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Title: Multiparametric fit method in reconstruction of Fletcher-Suit-Delclos applicator

Abstract

In our institution we have introduced the variable angle reconstruction method with a nonisocentric C-arm as brachytherapy localizer in gynecological treatments. The main advantage of this method is that on the posterior oblique images the ovoids of the Fletcher-Suit-Delclos (FSD) applicator are clearly separated. The main problem with the nonisocentric machine is that the magnification factor is not known exactly and varies with the C-arm angle. For generation of treatment plans with a commercial brachytherapy planning system the magnification factors of the reconstruction images have to be determined previously. We present a multiparametric fit method (MPF) that is suitable for reconstruction of FSD applicators and that utilizes pairs of posterior-anterior and lateral or preferably posterior oblique reconstruction images obtained by a C-arm. The MPF reconstruction relies on the known geometry of the tandem and the ovoid. The actual FSD insertion is reconstructed by adaptation of the geometry of tandem and ovoid by translations and rotations. The fixation mechanism limits the possible excursions of the FSD applicator's parts. The limited freedom of excursions and the determination of the magnification factors are also incorporated.

Authors:
 [1]
  1. A. Petz County Teaching Hospital, Gyor, Zrinyi str. 13, H-9002 Gyor, Pf. 92 (Hungary)
Publication Date:
OSTI Identifier:
20774987
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 33; Journal Issue: 1; Other Information: DOI: 10.1118/1.2138012; (c) 2006 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; BRACHYTHERAPY; EXCURSIONS; GEOMETRY; GYNECOLOGY; IMAGE PROCESSING; IMAGES; PLANNING

Citation Formats

Palvolgyi, Jeno. Multiparametric fit method in reconstruction of Fletcher-Suit-Delclos applicator. United States: N. p., 2006. Web. doi:10.1118/1.2138012.
Palvolgyi, Jeno. Multiparametric fit method in reconstruction of Fletcher-Suit-Delclos applicator. United States. doi:10.1118/1.2138012.
Palvolgyi, Jeno. Sun . "Multiparametric fit method in reconstruction of Fletcher-Suit-Delclos applicator". United States. doi:10.1118/1.2138012.
@article{osti_20774987,
title = {Multiparametric fit method in reconstruction of Fletcher-Suit-Delclos applicator},
author = {Palvolgyi, Jeno},
abstractNote = {In our institution we have introduced the variable angle reconstruction method with a nonisocentric C-arm as brachytherapy localizer in gynecological treatments. The main advantage of this method is that on the posterior oblique images the ovoids of the Fletcher-Suit-Delclos (FSD) applicator are clearly separated. The main problem with the nonisocentric machine is that the magnification factor is not known exactly and varies with the C-arm angle. For generation of treatment plans with a commercial brachytherapy planning system the magnification factors of the reconstruction images have to be determined previously. We present a multiparametric fit method (MPF) that is suitable for reconstruction of FSD applicators and that utilizes pairs of posterior-anterior and lateral or preferably posterior oblique reconstruction images obtained by a C-arm. The MPF reconstruction relies on the known geometry of the tandem and the ovoid. The actual FSD insertion is reconstructed by adaptation of the geometry of tandem and ovoid by translations and rotations. The fixation mechanism limits the possible excursions of the FSD applicator's parts. The limited freedom of excursions and the determination of the magnification factors are also incorporated.},
doi = {10.1118/1.2138012},
journal = {Medical Physics},
number = 1,
volume = 33,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • Measurements were made in water about the tandem and ovoid structures of the Fletcher--Suit applicator loaded with a $sup 137$Cs source. The dose rate was found to vary as much as 25% as a result of differential absorption in the ovoid. Empirically based trigonometric expressions are suggested which provide the absorption correction as a function of the two angles of a spherical coordinate system. Computer-calculate dose rates, with and without the absorption corrections, are compared. (AIP)
  • Using a small silicon diode and the Therados RFA-3 automated dosimetry system, the relative dose distribution around Fletcher-Suit-Delcos colpostats was measured. Thermoluminescent dosimeters (LiF) were used for absorbed dose measurements. These data provide the basis for computerized dose calculations which will account for the attenuation effects of the rectal and bladder shieldings. The stainless-steel housing attenuated the radiation of a Cs-137 source by 6%. The tungsten shields caused a further dose reduction of 15%-25%.
  • The Fletcher Suit Delclos (FSD) ovoids employed in intracavitary brachytherapy (ICB) for cervical cancer contain shields to reduce dose to the bladder and rectum. Many treatment planning systems (TPS) do not include the shields and other ovoid structures in the dose calculation. Instead, TPSs calculate dose by summing the dose contributions from the individual sources and ignoring ovoid structures such as the shields. The goal of this work was to calculate the dose distribution with Monte Carlo around a Selectron FSD ovoid and compare these calculations with radiochromic film (RCF) and normoxic polymer gel dosimetry. Monte Carlo calculations were performedmore » with MCNPX 2.5.c for a single Selectron FSD ovoid with and without shields. RCF measurements were performed in a plane parallel to and displaced laterally 1.25 cm from the long axis of the ovoid. MAGIC gel measurements were performed in a polymethylmethacrylate phantom. RCF and MAGIC gel were irradiated with four 33 {mu}Gy m{sup 2} h{sup -1} Cs-137 pellets for a period of 24 h. Results indicated that MCNPX calculated dose to within {+-}2% or 2 mm for 98% of points compared with RCF measurements and to within {+-}3% or 3 mm for 98% of points compared with MAGIC gel measurements. It is concluded that MCNPX 2.5.c can calculate dose accurately in the presence of the ovoid shields, that RCF and MAGIC gel can demonstrate the effect of ovoid shields on the dose distribution and the ovoid shields reduce the dose by as much as 50%.« less
  • The improved Fletcher Applicator is a recent modification of the afterloading Fletcher system. Its aluminum construction reduces the weight by 50% and is more comfortable for the patient. Removable caps contain medially placed tungsten screens that shield tissues anteriorly and posteriorly. A method for evaluating the dosimetry of brachytherapy applicators in a water phantom was devised so this applicator could be studied and compared with other gynecologic applicators. The results show that the transmission ratios differ from those of the preloaded Fletcher colpostat, but are similar to the transmission ratios of the Fletcher-Suit applicator. There is a 10% to 25%more » reduction in the radiation dose to the region of the bladder trigone and anterior rectum with the shield containing cap in place.« less
  • Experimental measurements in a water phantom were made for a new shielded plastic Fletcher applicator. A dose calculation algorithm which allows the description of asymmetrically shielded source containers is presented. The traditional primary plus build-up factor description of the dose in a homogeneous volume is corrected by using effective attenuation coefficients measured in a water phantom for all the source-shield-container materials. Comparison of the theoretical results to the experimental data shows excellent agreement.