Japanese Journal of Clinical Oncology Advance Access originally published online on November 9, 2006
Japanese Journal of Clinical Oncology 2007 37(1):62-65; doi:10.1093/jjco/hyl120
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© 2006 Foundation for Promotion of Cancer Research
Carcinoma of the Floor of the Mouth: A Case Treated with Precisely Controlled External Beam Radiotherapy
1 Department of Radiology, NTT East-Japan Sapporo Hospital
2 Department of Health Sciences Laboratory of Radiation Therapy, Hokkaido University School of Medicine, Sapporo, Japan
For reprints and all correspondence: Takeshi Nishioka, Department of Health Sciences Laboratory of Radiation Therapy, Hokkaido University School of Medicine, Kita 14, Nishi 5, Kita-ku, Sapporo, Hokkaido, Japan. E-mail: trout{at}radi.med.hokudai.ac.jp
Received May 16, 2006; accepted July 27, 2006
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Abstract |
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 TOP Abstract INTRODUCTIONCASE REPORTDISCUSSIONConflict of interest statementReferences |
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A new external radiotherapy system has been developed for head and neck cancer and a case with T2 oral floor carcinoma treated with this system is presented in this report. The system consists of real-time tumor-tracking equipment and a gold-marker implanted mouthpiece. Accuracy of the order of 2 mm was achieved during the entire course of fractionated radiotherapy (a total of 52.5 Gy in 15 fractions). Planning target volume became smaller compared to the conventional parallel-opposed technique. Dose–volume histogram analysis demonstrated a significant reduction in the dose to the mandible bone compared to the conventional technique. A confluent fibrinous mucositis developed in the oral floor mucosa that corresponded to 90% dose area. Mucositis in the lower gum was minimal and analgesics were not required. The patient is currently free from both tumor and complication during a follow-up period of 48 months. External radiotherapy can be an option as a curative treatment for early stage carcinoma of the floor of the mouth provided that patient set-up is rigid and reproducible.
Key Words: Oral floor cancer • external radiotherapy • RTRT
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INTRODUCTION |
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TOPAbstractINTRODUCTIONCASE REPORTDISCUSSIONConflict of interest statementReferences |
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Carcinoma of the floor of the mouth has been treated with surgery, radiotherapy, or their combination. From a functional preservation viewpoint, radiotherapy is a preferred mode of therapy in many institutions. In particular, brachytherapy is effective in achieving a high local control rate because it can give a higher biological dose to a tumor compared to external beam radiation. However, owing to the proximity of the lesions to the mandible, necrosis of the bone is an inevitable complication of brachytherapy. A large brachytherapy center in Europe, the Gustav-Roussy Institute, reports that mandibular bone necrosis occurs in 15.5% of their patients (1). This rate is not low but is acceptable when one sees their excellent local control rates: 93% for T1 tumors and 88% for T2 tumors. External radiotherapy alone has not been used widely because of the concern about damage to the mandible. Providing a sufficient radiation dose to a tumor while keeping the mandible out of the high dose area has been technically difficult. In this paper, we report on a new method of external radiotherapy. This new method involves a real-time tumor-tracking radiotherapy (RTRT) (2–4) system in which a gold marker implanted in a mouthpiece is used. This system facilitates a highly conformal radiotherapy.
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CASE REPORT |
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An 81-year-old female presented in May 2002 with a lump in the floor of her mouth. She had felt soreness in the oral floor for about 1 year and had a 60-year history of cigarette smoking. The tumor was located just in the middle of sublingual ligament and in the medial aspect of the sublingual gland fold (Fig. 1A, B) The tumor measured 2.2 cm in maximal diameter and had a thickness of about 1 cm on palpation. There was no lymph node swelling; no sign of distant metastasis and the clinical stage was T2N0M0. Biopsy performed on the center of the tumor showed well-differentiated squamous cell carcinoma. She was a frail woman with apparent emphysema on chest X-ray. Neither operation with skin graft nor brachytherapy was considered suitable for this patient. External radiotherapy was the remaining choice.
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At this stage, our concern was to give a sufficient dose to the tumor with minimum treatment side effects. She was referred to the department of oral surgery with the aim of making a mouthpiece with a mold inside. The patient had only one tooth, which was the right lower canine. This tooth was effective in maintaining the mouthpiece at the same position on each treatment session. The mouthpiece pushed the tumor in a posterior direction and thereby made a space between the mandible and the tumor (Fig. 1C). A plastic shell and customized pillow (MOLDCARE RI-II) were also made for the patient (Fig. 1D) (5). The patient then received computerized tomography (CT) taken with a slice thickness of 2 mm. The CT data were exported to our treatment planning workstation (FOCUS). The RTRT 4MV photon generating machine (MHCL-15DP) was used and the field arrangement was as follows: two anterior oblique with 15° wedge, and two L-R parallel opposites with 15° wedge. Each field utilized MLC. 52.5 Gy was given to the isocenter in 15 fractions over 26 days. Figure 2 shows the dose distribution of the treatment. As to the targets, CTV (clinical target volume) was defined as GTV (gloss tumor volume) plus 1 cm. The RTRT system enabled us to monitor the position of a 2.0-mm gold marker implanted in a CTV or in a tissue near CTV. The details of this system were described in previous reports (2–4). Patient set-up was performed first by laser localization on the plastic shell and then by using the RTRT system. If a dislocation of more than 2 mm (i.e. set-up error) was detected, the patient couch was moved to the planned position according to the RTRT x–y–z automatic calculation. The median value of set-up error for the laser localization was 3.4 (0.1–8.9) mm, 4.1 (0.2–8.1) mm, and 2.3 (0.0–10.6) mm for lateral, anterior–posterior, and cranio-caudal directions, respectively. After adjusting the patient position, the RTRT monitoring did not show any patient movements greater than 2 mm. At the same time, the shape of the tongue (or tumor) was checked on fluoroscopic images by the physician, and reproducibility of the tumor position was confirmed each time. Figure 3 shows a dose–volume histogram: where the numbers show each treatment plan (i.e. ‘1’ for a conventional parallel-opposed plan and ‘2’ for the present real-time, tumor-tracking, radiation-therapy system 4-beam plan). The CTV histograms were the same in the two plans. Apparent improvement in DVH was noted for the mandible. The patient tolerated radiotherapy without any need for analgesics. Confluent mucositis developed only in a limited area of the oral floor that corresponded with the 90% dose area (Fig. 2C). The tumor disappeared 1 month following the completion of radiotherapy and the mucositis subsided around the same time. Forty-eight months after the start of therapy, the patient was tumor free with no mucosal or mandibular necrosis.
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DISCUSSION |
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TOPAbstractINTRODUCTIONCASE REPORTDISCUSSIONConflict of interest statementReferences |
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The management of patients with carcinoma of the floor of the mouth varies among institutions. The French group has a preference for using brachytherapy over surgery if the tumor is small and functional preservation is considered the priority. As stated earlier, local control rates for T1 and T2 tumors are excellent. Other groups report local control of around 80% for T1 tumors using brachytherapy with either 192Ir or 198Au grains as the source (6–9). However, mucosal or mandibular necrosis developed in these study groups. The incidence of necrosis in these groups was 5–30% and 5–38%, respectively (6–9). On the other hand, surgery rarely causes these complications. However, tongue movement can be restricted after surgery particularly when a tumor infiltrates the sublingual ligament or when a large area of the oral floor is involved. In the current patient, surgery would have caused such a functional problem given the tumor location. Electron beam irradiation using intra-oral cone is also an option, but precise dose delivery requires a great deal of patient cooperation, which would have been difficult to achieve for the present case.
The dose–fractionation regimen used in this patient was different from the commonly used 70 Gy in 35 fractions. If we apply the linear-quadratic model to our dose–fractionation and assume 
/ß values of 10 and 8 for tumor control, then the respective biological equivalent doses (BED) of our regimen will be 71 Gy10 and 76 Gy8. These BEDs correspond to that of 60 Gy in 30 fractions. Despite our seemingly weaker regimen, complete remission was obtained. This was probably due to the short treatment period of our regimen. There is accumulating evidence that suggests overall treatment time is a definite prognostic factor. In particular, the Manchester group has been using a similar regimen with 52.5 Gy in 16 fractions over 21 days. This group reported high local control rates for various head and neck cancers (10,11). However, by shortening overall treatment time, the BED for late responding tissues inevitably increases. For example, 52.5 Gy in 15 fractions, which was the dose–fractionation schedule for our patient, yields a BED of 144 Gy2 assuming /ß value of 2. The dose–fractionation schedule with a probability of 50% mandible complication is reported to be 72 Gy in 36 fractions (BED, 144 Gy2) (12). Hence, mandible sparing was employed using the RTRT system. As shown in Fig. 2, at least half of the bone was spared on the tangential plane. Our patient will probably be free from severe bone damage. Recently, the Manchester group reported an interesting method for reducing irradiated volume of the mandible (13). They employ barium paste for tumor marking and this method allows accurate delineation of the primary tumor for radiotherapy planning. At institutions where a tumor-tracking system is not available, this type of tumor localization would be a viable option for conformal radiotherapy.
A precise patient set-up is the key to success of small volume external beam irradiation (4,14,15). Patient immobilization of the order of 1 mm was obtained in our RTRT system. Several authors have reported the importance of rigid patient set-up. An extended shell that covers the entire neck and shoulder was used in a study (15), and a metal marker attached to an immobilization shell was used in another study (16). In both studies, patients were fixed to the treatment couch with a very rigid mask. This allowed accuracy of the order of 2 mm to be achieved. The benefit of using our system is patient comfort in each treatment session. This level of comfort was achieved by using a small mouthpiece that was tightly attached to her lower gum. We were then able to adjust patient position by visualizing the gold marker. This technique of patient immobilization is easier to perform compared to the methods mentioned above.
In conclusion, precisely controlled short-course external radiotherapy can be an option as a curative treatment for medically inoperable patients with early stage carcinoma of the floor of the mouth.
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Conflict of interest statement |
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TOPAbstractINTRODUCTIONCASE REPORTDISCUSSIONConflict of interest statementReferences |
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None declared.
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Acknowledgments |
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We thank Dr Nakamura, Dr Takizawa and Mr Kawahara.
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References |
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