Evaluation of localization uncertainty of fiducial markers due to length and position variations induced by motion in CT imaging by measurement and modeling

PURPOSE

To quantify the variations in the length and position of fiducial markers induced by motion in axial (ACT), helical (HCT) and cone-beam CT (CBCT) imaging and associated uncertainty in image-guided radiotherapy (IGRT) by measurement and modeling.

METHODS

A mobile thorax phantom containing markers of various lengths was imaged using ACT, HCT and CBCT imaging. The phantom was imaged while stationary and moving where it was moved sinusoidally with different motion amplitudes and frequency. An analytical motion model was developed that predicts the localization accuracy of IGRT based on fiducial markers in mobile phantom with ACT, HCT and CBCT.

RESULTS

The apparent lengths of the markers varied with the different motion patterns and CT imaging modalities. In CBCT, the apparent length of the markers increased linearly with the motion amplitude for both half-fan and full-fan modes. In HCT and ACT, the apparent length of the markers increased or decreased non-linearly with motion parameters and speed of the imaging couch. When the marker moved opposed to couch motion the apparent lengths decreased, while they increased when the phantom moved along the direction of the imaging couch as predicted by the motion model. The position of marker centers did not shift and distance between makers did not change in CBCT images. However, in HCT and ACT, the position of marker center and distance between markers varied depending on motion parameters during imaging. The marker center could move superiorly or inferiorly and the distance between markers could increase or decrease depending on the phase of motion as predicted by the motion model.

CONCLUSIONS

The variations of marker length and position due to phantom motion were quantified by measurement and modeling. These variations may lead to large positioning uncertainties in patient setup and tumor localization based on IGRT with fiducial marker registration.

No Scalpel Vasectomy (NSV) with Ligation and Excision: A Single Centre Experience

No scalpel vasectomy (NSV) has proved to be a safe and simple procedure for permanent sterilization for men. Ligation and excision of the vas deferens followed by fascial interposition is the procedure of choice. It is believed that vas excision without fascial interposition has a risk of failure. The objective of this study was to evaluate the technique of NSV with ligation and excision only. No scalpel vasectomy performed in an urban centre was taken for this prospective study. Only ligation and excision procedure was applied in its execution. It was demonstrated and performed under the supervision of an expert. Information regarding early and late complications including failure was gathered. A total number of 3,392 NSVs were performed in an urban training centre between Apr' 2009 to Mar' 2013. The procedure applied was only excision and ligation of the vas deferens. The fascial interposition was not included in the procedure. Haematoma (1), bleeding (3), foreign body granuloma (1), scrotal pain (3), epididymitis (1) and sinus formations (1) were encountered. There was only one failure in the whole group of acceptors. NSV with ligation and excision is a simple and easy procedure to learn and perform. Complications and failures are negligible. The additional fascial interposition needs more surgical skill and is time-consuming, hence can be avoided where a large number of acceptors need to undergo NSV in a rural camp.

Quantitative evaluation of the dosimetric effects of balloon deformation and source position in high-dose rate mammosite breast brachytherapy

PURPOSE

To investigate quantitatively the deformation of the mammosite balloon, eccentricity of the source position and their effects on the dose delivered to the tumor lumpectomy site and critical structures.

MATERIALS AND METHODS

The distances of the brachytherapy source to the surface of the mammosite balloon were measured in using radiographic images for fractions 1 to 10 for twelve patients. The dose at the balloon surface (nearly 680cGy) and prescription dose of 340cGy at 1cm from the balloon surface were calculated for the different fractions and their dependence on the balloon volume and source position were investigated.

RESULTS

The position of the source can be offset from the center of the mammosite balloon by up to 6mm. Deformation of the balloon led to variations in its dimensions by up to 8mm. The dose at 1cm from the balloon surface that covers the lumpectomy site varied by up to 19% from 340cGy along the elongated diameter of the balloon and by up to 40% along the short diameter. Maximal doses to the skin, ribs and lung were 420cGy, 630cGy and 500cGy per fraction, respectively, which depended mostly on their distance from the balloon surface.

CONCLUSION

The geometric variations in the shape of the balloon and position of the source can cause lack of dose coverage to the lumpectomy site or create hot dose spots in the surrounding normal tissue that might compromise intended clinical goals. Users as well as vendors should consider correction measures for the deformation of the balloons and the eccentricity of the position of the high dose source.