Limitation of conventional two dimensional radiation therapy planning in nasopharyngeal carcinoma.
OBJECTIVE
To assess the adequacy of coverage of gross tumor volume (GTV) with traditional two dimensional (2D) radiation therapy (RT) planning in patients with nasopharyngeal cancer (NPC).


METHODS
The study comprised 94 of 179 patients treated with definitive RT between 1993 and 1997. The inclusion requirement was the availability of a digitally archived pretreatment magnetic resonance imaging. The digital images were used to record the precise location of the GTV in the sagittal plane. As a separate procedure, sagittal dose distributions for each treatment phase were created by digitizing the simulation field parameters into treatment planning software without knowledge of the GTV. The location of the GTV and dose distribution in the sagittal plane were superimposed on each other and GTV coverage by the 50, 90 and 95% isodose lines determined for each phase of treatment.


RESULTS
The 1997 tumour node metastasis (TNM) stage distribution was: 7 (8%) stage I, 16 (16%) stage II, 30 (32%) stage III and 41 (44%) stage IV. Median follow-up was 4.4 years. Median primary dose was 66 Gy. The actuarial 5-year overall survival, disease free survival and local relapse free rates were 88, 54 and 66%, respectively. The GTV was covered by the 50, 90 and 95% isodose lines for all phases of the multiphase plan in only 53, 20 and 9% of patients, respectively. The GTV was more likely to be undercovered in the latter phases of the plan particularly in those patients with advanced T category.


CONCLUSIONS
2D RT planning has significant limitations in achieving adequate GTV coverage in NPC. We strongly recommend 3D planning using either conformal techniques of dose delivery or intensity modulated radiation therapy for the treatment of these patients.
Waldron
John
J
Department of Radiation Oncology, The Princess Margaret Hospital, University of Toronto, 610 University Avenue, Toronto, Ont. M5G 2M9, Canada.
Tin
Mo Mo
MM
Keller
Anne
A
Lum
Cheemun
C
Japp
Barbara
B
Sellmann
Susanna
S
van Prooijen
Monique
M
Gitterman
Leah
L
Blend
Ralph
R
Payne
David
D
Liu
Fei-Fei
FF
Warde
Padraig
P
Cummings
Bernard
B
Pintilie
Melania
M
O'Sullivan
Brian
B
D000293:Adolescent; D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000473:pathology / Q000532:radiotherapy* / Q000556:secondary; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008207:Lymphatic Metastasis; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D009897:Optic Chiasm / Q000528:radiation effects; D011832:Radiation Injuries / Q000517:prevention & control; D011835:Radiation Protection; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D013116:Spinal Cord / Q000528:radiation effects