Özçelik et al It is challenging to treat and irradiate empty cavities with external-beam radiation therapy (EBRT) because body con- tour irregularities can result in dose heterogeneities. The use of compensator materials to fill the empty cavities can provide a more homogeneous radiation dose distribution. The purposes of this clinical report are to describe the use of 3 different materials (elastomeric material, water-filled balloon, and acrylic resin) in an orbital defect and compare the dosimetric parameters and photon-electron dose distribution during EBRT. (J Prosthet Dent 2012;107:227-231) Effect of different prosthetic materials on radiation dose distribution in an orbital defect: A clinical report Tuncer Burak Özçelik, DDS, PhD, a Cem Onal, MD, b Esma Efe, MSc, c and Burak Yilmaz, DDS, PhD d School of Dentistry and Faculty of Medicine, Baskent University, Adana, Turkey; College of Dentistry, The Ohio State University, Columbus, Ohio a Assistant Professor, Department of Prosthodontics, Baskent University, School of Dentistry. b Associate Professor, Department of Radiation Oncology, Baskent University Faculty of Medicine. c Medical Physicist, Department of Radiation Oncology, Baskent University Faculty of Medicine. d Assistant Professor, Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry. Orbital rhabdomyosarcoma (RMS) is usually seen in the first decade of life with a mean age of diagnosis at 8 years. Males are affected more often than fe- males. A history of trauma may be as- sociated with the clinical presentation of this tumor. 1,2 The treatment of choice for RMS is a combination treatment in- cluding chemotherapy, external-beam radiation therapy (EBRT), and surgery. The therapeutic role of surgery is limit- ed to excisional biopsy only; however, extensive surgery may be performed to remove or debulk the tumor for locally infiltrative large tumors or re- current tumors. The extent of surgical enucleation or exentration should be preplanned according to the clinical and imaging findings. Since the enu- cleated patients are generally at a high risk for recurrence or metastasis, ad- ditional adjunctive EBRT is generally required with a total dose of 40-50 Gy for curative intent. 3 In EBRT, it is technically chal- lenging to treat and irradiate empty cavities because of body contour ir- regularities that can result in dose heterogeneities with low and high dose regions. Use of a compensa- tor material in the empty cavities has been suggested to minimize dose het- erogeneities and to achieve a more homogeneous radiation dose distri- bution. 4,5 Traditionally, a water filled balloon is used to fill an empty cav- ity, especially the enucleated orbital defect, because water is accepted as tissue equivalent for radiation dose distribution. 6 In 3-dimensional (3-D) conformal RT and intensity-modulat- ed RT, immobilization of the patient and maintenance of prosthetic mate- rial shape in each treatment session is important for achieving accurate dose distribution and precise patient treat- ment. For this reason, a customized prosthetic material may provide more reproducible results. Previously, it has been reported that acrylic resin is a simpler and more practical prosthetic material than elastomeric material for filling the air cavities of the external ear. 5 However, the authors identified no published information regarding the dosimetric data of these materials and the water-filled balloon used dur- ing treatment of an enucleated orbital defect. Thus, the purpose of this clini- cal report was to describe the use of an elastomeric material, a water-filled balloon, and acrylic resin to fill the orbital defect. The compared param- eters were ease of use and radiation dose distribution. The dose distribu- tions of both photons (x-ray), which are used for treating deep-seated tu- mors, and electrons, which are used for treating superficial tumors, were also compared with the collaboration of oncologists and prosthodontists. CLINICAL REPORT A 3-year-old girl presented to the Department of Radiation Oncology, Baskent University Faculty of Medi- cine with a large retroorbital mass protruding from the orbit. In preop- erative magnetic resonance imaging studies (MRI), a mass in the left retro- orbital region extending through the left temporal fossa was observed. No distant metastasis was noted. The tis- sue diagnosis was orbital RMS. After tissue diagnosis, 3 cycles of chemo- therapy consisting of vincristine, ac- tinomycine, and cyclophosphamide were administered to shrink the tu- mor. A subsequent brain MRI revealed