Dose mapping

Proper control of food irradiation applications should fulfill the requirements for both food technologies and radiation technologies. Application of well-established methods for measurement of absorbed radiation dose and the dose distribution helps to provide assurance that the radiation treatment is both effective and legally correct [133]. Computer tomography (CT) can provide detailed, high-resolution, and accurate dose maps for any arbitrary product and package configurations [134]. Such dose maps are an essential part of process validation. 

The space distribution of UV radiation in Italy, available through monthly UV dose maps, can be useful for epidemiology research in skin cancer and eye pathologies as well as in those studies dealing with the impact of UV on the biosphere. 

Dose mapping, using dosimeters, on a shipping container filled with components. Irradiate and determine the maximum and minimum doses (Umax and Dmin) received in the container... 

The dose mapping inside the irradiated object is important. In the dose range 25-32 kGy, regulatory agencies require a ratio of Dmax/Dmin of 1.28 maximum value. The distribution of absorbed dose depends on the radiation used and is affected by the geometry ofthe vials (containers) as well as the nature (electron density) of packaging material. 

Valuation by Dose Mapping All variable conditions must be specified during validation and controlled in routine practice thereafter. A loading pattern must be established for each type of product. This should specify the number, position, and orientation of product packages within the irradiation container. The distribution of density within the loading pattern should be chosen to be as near uniform as possible in order to minimize dose variations. 

Dose mapping validations arc necessary for new products, new irradiation container loading patterns, altered conveyor configurations, and changes to the source, including source replenishments. 

Routine Dose Control Routine dose control is straightforward as long as reliable validation-dose mapping information is available. The conveyor speed that assures a dose of x kGy on a particular date need only be adjusted toi com-... 

Validation should include dose mapping to establish the distribution of absorbed dose within the irradiation container when packed with product in a defined configuration. 

For the dose mapping procedure, the irradiator should be filled with irradiation containers packed with dummy products or a representative product of uniform density. Dosimeters should be placed throughout a minimum of three loaded irradiation containers which are passed through the irradiator, surrounded by similar containers or dummy products. If the product is not uniformly packed, dosimeters should be placed in a larger number of containers. 

Ideally, reference dosimeters should be used for the dose mapping exercise because of their greater precision. Routine dosimeters are permissible but it is advisable to place reference dosimeters beside them at the expected positions of minimum and maximum dose and at the routine monitoring position in each of the replicate irradiation containers. The observed values of dose will have an associated random uncertainty which can be estimated from the variations in replicate measurements. 

Irradiator parameters should be kept constant, monitored and recorded during dose mapping. The records, together with the dosimetry results and all other records generated, should be retained. 

For the dose mapping procedure, dosimeters should be placed between layers of homogeneous absorber sheets making up a dummy product, or between layers of representative products of uniform density, such that at least ten measurements can be made within the maximum range of the electrons. Reference should also be made to sections 18 to 21. 

The basic procedure in performance qualification (PQ) exercises is the measurement of dose distribution in real products. In gamma processing, similar dosimetry systems can be applied like in OQ exercises. In electron processing, usually film dosimeters are suggested for use with the restriction of the application of only thin film dosimeters for dose mapping in inhomogeneous products. 

This dosimetry system has been applied widely for dose mapping and routine process control, especially due to dedicated commercially available instruments such as potentiometric electrochemical cells. 

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