Dose calculation prevention

The accuracy of radiotherapy dose calculations, based on the attenuation values of the CT scan of the patient, needs to be very high to prevent underexposure of the tumor and overexposure of the healthy tissue. Typically the isodose surfaces are calculated and viewed in 3D in the context of the local anatomy. Increasingly the images made in the linear accellerator with the electronic portal imaging device" (EPID) are used for precise localization of the beam and repeat positioning of the patient. 

Tromethamine, a highly alkaline solution, is a sodium-free organic amine that acts as a proton acceptor to prevent or correct acidosis. However, no evidence exists that tromethamine is beneficial or more efficacious than sodium bicarbonate. The usual empiric dosage for tromethamine is 1 to 5 mmol/kg administered IV over 1 hour and an individualized dose can be calculated as follows ... 

Baldessarini and Davis (1980) attempted to clarify whether there is a significant relationship between the antipsychotic maintenance dosages administered and the risk of relapse in the case of chronic schizophrenics. Correlations calculated for 23 controlled studies showed no relationship between the administered doses of antipsychotics and the risk of relapse within a wide range. Based on this result, the authors ruled that the maintenance dosage for each individual patient should be kept as low as possible in order to prevent antipsychotics from causing undesirable delayed effects. 

The risk index in Equation 6.2 is expressed in terms of risk (i.e., the probability that an adverse response will occur during an individual s lifetime). This definition is consistent with the fundamental objective of developing a risk-based hazardous waste classification system. However, the use of health risk per se in calculating the risk index presents some difficulties because risk is not proportional to dose for substances that cause deterministic effects. For this type of substance, the risk is presumed to be zero at any dose below a nominal threshold. Since the allowable dose should always be less than the threshold in order to prevent the occurrence of adverse responses, expressing the risk index in terms of risk would result in an indeterminate value and, more importantly, a lack of distinction between doses near the nominal thresholds and lower doses of much less concern. For any hazardous substance, including carcinogens for which risk is assumed to be proportional to dose without threshold, it is generally useful to express the risk index as the ratio of a calculated dose [e.g., sieverts, mg (kg d)-1] to an allowable dose that corresponds to an allowable risk ... 

Table 9.11 Calculated effective dose (EDjq) of neomycin sulfate required to prevent infection in 50% of rabbit corneas when incorporated into various vehicles ...

These dosing models use complex calculations that may prevent widespread adoption by clinicians. To facilitate the estimates, an Internet-based calculator has been implemented [46]. This system is not only capable of predicted final dose but also can be used to refine dosing once the first few INR measurements have been taken. Additionally, a software-based system has been developed that can model the pharmacokinetics of individual patients given their genotypes and INR measurements [47]. This system attempts to use these data to provide dosing attempting to get the INR into the desired... 

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