Intraspinal epidermoid cyst successfully treated with radiotherapy: case report.

OBJECTIVE AND IMPORTANCE: Epidermoid cysts are benign lesions that account for 0.7% of all intraspinal tumors. Standard treatment is complete resection. The recurrence rate after surgery cannot be estimated from the scarce literature, but it has been acknowledged that, in some patients, curative surgery may be impossible and temporary relief of symptoms is the only aim. CLINICAL PRESENTATION: In 1996, a 59-year-old woman presented with a 30-year history of a spinal epidermoid cyst, for which she had previously undergone eight operations. Spastic paraplegia of the lower limbs had been present from initial diagnosis, and the neurological level had moved upward to C6. At the time of presentation, paresthesia in her arms and hands had developed. A magnetic resonance imaging scan revealed typical sequelae of previous surgery and a fibrotic region starting at the level of C5-C6 with formation of a cyst that extended to the conus terminalis. The spinal cord could not be visualized caudally at C7. INTERVENTION: Because both patient and surgeons did not want further surgical interventions that might comprise upper limb function, radiotherapy was performed. A dose of 46 Gy was delivered to the cervicothoracic spine (C4-T1) by opposing anteroposterior high-energy photon beams. The treatment was well tolerated, and after treatment, the patient's clinical symptoms improved slightly, without evolution on magnetic resonance imaging. CONCLUSION: Irradiation was effective in stabilizing the patient's disease. Although radiotherapy is not established in the treatment of epidermoid cysts, it should be considered as an alternative to palliative surgery and in patients who cannot undergo operations.

Evaluation of dose calculation algorithms for dynamic arc treatments of head and neck tumors.

BACKGROUND AND PURPOSE: To investigate if the Pencil Beam (PB) algorithm takes the disturbance of the dose distribution due to tissue inhomogeneities sufficiently into account in dynamic field shaping rotation therapy (called the dynamic arc treatment modality) for fractionated stereotactic radiation therapy of head and neck tumors. MATERIAL AND METHODS: A treatment plan using the dynamic arc treatment modality of an oropharynx lesion on a humanoid phantom was evaluated. The same plan was calculated with three different calculation algorithms: the Clarkson and the PB algorithm (both available on the planning system of the Novalis system used for dynamic arc treatments), and the Collapsed Cone Convolution Superposition (CC) algorithm (used by the Pinnacle planning system). The three resulting plans are compared using isodose distributions and cumulative dose volume histograms (CDVHs). An intercomparison of the results of the three algorithms was performed to investigate how accurately each of them takes the influence of tissue inhomogeneities into account such as bony structures and air cavities often appearing in the head and neck region. Additionally, the resulting plans were compared with absolute and relative dosimetric measurements of the treatment plan on the humanoid phantom with thermoluminescent detectors and radiographic film, respectively. RESULTS: All calculated dose distributions show a good agreement with the measured distribution except in the planning target volume (PTV) in and at the border of the air cavity. All three algorithms overestimate the dose in the PTV at the boundary with the low-density tissue, with 12, 10 and 7% for the Clarkson, the PB and the CC algorithm, respectively. The correspondence between the calculated dose distributions is reflected in the graphs of the CDVHs. They show similar curves for the PTV and the structures except for the left parotic gland and the myelum. CONCLUSIONS: The PB algorithm of the Novalis system calculates a treatment plan for the dynamic arc treatment modality adequately for fractionated stereotactic radiation therapy of head and neck tumors, except in the PTV in and at the border of the air cavity where the actual dose is overestimated. Care needs to be taken in clinical cases where it is critical to irradiate the air-tissue boundary to a sufficient dose.