Average CT in PET studies of colorectal cancer patients with metastasis in the liver and esophageal cancer patients

Elena Tonkopi,Eric M Rohren,Pai‐Chun Melinda Chi,Tinsu Pan,Adam C Riegel,Osama Mawlawi,Homer A Macapinlac

doi:10.1120/jacmp.v11i1.3073

Elena Tonkopi, Eric M Rohren + Show 5 more

Open Access

https://doi.org/10.1120/jacmp.v11i1.3073

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Abstract

Average CT (ACT) and PET have a similar temporal resolution and it has been shown to improve registration of the CT and PET data for PET/CT imaging of the thorax. The purpose of this study was to quantify the effect of ACT attenuation correction on PET for gross tumor volume (GTV) delineation with standardized uptake value (SUV) for liver and esophageal lesions. Our study included 48 colorectal cancer patients with metastasis in the liver and 52 esophageal cancer patients. These patients underwent a routine PET/CT scan followed by a cine CT scan of the thoracic region for ACT. Differences between the two PET data sets (PETHCT and PETACT) corrected with the helical CT (HCT) and ACT were quantified by analyzing image alignment, maximum SUV (SUVmax), and GTV. The 67% of the colorectal and 73% of the esophageal studies demonstrated misregistration between the PETHCT and HCT data. ACT was effective in removing misregistration artifacts in 65% of the misregisted colorectal and in 76% of the misregisted esophageal cancer patients. Misregistration between the CT and PET data affected GTVs due to the change in SUVmax with ACT. A change of SUVmax greater than 20% between PETHCT and PETACT was found in 15% of the colorectal and 17% of the esophageal cases. Our results demonstrated a more pronounced effect of misregistration for the smaller lesions (<5cm3) near the diaphragm (<5cm). ACT was effective in improving registration between the CT and PET data in PET/CT for the colorectal and esophageal cancer patients.PACS number: 87.58.Fg

Highlights

218 Tonkopi et al: Average CT in PET of liver and esophageal tumors can increase or decrease the treated volume between 15% to 60%.(19) Since CT data is used for attenuation correction (AC) of PET data, spatial misregistration between the CT and PET data may compromise the quantification of PET
We have proposed the use of respiration-averaged CT (ACT) to match the temporal resolution of CT and PET, and have shown that Average CT (ACT) reduces respiratory artifacts in positron emission tomography/computed tomography (PET/CT).[46,47] ACT acquisition has been optimized for clinical implementation and is available on the PET/ CT scanners in our institution
Patients were free breathing during all scans without any coaching of respiration. Both helical CT (HCT) and ACT were used for AC of the PET data, resulting in two data sets: PET corrected with HCT (PETHCT) and PET corrected with ACT (PETACT)

Summary

Introduction

The emergence of positron emission tomography/computed tomography (PET/CT) made it possible to provide anatomic and functional information in a single examination and to improve the sensitivity and specificity of tumor detection over PET or CT alone.[1,2,3] PET/CT imaging is part of routine clinical practice in oncology for diagnosis, staging, and monitoring of tumor response to therapy.[4,5,6] PET/CT has gained acceptance in cardiology for coronary artery imaging and myocardial functional assessment.[7,8,9,10,11,12,13] Standardized uptake value (SUV) is normally used as an indicator of malignancy.[14,15] Over 50% of all patients with cancer receive radiation therapy and FDG-PET has been shown to influence the decision of target volumes for non-small–cell lung cancers (NSCLC), esophageal tumors, and head-and-neck squamous cell carcinomas.[16,17,18,19,20,21,22,23,24] Incorporation of PET data into treatment volume delineation for NSCLC218 Tonkopi et al: Average CT in PET of liver and esophageal tumors can increase or decrease the treated volume between 15% to 60%.(19) Since CT data is used for attenuation correction (AC) of PET data, spatial misregistration between the CT and PET data may compromise the quantification of PET. Respiratory motion during imaging – in combination with the difference in temporal resolution between the PET and CT data – could cause misregistration between the PET and CT data, compromising the advantages of this hybrid imaging modality.[25] This misregistration problem did not exist in the stand-alone PET scanners, which used transmission rod sources to acquire transmission data for AC. Stand-alone PET scanners suffered from a long transmission scan time. Most patients were scanned in the position of arms down, different from the arms up position typically used in the radiotherapy simulation or treatment, making it more complex in registration of the PET and CT data. The PET and CT data were acquired as two different sessions and at two different times. Issues pertaining to software registration of the PET and CT data acquired in two different scanners have been reduced significantly with hardware registration of the PET/CT scanner.[26]

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