Computed Tomography Scan — Detailed cross-sectional imaging

A computed tomography scan utilises specialised radiological equipment comprising a motorised rotating gantry housing an X-ray tube and digital detectors. As the patient passes through the doughnut-shaped opening, narrow beams of X-rays traverse the body. The detectors measure the attenuation of these beams as they penetrate various anatomical tissues of differing densities.

Sophisticated computer algorithms reconstruct these raw attenuation data into high-resolution, two-dimensional cross-sectional slices. These slices can also be stacked to render three-dimensional reconstructions of anatomical structures. Clinicians frequently administer iodinated contrast media intravenously, orally, or rectally to enhance vascular definition and delineate soft tissue boundaries between healthy organs and potential tumours.

CT scans are indispensable tools across every stage of the cancer pathway. They help detect primary tumours, determine precise tumor size, evaluate whether cancer has spread to regional lymph nodes or distant organs (staging), and guide targeted needle biopsies safely. During and after treatment, repeated scans allow oncologists to evaluate how effectively treatments are shrinking the tumour, guiding timely therapy adjustments.

Before a CT scan involving contrast dye, renal function tests (serum creatinine and estimated glomerular filtration rate) are performed to confirm kidney safety. CT does not directly detect molecular biomarkers, but it evaluates anatomical response based on standard criteria like RECIST. It is often combined with functional positron emission tomography to form integrated PET-CT scans.

CT scans are utilised extensively in almost all solid malignancies. They are especially critical in diagnosing, staging, and monitoring lung, colorectal, pancreatic, liver, kidney, ovarian, and prostate cancers. They are also standard tools for staging lymphomas and evaluating potential bone metastases throughout the skeleton.

CT findings are central to oncology treatment planning. High-resolution scans determine whether a tumour is surgically resectable or closely adhered to major blood vessels. Radiation oncologists use specialised CT simulation scans to calculate precise radiation delivery fields that target tumours while sparing adjacent normal tissues. Scans also document objective responses to systemic chemotherapies.