Room: AAPM ePoster Library
Purpose: fractionated radiation therapy (SFRT) has very promising results for the treatment of bulky and/or radio resistant tumors. The two ways to implement treatment is through a solid grid block, or multi-leaf collimators (MLCs). MLC based delivery makes it easier to customize treatment plans and is more cost effective than the solid grid applicator. This investigation utilized a novel delivery method using 12 static MLC patterns delivered by rotating through various collimator angles. The dosimetry and overall feasibility of this MLC technique is compared to that of the solid brass grid block applicator.
Methods: treatment plan using MLCs was conducted using 12 different sub fields. The collimator rotated from 0-165° in 15° increments to deliver each sub field of 6 MV beam energy. The delivered MLC plan was compared to the original MLC plan from the treatment planning system (TPS) using gamma analysis. In addition, dosimetry measurements from the MLCs were analyzed and compared to those from a brass grid block.
Results: gamma analysis of the MLC plan determined the passing rate was 99% at 2%/3mm within the tolerance levels of 4%/4mm. Peak to valley ratios obtained from the MLC plan across the central axis were 7.09 along the vertical, 6.586 along the horizontal, and 5.65 and 5.72 across each diagonal. The peak to valley ratio along the horizontal axis of the solid grid block was 2.34. The total treatment time for the rotating MLC method was 12 minutes, while the brass grid took less than one minute.
Conclusion: investigation shows that a SFRT plan is deliverable by rotating MLCs at various angles. Rotating MLC patterns deliver dosimetrically equivalent profiles to that of the brass grid, are more efficient than other MLC techniques, and provides an alternative to lifting the brass grid block (up to 48 lbs.) into position.