Comparison of positron emission tomography (PET) and computed tomography (CT) for better target volume definition in radiation therapy planning.
BACKGROUND
In cancer patients, positron emission tomography/ computed tomography (PET/CT) fused images present less variability in target contouring, respect to use only CT images, respectively. However, the gold standard has not yet been clearly established between radiation oncologists with regard to PET images and the methodology of contouring targets with confidence using PET/CT fused images. The aim of this study was to determine whether integrated PET/CT fused images provide advantages in virtual simulation compared with morphological contouring only with CT.


METHODS
Thirty cancer patients were evaluated in an adapted PET/CT hybrid in radiotherapy (RT) setup position, with 20 of them being suitable for RT: 17 were suitable for curative intent, which was the group of interest in this study. All image series were sent to the RT work station (WS) where CT and PET series were automatically fused by Digital Imaging and Communications in Medicine (DICOM) in each case. PET series were threshold and were subjected to source-to-background contrast algorithms to fi nally redefine the original tumour description. Three different radiotherapy plans (RTP) for each patient were compared after targets were contoured: [1] planning over metabolic (PET) contoured targets, [2] planning over only morphologic (CT) targets, and [3] planning over targets obtained for treatment based on fused PET/CT images.


RESULTS
PET/CT findings altered initial-stage planning in four patients (23.5%) because they had been undergoing chemotherapy. Gross target volume (GTV) and planning target volume (PTV) based only on PET showed more homogeneity to obtain mean doses (p = 0.025) with respect to those based on PET/CT, respectively. However, no percentage differences were observed in median PTV doses between the planning methods, although there was higher variability in PET/CT planning. Morphological (CT) and PET/ CT target volumes were more voluminous than metabolic (PET) volumes. On the other hand, 20% of metabolic (PET) PTV were out of those defined by PET/CT. Thoracic RT plans based on PET preserved better bilateral lung [percentage volume of lung irradiated with a dose of 20 Gy (V20); significance, R(2) = 0.559, p = 0.006].


CONCLUSIONS
For our physicians, PET/CT fused images allowed better contouring of primary tumours in 40% of head and neck cancers and 34% of thoracic cancers. PET/CT provides useful information for virtual simulation therapy. Image treatment and planning in an RT workstation is mandatory.
Vila
Antoni
A
Unitat de Radioteràpia i Oncologia, Hospital Plató, Barcelona, Spain. 3167avc@comb.es
Sánchez-Reyes
Alberto
A
Conill
Carles
C
Gispert
Juan Domingo
JD
Trampal
Carlos
C
Láinez
Carmen
C
Vayreda
Jordi
J
Pedro
Agustí
A
D000368:Aged; D003198:Computer Simulation; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008875:Middle Aged; D009367:Neoplasm Staging / Q000379:methods; D009369:Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D049268:Positron-Emission Tomography / Q000379:methods*; D011832:Radiation Injuries / Q000453:epidemiology / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden
Int J Radiat Oncol Biol Phys. 2007 Feb 1;67(2):410-6
17236964
Int J Radiat Oncol Biol Phys. 2008 Nov 1;72(3):702-6
18374513
Int J Radiat Oncol Biol Phys. 2008 Oct 1;72(2):335-42
18793953
Semin Radiat Oncol. 2008 Apr;18(2):136-48
18314068
Radiother Oncol. 2009 Apr;91(1):85-94
19100641
Br J Radiol. 2006 Sep;79 Spec No 1:S27-35
16980683
Int J Radiat Oncol Biol Phys. 2008 Mar 15;70(4):1035-8
17996383
Clin Transl Oncol. 2007 Aug;9(8):473-4
17720648
Radiother Oncol. 2006 Nov;81(2):209-25
17064802
J Nucl Med. 2004 Nov;45(11):1843-50
15534053
Radiother Oncol. 2008 Oct;89(1):13-8
18555547
Crit Rev Oncol Hematol. 2005 Dec;56(3):345-51
15990331
Int J Radiat Oncol Biol Phys. 2002 Aug 1;53(5):1174-84
12128118
Int J Radiat Oncol Biol Phys. 2008 May 1;71(1):2-4
18406881
Int J Radiat Oncol Biol Phys. 2006 May 1;65(1):143-51
16618577
Int J Radiat Oncol Biol Phys. 2005 Nov 15;63(4):1016-23
15979817
J Nucl Med. 2005 Aug;46(8):1342-8
16085592
Biomed Imaging Interv J. 2007 Jan;3(1):e4
21614264
Int J Radiat Oncol Biol Phys. 2008 Oct 1;72(2):311-2
18793948
Radiother Oncol. 2006 Mar;78(3):254-61
16545881
Int J Radiat Oncol Biol Phys. 2008 Mar 1;70(3):678-84
18262086
Int J Radiat Oncol Biol Phys. 2008 Feb 1;70(2):322-9
17889447
Int J Radiat Oncol Biol Phys. 2005 May 1;62(1):70-5
15850904