Consensus Report from Oncology Advisory Board Meeting

Introduction Imaging in patients with cancer has increased exponentially for diagnosis, staging, follow-up, and surveillance. The radiologist has to be prudent in choosing the modality for investigation and use of contrast media (CM) so that imaging studies do not further contribute to morbidity in patients undergoing chemo or immunotherapy. Radiologists have to work closely with oncologists and nephrologists to ensure optimum renal health in these patients. In this chapter, we will discuss optimization of imaging protocols and contrast usage to reduce the risk of renal injury in an oncologic setting. Computed Tomography (CT) Protocols Low radiation-dose CT examinations would be the norm in not too distant future. Low-kVp CT protocols have been developed to decrease quantity of CM administered and radiation dose. Relative attenuation of iodinated CM is increased at lower kVp resulting in higher contrast enhancement than that obtained at higher kVp for a similar amount of administered CM. Iodine attenuation is higher at low-kVp and thus signal-to-noise ratio (SNR) can be kept constant with reduced radiation exposure. Use of high iodine concentration produces more noise but can be offset by lowering the mAs which in turn implies reduced radiation dose. The low kV and “low mAs–high iodine concentration” options can be combined to maximize the reduction in radiation dose and contrast volume. Iterative Reconstruction (IR) [1] Iterative reconstruction is a new technique of image reconstruction for reducing radiation exposure that utilizes an alternative image reconstruction algorithm to filtered back projection to reduce noise without impairing signal. This is available in all new generation scanners and is known by several acronyms like ASIR and ASIR-v (from GE Healthcare), IRIS and ADMIRE (Siemens), iDOSE4 (Philips Healthcare), and AIDR (from Toshiba). Higher SNR can be used to improve image quality and visualization of small enhancing structures and arterially enhancing lesions. Low-kVp by itself can lead to an increase in image quality. With IR, further reduction of noise and thus an increase in SNR would be possible, resulting in increased image quality without compromising on diagnostic capabilities. IR additionally reduces radiation dose. SNR values are similar to “low-kVp alone” and low-mAs/high-iodine signal approaches. Another advantage is reduced iodine dose. The benefits of using low-kVp CT include reduction in the dose of CM and dose of ionizing radiation [2]. Combined with automatic kVp selection tools, reference mAs should be set at a lower level when using a contrast injection protocol that provides higher signal. With IR, there is lowered radiation exposure and mAs can be reduced to obtain an SNR that is likely to be low-kVp without IR. IR additionally reduces radiation dose. SNR values are similar to “low-kVp alone” and low-mAs/high-iodine signal approaches. Another advantage is reduced iodine dose. The benefits of using low-kVp CT include reduction in the dose of CM and dose of ionising radiation [2]. The Optimal Use of Contrast Media in Cancer Patients – Radiologists' Perspective This chapter has been written with expert scientific inputs by Dr Ravikanth Balaji (Head of Department - Radiology, Apollo Speciality Hospital, Chennai).