Variations in tumor size and position due to irregular breathing in 4D-CT: a simulation study.

PURPOSE: To estimate the position and volume errors in 4D-CT caused by irregular breathing. METHODS: A virtual 4D-CT scanner was designed to reproduce axial mode scans with retrospective resorting. This virtual scanner creates an artificial spherical tumor based on the specifications of the user, and recreates images that might be produced by a 4D-CT scanner using a patient breathing waveform. 155 respiratory waveforms of patients were used to test the variability of 4D-CT scans. Each breathing waveform was normalized and scaled to 1, 2, and 3 cm peak-to-peak motion, and artificial tumors with 2 and 4 cm radius were simulated for each scaled waveform. The center of mass and volume of resorted 4D-CT images were calculated and compared to the expected values of center of mass and volume for the artificial tumor. Intrasubject variability was investigated by running the virtual scanner over different subintervals of each patient's breathing waveform. RESULTS: The average error in the center of mass location of an artificial tumor was less than 2 mm standard deviation for 2 cm motion. The corresponding average error in volume was less than 4%. In the worst-case scenarios, a center of mass error of 1.0 cm standard deviation and volume errors of 30%-60% at inhale were found. Systematic errors were observed in a subset of patients due to irregular breathing, and these errors were more pronounced when the tumor volume is smaller. CONCLUSIONS: Irregular breathing during 4D-CT simulation causes systematic errors in volume and center of mass measurements. These errors are small but depend on the tumor size, motion amplitude, and degree of breathing irregularity.

Avoiding "pseudo-reversibility" of CT-CBV infarct core lesions in acute stroke patients after thrombolytic therapy: the need for algorithmically "delay-corrected" CT perfusion map postprocessing software.

BACKGROUND AND PURPOSE: Rarely, acute ischemic stroke (AIS) patients have pretreatment CT-CBV abnormalities larger than final infarct volumes. We sought to determine: (1) the prevalence of CT-CBV "reversibility" in AIS patients treated with thrombolytic therapy, and (2) whether the presumed tissue salvage of these CT-CBV lesions depends on the CTP software. METHODS: We reviewed the admission CT-CBV maps (calculated with an algorithm sensitive to tracer arrival time) and follow-up images of 148 AIS patients who received thrombolytic therapy. When the follow-up infarct appeared smaller than the admission CT-CBV lesion, the CTP source images were reprocessed using "delay-correction" software (GE, CTP 4). Original and "delay-corrected" CT-CBV ischemic lesion volumes were compared to each other and follow-up infarct volumes using the Student t test. RESULTS: 11/148 (7.4%) patients had admission CT-CBV larger than follow-up lesions (mean difference -69.5 cc, range -146.0 to -14.0 cc; P<0.05). For all patients, the admission CT-CBV lesions were smaller on the delay- versus nondelay-corrected maps (mean difference -83.1, range -233 to -2 cc; P<0.05). Only 2 patients had delay-corrected CT-CBV lesions larger than follow-up infarctions, with a 12- to 17-cc difference in volume. 7/9 of the remaining patients had extracranial hemodynamic factors potentially delaying tracer arrival, including atrial fibrillation (AF; n=4), congestive heart failure (CHF; n=4), or extracranial internal carotid artery (ICA) stenosis (n=1). CONCLUSIONS: True "reversibility" of CT-CBV "core" lesions in AIS patients after thrombolytic therapy is rare, with small volumes of "salvaged" tissue. Pseudoreversibility of core lesions in standard CT-CBV maps can be avoided by using specific algorithmically optimized delay-correction software. Further investigation is warranted to determine whether this finding applies to algorithms provided by other vendors.

Anatomic differences after robotic-assisted radical prostatectomy and open prostatectomy: implications for radiation field design.

PURPOSE: To investigate the anatomy of the pelvis following robotic-assisted radical prostatectomy (RARP) compared to the anatomy of the pelvis following open prostatectomy (OP), and to determine if postoperative radiation field design should take surgical approach into consideration. METHODS AND MATERIALS: This report is a retrospective review of the postoperative pelvic magnetic resonance imaging (MRI) scans for all OP patients (10) and all RARP patients (15) who presented consecutively to the radiation oncology clinic and subsequently underwent MRI scanning between January 2007 and December 2008. All patients who presented are included in the study. We measured 13 distinct anatomic distances, and we used t tests to examine mean differences in each of the parameters between RARP and OP and analysis of variance to examine mean differences controlling for length of follow-up MRI postsurgery (in days) and body mass index as covariates. RESULTS: Of the measurements, we found that the superior levator separation is statistically significantly greater in the post-RARP group than in the post-OP group (P < .01). Similarly, the post-RARP group had a greater mean resection defect measurement (P = .01) as measured by a larger width of the bladder infundibulum. This suggests that the size of trigonal musculature defect is more pronounced after RARP. The total urethral length was statistically significantly longer in the RARP group (P = .03). The vesicorectal distance was variable depending on the location along the rectal wall but trended toward larger separation in the post-RARP group (P = .05). CONCLUSIONS: The pelvic anatomy after RARP is considerably different from that after OP. The current standard field design for post-prostatectomy radiation is defined by the post-OP pelvis. Our data support that the clinical target volume borders be expanded posteriorly and laterally in men who have undergone RARP. As RARP continues to become a more widespread surgical option for the management of localized prostate cancer, radiation field design may need to be adjusted.