Optimizing radiosurgery with photons for ocular melanoma

Abstract

Background and purpose: Photon radiotherapy has been established for the treatment of ocular melanoma (OM). Here we investigate the planning qualities of two different planning approaches, a combination of dynamic conformal arcs (DCA) complemented with multiple non-coplanar static intensity-modulated (IMRT) fields (DCA-IMRT), and volumetric modulated arc therapy (VMAT) in combination with automated planning (AP).

Materials and methods: Thirteen consecutive patients treated for ocular melanoma with curative intent on a Linac-based radiosurgery system were analyzed. Fractionated stereotactic radiosurgery (fSRS) was applied using 50 Gy in 5 fractions using the combination of DCA-IMRT. Plans were reviewed and the thirteen cases were compared to plans obtained with optimized automated VMAT based on a set of 28 distinct patients treated with DCA-IMRT who were selected to generate the AP model for the prediction of dose volume constraints.

Results: Overall, plan quality of DCA-IMRT was superior to AP with VMAT. PTV coverage did not exceed 107% in any case treated with DCA-IMRT, compared to seven patients with VMAT. The median PTV covered by >95% was 98.3% (91.9%-99.7%) with DCA-IMRT, compared to 95.1% (91.5%-97.9%) (p < 0.01) with VMAT. The median mean dose delivered to the treated eye was 22.4 Gy (12.3 Gy-33.3 Gy) with DCA-IMRT compared to 27.2 Gy (15.5 Gy-33.7 Gy) (p < 0.01). Dose to the ipsilateral lacrimal gland and the ipsilateral optic nerve were comparable for DCA-IMRT and VMAT, however, the dose to the lens was lower with DCA-IMRT compared to VMAT.

Conclusions: The combination of multiple arcs complemented with multiple IMRT fields sets the gold standard for fSRS of ocular melanoma for photon therapy.

Keywords: Automated planning; Choroidal melanoma; HybridArc; IMRT; Melanoma; Ocular melanoma; Radiosurgery; SBRT; Stereotactic; Uveal melanoma; VMAT.

Fig. 1

Isodoses of DCA-IMRT (a,b,c) and VMAT (d,e,f) of a representative case. Axial (a and d), coronal (b and e), and sagittal planes (c and f). Scale as in Fig. 1a applies to all images, showing dose ranging from 20 to 52 Gy.

Fig. 2

Average dose volume histograms of 13 plans calculated with DCA-IMRT (dotted line) or VMAT (solid line). (a) PTV, (b) Eye without PTV, (c) ipsilateral cornea, (d) ipsilateral lens, (e) ipsilateral lacrimal gland, and (f) ipsilateral optic nerve.

Fig. 3

Analysis of robustness for DCA-IMRT and VMAT. Shift in 6 directions was analyzed. Significant differences were noticed in lateral, caudal, and dorsal direction (p < 0.05).