Volume 18 (2012): Issue 2 (June 2012)

The aim of this work was to create a numerical model of scintillation detector and to check whether such detector can be used for the measurements of internal contamination in emergency conditions. The purpose of the measurements would be only detection of possible contamination, without identification of radioactive isotopes, and hence without estimation of effective dose. However, in emergency conditions, it is sufficient for the rapid selection of a group of contaminated persons, who should be subjected to careful inspection in the laboratory conditions. The calculations were performed for three detector positions relatively to the phantom. The distribution of dose rate was also calculated, in order to find the best geometry for dose rate measurements around human body. Another problem under consideration was the possible influence of radioactive contamination in the environment on the registration of the gamma spectrum emitted from the whole body phantom. Performed calculations showed that there is a possibility to measure internal contamination outside laboratory, even in contaminated area.

Fission products of 235U or isotopes from activation may appear in technological waters at normal operation of a research reactor. Therefore, reactor cooling water may contain a number of beta radioactive isotopes including yttrium and strontium isotopes, which can pose potential hazard to reactor personnel. In order to asses internal exposure urinalysis is carried out. This work presents the method of sample preparation and measurement used by Radiation Protection Measurements Laboratory (RPLM) of the National Centre for Nuclear Research (NCNR). Method of various isotopes of yttrium and Sr-90 activity calculation is also shown. Determination of these isotopes activities in urine sample allows estimating the effective doses

Radiotherapy given after mastectomy (PMRT) will reduce the risk of local recurrence by about two-thirds. Clinical and dosimetric trials were carried out using various techniques to optimize the treatments by maximizing the dose to the tumour and minimizing it to the healthy tissues at proximity. Different conventional techniques which have been studied suffer from important dose inhomogeneities due to the complex anatomy of the chest, which reduces the benefits from such treatments. Moreover, due to the heterogeneity of breast cancer, the response to therapy and a systematic approach to treatment cannot be derived and treatment regimens must be determined on a patient-by-patient basis. This is only possible if accurate and fast treatment planning systems are available. Intensity Modulated Radiotherapy (IMRT) allows delivering higher doses to the target volume and limits the doses to the surrounding tissues. The objective of this study is to test the feasibility of applying a Monte Carlo-based treatment planning system, Hyperion accurately in routine Intensity Modulated Radiotherapy (IMRT) postmastectomy. In order to use a treatment planning system for routine work it should prove to provide optimized dose delivery in a suitable time. Treatment planning for IMRT application to PMRT was performed using Hyperion. Constraints were set to deliver the prescribed dose to the target and minimize the dose to the organs at risk. Dose Volume Histograms (DVH) were used to evaluate the set up plans. Time taken to optimize the plan was measured. The target coverage was within the accepted values. Approximately 90% of the breast and 80% of the PTV received 45 Gy or above. The volume of the lung that received 40Gy was less than 10% and the volume that received 20Gy (V20) was less than 25%. The volume of the heart receiving 30 Gy (V30) or above was negligible. This indicates low NTCP of these organs. The time taken for optimization, showed it possible to apply Monte Carlo-based treatment-planning systems for patient-to-patient PMRT.

The possibility of the ultrasound-induced lung haemorrhage occurring in adult human during diagnostic ultrasound examination is studied here. This study is based on the hypothetical alveolar resonance mechanism of the ultrasound-induced lung haemorrhage. The alveolar wall is initially modelled here as a square membrane with fixed-boundary, and then theoretically subjected to vibration analysis. The equation of threshold pressure for the occurrence of ultrasound-induced lung haemorrhage is derived. A comparison test against past experimental data validates the use of the square membrane model of the alveolar wall in studying the ultrasound induced lung haemorrhage. This study predicts that the ultrasound-induced lung haemorrhage in adult human can be prevented if the ultrasound frequency is kept above 1.69 MHz while the Mechanical Index does not exceed 1.9.