[The predictability of the radiotherapy response in epidermoid tumors of the head and neck. A review of the literature and mathematical models for choosing the fractionated doses].
Literature data show that the term "squamous-cell head and neck cancer" includes a wide range of epidermoid cell subgroups, each of them with its own intrinsic radiosensitivity (Do values ranging from 107 to 184 in primary tumors, and 146-263 in recurrences; n values ranging from 1 to 5; and, if we consider linear-quadratic model alpha values from 0.273 to 0.490 and beta values from 0.029-0.045). Different sublethal and potential lethal repair times are also observed (4-6 hours and 12-24 hours, respectively), and structural tissue heterogeneity (hypoxic fraction oscillating 5%-30% of the neoplasm). Most important, different kinetic parameters are demonstrated, with Labelling Index ranging from 4% to 30%, phase-S time from 6 to 19 hours, and potential doubling time from 2 to 20 days. On the basis of Fowler's and Barendsen's mathematical models and knowing the potential doubling time and Labelling Index values (derived from bioptic specimens), as well as alpha/beta ratio for both tumor and normal tissue, we tried to identify the optimal fractionation (standard, accelerated, hyperfractionated) for slow/fast-growth tumors, also evaluating the relative acute and late side effects. Our analysis shows that: 1) tumors with aggressive biological behavior (Labelling Index greater than 15%, aneuploidy, potential doubling time less than 5 days) seem to respond to accelerated fractionation/hyperfractionation without split better than to standard regimens: 2) tumors with slow growth (Labelling Index less than 15%, potential doubling time greater than 5 days, euploidy) seem to respond not only to standard regimens, but also--and mainly--to hyperfractionation.
Istituto Nazionale per la Ricerca sul Cancro, Genova.
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Corvò
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Scarpati
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Sanguineti
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Vitale
D002294:Carcinoma, Squamous Cell / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D002453:Cell Cycle / Q000528:radiation effects; D006258:Head and Neck Neoplasms / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008433:Mathematics; D008954:Models, Biological; D011379:Prognosis; D011836:Radiation Tolerance; D011879:Radiotherapy Dosage
La predittività della risposta radioterapica nei tumori epidermoidi della testa e del collo. Revisione della letteratura e modelli matematici per la scelta dei frazionamenti.