[Dose fractionation in cancer radiotherapy]. / Fraccionamiento de la dosis en la radioterapia del cáncer.

Radiobiological research have enlarged the field of applications of radiotherapy in cancer treatment. The study of the biological effects of radiation on tumours (T) and normal tissues (NT) has showed that: 1) damage to NT is related directly with dose per fraction and inversely with the alpha/beta ratio; 2) the maximum differential effect of irradiation between T and NT is obtained when lower doses per fraction and shorter time periods are used. One exception to this rule is given by T whose alpha/beta ratio is lesser than that of NT. In these T treatment with high doses per fraction does increase tumour control and reduce late complications.

Hypofractionation in radiotherapy.

Major changes in cancer radiotherapy have followed a greater understanding of the biological effects of radiation on tumours and normal tissues. Clinical radiotherapy is today a solid body of knowledge with well defined scientific foundations. Key concepts in current radiobiology include lethal and sublethal injuries, dose-effect coefficients, alpha/beta ratios, acute and late response, biologically equivalent dose, fraction dose, irradiation time and tumour regeneration between others. Effects of irradiation time and dose per fraction on tumours versus normal tissues are of special importance. Dose per fraction must be considered for analysis of effects in normal late-responding tissues. In contrast, both dose per fraction and irradiation time influence the response to radiation of malignant tumours and acute-responding tissues. Finally, the ability to quantify relationships between radiation dose and biological effect has been of particular value in the development of radiotherapy. This is illustrated by the growing use of high doses per fraction for the treatment of some cancers.

Diagnosis efficacy of structural (CT) and functional (FDG-PET) imaging methods in the thoracic and extrathoracic staging of non-small cell lung cancer.

PURPOSE: To evaluate the efficacy of FDG-PET in the definition of tumour lung node lesions and to compare the diagnostic validity of CT and FDGPET in the staging of patients with non-small cell lung cancer (NSCLC). MATERIAL AND METHODS: Patients with clinical suspicion of potentially resectable NSCLC (n = 108) were studied by standard procedures in our setting, including fibrobronchoscopy, transthoracic fine-needle aspiration, thoracoabdominal CT and FDG-PET. PET images were analysed by researchers blinded to results of other imaging modalities. Definitive tumour diagnosis was by histopathological study in patients who underwent surgery and by specific imaging methods and biopsy, when available, in patients who did not. Diagnostic accuracy was evaluated by comparing CT/PET results with the definitive diagnosis. RESULTS: In 13% of patients, no FDG-PET findings were observed and the histological study was negative for tumour. In 22% of patients, FDG-PET detected metastatic disease (M0 by CT). For mediastinal involvement, global diagnostic accuracy was 0.90 with FDG-PET and 0.59 with CT. False positive FDG-PET findings were produced by inflammatory conditions and false negative findings by the small size or proximity of lymph nodes to primary tumour. Mediastinal staging by CT and FDG-PET was correct in 56% and 87% of patients, respectively. CT indicated mediastinal invasion in 17% of patients with no FDG-PET finding of mediastinal involvement. Conversely, mediastinal spread was undetected by CT in 14% of patients with FDG-PET findings of mediastinal involvement. CONCLUSIONS: Although complementary, the functional method (FDG-PET) is significantly superior to the structural method (CT) for detection of mediastinal tumour disease.

The impact on oncology of the interaction of radiation therapy and radiobiology.

The quantitative analysis of the cell dose-survival curves, the randomness of cell killing by radiation, the probabilistic basis of the response to irradiation of tumors and normal tissues, the understanding of the biological mechanisms underlying to this response, the rationale for dose-time and fractionation in radiotherapy, the introduction of the concepts of tumor control probability (TCP) and biologically effective dose (BED), the relationships TCP-dose, BED-alpha/beta BED-fraction size and BED-treatment time, the problems associated with the accelerated regeneration of surviving tumor clonogens during the course of fractionated radiotherapy, the new demands of knowledge on oncology and radiation biology derived from heterogeneous dose distributions in conformal radiation therapy programs and the definition of the biological basis of normal tissues tolerance to reirradiation are, probably, the most important contributions of radiobiology to clinical radiotherapy in the last twenty five years. Radiotherapy is today a scientific discipline based on the interplay of mathematics, physics, biology and oncology. The knowledge of the basic concepts of radiobiology is essential for daily radiotherapy practices and for all oncologists. The most efficient use of multimodality treatments in cancer therapy cannot be done without a clear understanding of these principles.

Increased fluoride uptake in human dental specimens treated with diode laser.

The hypothesis of this study was the fact that diode lasers can increase the fluoride uptake in dental structures. The main objectives were: (1) to evaluate the effect of diode laser-NaF varnish combination on binding fluoride to dental enamel in an in vitro model and (2) to analyse outer enamel surface changes produced by the laser energy. After NaF enamel varnish and laser irradiation at different levels of energy, specimen surfaces were examined by environmental scanning electron microscopy. The incorporation of F(-) ion into the dental structure was quantitatively determined by using a fluoride ion-selective electrode. Results showed that the laser treatment significantly increased the binding of fluoride to the enamel surface without damaging it. The amount of F(-) estimated was 37 +/- 7 mg/l to the power of 5 W and 58 +/- 12 mg/l to the power of 7 W. These increases were significantly greater than the ones achieved by conventional topical fluoridation. The results were analysed and compared by Kruskal-Wallis and Dunn's multiple comparison tests, and significant statistical differences were found. These suggest that the NaF varnish-diode laser combination may be a useful option for the effective fluoridation of teeth.

The impact on oncology of the interaction of radiation therapy and radiobiology

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The quantitative analysis of the cell dose-survivalcurves, the randomness of cell killing by radiation,the probabilistic basis of the response to irradiationof tumors and normal tissues, the understanding ofthe biological mechanisms underlying to this response,the rationale for dose-time and fractionationin radiotherapy, the introduction of the concepts oftumor control probability (TCP) and biologicallyeffective dose (BED), the relationships TCP-dose,BED-á/â, BED-fraction size and BED-treatment time,the problems associated with the acceleratedregeneration of surviving tumor clonogens duringthe course of fractionated radiotherapy, the new demandsof knowledge on oncology and radiationbiology derived from heterogeneous dose distributionsin conformal radiation therapy programs andthe definition of the biological basis of normal tissuestolerance to reirradiation are, probably, themost important contributions of radiobiology to clinicalradiotherapy in the last twenty five years. Radiotherapyis today a scientific discipline based onthe interplay of mathematics, physics, biology andoncology. The knowledge of the basic concepts ofradiobiology is essential for daily radiotherapypractices and for all oncologists. The most efficientuse of multimodality treatments in cancer therapycannot be done without a clear understanding ofthese principles

Formación médica y necesidades sociales / Medical formation and social needs

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Recursos humanos del sistema de salud: una reforma pendiente / Human resources in the health care system: pending reforms

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