Abstract
Object. The authors hypothesized that the efficacy of intensity-modulated radiation therapy (IMRT) can be enhanced by selectively increasing the radiation dose to the biologically active positron emission tomography (PET)-documented positive tumor subregions while simultaneously maintaining the overall clinically established target dose. Methods. The authors undertook a feasibility study to evaluate IMRT PET/computerized tomography (CT) protocol for boost treatment in selected cancer patients. Prior to treatment, FDG-PET and CT scans were acquired using an integrated PET/CT scanner, ensuring accurate correlation between image sets. After acquisition, tumor volume and objects-at-risk (OARs) were outlined on the CT scans; any PET-positive tumor subregions were similarly outlined. Daily dosages of 1.8 to 2 Gy were prescribed to tumor volume and the margin whereas additional dosages of 10 to 20% were delivered to PET-positive subregions. Dosage—volume histogram—derived constraints were used in inverse planning to specify the desired dose to one or more PET-positive tumor subregions, CT-delineated tumor volume, and OARs. The IMRT treatment was delivered using a micromultileaf collimator. Simultaneous integrated boost radiation was successfully delivered using IMRT with PET/CT planning. Excellent dose conformality was achieved in the tumor volume and the dose to PET-positive tumor subregions was increased while minimizing the dose to OARs. Conclusions. When coupled with IMRT, PET/CT scanning allows dose escalation to biologically active subregions within the tumor volume. Further study is needed to determine if dose escalation to FDG-PET—active sites correlates with improved treatment outcome. Finally, in extracranial sites, PET scanning should only be performed with a dedicated PET/CT device because present image fusion technologies are inadequate for accurately registering deformable objects.
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