The incorporation of SPECT functional lung imaging into inverse radiotherapy planning for non-small cell lung cancer.

BACKGROUND AND PURPOSE Patients with non-small cell lung cancer (NSCLC) often have inhomogeneous lung perfusion. Radiotherapy planning computed tomography (CT) scans have been accurately co-registered with lung perfusion single photon emission computed tomography (SPECT) scans to design radiotherapy treatments which limit dose to healthy 'perfused' lung. PATIENTS AND METHODS Patients with localised NSCLC had CT and SPECT scans accurately co-registered in the planning system. The SPECT images were used to define a volume of perfused 'functioning' lung (FL). Inverse planning software was used to create 3D-conformal plans, the planning objective being either to minimise the dose to whole lungs (WL) or to minimise the dose to FL. RESULTS Four plans were created for each of six patients. The mean difference in volume between WL and FL was 1011.7 cm(3) (range 596.2-1581.1cm(3)). One patient with bilateral upper lobe perfusion deficits had a 16% reduction in FLV(20) (the percentage volume of functioning lung receiving >or=20 Gy). The remaining patients had inhomogeneous perfusion deficits such that inverse planning was not able to sufficiently optimise beam angles to avoid functioning lung. CONCLUSION SPECT perfusion images can be accurately co-registered with radiotherapy planning CT scans and may be helpful in creating treatment plans for patients with large perfusion deficits.