WHOLE-BODY DOSES FROM LINEAR ACCELERATOR-BASED STEREOTAXIC RADIOTHERAPY

Purpose: The objective of this work was to measure whole body radiatio n doses in a humanoid phantom from linear accelerator-based cranial st ereotactic radiosurgery/therapy (SRS/T), using different beam arrangem ents, Methods and Materials: A standard noncoplanar five-are beam arra ngement and a four-are technique without a sagittal are were used to d eliver 20 Gy in a single fraction to a midline spherical target volume in the corpus callosum region of an Alderson-Rando anthropomorphic ph antom using (i) a 20-mm and (ii) a 40-mm circular collimator, Whole bo dy dose measurements were made using lithium fluoride thermoluminescen t dosimetry, Whole body isodose plots in the sagittal and coronal plan es and organ doses were compared for the two arcing beam arrangements, An ionization chamber was used to record the exit dose at intervals a long the length of the phantom at midline and 4.5 cm off-axis for (i) a single fixed field and (ii) a solitary 90 degrees sagittal are using a 40-mm circular collimator. Results: The sagittal are was the major contributor to neck and trunk doses when the five- and four-are arrang ements were compared, with fourfold greater thyroid dose, The gonad do se was increased by the sagittal are, but was largely due to leakage r adiation, The dose from a fixed field exiting down the long axis of th e phantom was tenfold greater than that from a solitary 90 degrees sag ittal are. When the fixed field or are traversed the lung or exited th rough the pharynx and major upper airways, the dose measurements below the diaphragm were 30-40% higher than those along the exit path of ma ximum soft tissue density, Conclusion: When SRS/T is used in nonmalign ant conditions such as cranial arteriovenous malformations or benign t umors the exit paths of arcing beams or fixed fields should be taken i nto account when deciding upon the final treatment plan, Such consider ation should minimize the risk of radiation-induced malignancy, notabl y in the thyroid gland of younger patients. (C) 1997 Elsevier Science Inc.