Modulation indices and plan delivery accuracy of volumetric modulated arc therapy

Abstract

Purpose We evaluated the performance of various modulation indices (MI) for volumetric modulated arc therapy (VMAT) to predict plan delivery accuracy. Methods The specific indices evaluated were MI quantifying the mechanical uncertainty (MIt), MI quantifying the mechanical and dose calculation uncertainties (MIc), MI for station parameter optimized radiation therapy (MISPORT), modulation complexity score for VMAT (MCSv), leaf travel modulation complexity score (LTMCS), plan averaged beam area (PA), plan averaged beam irregularity (PI), plan averaged beam modulation (PM), and plan normalized monitor unit (PMU) to predict VMAT delivery accuracy. By utilizing 240 VMAT plans generated with the Trilogy and TrueBeam STx, Spearman's rank correlation coefficients (r) were calculated between the MIs and measures of conventional methods. Results For the Trilogy system, MIc showed the highest r values with gamma passing rates (GPRs) (r = −0.624 with P < 0.001 for MapCHECK2 and r = −0.655 with P < 0.001 for ArcCHECK). For TrueBeam STx, MIc also showed the highest r values with GPRs (r = −0.625 with P < 0.001 for the MapCHECK2 and r = −0.561 with P < 0.001 for the ArcCHECK). The MIt and MIc showed the highest r values to the MLC position errors for the Trilogy and TrueBeam STx systems (r = 0.770 with P < 0.001 and r = 0.712 with P < 0.001, respectively). The PA showed the highest percent of r values (P < 0.05) to differences in the dose‐volume parameters between original VMAT plans and actual deliveries for the Trilogy systems (30.9%). Both the MIt and MIc showed the highest percent of r values (P < 0.05) to differences in the dose‐volume parameters between original VMAT plans and actual deliveries for the TrueBeam STx systems (31.8%). Conclusion To comprehensively review the results, the MIc showed the best performance to predict the VMAT delivery accuracy.

Trajectory log analysis and cone‐beam CT‐based daily dose calculation to investigate the dosimetric accuracy of intensity‐modulated radiotherapy for gynecologic cancer

“…Table 2 shows the DSCs of bladder, rectum and right/left femoral head. Except for the patient 8 bladder, the DSCs exceeded 0.8, which was a sufficient deformation accuracy 18 . Bladder of patient 8 had low DSC in some fractions due to interactional volume variations.…”

Progressive resolution optimizer (PRO) predominates over photon optimizer (PO) in sparing of spinal cord for spine SABR VMAT plans

“…In this regard, our institution acquired the gamma passing rates of portal dosimetry with gamma criteria of 2%/1 mm, and all VMAT PRO and VMAT PO (> 90%) were found to be clinically acceptable. Additionally, our previous study investigated the correlation between gamma passing rates and the modulation degree of VMAT plans [23]. We utilized identical TrueBeam STx with a high-de nition 120 TM MLC and then generated 100 VMAT plans with various tumor sites, including the lung, spine, liver, brain, and head and neck, using the PRO algorithm.…”

Progressive resolution optimizer (PRO) predominates over photon optimizer (PO) in sparing of spinal cord for spine SABR VMAT plans

“…In this regard, our institution acquired the gamma passing rates of portal dosimetry with gamma criteria of 2%/1 mm, and all VMAT PRO and VMAT PO (> 90%) were found to be clinically acceptable. Additionally, our previous study investigated the correlation between gamma passing rates and the modulation degree of VMAT plans [23]. We utilized identical TrueBeam STx with a high-de nition 120™ MLC and then generated 100 VMAT plans with various tumor sites, including the lung, spine, liver, brain, and head and neck, using the PRO algorithm.…”