Comparison of treatment planning for Stereotactic Radiosurgery(SRS) and Stereotactic Body Radiation Therapy(SBRT) techniques with 2.5mm and 5mm multileaf collimator(MLC)- a Pilot Study

Summary: The study compares two different types of multi-leaf collimators (MLCs) for treatment planning in Stereotactic Radiosurgery (SRS) and Stereotactic Body Radiotherapy (SBRT) using the Elekta Versa HD machine. The APEX micro-MLC (mMLC) offers excellent dose distribution but has drawbacks like longer treatment duration and technical errors. The aim is to compare treatment plans using a 2.5mm APEX mMLC and a 5mm MLC (Agility) for brain and lung targets. Methods: The study involves 10 patients with brain and lung targets. Two treatment plans are created for each case using the MONACO 5.11.03 treatment planning system, with 2.5mm and 5mm MLCs. A 6FFF x-ray photon beam is utilized with various gantry, couch, and collimator setups. Plans are compared using target coverage, conformity index, homogeneity index, gradient index, and organ at risk doses. Results: No significant differences are observed in target coverage, conformity index, homogeneity index, and organ at risk doses between the two MLC designs. The 5mm MLC plan requires more monitor units but provides comparable tumor coverage. For brain targets, organ at risk doses are similar for both MLC widths, while lung targets show slightly lower organ at risk doses with the 2.5mm mMLC. The gradient index is better with the 2.5mm mMLC, indicating steeper dose falloff (p=0.158). Conclusion: The study concludes that both 2.5mm and 5mm MLCs yield similar results in terms of target coverage, conformity index, homogeneity index, and organ at risk doses in VMAT plans for SRS/SBRT. The 2.5mm mMLC offers an advantage in gradient index, resulting in sharper dose gradients and reduced lower isodose volumes. However, the 5mm MLC can still be used effectively with further reduction in gradient index. The study suggests the need for more extensive research with larger sample sizes and diverse parameters for comparison.