Comparison of Spine SRS VMAT plans with Flattening Filter Free 6 MV or 10 MV beams

Abstract

Gy to 20Gy depending on tumor volume and location. All patient's contours were transferred to single isocenter automated multimets element software. Three to four non-coplanar arcs were used for each lesion in MIDCA plans whereas 5 non-coplanar arcs were used for each patient to treat all lesions in SIDCA plans. For dosimetric plan quality evaluation, conformity index (CI), volume of 12 Gy (V12) and volume of 5Gy (V5) were collected for all the plans and compared. Results: Average CI for SIDCA was 1.45 (SD 0.8) versus 1.63 (SD 0.2) for MIDCA. Average V12 for SIDCA 24.3cc (SD 23.3cc) versus 29.8 cc (SD 29.1cc) for MIDCA technique. As number of targets increases V5 and V12 dramatically increased for SIDCA technique, for 10 lesions plans V12 values were 65.7cc and 50.5cc for SIDCA and MIDCA respectively. Similarly, V5 values were 373cc and 272cc for SIDCA and MIDCA respectively. As expected Monitor units were significantly lower for SIDCA as compared to MIDCA hence shorter treatment delivery time. Conclusion: Single isocenter plans done using automated multiments element software were better in conformity index however they were inferior in lower dose volumes such as 12 and 5 Gy. This difference was observed larger when number of brain lesions increased. Single isocenter technique is very convenient and time saving for treating multiple brain mets SRS, however, it could compromise lower dose conformity and potentially could deliver higher volumes of lower doses to normal brain tissue.

Interinstitutional Plan Quality Assessment of 2 Linac-Based, Single-Isocenter, Multiple Metastasis Radiosurgery Techniques

“…These were unavoidable consequences of the commissioned beam availability at each respective institution. Comparisons of 6 MV and 10 MV VMAT plans have been made for spine 29 and lung 30 but not for multiple brain metastases. We suspect that there are very little differences between the beam types for high and moderate isodoses, but differences in the shapes of the lateral edge of the penumbras between the 6 MV and 10 MV FFF beams might cause small differences in the low isodose volumes or the mean dose to the brain, particularly for the treatment of small targets on field edge being or near the penumbra.…”