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Tradeoffs of integrating real-time tracking into IGRT for prostate cancer treatment.

Abstract：

:This study investigated the integration of the Calypso real-time tracking system, based on implanted ferromagnetic transponders and a detector array, into the current process for image-guided radiation treatment (IGRT) of prostate cancer at our institution. The current IGRT process includes magnetic resonance imaging (MRI) for prostate delineation, CT simulation for treatment planning, daily on-board kV and CBCT imaging for target alignment, and MRI/MRS for post-treatment assessment. This study assesses (1) magnetic-field-induced displacement and radio-frequency (RF)-induced heating of transponders during MRI at 1.5 T and 3 T, and (2) image artifacts caused by transponders and the detector array in phantom and patient cases with the different imaging systems. A tissue-equivalent phantom mimicking prostate tissue stiffness was constructed and implanted with three operational transponders prior to phantom solidification. The measurements show that the Calypso system is safe with all the imaging systems. Transponder position displacements due to the MR field are minimal (<1.0 mm) for both 1.5 T and 3 T MRI scanners, and the temperature variation due to MRI RF heating is <0.2 degrees C. The visibility of transponders and bony anatomy was not affected on the OBI kV and CT images. Image quality degradation caused by the detector antenna array is observed in the CBCT image. Image artifacts are most significant with the gradient echo sequence in the MR images, producing null signals surrounding the transponders with radii approximately 1.5 cm and length approximately 4 cm. Thus, Calypso transponders can preclude the use of MRI/MRS in post-treatment assessment. Modifications of the clinical flow are required to accommodate and minimize the substantial MRI artifacts induced by the Calypso transponders.

journal_name

Phys Med Biol

journal_title

Physics in medicine and biology

authors

Zhu X,Bourland JD,Yuan Y,Zhuang T,O'Daniel J,Thongphiew D,Wu QJ,Das SK,Yoo S,Yin FF

doi

10.1088/0031-9155/54/17/N03

subject

Has Abstract

pub_date

2009-09-07 00:00:00

pages

N393-401

issue

eissn

0031-9155

issn

1361-6560

pii

S0031-9155(09)19265-5

journal_volume

pub_type

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Tradeoffs of integrating real-time tracking into IGRT for prostate cancer treatment.