Feasibility of Treating Ocular Melanoma Using Commercial Proton Gantry Nozzle: Optimizing for Acceptable Solutions with Minimal Tertiary Nozzle Attachment.
Abstract
Purpose
Dedicated Eyeline is considered industry standard for ocular proton therapy (OPT). Due to relatively low incidence of intra-ocular malignancies, Eyeline implementations of OPT are cost-prohibitive for many interested institutions. Among small number of gantry-based implementations for ocular proton therapy (OPT), majority if not all involve highly customized in-house solutions for the required hardware and software. This work was to investigate feasibility of using IBAProteusONETM gantry for OPT with a simple tertiary nozzle attachment (TNA) of varying sizes.
Methods
Using RayStation2023B previously commissioned MonteCarlo algorithm, distal and lateral fall-off (DFO and LFO) were determined in a water phantom inverse-optimized plans for two target sizes (‘large’, 2x2x2.5cm3 and ‘small’, 1.5x1.5x2cm3), using TNAs of 3 lengths (10cm,20cm,30cm), modeled as hollow brass cylinders with BPA layer and 2.5cm thick, 5cm diameter brass block with additional 3 and 5mm margins.
Results
Average DFO and LFO for the three tertiary nozzle attachment lengths were 0.265+/-0.008cm, 0.0.278+/-0.012cm, 0.28+/-0.00cm and 0.278+/-0.021cm, 0.295+/-0.01cm, 0.305+/-0.01cm, respectively. For the most likely clinical scenario of using 3mm block margin, all planning parameters being equal, the LFO data trends slightly up with increasing TNA length, ranging from 0.26cm to 0.3cm, while DFO fluctuates within 0.2mm.
Conclusion
Based on our preliminary experience with inverse optimization for the targets of similar size and depth used in planning ocular melanoma cases, the tertiary nozzle attachment of 10 cm length shows acceptable dosimetric parameters while not requiring major nozzle modifications.