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CAUSALITY OF A GIVEN CANCER AFTER KNOWN RADIATION EXPOSURE 26 original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. authoritative judgment as to the amount of harm caused in any single individual or the risk of quantal response to such harm in that individual. The public health official is trained to estimate the actual or statistically expected excess incidence of a given illness or traumatic condition in a population of otherwise normal individuals (see Table 1). This fractional number is equal to the risk of the given condition for the average individual in a normal population. In other words, one can never determine the actual risk to any one person; only average values can be obtained. The risk dealt with by the public health officer is, in principle, purely physical: it is the probability not only that an accidental event will bring together two objects, the agent source and the biological target, but also that a resulting transfer of agent will occur. Public health officers usually do not attempt to estimate the subsequent purely biological probability that a particular above-threshold amount of harm will cause a quantal response. QUANTAL RESPONSE IN A POPULATION OF HARMED PERSONS An individual is brought to the attention of a physician because of illness or injury and therefore has presumably been harmed by some agent or process. Then begins the process of collecting medical information from the patient's history, a physical examination, or specialized diagnostic procedures. This information permits the physician to diagnose the kind, amount, and probable cause of harm sustained; to prescribe therapy; and usually to forecast the prospect of recovery based on the prescribed regimen of treatment. In particular, the physician assesses whether the amount of harm is near the threshold for a quantal response, either in the form of lethality or in a permanent functional incapacitation. If the patient dies, an autopsy may be performed to obtain further diagnostic information about the injury and its causes. If the illness or injury is associated with exposure to a presumably excessive amount of a specific agent or agents, then an estimate of the amount (or dose) 2 of each agent involved would be helpful, but not necessarily decisive to the overall evaluation. That is to say, the physician is always mindful of agent-amount-effect relationships in two contexts: (1) the amount of a potentially harmful agent received by the patient and (2) the amount (dose) of a therapeutic agent that could be prescribed to destroy or control the causative agent but at the same time cause only minimal damage to the normal tissues. The amount of harm due to a specific agent is determined principally by the dose. Even though the severity of harm caused by a given dose varies among individuals (see Bingham, in this volume), severity and dose are
About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. TABLE 1 Calculating the Probability of a Quantal Response From the Delivery of a Measured Dose Versus That From the Risk of Receiving a Dose Type of Quantal Mode of Agent Transfer Ratio, for the Risk of a Quantal Response Discipline for Risk and Response: Individual at Denominator Numerator Cause Evaluation Risk Incapacitation or death: Controllable Those given the same The quantal responders Industrial hygiene; medical person (organ) measured dose of agent, or among those (equally) practice equally harmed dosed or harmed Incapacitation or death: Uncontrollable (accidental) Those exposed to the risk of The quantal responders Epidemiology; medical person (organ) receiving any of a wide among the exposed who practice distribution of doses and have actually been severities of harm (unequally) dosed and harmed Cancer induction: cell Uncontrollable (accidental) Cells exposed to the risk of Cancer cases or deaths Public health; epidemiology (organelle) an undeterminable dose and from unobservable an unobservable transformed cells transformation Cancer expression: person Not applicable Cancer cases Cancer deaths Medical practice (organ) CAUSALITY OF A GIVEN CANCER AFTER KNOWN RADIATION EXPOSURE 27
