The clinical effect of perfusion single-photon emission computed tomography (SPECT) image-guided planning in patients treated for locally advanced and metastatic lung cancers is assessed.
Jonathan W. Thompson, MD, Sui Shen, PhD, Luvenia Bender, MD, Sharon A. Spencer, MD; Department of Radiation Oncology, University of Alabama, Birmingham
Purpose: To assess the clinical effect of perfusion single-photon emission computed tomography (SPECT) image-guided planning in patients treated for locally advanced and metastatic lung cancers.
Methods: Seventeen patients with lung cancer who had perfusion imaging obtained in the treatment position fused with treatment planning scans were evaluated to assess the effects of radiation to regions of perfusion, as defined by the pixelated value of the perfusion image (PVPI) method. This method created regions of perfusion, defined as full perfusion (P60–100), moderate perfusion (P40–60), poor perfusion (P20–40), and very poor perfusion (P0–20). All patients were planned prospectively at the time of treatment, with the intent of avoidance of actively perfusing lung while respecting known parameters associated with increased risk of pneumonitis. Volumes of each perfusion region were recorded in all patients, and ratios of planning target volume (PTV) to total lung and active lung were generated. Values for V20, V5, and mean lung dose (MLD) were recorded for whole lung as well as in each perfusion region. Dosimetric variables in each perfusion region were recorded, and patients were retrospectively evaluated for the development of radiation pneumonitis.
Results: Five patients required systemic steroids for radiation pneumonitis. There were no significant differences in pretreatment pulmonary function tests (PFTs); dose delivered; PTV volume; or whole-lung V20, V5, or MLD between patients who did and did not require systemic steroids for pneumonitis. There was a trend for less volume of P60–100 in those with pneumonitis (171 cc vs 273 cc; P = .1). There were a number of differences noted in P20–40 with regard to trends of increased V20 (28% vs 23%; P = .1) and V5 (59% vs 47%; P = .1) in patients with pneumonitis. There was also a statistically significant increase in MLD in P20–40 (1,696 cGy vs 1,357 cGy; P = .04) as well as V5 in P40–60 (63% vs 40%; P = .05). In patients who developed pneumonitis, there was a trend for a decreased ratio of P60–100 to PTV (0.41 vs 1.98; P = .09). Of the six patients who were treated using IMRT, there were statistically significant increases in V5 (61% vs 48%; P = .05) in the whole lung as well as increases of V20 in P0–20 (23% vs 33%; P = .02) and P20–40 (19% vs 27%; P = .03).
Conclusion: SPECT-based perfusion imaging has utility in terms of functional treatment planning for lung cancer and may assist with avoidance of actively perfusing lung, although the clinical significance of this remains in question due to results suggesting some predictability of pneumonitis associated with higher doses delivered to poorly perfusing regions. Since treatment plans were designed with the intention of minimizing dose to the active regions and thereby pushing this dose to regions of lower perfusion, it can be inferred that the avoidance of highly perfusing regions may make moderately perfusing regions more vulnerable to the effects of radiation pneumonitis, especially in patients with small volumes of active lung. With the advantage of increased conformity, IMRT has utility in avoidance of these concerning regions and is a subject of ongoing research.