STUDY OF CERR TREATMENT PLANNING SYSTEM BASED ON 2D DOSE DISTRIBUTION ANALYSIS IN WATER PHANTOM

• Main Author: Hardiyanti, Yati
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/52041
• Institution: Institut Teknologi Bandung

A radiotherapy is a form of radiation therapy application. The tumor as the target volume is irradiated with a high enough radiation level, while the healthy tissue around the tumor is irradiated with the minimum possible radiation level. Therefore, harmony between the accuracy and the efficiency of the dose calculation speed is required in therapeutic techniques. A therapeutic technique known as Intensity Modulated Radiation Therapy (IMRT) can allow 3D dose distribution to patients. The dosage calculation algorithm using the IMRT technique is implemented in the Computational Environment for Radiotherapy Research (CERR). The dosage calculation algorithm used by CERR is the Quadrant Infinite Beam (QIB) algorithm. This study aims to examine the performance of the QIB algorithm on CERR, both in terms of its treatment planning system and the distribution of doses generated by CERR on the photon beam for various sizes of target volumes and depths being modeled. In this study, the validation process of the calculation results of the QIB algorithm at CERR was carried out by comparing the results obtained from the calculations with experimental data from the hospital. This research consists of three stages. The first step is to determine the homogeneity of the water phantom CT image data type IBA Dose 1. The objective is to examine the CT number / Hounsfield Unit (HU) distribution on the water phantom to obtain the accuracy of the dose calculation. Determining the water phantom's homogeneity is reviewed into several steps, namely taking the DICOM image data for the IBA Dose 1 water phantom and processing the DICOM image data from the water phantom. Processing of DICOM image data from water phantoms consists of determining the number of slices used, determining the water phantom area's geometry for each slice, and determining the homogeneity of the water phantom to be used. In this study, a method of determining the cross-sectional area of water phantom's geometry has been developed. The determination of the water phantom cross-sectional area's geometry as a result of the calculation is the area under the normal distribution curve for each slice, which has been corrected for the symmetrical shape of the gaussian curve. Meanwhile, determining the homogeneity of the water phantom consists of calculating the average, standard deviation of the CT number distribution, and the difference between the calculation results and the water phantom cross-sectional area measurement. The measured water phantom cross-sectional area is 2.67% different from the calculated cross-sectional area. The second stage is to analyze the calculation of the distribution of doses on the water phantom with CERR. Determination of input parameters and analysis of dose distribution for RTPS CERR has been carried out to assess the exposure field size's sensitivity from variations in the size of the target volume, depth, and position. The target volume of deformation analysis is used to determine the width of the exposure field. In this way, the quality control of the illumination beam can be obtained. Variations in the size of the target volume were modeled in dimensions of 10×10×10 cm3, 10×12 ×10 cm3, 10.2×10×10.2 cm3, and 15 × 15 × 15 cm3. Beam parameters use one beam of irradiation, namely on the central axis 0 °, energy 6 MV, Source Skin Distance (SSD) 100 cm, beamlet_delta x, and y are set to 0.1 cm. Dose distribution in the form of the XZ isodose curve and dose profile was used to see the exposure field. In this study, the isodose curve was successfully displayed in the form of an XZ isodose curve. The exposure field size's sensitivity has been successfully assessed from variations in the size of the target volume, depth, and position. The analysis of the change of the target X direction is used in determining the width of the exposure field, while the Y direction is used in determining the length of the exposure field. Analysis related to the sensitivity study of the exposure field size was obtained from relatively valid calculations. The exposure field's size was obtained from variations in the target volume shape and evaluated with variations in depth of 1.5 cm, 5 cm, 10 cm, and variations in the position of 10 cm, 12 cm, 14 cm, 18 cm, and 20 cm. The third stage is to examine the performance of the QIB algorithm. The results of the CERR dose calculation using the QIB algorithm are validated with the experimental results using the PBC algorithm in Eclipse, which are derived from the data commissioning in the hospital. The beam parameters that were set consisted of the gantry angle at the center of the beam 0º, 6 MV energy, 100 cm SSD, delta_x beamlet size, and y, namely 0.1 cm for medium water phantom. The target volume is modeled as a cube with dimensions of 10×10×10 cm3 and 15×15×15 cm3. Dose distribution analysis in the form of PDD curve and dose profile was compared at various depths of 10 cm, 5 cm, and 1.5 cm. The PDD curve calculated by the CERR with the measured curves precisely coincide with each other in the build-up area, which is around a depth of 0.09 cm to 4.99 cm. The deviation is less than 5%, namely 3.01%, 2.51%, and 2.49% at a depth of 10 cm, 5 cm, and 1.5 cm. However, if observed at all points, the deviation from the PDD calculated by the CERR and the measurement results exceeds the maximum allowable limit, which is 5% because the machines used are different. The dose profile curve between the CERR calculation result and the measurement result curve coincides in the FWHM area. The difference in the dose profile deviation is still below 5%.