Potential and pitfalls of 1.5T MRI imaging for target volume definition in ocular proton therapy

IntroductionOcular proton therapy (OPT) for the treatment of uveal melanoma has a long and remarkably successful history. This is despite that, majority patients treated, definition eye anatomy based on simplified geometrical model embedded in planning system EyePlan. In this study, differences anatomical tumor structures from EyePlan, those 1.5T magnetic resonance imaging (MRI) are assessed.Materials methodsThirty-three treated with OPT at our institution were subject to MRI. The target volumes manually delineated images by two radiation oncologists. resulting geometrically compared clinical standard. addition, dosimetric impact using different models evaluated.ResultsTwo (6%) presented lesions too small be visible Target identified MRI scans average smaller than EyePlan discrepancies arising mostly base. Clip-to-tumor base distances measured exhibited higher discrepancy ophthalmological measurements For 53% cases, plans optimized only, failed achieve sufficient coverage volumes.DiscussionThe analysis shown that might more susceptible misses flat extension volume current Thus, proper integration ancillary modalities, leading better characterization full lesion, required.