Proton therapy of uveal melanomas: intercomparison of MRI-based and conventional treatment planning.
OBJECTIVE
Proton therapy for uveal melanoma provides high-conformal dose application to the target volume and, thus, an optimal saving of the organs at risk nearby. Treatment planning is done with the model-based treatment-planning system EYEPLAN. Tumor reconstruction is based only on a fundus composite, which often leads to an overestimation of the clinical target volume (CTV). The purpose was to exploit MRI on trial in a proton therapy-planning system by using the novel image-based treatment-planning system OCTOPUS.


METHODS
Ten patients with uveal melanomas received both a high-resolution planning CT and MRI of the eye. MR examinations were made with an eye coil. EYEPLAN requires eye geometry data for modeling, and tantalum marker clips for submillimeter positioning and additional information from ultrasound and 3-D imaging. By contrast, OCTOPUS provides the full integration of 3-D imaging (e. g., CT, MRI). CTVs were delineated in each slice. For all patients, CTVs (EYEPLAN vs. OCTOPUS) were compared intraindividually.


RESULTS
OCTOPUS planning led to a mean reduction of the target volume by a factor of 1.7 (T1-weighted [T1w]) and 2.2 (T2w) without compromising safety. The corresponding field size could be scaled down on average by a factor of 1.2 (T1w) and 1.4 (T2w), respectively.


CONCLUSIONS
Compared with the conventional EYEPLAN, MRI-based treatment planning of ocular tumors with OCTOPUS could be a powerful tool for reducing the CTV and, consequently, the treatment volume and the field size. This might be translated into a better patient compliance during treatment and a decreased late toxicity.
Marnitz
Simone
S
Department of Radiooncology, Charité University Medicine, Berlin, Germany. simone.marnitz@charite.de
Cordini
Dino
D
Bendl
Rolf
R
Lemke
Arne-Jörn
AJ
Heufelder
Jens
J
Simiantonakis
Ioannis
I
Kluge
Heinz
H
Bechrakis
Nikolaos E
NE
Foerster
Michael H
MH
Hinkelbein
Wolfgang
W
D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008545:Melanoma / Q000532:radiotherapy*; D008875:Middle Aged; D061766:Proton Therapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D014604:Uveal Neoplasms / Q000532:radiotherapy*; D011522:Protons
D011522:Protons