COMPARATIVE STUDY OF IMRT DELIVERY TECHNIQUE STEP-AND-SHOOT WITH DYNAMIC MLC BASED ON DOSE DISTRIBUTION ANALYSIS

• Main Author: Lynn Johanes, Audrey
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/83858
• Institution: Institut Teknologi Bandung

The multileaf collimator (MLC) is used in the delivery of radiation beams through intensity-modulated radiation therapy (IMRT) so that radiation beams can form irregular fields and be shaped similarly to the planning target volume (PTV). Generally, MLC in IMRT can be operated using two irradiation techniques, stepand-shoot and dynamic MLC. This study aims to analyze the effect of different irradiation techniques on different PTV sizes. The analysis was conducted based on the study of total irradiation time, monitor units per fraction (MU/Fx), the percentage of PTV volume receiving dose at a certain value, and the result of dose distribution. The study was conducted by simulation using Monaco software, with PTV as test objects placed in a computational water phantom with sizes of 10 x 10, 10 x 5, 5 x 10, and 5 x 5 cm2 . Each PTV was given a prescribed absorbed dose of 5000 cGy emitted through 3 photon beam sources. Then, dosimetry criterion were set for the PTVs within the range of 95 - 107% of the prescribed absorbed dose. The value of monitor units obtained from the movement of MLC leaves when forming segments will be analyzed based on RT Plan data. While the gamma index value with 5%/5mm gamma criterion is used to analyze the dose distribution comparison obtained from RT Dose data. The results showed that the irradiation time for the step-and-shoot technique was 21.11 - 53.64% longer with MU/Fx required 0.1 - 36.61% less than dynamic MLC. The percentage of PTV values that received a dose of more than 107% of the prescribed or near-max dose ranged from 0 - 0.33%. The larger the volume of PTV receiving dose at near-max dose dosimetry criterion, the smaller homogeneity of the resulting dose distribution. The gamma passing rate (GPR) obtained was ranged from 95.04 - 100%, with the dynamic MLC technique dose distribution data as the reference. The high GPR value indicates that the different irradiation techniques do not produce significant differences in dose distribution. Based on the percentage of PTV volume receiving radiation dose at near-max dose dosimetry criterion, the dose distribution quality of the dynamic MLC irradiation technique is better than step-and-shoot.