Optical-Ct Gel-Dosimetry - Article Example

? OPTICAL COMPUTERIZED TOMOGRAPHY (CT) SCANNERS (IMRT) Intensity Modulated Radiation Therapy has in the resent past been subjected to highly intricate procedures which have threatened to render the traditional systems of delivery obsolete. These traditional systems of delivery were restricted to single point delivery and 2-Dimensional plane deliveries which are not adequate for the highly complex contemporary requirements of delivery. In an effort to curb this menace, work has been done on a new system which has highly promising results. This new system incorporates the use of both Optical Computer Tomography (CT) Scanning and Gel- Dosimetry which as shall be shown do deliver dose maps with high degrees of resolution, precision and accuracy. 2. Introduction One of the key elements in the world is the aspect of radiation treatment. This has come in handy in the fight against some of the world’s deadliest ailments which the scientific world has always grappled with to fix. A major part of radiation treatment is radiation dosimetry which has had an increased need for a system that has a high degree of accuracy, precision and efficiency in the measuring of dose and in full 3D and high resolution (INTERNATIONAL CONFERENCE ON 3D RADIATION DOSIMETRY, & OLDHAM, M 2010). A lot of work has gone into the traditional systems like the Fricke dosimetry and this has had a tremendous result which is manifested by the effectiveness of Gel-dosimetry. A further development has seen the incorporation of Optical Computer Tomography (CT) Scanning into the system of Gel-dosimetry and this complementary system has been observed to have a high degree of accuracy, precision and efficiency. The main objective of this paper is to manifest the authenticity of this statement. In an effort to prove the effectiveness of the newly developed system, an experimental setup was put in place which has delivered results that have received thumbs up from the scientific world. The setup makes use of some 2-dimensional images from defined planes in a gel-dosimeter that is well constructed from a perfect design. Moreover, the performance of Optical Computer Tomography (CT) Scanning is compared with that of a MR scanning with focus being on accuracy and sensitivity of imaging, calibration, resolution and noise in the images of dosimetry. Work has been done to eliminate the sources of geometric distortion and optical artifacts in optical Computer Tomography Scanning. The new design has mechanisms to compensate for refraction, reflection, signal drift, water-bath imperfections amongst other factors that cause incorrect reconstructions of coefficients of absolute attenuation. It is also the objective of this paper to show that indeed for phantoms which are used in the validation of optical CT scanners used together with the polymerizing gel dosimeters that are radiation induced, stable gel materials are needed. Phantoms on which light dyes are added are the basis of the simulation used as gel dosimeters. More accurate simulations are done with the use of phantoms with light scattering suspensions of colloidal mixed with the gal. 3. Body An experimental setup to prove the effectiveness of the newly developed system involved filling up three identical flasks with 300cc MGS Research BANG3™ gel. The flasks had their heads stopped with a threaded screw allowing vertical mounting of the flask into the desired optical scanner as well as head phantom. One of the flasks was used in the study of a complex radio surgical delivery as a dosimeter while the other two were used to examine calibration issues of gel. The two gel-flasks of calibration were put in a birth of water upright and 6MV beams of radiosurgery used to irradiate them shooting through their flat bases vertically upward. The beams gave doses of 1.5, 0.75, and 0.25 Gy into the first flask and in the second one 1.25, 1.0 and 0.5 Gy. Before the end of 48 hours, these flasks were scanned using both imaging modalities. Data on calibration was gotten by taking the dose delivered at the maximum depth of every beam and the mean pixel reading. The mean pixel value’s standard deviation was determined as an indication of the precision of the imaging modality of the dosimeter. A separate gal flask that was not radiated was used to determine the pixel values of the gel in a non-radiated state. The other remaining flask filled with gel was irradiated using a head phantom that is water filled and designed specifically for radiosurgery technique verification. The assembly of the Interior gel flask and head phantom was put through the procedure of radiosurgery in a fashion that mimics a real patient treatment. Phantom assembly verification of CT scan mounted both upside down and upright showed insignificant movement of flask position inside the phantom in the limits of detection. The assembly of the phantom flask was then given a 3 isocentre treatment which made use of 6MV radiation coming from some Varian Clinac 2100c. The set up was taken through a well-choreographed system of gel scanning using MR and Optical CT modalities. As an experiment that is geared towards establishing the effectiveness of the newly developed system, this was crucial as it gives firsthand information on just how much effective the system really is. Using C++ codes and a Matlab script, the process was made much easier and more convenient. It was also more accurate and error free. The results obtained from the experiment were quite alarming and satisfying. They showed a tremendous difference between the traditional systems and the newly developed system. Images obtained from the optical CT scanner and the MR scanner were put side to side and an in-depth comparison carried out. It was observed that there was a great reduction in the degree of noise in the image from the optical CT scanner as compared with the image from the MR scanner. A comparison of the line profiles from the two images made this very apparent. It was observed that the noise signal in the higher peak of dose was estimated as being about 6.6% in the image from the MR scanner as compared to a much lower estimation that was made from the image obtained from the optical CT scanner that stood at a meager 1.3%. In the more recent similar works, the percentage error of the MR scanner image has been reduced quite significantly as caution has been taken to eliminate some of the discrepancies that had not been taken into account initially. One of these discrepancies is the issue of voxel size. The voxel size used in an experiment is directly proportional to the degree of noise level that shall be obtained in the long run from the image obtained through the MR scanner. In a bid to eliminate this discrepancy, the aspect of voxel size has been put into account and true to the expectations, the resent images obtained through the MR scanner have had relatively lower noise levels than the initially estimated value of 6.5%. Other discrepancies that led to the contemporary low values of the noise levels obtained from the image from the MR scanner is the issue of smoothing algorithm. It is essential to apply smoothing algorithm so as to obtain much smoother images. In a bid to cut down on the discrepancies discovered in the current experiment, subsequent experiments have put into consideration the element of applying smoothing algorithm and this as well has seen a reduction in the estimated degree of the level of noise in the image from the MR scanner from the current 6.6% (INTERNATIONAL CONFERENCE ON RADIOTHERAPY GEL DOSIMETRY 2006). The level of uncertainty in the gel dosimeter is also different when measured using the MR scanner and when using the optical CT scanner measured. The level of uncertainty is only 1.1% when the measurement is done using the newly developed optical CT scanning method. On the contrary, when the measurement is done using the MR scanner, the level is found to be 4.5 %. This is a very huge difference which is not only quantifiable but also literally visible. It explains with no doubt the supremacy of the optical SC scanner over the MR scanner. This figures have however been observed to be slightly different in subsequent experiments as in the present one the earlier discussed discrepancies were not taken into account (ABDELSALAM& BIRKIN 2002). These are the issues of the size of the voxel and the application of smoothing algorithm. Nevertheless, one principle common factor is the fact that in all experiments carried out, the optical CT scanner has maintained its superiority over the MR scanner. One of the sources of geometric distortion and optical artifacts in optical Computer Tomography Scanning has been established to be the aspect of reflection and refraction. These are causes of defects in the mechanism which lead to a reduction in the effectiveness and efficiency of the system as a mode of producing high resolution 3D images with precision, accuracy and efficiency. In the system of scanning, there happens to be produced numerous reflected rays along the path which in essence minimize the clarity of the henceforth produced image. It acts to increase the noise levels as well as the degree of inaccuracy in mapping of the image. In order to compensate for this and to eliminate the discrepancy, these rays are eliminated by angling components judiciously so as to deflect away from the desired ray path these reflected rays. Another ingenious mechanism that has been adopted is the incorporation of a collimator into the system. This does away with the reflected rays quite effectively. Moreover, a black tape is also used especially in water baths and it functions quite effectively in the absorption of the reflected rays. Refraction being another menacing aspect to the accuracy of optical CT scanners is eliminated by taking into account the refraction index of the used liquid film as well as the angle of incidence of the ray that is used. A correct framework of the incident ray and the refraction index produces a perfect mode by which discrepancies on the image produced by the optical CT scanner are eliminated or compensated for. Another source of geometric distortion and optical artifacts in optical Computer Tomography Scanning has been established to be the aspect of scatter (INTERNATIONAL CONFERENCE ON 3D RADIATION DOSIMETRY, & OLDHAM, M 2010). This is also responsible for the production of images which have a high degree of the level of noise as well as having a high level of inaccuracy. It is essential for the sake of producing the best images and for the sake of offering the best medical services to the world that this element of scatter is eliminated effectively or compensated for so that the images produced are the desirable ones. Scatter lights find their way into the desired ray path and they function to distort the image so produced. An experiment carried out that varied the amount of scatter light that got in the way of the path of the desired ray proved that the rays which had more of the scatter light rays produced images with higher noise levels and much more inaccuracy as compared to the rays which had relatively less scatter light rays in them. In an effort to do away with the scatter light effect, circular collimator Variable aperture has been developed which eliminates effectively the aspect of scatter light finding its way into the path of the desired light rays. In an effort to show that for phantoms which are used in the validation of optical CT scanners used together with the polymerizing gel dosimeters that are radiation induced, stable gel materials are needed, an experiment was carried out. It is known that for absorbing material that is non-scattering, the determined extinction coefficient spectrophotometrically has got to be the same as those that are determined from reconstructed images of 3D scanner. For beams that are scattering this is found not to be the case necessarily since the emerging beam is not collimated. This forms the basis of the experiment which proves with no doubt that indeed for phantoms which are used in the validation of optical CT scanners used together with the polymerizing gel dosimeters that are radiation induced, stable gel materials are needed (LEPAGE et al 2001). Conclusion It has become very essential in the modern world to establish a mechanism that has a high degree of accuracy, precision and efficiency in the measuring of dose and in full 3D and high resolution. This is the key in the fight against some of the world’s most deadly ailments which are treated by use of radiotherapy. Radiation dosimetry has been in need of a more accurate and precise mode of measuring dose and a lot of work has been put in place over the years. This work is slowly paying off as in deed promising results have been observed from the incorporation of Optical Computer Tomography (CT) Scanning into the system of Gel-dosimetry and this complementary system has been observed to have a high degree of accuracy, precision and efficiency. In an experiment where the performance of Optical Computer Tomography (CT) Scanning is compared with that of a MR scanning with focus being on accuracy and sensitivity of imaging, calibration, resolution and noise in the images of dosimetry, it has been shown with no doubt that indeed the newly developed optical CT scanning mechanism is a breakthrough in the scientific world (INTERNATIONAL CONFERENCE ON RADIOTHERAPY GEL DOSIMETRY 2006). Work has been done to eliminate the sources of geometric distortion and optical artifacts in optical Computer Tomography Scanning and the new design has mechanisms to compensate for refraction, reflection, signal drift, water-bath imperfections amongst other factors that cause incorrect reconstructions of coefficients of absolute attenuation. It has also been proven conclusively that for phantoms which are used in the validation of optical CT scanners used together with the polymerizing gel dosimeters that are radiation induced, stable gel materials are needed 4. Acknowledgements I would like to express my heartfelt gratitude to all the men and women whose efforts were employed in one way or the other in the piecing together of this work. The most important among them are the university librarian whose influence and efforts saw to it that I obtained all the material I needed. I would also like to thank all my friends and family for the moral support that they offered. Without these people all would not have been well in regard to writing this work. Thank you all. BIBLIOGRAPHY International Conference on radiotherapy gel dosimetry. (2006). Fourth International Conference on Radiotherapy Gel Dosimetry 7-10 August 2006, Sherbrooke, Quebec, Canada. Bristol, IoP. Available at http://www.iop.org/EJ/toc/1742-6596/56/1. International Conference on 3D radiation dosimetry & Oldham, M. (2010). IC3DDose 6th International Conference on 3D Radiation Dosimetry: 22-26 August, 2010, South Carolina, USA. Bristol, IOP. Available at http://iopscience.iop.org/1742-6596/250/1. Lepage, M, Whittaker, A K, Rintoul, L, Back, S, & Baldock, C. (2001). Modelling of post-irradiation events in polymer gel dosimeters. Institute of Physics. Available at http://lup.lub.lu.se/record/1297219. Abdelsalam, M. E., & Birkin, P. R. (2002). A study investigating the sonoelectrochemical degradation of an organic compound employing Fenton's reagent. Physical Chemistry Chemical Physics (Incorporating Faraday Transactions). 4, 5340-5345. Read More