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On the validity of the superposition principle in dose calculations for intracavitary implants with shielded vaginal colpostats
Author(s) -
Markman Jerry,
Williamson Jeffrey F.,
Dempsey James F.,
Low Daniel A.
Publication year - 2001
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1339224
Subject(s) - monte carlo method , superposition principle , dosimetry , brachytherapy , shielded cable , imaging phantom , thermoluminescent dosimeter , percentage depth dose curve , nuclear medicine , physics , electromagnetic shielding , attenuation , dose profile , dosimeter , optics , computational physics , ionization chamber , medicine , mathematics , radiation therapy , computer science , statistics , radiology , ion , telecommunications , quantum mechanics , ionization
Intracavitary vaginal applicators typically incorporate internal shielding to reduce dose to the bladder and rectum. While dose distributions about a single colpostat have been extensively measured and calculated, these studies neglect dosimetric perturbations arising from the contralateral colpostat or the intrauterine tandem. Dosimetric effects of inhomogeneities in brachytherapy is essential for both dose‐based implant optimization as well as for a comparison with alternate modalities, such as intensity modulated radiation therapy. We have used Monte Carlo calculations to model dose distributions about both a Fletcher–Suit–Delclos (FSD) low dose‐rate system and the microSelectron high dose‐rate remote afterloading system. We have evaluated errors, relative to a Monte Carlo simulation based upon a complete applicator system, in superposition calculations based upon both precalculated single shielded applicator dose distributions as well as single unshielded source dose distributions. Errors were largely dominated by the primary photon attenuation, and were largest behind the shields and tandem. For the FSD applicators, applicator superposition showed differences ranging from a mean of 2.6% at high doses (>Manchester Point A dose) to 4.3% at low doses (