CASE REPORTStereotactic Radiosurgery with an Upper Partial Denture
1Shusaku Tayama,1 Etsuo Kunieda,2, 3 Yohei Oku,3 Atsushi Takeda2, 4 and Toshiaki Takeda2

Department of Dentistry and Oral Surgery, Tokyo Metropolitan Hiroo General Hospital, Tokyo, Japan2
Department of Radiology, Tokyo Metropolitan Hiroo Hospital, Tokyo, Japan3
Department of Radiation Oncology, School of Medicine, Keio University, Tokyo, Japan
4
Department of Radiology, Ofuna Chuo Hosptital, Kanagawa, Japan(Received for publication on July 18, 2008)(Revised for publication on September 18, 2008)(Accepted for publication on October 9, 2008)

Abstract
A 54-year-old male with partial denture underwent stereotactic radiosurgery with an infrared camera-guided system for a metastatic brain tumor arising from lung cancer. Although
this method utilizes a biteplate mounted on the upper jaw to detect head movement, the patient only had four teeth in his upper jaw. In order to stabilize the biteplate, the maxillarydenture was fixed to the biteplate with an autopolymerizing resin. In addition, the rest-occlusal position of the lower jaw was impressed on the inferior surface of the biteplate withan autopolymerizing resin. To assess reproducibility and stability, the distance between theleft and right incus and left and right markers was measured during pre-planning, as well as
before and after stereotactic irradiation. Wearing the biteplate ensures the accuracy of radiotherapy planning for the implementation of radiosurgery in patients who have manymaxillary teeth missing. However, a large degree of error was observed when the biteplate
was removed. (Keio J Med 58 (2) : 120－123, June 2009)

Keywords: stereotactic radiotherapy, biteplate, partial denture
Introduction
Stereotactic radiosurgery (SRS) for cranial lesions wasoriginally proposed by Lars Leksell1 to deliver high-dose
narrow beams to a target lesion with a gamma knife.
More recently, SRS with a linear accelerator has beendeveloped and many researchers have reported good results with intracranial lesions such as metastatic tumors,2vascular malformations,3 and other malignant or benign
lesions.4, 5 With the gamma knife, the patient’s head issecured with screws in a metallic frame under local anesthesia and treated with a concentrated high dose of
gamma rays delivered in a single session. This type offrame fixation method, which requires local anesthesia,
is also used for SRS with a linear accelerator.6
However, stereotactic frames such as the original Leksell frame are impractical for long periods of applicationand thus are not suitable for fractionated stereotactic radiotherapy using linear accelerators.7 Intracranial stereo-tactic positioning systems (ISPSs) are used to position
patients for fractionated stereotactic radiotherapy or noninvasive radiosurgery.7 Some ISPSs utilize a biteplate forthe purpose of immobilization8 or motion detection of
the head, 9 using the maxillary teeth to support thebiteplate. The reproducibility and stability of thebiteplate depend on the number of teeth, teeth mobility,and residual ridge condition. Therefore, it is necessary toconsider biteplate reproducibility and stability in patients
who have lost a lot of upper teeth. In addition the elasticity of silicon impression affects biteplate stability. Thestability of a denture base with clasps can be adjusted asrequired, and denture base reproducibility can be visually assessed based on the positional relationship between
the denture base and the teeth.
We present a successful case of frameless stereotactic
radiosurgery that made use of a denture base as a support
system in a patient who was missing many of his upper
teeth.

Reprint requests to: Etsuo Kunieda, M.D., Ph.D., Department of Radiology, School of Medicine, Keio University, 35 Shinaomachi, Shinjuku-Ku, Tokyo
160-8582, Japan, Tel: +81-3-3353-1211 ex.62531; Fax: +81 3-3359-7425; E-mail: kunieda-mi@umin.ac.jp120Keio J Med 2009; 58 (2):120－123

121Fig. 1 MRI shows a metastatic tumor in the right cerebellar hemisphere that originated from lung adenocarcinoma. Transaxial FLAIR
images before stereotactic radiosurgery (a), and 6 months after radiosurgery (b).

Case Presentation and Methods
The patient was a 54-year-old man who was scheduled
for stereotactic radiosurgery due to a metastatic brain tumor located in his right cerebellar hemisphere that originated from lung adenocarcinoma (Fig. 1). We used a stereotactic fixation system (Linac Scalpel, Varian MedicalSystems, Palo Alto, California, USA) that can be used
for stereotactic radiosurgery or stereotactic radiotherapy.9-11 With this system, patient localization is achieved
through detection and digital registration of an independent biteplate system. The biteplate is linked to a set of
spherical-shaped reflectors and the positions of these reflectors are detected by a pair of infrared cameras. In ourcase, the patient’s upper jaw contained only four teeth(12, 13, 17, and 18). The degree of mobility for teeth 12and 13 was within the physiological range, but that of 17and 18 indicated advanced periodontitis and grade IIIº ofteeth mobility of teeth mobility. Therefore, 17 and 18
were inadequate for biteplate support if they were fixed.
Residual ridge absorption was of medium level, andthere was flabby gum in the anterior maxillary ridge.
Stability of the partial denture was inadequate. Therefore, a denture base with wire clasps was made for SRS
support system, and its retainer was placed on teeth 12and 13 alone (Fig. 2a). After adjusting the retainer, themaxillary denture base was fixed to the biteplate using
an autopolymerizing resin. We also used this resin to obtain an impression of the rest-occlusal position for themandible on the bottom surface of the biteplate (Fig. 2b, c).
Stereotactic radiosurgery (26 Gy at the isocenter) wasperformed using a cylindrical collimator with a diameterof 16 mm. The dose concentration was carried out withfive non-coplanar 120-degree arc rotations. The treatment time was approximately 40 minutes. Before starting stereotactic radiosurgery, the patient’s denture andteeth 12 and 13 were fixed using the autopolymerizing
resin. After stereotactic radiosurgery was completed, weremoved the resin from around 12 and 13, as well as thebiteplate. To assess reproducibility and stability, the distance between the left and right incus (Fig. 3a) and left
and right markers (Fig. 3b) was measured during preplanning (CT1), and before (CT2) and after (CT3) stereotactic irradiation. All the procedures, including theCT scans as well as the dose delivery, were carried out
within 4 hours in a single day.
Results
The difference in the distance between the left ball andthe left incus before (CT2) and after (CT3) radiosurgery
irradiation was 0.54 mm. The distance between the leftball and the right incus was 0.23 mm and that between
the right ball and the right incus was -0.28 mm. These
results suggest that the biteplate was very stable. However, the CT2-CT1 for each distance was ≥5 mm, indicating low reproducibility if the biteplate were to be removed.
Discussion
Some reports have been published examining non-in-122

Tayama S, et al: Radiosurgery with an Upper Partial Denture

Fig. 2 (a) The patient had four teeth (12, 13, 17, and 18) in the maxilla. The mobility of teeth 12 and 13 was within physiologicalrange, but 17 and 18 were beyond it. (b) The maxillary denture was fixed to the biteplate with an autopolymerizing resin and a dentureretainer was placed on teeth 12 and 13. (c) The rest-occlusal position was impressed on the inferior surface of the biteplate with an
autopolymerizing resin.

Fig. 3 To assess reproducibility and stability, the distance between the left and right incudes (a) and left and right markers (b) wasmeasured from three series of CT scans; during pre-planning, before stereotactic irradiation and after it. The markers worked asreflectors for infrared rays from a light source fixed to the wall of the treatment room.

vasive repositioning methods applied to stereotactic radiotherapy, including frameless9, 1 2 and frame-based relocatable immobilization systems.13, 14 Frameless relocation of the head utilizes image guidance systems1 2 andfiducial markers visualized with room-mounted cameras.9
Immobilization of the patient’s head is generallyachieved by a head mold and thermal plastic mask. Reports have shown that the repositioning error of the
biteplate in denture patients was within 1 mm.1 0, 11 Because maxillary dentition is a part of the skull with a particularly complicated convexo-concave shape, fixation
using a dental cast that conforms to maxillary dentition
can increase positioning reproducibility. However, incases where there are few or no teeth, in the maxillary,
the reliability of the biteplate has been believed to be insufficient for radiosurgery, since the residual ridge support might cause more biteplate instability than teeth
support in the mouth. In addition, the elasticity of silicon
could be an unfavorable factor regarding biteplate stability in these cases. Thus, biteplate stability is important
for the accuracy and reproducibility of stereotactic radiosurgery.
There is a probability that the relationship between
maxilla and the biteplate will change depending on theforce exerted on the biteplate; for example, when swallowing. Obstruction of denture space causes instabilityof the denture, and biteplates often present an obstacle toKeio J Med 2009; 58 (2):120－123

denture space. In such cases, it should be possible toshape the biteplate down. In addition the denture basewith retainer is useful for ensuring biteplate stability, due
to the fact that it allows for a greater degree of control
over retention of the biteplate than with a silicone impression.
Stereotactic irradiation using a biteplate is thought tobe impossible in patients who have lost upper teeth.
However, in this case, there was enough geometrical accuracy for a single-fraction stereotactic radiosurgery tobe maintained from planning CT to the therapy using a
biteplate in a patient who was missing many maxillaryteeth. On the other hand, replacement of the biteplate led
to poor reproducibility of biteplate attachment. Although
this is a single case report, it indicates the possibility thatsuccessful frameless radiosurgery can be applied to patients with just a few maxillary teeth using a dedicatedbiteplate customized by a dentist, and with repeated CT
confirmations.
Conclusion
Stereotactic irradiation using a biteplate has beenthought to be impossible in patients who have lost manyteeth. However, the CT measurements proved that our
proposed method has enough stability for a single-fraction stereotactic radiosurgery in a patient who was missing many maxillary teeth.
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