PET-Based Biological Imaging for Radiation Therapy Treatment Planning

Abstract

Biologically conformal radiation therapy (BCRT), a convergence of intensity-modulated radiation therapy (IMRT) and positron emission tomography (PET)-based functional imaging, incorporates patient-specific, image-derived biological information. This approach may potentially lead to a paradigm shift in radiation therapyspatially varying dose prescriptions, or dose sculpting, for individualized and dosimetrically optimized treatment. This article reviews the current status of the technical, biological, and clinical aspects of PET-guided radiation therapy. It remains unclear, however, whether PET is currently capable of delineating the true extent of viable tumor with sufficient accuracy and precision to reliably guide therapy on a routine basis.

Fluorine-18-Labeled Fluoromisonidazole Positron Emission and Computed Tomography-Guided Intensity-Modulated Radiotherapy for Head and Neck Cancer: A Feasibility Study

“…One could dose escalate the entire GTV; however, an indiscriminate increase in the dose to the GTV could deliver unnecessary radiation to the normal tissues found within or around the GTV, possibly at the expense of increasing the incidence of late complications. An alternative method is to differentially dose escalate within the GTV (37)(38)(39)(40)(41). Because IMRT has the ability to dose paint different regions within the target, one can use this technology to selectively deliver an increased dose to the GTV h if the intratumor location can be identified.…”

Towards Biological Target Volumes Definition for Radiotherapy Treatment Planning: Quo Vadis PET/CT?

“…According to recommendations suggested by Ling et al [65], and later adopted by others, [85][86][87] a GTV defined by inherently low spatial resolution functional imaging such as PET should not be a surrogate for a GTV_CT, which has a superior spatial resolution necessary for dose pin-pointing in the future biologically-based dose painting radiotherapy treatment. The incorporation of regions with increased FDG uptake (indicative of the glycolytic phenotype) as the glycolytic BTV within the GTV_CT may allow escalated radiotherapy doses to part of the tumor and lead to a better outcome for NSCLC patients referred for curative radiotherapy [19,88,89].…”

Rationale, Instrumental Accuracy, and Challenges of PET Quantification for Tumor Segmentation in Radiation Treatment Planning

“…PET reveals functional information about elevated cell metabolic activity, including proliferation or molecular processes that may help localize the most active or potentially radiation-resistant parts of a tumor as well as cancerous metabolic activity not visible in CT images (Erdi et al, 2002;Zanzonico, 2006). Fig.…”

“…Distance the positron travels prior to annihilation, typically up to about 3 mm for the most often used radioactive isotopes (Zanzonico, 2006) 2 Detector Size and Distance to Detector PET spatial resolution usually cannot be less than half the size of the face of detector elements; increasing the diameter of the detector ring decreases its efficiency and increases the effect of photon non-colinearity 3 Photon Non-colinearity Photons are not emitted exactly back-to-back since the positron is not fully stopped at the time of annihilation 4 Block Effect…”