Document Type : Original Paper
Prof. of Medical physics ; National Cancer Institute, cairo university & Children Cancer Hospital , Egypt
Cairo University, Cairo, Egypt
Introduction: Geometric changes in the multileaf collimator (MLC) led to dosimetric considerations in intensity-modulated radiation therapy (IMRT) due to the number and size of the pixels in the intensity map, which are determined by the MLC leaf width. In this study, we evaluated the dosimetric effects of different MLC widths on physical dose distributions for IMRT plans.
Materials and Methods: Forty-two IMRT plans based on different MLC devices were generated and analyzed to study the effect of MLC width on plan quality.
Results: Improvements in IMRT plan quality using 0.4 cm leaf width in comparison with 1 cm leaf width were evaluated. The 0.4 cm leaf-based plans resulted in significantly higher Dmean, D98%, D95% , D5%, and V95 (58.86 Gy, 95.11%, 96.57%, 104%, and 97.92%, respectively) compared to the 1 cm leaf plans (58.66 Gy, 92.56%, 94.56%, 104.14%, and 95.72%, respectively). Conformation number (CN) for planning target volume in 0.4 cm leaf plans was significantly higher than the 1 cm leaf plans (0.74 vs. 0.67; P<0.05). In addition, the 0.4 cm leaf plans significantly improved dose homogeneity compared to the 1 cm leaf plans (1.08 vs. 1.10; P<0.05). We found that 0.4 cm leaf width significantly decreased the integral dose to normal tissue compared to the 1 cm leaf width (from 56.09 to 49.46 Gy.Kg P<0.05). Conclusion: No significant clinical differences were observed between the two plans for a serially functioning tissue, while the differences in mean doses were statistically significant for parallel functioning normal tissues.