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 single photon emission computed tomography (SPECT) lung perfusion scans and F-18 fluorodeoxyglucose positron emission computed tomography (PET) during X-ray computed tomography (CT)-based treatment planning for patients with lung cancer. Pre-radiotherapy SPECT (n = 104) and PET (n = 35) images were available to the clinician to assist in radiation field design for patients with bronchogenic cancer. The SPECT and PET scans were registered with anatomic information derived from CT. The information from SPECT and PET provides the treatment planner with functional data not seen with CT. SPECT yields three-dimensional (3D) lung perfusion maps. PET provides 3D metabolic images that assist in tumor localization. The impact of the nuclear medicine images on the treatment planning process was assessed by determining the frequency, type, and extent of changes to plans. Pre-radiotherapy SPECT scans were used to modify 11 (11%) treatment plans; primarily altering beam angles to avoid highly functioning tissue. Fifty (48%) SPECT datasets were judged to 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 data in the treatment planning process. Initial implementation of advanced SPECT image reconstruction techniques that are not typically used in the clinic suggests that the reconstruction method may influence dose response data derived from the SPECT images and improve image registration with CT. The use of nuclear medicine transmission computed tomography (TCT) for both SPECT and PET is presented as a possible tool to reconstruct more accurate emission images and to aid in the registration of emission data with the planning CT. Nuclear medicine imaging techniques appear to be a potentially valuable tool during radiotherapy treatment planning for patients with lung cancer. The utilization of accurate nuclear medicine image reconstruction techniques and TCT may improve the treatment planning process.