Development Of Gk Perfexion Fractionated Treatment Technique For The Choroidal Melanoma

Keywords: Perfexion, melanoma, Fractionated radiosurgery, Choroidal metastasis, vision

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     To develop Gamma Knife® (GK) PerfexionTM (PFX) fractionated treatment technique for the Choroidal Melanoma (CM) and compare with our existing linac-based Radionics (LBR) technique.
     A relocatable frame was developed by Elekta with our collaboration to perform PFX fractionated techniques at Princess Margaret hospital (PMH). An eye real-time monitoring device has also been developed at PMH to ensure eye position fixation during scanning and treatment. PFX treatment plans (prescribed to 50%) were compared with our existing LBR plans of 70 Gy in 5 fractions for five previously treated CM cases of small, medium and large size tumors. All doses were normalized such that 99% of the tumors received at least a dose of 70 Gy. Dosimetric comparison was for tumor dose coverage and sparing of organs at risk, such as the eye, lens, anterior chamber and retina of treated eye.
     Averaged normalized tumors mean and maximum doses for LBR plans were 73.17 Gy (range 71.41 to 75.10) and 74.58 Gy (range 72.02 to 77.83) and for PFX plans 102.08 Gy (range 97.11 to 106.98) and 134.48 Gy (range 126.15 to 146.76), respectively. LBR overall mean and maximum doses to the lens were 5.44 and 11.17 Gy and to anterior chamber 2.93 and 7.05 Gy, whereas the corresponding values for PFX were 8.84 and 15.53 Gy for the lens and 6.52 and 14.09 for anterior chamber. Overall mean doses to non-tumor parts of the eye and retina were 35.15 and 48.78 Gy for LBR and 23.90 and 34.82 Gy for PFX plans. Averaged conformity index for LBR was 0.39 and for PFX 0.54.
     This is a retrospective study.
     In this study we have shown that LB SRT and PFX provide dosimetrically comparable treatments for Choroidal Melanoma.
     LBR delivers more uniform dose to the tumor and less dose to the lens and anterior chamber. PFX plans deliver more conformal dose to the tumor and therefore have a lower integral dose to normal structures, so that overall mean doses to healthy parts of treated eye and retina are around 30% less. This may result in less chance of developing neovascular glaucoma (NVG).


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