Three-dimensional dose reconstruction-based pretreatment dosimetric verification in volumetric modulated arc therapy for prostate cancer

Purpose@#We performed three-dimensional (3D) dose reconstruction-based pretreatment verification to evaluate gamma analysis acceptance criteria in volumetric modulated arc therapy (VMAT) for prostate cancer. @*Materials and Methods@#Pretreatment verification for 28 VMAT plans for prostate cancer was performed using the COMPASS system with a dolphin detector. The 3D reconstructed dose distribution of the treatment planning system calculation (TC) was compared with that of COMPASS independent calculation (CC) and COMPASS reconstruction from the dolphin detector measurement (CR). Gamma results (gamma failure rate and average gamma value [GFR and γAvg]) and dose-volume histogram (DVH) deviations, 98%, 2% and mean dose-volume difference (DD98%, DD2% and DDmean), were evaluated. Gamma analyses were performed with two acceptance criteria, 2%/2 mm and 3%/3 mm. @*Results@#The GFR in 2%/2 mm criteria were less than 8%, and those in 3%/3 mm criteria were less than 1% for all structures in comparisons between TC, CC, and CR. In the comparison between TC and CR, GFR and γAvg in 2%/2 mm criteria were significantly higher than those in 3%/3 mm criteria. The DVH deviations were within 2%, except for DDmean (%) for rectum and bladder. @*Conclusions@#The 3%/3 mm criteria were not strict enough to identify any discrepancies between planned and measured doses, and DVH deviations were less than 2% in most parameters. Therefore, gamma criteria of 2%/2 mm and DVH related parameters could be a useful tool for pretreatment verification for VMAT in prostate cancer.

PTBD Spiral CT Cholangiography: Utility in Patients with Extrahepatic Biliary Obstruction

PURPOSE: The purpose of this study is to assess the utility of PTBD spiral CT cholangiography, after infusion of contrast media through a PTBD tube, for evaluation of a biliary lesion after emergency PTBD due to severe jaundice. MATERIALS AND METHODS: Forty patients with emergency PTBD due to extrahepatic biliary obstruction were transferred to our clinic and prospectively studied. The causes of obstruction were 17 extrahepatic cholangiocarcinomas (including three Klatskin's tumors), seven pancreatic head carcinomas, six calculous diseases of the common bile duct, six periampullary lesions, two ampulla of Vater carcinomas, one gall bladder carcinoma with invasion of the common hepatic duct, and one cholangitis. Diagnosis was on the basis of pathologic, radiologic, and clinical findings. Pre-contrast CT scanning was performed. After the infusion of contrast media (iothalamate : normal saline=1:10) through a PTBD tube, spiral CT scans were obtained. After IV infusion of contrast media (Ultravist, 100cc), early- and delayed-phase spiral CT scans were obtained at 45 and 210 seconds, respectively, with an interscan interval of 5mm. 3-D CT cholangiograms were then reconstituted. Spiral CT without infusion of contrast media through a PTBD tube and PTBD spiral CT cholangiography were performed in 14 cases. The level of extrahepatic biliary obstruction was categorized as either upper, middle, or lower third. In 21 surgically confirmed cases, we evaluated the accuracy with which the level and cause of obstruction was determined; levels and causes during surgery and by as seen on PTBD cholaniography were compared. RESULTS: The levels of obstruction diagnosed on PTBD spiral CT cholangiography and on 3-D CT cholangiography corresponded in all cases to the levels during surgery and on PTBD cholangiography [upper third (n=7), middle third (n=12), lower third (n=21)], and the level diagnosed on spiral CT without infusion of contrast media through a PTBD tube corresponded to the level during surgery in ten of 14 cases. The cause of obstruction diagnosed on PTBD spiral CT cholangiography corresponded to pathologic findings in 19 of 21 cases. In 15 cases, 3-D CT cholangiography was diagnostically helpful. CONCLUSION: PTBD spiral CT cholangiography is a useful diagnostic method for determining the level and cause of biliary obstruction.

Contrast Enhanced Two-Phase Spiral CT of Urinary Bladder

PURPOSE: To determine optimal scan time for the early phase of two-phase spiral CT and to evaluate its usefulness in the detection and assessment of extension of urinary bladder lesions. MATERIALS AND METHODS: In four normal adults, we performed dynamic scanning and obtained time-density curves for internal and external iliac arteries and veins, and the wall of the urinary bladder. Sixty patients with 68 lesions of the urinary bladder or prostate underwent precontrast and two-phase spiral CT scanning. After injection of 100ml of noninonic contrast material, images for the early and delayed phases were obtained at 60 seconds and 5 minutes, respectively. We measured CT H.U. of the wall, the lesion, and lumen of urinary bladder as seen on axial scanning, in each image in which the lesion was best shown. For the detection of bladder lesions and assessment of their extension, precontrast, early-, and delayed phase images were compared. RESULTS: Dynamic study of normal adults showed maximum enhancement of bladder wall between 60 and 100 seconds. The difference of CT H.U. between bladder wall and the lesion was greatest in the early phase. The best detection rate (98.5%) was seen during this phase, and for the detection of bladder lesion, this same phase was superior or equal (66/68,97.1%) to the delayed phase. The precontrast image was also superior or equal (31/68,45.6%) to that of the delayed phase. For the assessment of extension of bladder lesion, the early phase was superior (36/68,52.9%) to the delayed phase, and precontrast image was superior (1/68, 1.5%) to that of the delayed phase. For determining the stage of bladder cancer, the early phase was most accurate if the stages was below B2 or D, while for stage C, the delayed phase was most accurate. CONCLUSION: In two-phase spiral CT scanning, we consider the optimal time for the early phase to be between 60 and 100 seconds after injection of contrast material. For the detection and assessment of extension of urinary bladder lesion, the early phase was superior to the late phase, and for evaluation of the ureter, the delayed phase was useful. The precontrast image was inferior to that of the delayed phase. We suggest that for the detection and assessment of extension of urinary bladder lesion without scanning of the precontrast image, two-phase spiral CT is reliable.