Functional and molecular image guidance in radiotherapy treatment planning optimization

Abstract

Functional and molecular imaging techniques are increasingly being developed and used to quantitatively map the spatial distribution of parameters, such as metabolism, proliferation, hypoxia, perfusion, and ventilation, onto anatomically imaged normal organs and tumor. In radiotherapy optimization, these imaging modalities offer the promise of increased dose sparing to high-functioning subregions of normal organs or dose escalation to selected subregions of the tumor as well as the potential to adapt radiotherapy to functional changes that occur during the course of treatment. The practical use of functional/molecular imaging in radiotherapy optimization must take into cautious consideration several factors whose influences are still not clearly quantified or well understood including patient positioning differences between the planning computed tomography and functional/molecular imaging sessions, image reconstruction parameters and techniques, image registration, target/normal organ functional segmentation, the relationship governing the dose escalation/sparing warranted by the functional/molecular image intensity map, and radiotherapy-induced changes in the image intensity map over the course of treatment. The clinical benefit of functional/molecular image guidance in the form of improved local control or decreased normal organ toxicity has yet to be shown and awaits prospective clinical trials addressing this issue.

Figure 1

Coronal view showing plans with (bottom) and without (top) SPECT guidance. The central purple and pink structures are primary and boost targets; lung is shaded by SPECT activity intensity, ranging from red (highest) to green (lowest). Isodose lines demonstrate that SPECT-guidance decreased dose to higher perfusion regions. Reprinted with permission.

Figure 2

Plot of mean lung dose vs. beam angle, with arrows indicating beams selected. Reprinted with permission.

Figure 3

Distribution of Carbon-11 acetate in axial (top), coronal (middle) and sagittal (bottom) planes, superimposed on the corresponding CT planes through the prostate. Reprinted with permission.

Figure 4

Isodose lines and FDG-PET intensity colormap superimposed on axial (top), sagittal (middle) and coronal (bottom) slices. Numbers indicate the dose in Gy per fraction, reflecting dose escalation to regions of higher FDG uptake. Reprinted with permission.