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KMID : 1164220140260010127
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Journal of Korean Society for Radiotherapeutic Technology
2014 Volume.26 No. 1 p.127 ~ p.135
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USABILITY EVALUATION OF PLANNING MRI ACQUISITION WHEN CT/MRI FUSION OF COMPUTERIZED TREATMENT PLAN
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Park Do-Keun
Choi Byeong-Ki
Kim Jin-Man
Lee Dong-Hoon
Song Gi-Won
Park Young-Hwan
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Abstract
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Purpose : By taking advantage of each imaging modality, the use of fused CT/MRI image has increased in prostate cancer radiation therapy. However, fusion uncertainty may cause partial target miss or normal organ overdose. In order to complement such limitation, our hospital acquired MRI image (Planning MRI) by setting up patients with the same fixing tool and posture as CT simulation. This study aims to evaluate the usefulness of the Planning MRI through comparing and analyzing the diagnostic MRI image and Planning MRI image.
Materials and Methods : This study targeted 10 patients who had been diagnosed with prostate cancer and prescribed onhormone and definitive RT 70 Gy/28 fx from August 2011 to July 2013. Each patient had both CT and MRI simulations. The MRI images were acquired within one half hour after the CT simulation. The acquired CT/MRI images were fused primarily based on bony structure matching. This study measured the volume of prostate in the images of Planning MRI and diagnostic MRI. The diameters at the craniocaudal, anteroposterior and left-to-right directions from the center of prostate were measured in order to compare changes in the shape of prostate.
Results : As a result of comparing the volume of prostate in the images of Planning MRI and diagnostic MRI, they were found to be 25.01 cm³(range 15.84-34.75 cm³) and 25.05 cm³(range 15.28-35.88 cm³) on average respectively. The diagnostic MRI had an increase of 0.12 % as compared with the Planning MRI. On the planning MRI, there was an increase in the volume by 7.46 cm³(29 %) at the transition zone directions, and there was a decrease in the volume by 8.52 cm³(34 %) in the peripheral zone direction. As a result of measuring the diameters at the craniocaudal, anteroposterior and left-to-right directions in the prostate, the Planning MRI was found to have on average 3.82 cm, 2.38 cm and 4.59 cm respectively and the diagnostic MRI was found to have on average 3.37 cm, 2.76 cm and 4.51 cm respectively. All three prostate diameters changed and the change was significant in the Planning MRI. On average, the anteroposterior prostate diameter decrease by 0.38 cm (13 %). The mean right-to-left and craniocaudal diameter increased by 0.08 cm (1.6 %) and 0.45 cm (13 %), respectively.
Conclusion : Based on the results of this study, it was found that the total volumes of prostate in the Planning MRI and the
diagnostic MRI were not significantly different. However, there was a change in the shape and partial volume of prostate due to the insertion of prostate balloon tube to the rectum. Thus, if the Planning MRI images were used when conducting the fusion of CT/MRI images, it would be possible to include the target in the CTV without a loss as much as the increased volume in the transition zone. Also, it would be possible to reduce the radiation dose delivered to the rectum through separating more clearly the reduction of peripheral zone volume. Therefore, the author of this study believes that acquisition of Planning MRI image should be made to ensure target delineation and localization accuracy.
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KEYWORD
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CT/MRI, PROSTATE
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