Validation of a method utilising MR images for dose planning of prostate cancer treatment : Validation of new coil technology applied on the pelvis region of healthy volunteers

Abstract: By generating a synthetic CT image (sCT) directly from the MRI, the electron density can be calculated, and the CT examination can be excluded from the patient flow minimizing the risk of uncertainties in the registration. Basing the radiation treatment process solely on MR images is called MRI-only and is beneficial for the patient as it can provide more accurate radiation treatment than the standardised treatment with fewer CT examinations and possibly a more cost-effective radiation treatment process.  The conventional coils that are normally used in MRI for dose planning purpose cannot be placed directly on the patient as the outer body contour then can be deformed by these relatively heavy coils. The coils are therefore placed on a special holder which creates distance between the coil and the patient, this degrades the signal to noise ratio (SNR). The department for radiation treatment at Linköping University Hospital has access to a newly developed coil with so-called Air Technology. This type of coil is significantly lighter than the conventional ones and the idea is that this coil can be placed directly on the patient without causing deformation.  The aim of this project is to develop a software tool to validate an MRI-only workflow and to investigate if the radiation dose calculation based on sCT data differs from calculations based on CT data. Furthermore, to examine if the AIR coil has any effect on the body contour and the calculated dose.  For the evaluation of the AIR coil three similarity comparison methods were used, Hausdorff distance, Dice similarity coefficient (DSC) and Surface DSC. The result for the Hausdorff distance showed that eight out of eleven comparisons were within 4 mm difference, this corresponded good with Surface DSC where eight out of eleven had a result over 99% at a 3 mm tolerance. DSC measures gave above 98.5% for nine out of eleven of the comparisons.  The investigation on whether the radiation dose calculation differed was done using the dose- volume histogram statistics in Eclipse. A method calculating the gamma index was implemented in MICE. The results showed that nine out of ten gamma indexes had deviations that were within the same range. An explanation for why the results of one patient were not within the same range as the others could not be found and needs further investigations.