MO-E-AUD C-02: Incorporating SPECT Functional Lung Images in Routine Treatment Planning for Lung Cancer

Abstract

Purpose: SPECT lung perfusion images has been used to derive functional DVH for planning a decade ago (Marks et al 1994), however, it is still not widely used. The current study describes a method to incorporate functional images in routine planning based only on commercial TPS. Method and Materials: 12 patients were immobilized with the same Alpha‐Cradle on SPECT/CT combo unit and CT simulator. The SPECT was registered to the planning CT by registering the low‐resolution CT to the planning CT. The whole lung was divided into several sub‐volumes according to the pixel values of the perfusion image (PVPI) above the background. The lung functionality was assumed to be linear with the PVPI for up to 80% of its maximum value, as used by other investigators. The mean PVPI in each lung sub‐volume was used to defined the functionality weight factor. The V20function was determined based on the dose‐volume and weight factor for each sub‐volume. Results: The priority score was set for each sub‐volume according to the weight factor for IMRT optimization. For non‐IMRT plan, sub‐volumes with higher weight factors serve as avoidance structures for field optimization. The 22% (range 11–35%) lung volume had a weight factor ⩾ mean weight factor. The difference between perfusion weighted lung volume and actual lung volume was − 1565 cc (mean, range −491 to −3270 cc). V20function was smaller than V20 in 11 of 12 patient and the difference ranged from −0.4% to −12%. Conclusion: Because the exact relationship between lung functionality and PVPI is still uncertain, large bin number may not be required. Our method for reducing the number of functional bins to several/less than a dozen may still provide useful prediction for toxicity and significantly reduces the amount of effort in planning and can be routinely implemented in a clinical setting.