Abstract
The use of stereotactic body radiation therapy is rapidly increasing among patients with lung cancer not amenable to surgery. The authors report their experience using the CyberKnife system (Accuray Inc., Sunnyvale, CA, USA) as a treatment option for synchronous cancer of oral squamous cell carcinoma and a malignant lung tumour. An 88-year-old woman with two cancers (oral and lung masses) underwent CyberKnife treatment, with fiducial gold pins implanted using bronchoscopy. Toxicity was limited, and at the 2-year follow-up the lesions had not recurred.
Based on the reported success of stereotactic radiotherapy in the treatment of head and neck cancer, patients seeking a non-surgical alternative have increasingly been treated using CyberKnife ® radiation therapy (Accuray Inc., Sunnyvale, CA, USA). The CyberKnife is a frameless whole-body image-guided robotic radiosurgery system that has been utilized by numerous clinicians around the world to treat intracranial and extracranial tumors.
The CyberKnife image guidance system includes two orthogonally situated kilovoltage X-ray imaging sources and corresponding amorphous silicon detectors. Images taken before and during treatment are registered to digitally reconstructed radiographs derived from the planning computed tomography (CT) image obtained before treatment. An interplay between the image guidance system, an automated couch, and a compact linear accelerator mounted on an agile robotic arm, allows the real-time tracking of the target. The robotic manipulator that carries the linear accelerator can move freely in six degrees. The overall targeting error of the entire system has been shown to be less than 1 mm for head and lung targets. The lightweight linear accelerator can irradiate the target from over 1200 beam angles delivered from over 120 different positions around the patient. It is directed by a treatment plan developed on CT images or on fused CT and magnetic resonance images (MRI). The CyberKnife system differs from other image-guided radiosurgery/therapy devices because it is not attached to a gantry system and it can target outside a 360-degree radius; this extensive non-coplanarity gives it potential advantages regarding the distribution of the dose and thus the clinical outcome and toxicity. Strategies employing limited fractionation, where two to five radiosurgery sessions (fractions) are used instead of the traditional single fraction, have been applied to treat tumours adjacent to sensitive structures or the spinal cord. Fractionation allows time for normal tissue repair and leads to better protection of normal structures.
Stereotactic body radiation therapy has been shown to be an effective treatment for inoperable lung cancer. Several techniques have been employed to treat these mobile tumours with relatively tight margins (5–10 mm). This enhanced accuracy has facilitated the safe, swift delivery of extremely high radiation doses. Methods of motion management include respiratory gating, body frames, and abdominal compression, or real-time target and motion tracking. Two methods are available with the CyberKnife system to accomplish real-time tumour tracking: the first one, fiducial tracking, requires the use of radio-opaque markers implanted near or inside the tumour under local anaesthesia, while the other, the Xsight Lung Tracking System (XLTS), is fiducial-free. With XLTS, targeting is synchronized directly with the respiratory motion of the target. As anticipated, such treatment has improved local control and overall survival rates relative to historical controls.
The authors report their experience using the CyberKnife system as a therapeutic modality for the synchronous cancer of oral squamous cell carcinoma (SCC) and a lung malignant tumour.
Case report
An 88-year-old woman was referred to our clinic for treatment of a painful mass in the right maxillary gingiva in September 2011. The patient had felt pain when placing her upper denture for 1 month. A positron emission tomography (PET)/CT scan showed high uptake of fluorodeoxyglucose (FDG) in the mass in the right maxillary gingiva, which was 30 mm in diameter; a mass in the right lung of 27 mm in diameter was discovered at the same time. The standard uptake value was 10.9 for the gingival lesion and 7.6 for the lung lesion, suggesting malignant tumours ( Fig. 1 ). Clinical examination, including intraoral biopsy, revealed a well-differenced SCC of the right maxillary gingiva of T2N0. In order to avoid an invasive bronchoscopic biopsy in this elderly patient, the right lower lung mass was diagnosed as lung carcinoma on lung CT by an expert respiratory-organ surgeon. The final clinical diagnosis was synchronous cancer: SCC of the right maxillary gingiva T2N0M0 and right lung carcinoma. Because of her advanced age, the patient refused surgical treatments to cure these lesions, hence CyberKnife stereotactic radiotherapy was selected. This was started at the end of October 2011.
A radiation oncologist and a respiratory surgeon at Seiseikai Yokohama City East Hospital created a treatment plan based on thin-slice CT scan, MRI, and PET/CT. Before treatment of the maxillary gingival cancer, a customized face mask was fabricated to immobilize the head. A dose of 25 Gy in five fractions for the maxillary gingival cancer was administered to the tumour. Oral health care was provided pre- and post-irradiation to keep the radiation-induced side effects to a minimum. At 1 week post-radiotherapy mucositis was detected and assessed as grade 2 according to the Common Terminology Criteria for Adverse Events v. 4.0. Four weeks later, the mucositis had disappeared and the performance status of this patient was completely recovered (PS 0) through oral care and a liquid diet instituted immediately after irradiation.
In mid-December 2011 the lung cancer was treated, also by CyberKnife, using fiducial tracking of respiratory motion, to a dose of 15 Gy in three fractions. There was a grade 1 pneumonia event without symptoms after lung radiotherapy, but the pneumonia had almost recovered on lung CT by 12 months. Starting at 1 month after lung treatment, S-1 (TS-1; Taiho Pharmaceutical Company) 80 mg/day in two doses was administered for 1 year in treatments of 2 weeks followed by a 1-week rest, to reduce these tumours and to prevent recurrence or metastases.
At the 1-year post-CyberKnife follow-up, a complete response of both lesions was assessed using Response Evaluation Criteria in Solid Tumors (RECIST) v. 1.1 ( Fig. 2 ). Oral examination showed the right maxillary gingival mass to have disappeared completely. There was no chronic toxicity and no evidence of recurrence or metastases on PET/CT, MRI, and ultrasound at the 2-year follow-up.
