Name: Maria Holstensson
Institution: Institute of Cancer Research
Research: Optimisation of imaging during radionuclide therapy using simulations
Targeted radionuclide therapy is a cancer treatment in which drugs labelled with high activities of a radioactive element are used. Maria Holstensson’s research at the Institute of Cancer Research focuses on the treatment of children suffering from neuroblastoma cancer who are receiving this form of treatment. In particular they are being treated with the drug metaiodobenzylguanidine (mIBG) labelled with the radionuclide iodine-131.
Iodine-131 emits beta particles that travel only a short distance delivering a radiation treatment dose to the tumour. Iodine-131 also emits gamma rays that can be imaged with a conventional medical gamma camera making it possible to visualize the location of the tumour. These images can also be used to calculate the amount of drug taken up by the tumour and to estimate the radiation dose to the tumour. To gain an accurate estimation of the amount of iodine-131 taken up by a tumour, accurately quantified gamma camera images are required.
Maria's research is important in tackling one of the major problems with quantitative gamma camera imaging - scatter in the images which results in poor image quality. Another problem is photon penetration of the gamma camera collimator, which also degrades image quality. Currently scatter correction is currently applied to the images to try and solve these problems.
Maria is assessing the current correction method using Monte Carlo techniques to see how effective it is. Improving the gamma camera imaging will improve the accuracy of radiation dose calculations leading to more accurate studies of correlations between radiation doses with clinical outcome. The eventual outcome may be more accurate patient treatments with higher cure rates and lower toxicity.
Maria’s group have developed a computer model of the gamma camera used to image the patients using the Monte Carlo program GATE (Geant4 Application for Tomographic Emission). Using this model it is possible to investigate phenomena that cannot be measured directly experimentally, such as details of scattering processes within the patient and the camera as well as details of photons penetrating the collimator. This model has shown good agreement with experimental results.
The GATE program incorporates the Geant4 libraries which were developed for the simulation of the passage of particles through matter. GATE is becoming the standard for Monte Carlo simulations in nuclear medicine as it uses extremely detailed tracking algorithms. Unfortunately these algorithms make the code computationally demanding and so Maria contacted NGS who installed the GATE software on their resources.
Maria used an anatomical model of a patient being treated with the iodine-131 drug (see figure) and this has been measured experimentally using SPECT (Single Photon Emission Tomography) to generate 3D images. This model has been the base for a digitised representation of the patient, simulated in a full using GATE on the NGS.
Visual and quantitative comparisons between experiment and simulation have shown excellent agreement. Information which cannot be obtained from experimental measurements has been extracted from the simulations on the NGS. The results have shown that the current scatter correction method underestimates the scatter component by 7%. It was also found that 8% of the photons detected in the clinical image originate from photons which have penetrated the collimator of the camera. Any photons which have penetrated the collimator need to be eliminated as they degrade image quality as mentioned previously. Maria said “We have had absolutely fantastic help from the NGS and as a result of using the Grid we have been able to run multiple parallel simulations that we would not have been able to run otherwise”.
One of the PI's Dr Glenn Flux said "The availability and support of the NGS enabled us to obtain more accurate and detailed results than would otherwise have been possible. The results from this study are likely to have a significant impact on patient care in the years to come".
PI - Dr. Glenn Flux, Dr. Mike Partridge and Dr. Susan Buckley
Funding body - Institute of Cancer Research
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