title: Positron emission tomography for radiation treatment planning.
abstract: OBJECTIVE
  To evaluate the impact of positron emission tomography (PET) on target volume delineation for radiation treatment planning.
  
  
  METHODS
  The data of the literature concerning the use of PET in target volume delineation are summarized. The following points are discussed for each tumor entity: biological background for the PET investigation, sensitivity and specificity of PET (with different tracers) in comparison to computed tomography (CT) and magnetic resonance imaging (MRI) and impact of PET on target volume definition. New PET tracers, which could visualize biological pathways, such as hypoxia, proliferation, angiogenesis, apoptosis and gene expression patterns, will also be discussed.
  
  
  RESULTS
  The results of clinical studies on the integration of PET in target volume definition for lung, head-and-neck, genitourinary and brain tumors were analyzed. Fluorodeoxyglucose-(FDG-)PET has a significant impact on GTV (gross tumor volume) and PTV (planning target volume) delineation in lung cancer and can detect lymph node involvement and differentiate malignant tissue from atelectasis. In head-and-neck cancer, the value of FDG-PET for radiation treatment planning is still under investigation. For example, FDG-PET could be superior to CT and MRI in the detection of lymph node metastases and unknown primary cancer and in the differentiation of viable tumor tissue after treatment. Therefore, it might play an important role in GTV definition and sparing of normal tissue. Choline PET and acetate PET are promising tracers in the diagnosis of prostate cancer, but their validity in local tumor demarcation, lymph node diagnosis and detection of recurrence has to be defined in future clinical trials. FDG-PET seems to be particularly valuable in lymph node status definition in cervical cancer. In high-grade gliomas and meningiomas, methionine PET helps to define the GTV and differentiate tumor from normal tissue. For other entities like gastrointestinal cancer, lymphomas, sarcomas, etc., the data of the literature are yet insufficient. The imaging of hypoxia, cell proliferation, angiogenesis, apoptosis and gene expression leads to the identification of different areas of a biologically heterogeneous tumor mass that can individually be targeted using intensity modulated radiotherapy (IMRT). In addition, a biological dose distribution can be generated, the socalled dose painting. However, systematic experimental and clinical trials are necessary to validate this hypothesis.
  
  
  CONCLUSIONS
  Regarding treatment planning in radiotherapy, PET offers advantages in terms of tumor delineation and the description of biological processes. To define the real impact of this investigation in radiation treatment planning, subsequent experimental, clinical and cost-benefit analyses are required.
authors.affiliation: Department of Radiation Oncology, Klinikum rechts der Isar, Technical University, Munich, Germany. anca-ligia.grosu@lrz.tum.de
authors.forename: Anca-Ligia
authors.initials: AL
authors.lastname: Grosu
authors.forename: Morand
authors.initials: M
authors.lastname: Piert
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Weber
authors.forename: Branislav
authors.initials: B
authors.lastname: Jeremic
authors.forename: Maria
authors.initials: M
authors.lastname: Picchio
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schratzenstaller
authors.forename: Frank B
authors.initials: FB
authors.lastname: Zimmermann
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
authors.forename: Michael
authors.initials: M
authors.lastname: Molls
mesh_terms: D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D005260:Female; D019788:Fluorodeoxyglucose F18; D005910:Glioma / Q000000981:diagnostic imaging / Q000532:radiotherapy; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D008207:Lymphatic Metastasis / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging; D008297:Male; D009369:Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D009382:Neoplasms, Unknown Primary / Q000000981:diagnostic imaging; D010865:Pilot Projects; D049268:Positron-Emission Tomography / Q000379:methods; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal; D016032:Randomized Controlled Trials as Topic; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18