Multimodality nuclear medicine imaging in three-dimensional radiation treatment planning for lung cancer: challenges and prospects

The purpose of this study was to determine the utility of quantitative sing le photon emission computed tomography (SPECT) lung perfusion scans and F-1 8 fluorodeoxyglucose positron emission computed tomography (PET) during X-r ay computed tomography (CT)-based treatment planning for patients with lung cancer. Pre-radiotherapy SPECT (n = 104) and PET (n = 35) images were avai lable to the clinician to assist in radiation field design for patients wit h bronchogenic cancer. The SPECT and PET scans were registered with anatomi c information derived from CT. The information from SPECT and PET provides the treatment planner with functional data not seen with CT. SPECT yields t hree-dimensional (3D) lung perfusion maps. PET provides 3D metabolic images that assist in tumor localization. The impact of the nuclear medicine imag es on the treatment planning process was assessed by determining the freque ncy, type, and extent of changes to plans. Pre-radiotherapy SPECT scans wer e used to modify 11 (11%) treatment plans; primarily altering beam angles t o avoid highly functioning tissue. Fifty (48%) SPECT datasets were judged t o be 'potentially useful' due to the: detection of hypoperfused regions of the lungs, but were not used during treatment planning. PET data influenced 34% (12 of 35) of the treatment plans examined, and resulted in enlarging portions of the beam aperture (margins) up to 15 mm. Challenges associated with image quality and registration arise when utilizing nuclear medicine d ata in the treatment planning process. Initial implementation of advanced S PECT image reconstruction techniques that are not typically used in the cli nic suggests that the reconstruction method may influence dose response dat a derived from the SPECT images and improve image registration with CT. The use of nuclear medicine transmission computed tomography (TCT) for both SP ECT and PET is presented as a possible tool to reconstruct more accurate em ission images and to aid in the registration of emission data with the plan ning CT. Nuclear medicine imaging techniques appear to be a potentially val uable tool during radiotherapy treatment planning for patients with lung ca ncer. The utilization of accurate nuclear medicine image reconstruction tec hniques and TCT may improve the treatment planning process. (C) 1999 Elsevi er Science Ireland Ltd. All rights reserved.