title: Comparative evaluation of CT-based and respiratory-gated PET/CT-based planning target volume (PTV) in the definition of radiation treatment planning in lung cancer: preliminary results.
abstract: OBJECTIVE
  The aim of this study was to compare planning target volume (PTV) defined on respiratory-gated positron emission tomography (PET)/CT (RG-PET/CT) to PTV based on ungated free-breathing CT and to evaluate if RG-PET/CT can be useful to personalize PTV by tailoring the target volume to the lesion motion in lung cancer patients.
  
  
  METHODS
  Thirteen lung cancer patients (six men, mean age 70.0 years, 1 small cell lung cancer, 12 non-small cell lung cancer) who were candidates for radiation therapy were prospectively enrolled and submitted to RG-PET/CT. Ungated free-breathing CT images obtained during a PET/CT study were visually contoured by the radiation oncologist to define standard clinical target volumes (CTV1). Standard PTV (PTV1) resulted from CTV1 with the addition of 1-cm expansion of margins in all directions. RG-PET/CT images were contoured by the nuclear medicine physician and radiation oncologist according to a standardized institutional protocol for contouring gated images. Each CT and PET image of the patient's respiratory cycle phases was contoured to obtain the RG-CT-based CTV (CTV2) and the RG-PET/CT-based CTV (CTV3), respectively. RG-CT-based and RG-PET/CT-based PTV (PTV2 and PTV3, respectively) were then derived from gated CTVs with a margin expansion of 7-8 mm in head to feet direction and 5 mm in anterior to posterior and left to right direction. The portions of gated PTV2 and PTV3 geometrically not encompassed in PTV1 (PTV2 out PTV1 and PTV3 out PTV1) were also calculated.
  
  
  RESULTS
  Mean ± SD CTV1, CTV2 and CTV3 were 30.5 ± 33.2, 43.1 ± 43.2 and 44.8 ± 45.2 ml, respectively. CTV1 was significantly smaller than CTV2 and CTV3 (p = 0.017 and 0.009 with Student's t test, respectively). No significant difference was found between CTV2 and CTV3. Mean ± SD of PTV1, PTV2 and PTV3 were 118.7 ± 94.1, 93.8 ± 80.2 and 97.0 ± 83.9 ml, respectively. PTV1 was significantly larger than PTV2 and PTV3 (p = 0.038 and 0.043 with Student's t test, respectively). No significant difference was found between PTV2 and PTV3. Mean ± SD values of PTV2 out PTV1 and PTV3 out PTV1 were 12.8 ± 25.4 and 14.3 ± 25.9 ml, respectively. The percentage values of PTV2 out PTV1 and PTV3 out PTV1 were not lower than 10 % of PTV1 in 6/13 cases (46.2 %) and than 20 % in 3/13 cases (23.1 %).
  
  
  CONCLUSIONS
  Our preliminary data showed that RG-PET/CT in lung cancer can affect not only the volume of PTV but also its shape, as demonstrated by the assessment of gated PTVs outside standard PTV. The use of a gating technique is thus crucial for better delineating PTV by tailoring the target volume to the lesion motion in lung cancer patients.
authors.affiliation: Nuclear Medicine, San Gerardo Hospital, Monza, Italy, l.guerra@hsgerardo.org.
authors.forename: Luca
authors.initials: L
authors.lastname: Guerra
authors.forename: Sofia
authors.initials: S
authors.lastname: Meregalli
authors.forename: Alessandra
authors.initials: A
authors.lastname: Zorz
authors.forename: Rita
authors.initials: R
authors.lastname: Niespolo
authors.forename: Elena
authors.initials: E
authors.lastname: De Ponti
authors.forename: Federica
authors.initials: F
authors.lastname: Elisei
authors.forename: Sabrina
authors.initials: S
authors.lastname: Morzenti
authors.forename: Sarah
authors.initials: S
authors.lastname: Brenna
authors.forename: Andrea
authors.initials: A
authors.lastname: Crespi
authors.forename: Gianstefano
authors.initials: G
authors.lastname: Gardani
authors.forename: Cristina
authors.initials: C
authors.lastname: Messa
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D055425:Respiratory-Gated Imaging Techniques; D055752:Small Cell Lung Carcinoma / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed