity but that it is a useful tool as supplement to other detectors and verification of neutron source descriptions.

[How to decide with precision, justice, and equity? Reflections on decision-making in the context of extreme prematurity. Part two: moving toward making the best possible decision: defining conditions for putting decisions into practice]. / Comment décider avec justesse, justice et équité? Réflexion sur la décision en situation d'extrême prématurité. Deuxième partie: comment tendre vers une décision optimale? Définition des conditions d'exercice de la décision.

Extreme premature child's long-term prognostic is getting better and better known, and if a resuscitation procedure is possible at birth, it won't guarantee survival or a survival free of disability. Incertitude toward individual prognosis and outcome for those children remains considerable. In this field, we are at the frontier of medical knowledge and the answer to the question, "how to decide the ante and postnatal care" is crucial. This work is focused on this problematic of decision-making in the context of extreme prematurity. It attempts to deconstruct this concept and to explicit its stakes. Thus, with the support of the medical sources and of philosophical debates, we tried to build a decision-making procedure that complies with the ethical requirements of medical care, accuracy, justice and equity. This decision-making procedure is primarily concerned with the singularity of each decision situation and it intends to link it closely to the notions of rationality and responsibility.

[How to decide with precision, justice, and equity? Reflections on decision-making in the context of extreme prematurity. Part one: the problematics of decision-making in the context of extreme prematurity]. / Comment décider avec justesse, justice et équité? Réflexion sur la décision en situation d'extrême prématurité. Première partie: problématique de la décision dans le contexte de la prématurité extrême.

Extreme premature child's long-term prognostic is getting better and better known, and if a resuscitation procedure is possible at birth, it won't guarantee survival or a survival free of disability. Incertitude toward individual prognosis and outcome for those childs remains considerable. In this field, we are at the frontier of medical knowledge and the answer to the question, "how to decide the ante and postnatal care?" is crucial. This work is focused on this problematic of decision making in the context of extreme prematurity. It attempts to deconstruct this concept and to explicit its stakes. Thus, with the support of the medical sources and of philosophical debates, we tried to build a decision-making procedure that complies with the ethical requirements of medical care, accuracy, justice and equity. This decision-making procedure is primarily concerned with the singularity of each decision situation and it intends to link it closely to the notions of rationality and responsibility.

Calculation of relative biological effectiveness for proton beams using biological weighting functions.

PURPOSE: The microdosimetric weighting function approach is used widely for beam comparison studies. The suitability of this model to predict the relative biological effectiveness (RBE) of therapeutic proton beams was studied. The RBE(alpha) (i.e., linear approximation) dependence on the type of biological end point, initial proton energy, energy spread of the input proton beam, and depth of beam penetration was investigated. METHODS AND MATERIALS: Proton transport calculations for a proton energy range from 70 to 250 MeV were performed to obtain proton energy spectra at a given depth. The corresponding microdosimetric distributions of lineal energy were calculated. To these distributions the biological response function approach was applied to calculate RBE(alpha) the biological effectiveness based on a linear dose-response relationship. The early intestinal tolerance assessed by crypt regeneration in mice and the inactivation of V79 cells were taken as biological end points. RESULTS: The RBE(alpha) values approach about 1 in the plateau region and gradually increase with the proton penetration depth. In the center of the Bragg peak, at the maximum dose delivery, the values of RBE(alpha) range from 1.1 (250-MeV beam, early intestinal tolerance in mice) to 1.9 (70-MeV beam, Chinese hamster V79 cells in G1/S phase). Distal to the Bragg peak, where only a small fraction of dose is delivered, the RBE(alpha) was found to be even higher. For modulated proton beams we found an increasing RBE(alpha) with depth in the spread-out Bragg peak (SOBP). Values up to 1.37 at the distal end of the SOBP plateau (155-MeV beam, SOBP between 5.3 and 13.2 cm) were obtained. CONCLUSION: More experimental work on the determination of microdosimetric weighting functions is needed. The results of the presented calculations indicate that for therapy planning it may be necessary to account for a depth dependence on proton RBE, especially for lower energy.