Coregistration of prechemotherapy PET-CT for planning pediatric Hodgkin's disease radiotherapy significantly diminishes interobserver variability of clinical target volume definition.
OBJECTIVE
To assess the interobserver variability in clinical target volume (CTV) definitions when using registered (18)F-labeled deoxyglucose positron emission tomography (FDG-PET-CT) versus side-by-side image sets in pediatric Hodgkin's disease (HD).


METHODS
Prechemotherapy FDG-PET-CT scans performed in the treatment position were acquired from 20 children (median age, 14 years old) with HD (stages 2A to 4B) and registered with postchemotherapy planning CT scans. The patients had a median age of 14 years and stages of disease ranging between 2A and 4B. Image sets were coregistered using a semiautomatic coregistration system. The biological target volume was defined on all the coregistered images as a guide to defining the initial site of involvement and to avoid false-positive or negative results. Five radiation oncologists independently defined the CTV for all 20 patients: once using separate FDG-PET-CT images as a guide (not registered) to define CTVa and once using the registered FDG-PET-CT data to define CTVb. The total volumes were compared, as well as their coefficients of variation (COV). To assess the interobserver variability, the percentages of intersection between contours drawn by all observers for each patient were calculated for CTVa and for CTVb.


RESULTS
The registration of a prechemotherapy FDG-PET-CT scan caused a change in the CTV for all patients. Comparing CTVa with CTVb showed that the mean CTVb increased in 14 patients (range, 0.61%-101.96%) and decreased in 6 patients (range, 2.97%-37.26%). The COV for CTVb significantly decreased for each patient; the mean COVs for CTVa and CTVb were 45% (21%-65%) and 32% (13%-57%), respectively (p = 0.0004). The percentage of intersection among all CTVbs for the five observers increased significantly by 89.77% (1.99%-256.41%) compared to that of CTVa (p = 0.0001).


CONCLUSIONS
High observer variability can occur during CT-based definition of CTVs for children diagnosed with HD. Registration of FDG-PET and planning CT images resulted in significantly greater consistency of tumor volume definition.
Metwally
Hussein
H
Institut Claudius Regaud, Department of Radiation Oncology, Toulouse, France.
Courbon
Frédéric
F
David
Isabelle
I
Filleron
Thomas
T
Blouet
Aurélien
A
Rives
Michel
M
Izar
Françoise
F
Zerdoud
Slimane
S
Plat
Geneviève
G
Vial
Julie
J
Robert
Alain
A
Laprie
Anne
A
D000293:Adolescent; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage / Q000627:therapeutic use; D001761:Bleomycin / Q000008:administration & dosage; D002648:Child; D003520:Cyclophosphamide / Q000008:administration & dosage; D004317:Doxorubicin / Q000008:administration & dosage; D019788:Fluorodeoxyglucose F18; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D006689:Hodgkin Disease / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D008297:Male; D008479:Mediastinal Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D015588:Observer Variation; D049268:Positron-Emission Tomography / Q000379:methods*; D011241:Prednisone / Q000008:administration & dosage; D011344:Procarbazine / Q000008:administration & dosage; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden; D014747:Vinblastine / Q000008:administration & dosage; D014750:Vincristine / Q000008:administration & dosage
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D001761:Bleomycin; D011344:Procarbazine; D014750:Vincristine; D014747:Vinblastine; D004317:Doxorubicin; D003520:Cyclophosphamide; D011241:Prednisone