Dose-response relationship of nasopharyngeal carcinoma above conventional tumoricidal level: a study by the Hong Kong nasopharyngeal carcinoma study group (HKNPCSG).
OBJECTIVE
To define the dose-response relationship of nasopharyngeal carcinoma (NPC) above the conventional tumoricidal dose level of 66 Gy when the basic radiotherapy (RT) course was given by the 2D Ho's technique.


METHODS
Data from all five regional cancer centers in Hong Kong were pooled for this retrospective study. All patients (n = 2426) were treated with curative-intent RT with or without chemotherapy between 1996 and 2000 with the basic RT course using the Ho's technique. The primary endpoint was local control. The prognostic significance of dose-escalation ('boost') after 66 Gy, T-stage, N-stage, use of chemotherapy, sex and age (< or =40 years vs >40 years) was studied. Both univariate and multivariate analyses were performed.


RESULTS
On multivariate analysis, T-stage (P < 0.01; hazard ratio [HR], 1.58) and optimal boost (P = 0.01; HR, 0.34) were the only significant factors affecting local failure for the whole study population, and for the population of patients treated by radiotherapy alone, but not for patients who also received chemotherapy. The following were independent determinants of local failure for patient groups with different T-stages treated by radiotherapy alone: use of a boost in T1/T2a disease (P = 0.01; HR, 0.33); use of a boost (P < 0.01; HR, 0.60) and age (P = 0.01; HR, 1.02) in T3/T4 tumors. Among patients with T2b tumors treated by radiotherapy alone and given a boost, the use of a 20 Gy-boost gave a lower local failure rate than a 10 Gy-boost. There was no apparent excess mortality attributed to RT complications.


CONCLUSIONS
Within the context of a multi-center retrospective study, dose-escalation above 66 Gy significantly improved local control for T1/T2a and T3/4 tumors when the primary RT course was based on the 2D Ho's technique without additional chemotherapy. 'Boosting' in NPC warrants further investigation. Caution should be taken when boosting is considered because of possible increase in radiation toxicity.
Teo
Peter M L
PM
Department of Clinical Oncology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, China.
Leung
Sing Fai
SF
Tung
Stewart Y
SY
Zee
Benny
B
Sham
Jonathan S T
JS
Lee
Anne W M
AW
Lau
Wai Hon
WH
Kwan
Wing Hong
WH
Leung
To Wai
TW
Chua
Daniel
D
Sze
Wai Man
WM
Au
Joseph S K
JS
Yu
Kwok Hung
KH
O
Sai Ki
SK
Kwong
Dora
D
Yau
Tsz Kok
TK
Law
Stephen C K
SC
Sze
Wing Kin
WK
Au
Gordon
G
Chan
Anthony T C
AT
D000328:Adult; D000704:Analysis of Variance; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002277:Carcinoma / Q000188:drug therapy / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D017024:Chemotherapy, Adjuvant; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D006723:Hong Kong; D006801:Humans; D008499:Medical Records; D009303:Nasopharyngeal Neoplasms / Q000188:drug therapy / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D018714:Radiotherapy, Adjuvant; D012189:Retrospective Studies; D016019:Survival Analysis; D016896:Treatment Outcome