Room: AAPM ePoster Library
Purpose: TG135 (update in draft) recommends the patient specific QA for Cyberknife plans using MLC. This is the first comparison study between MapCHECK2 and SRS MapCHECK for Cyberknife IMRT QA, as well as the first clinical implementation of Cyberknife IMRT QA with MapCHECK2 using True Composite delivery method as recommended by TG218.
Methods: Treatment plans were designed using MultiPlan V5.3 with MLC or Cone for Trigeminal Neuralgia, Acoustic Neuroma, Cerebellum Brain Mets and Prostate targets, with various sizes.
SunNuclear SRS MapCHECK in StereoPHAN and MapCHECK2 in MapPHAN were scanned in 1mm slice with Philips CT. StereoPHAN and SRS MapCHECK density were overridden with 1.2g/cc; MapCHECK2 was overridden with density 1.2g/cc and MapPHAN with 1.05g/cc. Eight gold markers were taped to MapPHAN surface for alignment, while SRS MapCHECK has internal fiducials..
Diode arrays were calibrated with 54x54mm2 static MLC AP field. Treatment plan fields were applied to phantom without any angle, SSD or MU change, and phantom dose was calculated in fine grid. Coronal planar dose corresponding diode plane was exported to DICOM file as comparison baseline. SNC patient software was used for gamma analysis.
SRS MapCHECK can achieve 95+% pass rate with 1mm/2% gamma index, however prostate plan cannot be evaluated due to array size limit (77x77mm2); MapCHECK2 can achieve 95+% with 2mm/2% gamma index and 90+% with 1mm/2% gamma index.
Both SRS MapCHECK and MapCHECK2 can be used for Cyberknife IMRT QA. SRS MapCHECK is more suited for small targets due to relative smaller 0.47mm detector size, smaller array size (77x77mm) and finer 2.47mm orthogonal detector spacing, while MapCHECK2 is better for larger field for relative larger array size (260x320mm) and larger 0.8mm detector size, coarser 10mm orthogonal and 7.07mm diagonal detector spacing. The recommended target size criteria is: PTV<4~5cm for SRS MapCHECK and PTV>3~4cm for MapCHECK2.