VMAT SX1+SX2 compare

Comparison of various optimization settings with 5mm effective MLC(SX2)+kV imaging (Extended+MR3,On+MR3,Off+MR3,Off+MR4) and best case setting for 10mm MLC(SX1)+MV imaging @10MU CBCT (Extended+MR3)

Also available in xml template format in ZIP dowload below

The 2018 GYN ProKnow World Championship was a first of it’s kind four hour timed worldwide treatment planning competition.  A Halcyon nine field IMRT plan was submitted utilizing 5mm effective MLC mode (SX2) and utilizing kV CBCT imaging, features made available with the release of Halcyon 2.0+ and Eclipse 15.6+.  The submitted plan scored 135.37.

Retrospectively, using the same “frozen in time” optimization objectives created for the originally submitted nine field IMRT plan, multiple VMAT plan variations were made.  Specifically, the difference between the optimization calculation options available in Eclipse v15.5+ which increase optimization time but have the potential to unlock additional plan quality potential.  Additionally, looking at the plan quality difference between the MLC in 5mm effective (SX2) mode versus the native 10mm mode (SX1), and seeing what effect, if any, could be seen in plan quality by not performing a 10MU MV CBCT on the patient each fraction and instead utilizing the kV imager for kV CBCT which does not contribute imaging dose accounted for by Eclipse in the treatment plan.

The default optimization settings are convergence mode: off and intermediate dose optimization level return: MR4.  Allowing the optimizer to return to an earlier state (MR3) after completing the intermediate dose calculation allows for larger changes to be made to the plan, and by going back a step further there is a small impact (increase) to optimization time.  A more noticeable, but still relatively modest increase in optimization time can be found by increasing the convergence mode to “On” or a very noticeable increase in optimization time is experienced when utilizing “Extended”.  By allowing the optimizer more time to search the solution space better solutions can often be found.

The below chart shows the raw score differences in these optimization/MLC/imaging plan variations for both IMRT and VMAT variations.  See the IMRTv1+v2compare toggle at the top of this page for more information on the IMRT results.

Note: all of these scores could be made higher had the objectives been changed to values that were customized to maximize plan quality for those optimization settings.  The goal of this experiment was to quantify optimization differences while keeping objectives constant.  The ultimate highest scoring VMAT plan in this study (144.01) was made by Eclipse v13.7 user Jonathan Stenbeck manually pausing and interactively loading the optimizer.  A video walkthrough of his method can be found at www.proknowsystems.com after logging in and clicking the "learn" tab on this plan study.

 

	Extended or flat IMRT Score / total MU	On Score / total MU	Off or auto IMRT Score / total MU
SX2(kV) VMAT MR3 return	139.46 / 1020.7	133.96 / 936.1	122.31 / 857.7
SX2(kV) VMAT MR4 return	139.39 / 908.2	131.94 / 906.3	112.63* (111.96) / 833.8
SX2(kV) IMRT w/ID	135.37 / 2711.9		129.42**(105.4) / 2306.1
SX1(kV) VMAT MR3 return	133.63 / 969.5	126.13 / 928.5	112.7^*(111.01^) / 831.5
SX1(kV) VMAT MR4 return	131 / 913.6	123.09 / 913.1	115.91*(113.65) / 856.6
SX1(kV) IMRT w/ID	128.8 / 2202.5		125.6** (107.75) / 1996.8
SX1(MV CBCT10MU) VMAT MR3 return	132.39 / 950.4	125.43 / 911.6	114.36*(113.58) / 876.5
SX1(MV CBCT10MU) VMAT MR4 return	129.24 / 894.8	123.27 / 897.2	112.66*(110.17) / 839.4
SX1(MV CBCT10MU) IMRT w/ID	128.9**(105.56) / 2094.5		124.71**(107.59) / 1952.9
^ Max hotspot in PTV not CTV (-1.5 points)
*99percent normalization
**98percent normalization

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3rd party software plan report PDF

Dosimetric ScoreCard JSON

DICOM patient export          ZIP

_{Any reference to a "plan study" are simply what the organizers call each case and may not be a "study" in the FDA sense as they may not have been published in a peer reviewed journal.
Varian does not provide medical advice and these are illustrative examples only.
Leading plans by expert planner. Your results may vary.}