Date: Tue, 13 Jan 2015 07:04:21 -0800
From: Joseph Holmes <joseph.o.holmes@GMAIL.COM>
Subject: Varian Portal Dosimetry - Update
Thank you everyone for your responses. Here is a list of troubleshooting tips I received from the list and Varian support:
1. Calibrate at extended SID distance other than 100 cm up to 150 cm
2. Verify absolute dosimetry by creating a square 10x10 field in field plan but don't let MLC go into open square field
3. Try calibrating with SID of 105 from the Varian data diagonal profile
4. Verify acquisition technique is correct in AM Maintenance such as no sync beam pulse and resolution is correct for your license
5. Use commissioning files Varian provides CTB 87 (I think)and pay close attention to the dynamic chair it will tell you about DLG and leaf transmission
6. Tweak DLG and MLC transmission (should only be fine tuning)
7. Try calibrating without a diagonal profile since SRS uses small field sizes
8. Adjust Gamma criteria to 3% and 3 mm
9. Make sure you auto align your acquired images to remove detector offset from isocenter
10. Go into Beam Configuration and adjust output parameter from 100 MU to another value to slightly tweak a overall absolute offset
In my case I tried all of the above and eventually determined that my DLG and MLC could be increased slightly and my Gamma was increased from 2%/2mm to 3%/3mm as well as auto alignment of images. I can get all my plans to pass with 5%/5mm since some arcs slightly miss 3%/3mm passing criteria. Most of the failure is in high dose region. Hope this will help someone.
Joe
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