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KMID : 1164220070190020099
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Journal of Korean Society for Radiotherapeutic Technology
2007 Volume.19 No. 2 p.99 ~ p.106
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Daily Setup Uncertainties and Organ Motion Based on the Tomoimages in Prostatic Radiotherapy
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Cho Jung-Heui
Lee Sang-Kyu
Kim Sei-Joon
Na Soo-Kyung
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Abstract
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Purpose: The patient’s position and anatomy during the treatment course little bit varies to some extend due to
setup uncertainties and organ motions. These factors could affected to not only the dose coverage of the gross tumor but over dosage of normal tissue. Setup uncertainties and organ motions can be minimized by precise patient positioning and rigid immobilization device but some anatomical site such as prostate, the internal organ motion due to physiological processes are challenge. In planning procedure, the clinical target volume is a little bit enlarged to create a planning target volume that accounts for setup uncertainties and organ motion as well. These uncertainties lead to differences between the calculated dose by treatment planning system and the actually delivered dose. The purpose of this study was to evaluate the differences of interfractional displacement of organ and GTV based on the tomoimages.
Materials and Methods: Over the course of 3 months, 3 patients, those who has applied rectal balloon, treated for
prostatic cancer patient’s tomoimage were studied. During the treatment sessions 26 tomoimages per patient, Total 76 tomoimages were collected. Tomoimage had been taken everyday after initial setup with lead marker attached on the patient’s skin center to comparing with C-T simulation images. Tomoimage was taken after rectal balloon inflated with 60 cc of air for prostate gland immobilization for daily treatment just before treatment and it was used routinely in each case. The intrarectal balloon was inserted to a depth of 6 cm from the anal verge. MVCT image was taken with 5 mm slice thickness after the intrarectal balloon in place and inflated. For this study, lead balls are used to guide the registration between the MVCT and CT simulation images. There are three image fusion methods in the tomotherapy, bone technique, bone/tissue technique, and full image technique. We used all this 3 methods to analysis the setup errors. Initially, image fusions were based on the visual alignment of lead ball, CT anatomy and CT simulation contours and then the radiation therapist registered the MVCT images with the CT simulation images based on the bone based, rectal balloon based and GTV based respectively and registered image was compared with each others. The average and standard deviation of each X, Y, Z and rotation from the initial planning center was calculated for each patient. The image fusions were based on the visual alignment of lead ball, CT anatomy and CT simulation contours.
Results: There was a significant difference in the mean variations of the rectal balloon among the methods.
Statistical results based on the bone fusion shows that maximum x-direction shift was 8 mm and 4.2 mm to the y-direction. It was statistically significant (P=＜0.0001) in balloon based fusion, maximum X and Y shift was 6 mm, 16mm respectively. One patient’s result was more than 16 mm shift and that was derived from the rectal expansions due to the bowl gas and stool. GTV based fusion results ranging from 2.7 to 6.6 mm to the x-direction and 4.3∼7.8 mm to the y-direction respectively. We have checked rotational error in this study but there are no significant differences among fusion methods and the result was 0.37±0.36 in bone based fusion and 0.34±0.38 in GTV based fusion.
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KEYWORD
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prostate cancer, setup variation, tomotherapy, rectal balloon
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