Purpose: To investigate the dosimetric comparison of different collimators which are used in robotic radiosurgery (cyberknife-CK) and linear accelerator (LINAC) for stereotactic radiosurgery (SRS) in arteriovenous malformation (AVM). Materials and Methods: Twenty-five AVM patients were planned in CK using FIXED cone, IRIS collimator, and multi-leaf collimator (MLC) based in LINAC. Dosimetric comparison was performed using Paddick conformity index (CIPaddick) and International Commission on Radiation Units and measurements (ICRU) homogeneity index (HIICRU), gradient score (GS), normal brain dose received by 10cc (D10cc) and critical structure (brain stem, optic chiasma, optic nerves) doses. Paired sample t-test was used for statistical analysis. Results: Mean treatment volume was 3.16cc (standard deviation ± 4.91cc). No significant deviation (P =0.45, 0.237 for FIXED vs. IRIS and FIXED vs. MLC, respectively) was found in target coverage. For CIPaddick, the mean difference (MD) between FIXED- and MLC-based plans was 0.16(P = 0.001); For HIICRU, difference between FIXED and IRIS was insignificant (0.5, P = 0.823); but, when FIXED versus MLC, the deviation was 7.99% (P = 0.002). In FIXED- and MLC-based plans, significant difference was found in GS70 and GS40 (P < 0.041 and 0.005, respectively). MD between FIXED- and MLC-based plans for normal brain for 5Gy, 10Gy, 12Gy, and 20Gy were 36.08cc (P = 0.009), 7.12cc (P = 0.000), 5.84cc (P = 0.000) and 1.56cc (P = 0.000), respectively. AVM volume <0.7cc should be treated with CK FIXED and >0.7cc were treated by using FIXED or IRIS collimators. AVM volume > 1.4cc can be treated by either LINAC MLC-based SRS or CK. Conclusion: Our study shows CK collimator (IRIS and FIXED) could be able to treat brain AVMs in any size. Linac MLC-based SRS has some limitations in terms of conformity and low-dose spillage, and advantages like reduced treatment time and MU.

Purpose: Aim of this study is to evaluate the effect of planning parameters such as pitch & field width on tomotherapy treatment plan quality and treatment time. Methods: We chose three treatment plans from different sites for this study. Combination of three different field widths (1 cm, 2.5 cm & 5 cm) and three different pitch values (0.215, 0.287 & 0.430) are used to generate plans. For a given patient all plans were optimized with same objectives, constrains, number of iterations and modulation factor. Plan quality was compared using clinically significant Dose Volume Histogram (DVH) indices (D98%, D95%, D50%, Dmean, D2, Dmax) and Homogeniety Index (HI). Also treatment times for all plans were compared to evaluate the delivery efficiency Results: DVH indices of target (D98%, D95%, D50%, Dmean, D2) showed increasing trend with the increase in the pitch as well as field width. The difference in DVH indices was less than 1.5%. Similarly critical structure DVH indices (Dmax, Dmean) also had increasing trend with the pitch value field width. The difference in DVH indices is upto 10% for the pitch and upto 50% increase in dose for 5cm collimator. The variation in homogeneity index with reference to 1 cm field width was 1–4% and 2.2 – 5% for 2.5cm and 5cm field widths respectively. For a given field width increase in pitch reduces the treatment time upto 30%. Increase in field width from 1cm to 5 cm reduces the treatment time upto 75%. Conclusion: Effects of planning parameters on tomotherapy plan quality & treatment time were studied. The effect of pitch is found to be less than the field width on the target, critical structures dose as well as treatment time. Optimal selection of planning parameter will improve the treatment delivery efficiency with appropriate dose to target and critical structure.