(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: Design a method for tracking dose delivered to extra ocular structures, such as puncta, canaliculi, lacrimal and accessory glands, in the course of proton beam therapy. Based on 23 cases, this study presents results on possible range of doses delivered to lower puncta in proton treatment of uveal melanoma.
Methods: Limitation of the treatment planning system (EyePlanᵀᴹ TPS) used for ocular treatments at our institution are such that it is impossible to reconstruct 3D dose and DVH for a non-standard structure, such as any part of lacrimal system. Normally, target localization is done using orthogonal images of tantalum clips attached to patient’s sclera at known positions by an ophthalmologist prior to radiation treatment. For 23 patients, we also marked lower punctum by placing a radio-opaque 2mm diameter ‘ball-bearing’. The treatment plans were calculated and treated as normal. Retrospectively, EyePlanᵀᴹ TPS model was shifted so that the most anterior clip coincided with punctal marker position as extracted from radiographs. A new pseudo-tumor structure (cylinder 2mm height, 2mm base diameter) was created at the punctum location. With the skin surface shifted accordingly, this punctal structure DVH was calculated based on the range, modulation and aperture the original plan.
Results: Among the 23 cases studied, 8 (35%) had a non-zero punctal dose. Maximum dose delivered to the punctum ranged 4%-100% of prescription dose, median and average being 23.5% and 44% of prescription dose, correspondingly.
Conclusion: As lower punctum is a part of lacrimal system carrying up to 80% of the tear drainage function, it is important to have a systematic study of the dose delivered in the course of ocular treatment and the method of tracking such dose. As far as authors are aware, this study is the first to present both the dose and the method.
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