Room: AAPM ePoster Library
To investigate the feasibility and potential dosimetric advantages of using SPArc for ocular melanoma in comparison with gantry-based Intensity Modulated Proton Therapy (IMPT) and dedicated eyeline treatment.
A dataset of six ocular melanoma cases treated with proton eyeline was planned using 3-field IMPT and SPArc plan for dosimetric comparison. The cases included small and large anterior, posterior and optic disc tumors. Single-arc SPArc and three-field IMPT plans were generated using 3.5% range uncertainties. All 3 planning groups were normalized to 50 CGE to the target. Dose to the cornea, lacrimal gland, retina, optic nerve, and lens was analyzed.
SPArc consistently had a superior dose distribution over the 3-field IMPT in all the cases. Eyeline has a sharper lateral penumbra which offered a superior dosimetric advantage in sparing the cornea mean dose for anterior and optic disc tumors in comparison with SPArc[Table 1]. In addition, by taking advantage of the gazing angle, eyeline technique could effectively avoid the lens if possible, which were mostly seen in the anterior and optic disc tumor region. For the large tumor located in the posterior region where the lens and cornea were unavoidable in the beam path, SPArc shows its dosimetric advantage to spare the cornea and lens. More importantly, the study found that SPArc has the potential capability of further reducing the dose to the nerves which normally is unavoidable at the distal end of the beam path using eyeline.
Eyeline is still the best option for ocular melanoma in most of the scenarios. SPArc, as a new proton therapy technique, showed dosimetric advantage and flexibility in the treatment of ocular melanomas located in the posterior region compared to the eyeline. Such flexibility may reduce the possibility of complications associated with the high dose or LET to the optic nerve.
Funding Support, Disclosures, and Conflict of Interest: Research fund from Ion Beam Application. Xuanfeng Ding, Xiaoqiang Li, Di Yan has a patent related to partical arc therapy