Uncertainties exist both in the basic data from which a radiotherapy plan is produced and in the process whereby such a plan is translated into the patient set-up during treatment. Individual parts of the radiotherapy process are subject to checks, but the overall accuracy of treatment delivery is not routinely evaluated. In vivo dosimetry by means of a semiconductor detector system can be used to measure the cumulative error in the radiotherapy treatment dose delivered. A direct patient dosimetry system was commissioned and introduced in January 1993 for the routine evaluation of the doses patients receive. Since its introduction a total of 1000 patients have been monitored for a range of radiotherapy applications, comprising 300 breast treatments (6 MV X-rays), 150 head and neck treatments (6 MV X-rays) and 550 pelvis. abdomen and thorax treatments (10 MV X-rays). The results of this audit show that less than 5% of all patients monitored gave a systematic error more than +/- 5% for a single field, or more than +/- 2.5% for the "estimated overall error" in the isocentre dose. The causes of these errors were identified and appropriate action taken where necessary. It is suggested that this method could be used routinely in radiotherapy treatment to assess the overall performance of the treatment process.

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The dosimetric accuracies of CATPhan 504 and CIRS 062 have been evaluated using the kV-CBCT of Varian TrueBeam linac and Eclipse TPS. The assessment was done using the kV-CBCT as a standalone tool for dosimetric calculations towards Adaptive replanning. Dosimetric calculations were made without altering the HU-ED curves of the planning computed tomography (CT) scanner that is used by the Eclipse TPS. All computations were done using the images and dataset from kV-CBCT while maintaining the HU-ED calibration curve of the planning CT (pCT), assuming pCT was used for the initial treatment plan. Results showed that the CIRS phantom produces doses within ±5% of the CT-based plan while CATPhan 504 produces a variation of ±14% of the CT-based plan.

An empirical mathematical model, comprising 17 compartments, has been produced to describe the biokinetics of ingested inorganic arsenic (As) in man — required to interpret bioassay data and to predict As tissue concentrations resulting from acute and chronic intakes of inorganic As. The rate constants used to describe the bi-directional transfer of As between compartments were chosen to result in model outcomes that match published data on the distribution of As in tissues and on the retention and excretion of radioisotopes of As administered to human subjects. The model was deployed in acute and chronic intake modes to produce predictions of tissue concentrations and excretion levels. Under conditions of chronic daily intake (1 μg d-1) for 50 years predicted final tissue concentrations vary by a factor of ∼2. Highest concentrations are predicted to occur in skin and bone (∼230ng kg-1). Tissue concentrations in all tissues other than bone are predicted to reach equilibrium after ∼100 days, and at this time, the amount of As excreted in urine has also reached approximate equilibrium at 79% of the daily dietary intake. This level then remains relatively constant unless intake ceases when tissue levels of As fall rapidly. Data on organic and inorganic As concentrations in urine were used to predict inorganic As intake and average tissue content for the USA population. Predicted tissue concentrations ranged from 2.3 μg kg -1 in skin to 1.1 μg kg-1 in muscle for an average inorganic As intake of 9.3 μg d-1.

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