PubMed · 8153445
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J T Parsons, R R Million, W M Mendenhall. 1994. Regional lymph node irradiation.. https://doi.org/10.1007/978-3-642-84971-8_10
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PURPOSE: The matching or junctioning of two lateral fields with an anterior field is commonly performed in the treatment of head and neck cancer. A monoisocentric technique utilising asymmetric collimation is potentially associated with improved dosimetry in the plane of the junction due to decreased reliance on operator skill and the avoidance of couch movement. The aim of this study was not only to assess the average dose delivered in the plane of the junction, but also the reproducibility of this dose for the monoisocentric technique and two other commonly used techniques. METHODS AND MATERIALS: An anthropomorphic head and neck wax phantom was fashioned to allow the placement of 22 TLD chips in a 2-mm thick transverse plane positioned superior to the potential site of the larynx. Three different treatment techniques were used with the phantom being treated by four different operators a minimum of 20 times for each technique: (1) "straight fields"--using isocentric laterals with an anterior field junctioned in the midline. This technique makes no allowance for divergence; (2) "angled fields"--couch and gantry rotation are used to account for divergence; (3) "monoisocentric"--using asymmetric collimators to create a single isocenter. RESULTS: For an applied dose of 1 Gy the monoisocentric technique produced a mean dose measured of 1.01 Gy compared with 1.23 and 0.92 Gy for techniques 1 and 2. The reproducibility of the mean dose measured was better for the monoisocentric technique by a factor of 2. The superior reproducibility of the monoisocentric technique was not found to be operator dependent. CONCLUSIONS: A monoisocentric technique for the treatment of two laterals and an anterior field in head and neck cancer is likely to be associated with more accurate and reproducible dosimetry in the plane of the junction. Our center has subsequently adopted this technique for matching such fields.
BACKGROUND: The verification of intensity-modulated radiation therapy (IMRT) patient treatment dose distributions is currently based on custom-built or modified dose measurement phantoms. The only commercially available IMRT treatment planning and delivery system (Peacock, NOMOS Corp.) is supplied with a film phantom that allows accurate spatial localization of the dose distribution using radiographic film. However, measurements using other dosimeters are necessary for the thorough verification of IMRT. METHODS: We have developed a phantom to enable dose measurements using a cylindrical ionization chamber and the localization of prescription isodose curves using a matrix of thermoluminescent dosimetry (TLD) chips. The external phantom cross-section is identical to that of the commercial phantom, to allow direct comparisons of measurements. A supplementary phantom has been fabricated to verify the IMRT dose distributions for pelvis treatments. RESULTS: To date, this phantom has been used for the verification of IMRT dose distributions for head and neck and prostate cancer treatments. Designs are also presented for a phantom insert to be used with polymerizing gels (e.g., BANG-2) to obtain volumetric dose distribution measurements. CONCLUSION: The phantoms have proven useful in the quantitative evaluation of IMRT treatments.
Lipoblastoma and lipoblastomatosis are rare benign tumours of embryonal fat that exhibit a tendency to invade locally but not to metastasize. This condition most often presents before the age of 3 years, affects males more than females, and is typified by a slowly-growing, usually subcutaneous mass arising in a limb. Cases involving the head and neck are extremely rare, with only nine cases in the neck having been described to date. This tenth case arose in a 13-month-old male presenting with a rapidly enlarging lump in the right side of the neck, clinically mimicking a cystic hygroma. Diagnosis is by histology, and treatment involves complete surgical resection. We report this tenth known case of lipoblastoma in the neck and review the literature.