Purpose: Functional avoidance radiotherapy proposes to use functional imaging to design treatment plans that reduce doses to functional regions of lung. Prospective data has shown that reducing doses to functional lung results in reduced pulmonary toxicity. Various lung function imaging modalities have been proposed for functional avoidance; however, there have been no studies evaluating whether using different imaging modalities results in dosimetrically different functional avoidance plans. The purpose of this study was to quantify the differences in treatment plans as a function of lung function imaging modality. Methods: 25 lung cancer patients enrolled on a prospective trial underwent nuclear medicine SPECT ventilation/perfusion scans prior to radiotherapy. A functional perfusion (‘FuncPerf’) and ventilation (‘FuncVent’) contour was generated by selecting ≥75% perfusion/ventilation values. The similarity between the FuncVent and FuncPerf contours was calculated using DICE coefficients. 2 plans were generated for each patient: a FuncVent-based and FuncPerf-based functional avoidance plan. The differences in mean dose and V20Gy to the FuncVent/FuncPerf structure between the functional avoidance plans based on ventilation/perfusion were calculated (presented as mean [range]). Results: The DICE correlation between FuncVent/FuncPerf contours was 0.51 (0.21- 0.76). The difference in mean dose and V20Gy to the FuncVent structure between the ventilation/perfusion functional avoidance plans were 0.2 Gy (-0.9-3.4 Gy) and 0.82% (-2.5%-12.4%), respectfully. The differences in mean dose and V20Gy to the FuncPerf structure were 0.6 Gy (-0.3-2.4 Gy) and 1.6% (-0.5%-7.7%), respectfully. There was weak correlation between ventilation/perfusion DICE scores and differences in FuncVent/FuncPerf dose differences (all correlations <0.16). Conclusion: Our data showed that on average, selecting ventilation or perfusion for functional avoidance resulted in similar dosimetric distributions; however, for individual patients the differences could be significant. Our study uses prospective trial data to offer seminal guidance by underscoring the need to individually consider ventilation and perfusion for functional avoidance radiotherapy.
Belardo J, Zhang S, Castillo E, Castillo R, Rusthoven C, Jones B, et al [Guerrero T, Grills I] Does lung function imaging modality have a dosimetric impact on functional avoidance treatment planning: assessment using prospective clinical trial data. Med Phys. 2022 Jun; 49(6):E514.