Fetal dose estimates in treatment of superior vena cava syndrome
M. Mazonakis 1 , J. Damilakis 2 , N. Theoharopoulos 1 , N. Gourtsoyiannis 3
1. Department of Medical Physics, University
Hospital of Iraklion, Crete, (Greece)
2. Department of
Medical Physics, Faculty of Medicine, University of Crete,
(Greece)
3. Department of
Radiology, Faculty of Medicine, University of Crete, (Greece)
Manuscript received: September 20, 1999; revised: November 18, 1999.
Accepted for publication: November 19, 1999.
Abstract
The purposes of the present study were to measure fetal dose resulting from radiotherapy of superior vena cava syndrome (SVCS) and to study fetal dose reduction whenever lead shielding is present. Fetal dose measurements were performed with thermoluminescent dosimeters. A modified Rando phantom representing pregnancy at 12 and 24 weeks of gestation was used. An anterior – posterior pair of fields was applied to simulate radiotherapy of SVCS. The contribution of lateral field exposures to the total fetal dose was also measured. Fetal dose resulting from exposures with anterior and posterior fields was found to be lower than that resulting from lateral exposures. This was due to the high contribution of scatter arising within the phantom to the total fetal dose when irradiations performed with lateral fields. At early postconception weeks, fetal dose was below 100 mGy even for exposures without lead shielding. This implies that radiotherapy of SVCS may be generated without fetal shielding at the beginning of gestation. Pregnancy progression resulted in a significant increase of fetal dose. At 12 and 24 weeks of gestation, treatment of SVCS should always be performed with adequate fetal shielding in order to reduce the risks of biological effects of ionizing radiation to fetus.
KEYWORDS: Superior vena cava syndrome; Pregnancy; Fetal dose.