Reduction of radiation-induced xerostomia in nasopharyngeal carcinoma using CT simulation with laser patient marking and three-field irradiation technique.
OBJECTIVE
Tumor control and reduction of postirradiation xerostomia in patients with nasopharyngeal carcinoma (NPC) using the three-field irradiation technique based on the CT-based simulation with laser patient marking was investigated.


METHODS
Seventy-eight patients with NPC were consecutively treated between 1983 and 1993. In 33 patients treated before 1987, target volume was determined using a conventional x-ray simulator with a reference of CT images, and the primary site was treated by the conventional parallel-opposed two-field technique (Group I). In 45 patients treated from 1987, target volume was determined using a CT simulator slice by slice, the treatment field was projected onto the patient's skin by a laser beam projector mounted on a C-arm, and the primary site was irradiated by a three-fields (anterior and bilateral) technique (Group II). In Group II, the shape of each field was determined using a beam's eye view to reduce the dose to the bilateral parotid glands. The three-field technique reduced the dose to the superficial lobe of parotid gland to about two-thirds of the dose given by the two-field technique. Radiation-induced xerostomia was evaluated by clinical symptoms and radioisotope sialography.


RESULTS
The 5-year survival rate and disease-free survival rate were 46.6 and 31.2% in Group I, and 46.8 and 46.5% in Group II. A large variation in the volume of parotid glands were demonstrated, ranging from 9 cm3 to 61 cm3 among patients treated with CT simulation. Forty percent of the patients in Group II showed no or mild xerostomia, whereas all of the patients in Group I showed moderate to severe xerostomia (p < 0.01). The radioisotope sialography study showed that the mean secretion ratio by acid stimulation was improved from 3.8% in the Group I to 15.2% in the Group II (p < 0.01).


CONCLUSIONS
CT simulation was useful to determine the size and shape of each field to reduce the dose to the parotid gland, of which size varies largely among individual patients. The three-field technique based on CT simulation with laser patient markings is suggested to result in superior complication-free survival in terms of salivary dysfunction than did the conventional two-field technique with x-ray simulatior for NPC.
Nishioka
T
T
Department of Radiology, Hokkaido University, Sapporo, Kita-ku, Japan.
Shirato
H
H
Arimoto
T
T
Kaneko
M
M
Kitahara
T
T
Oomori
K
K
Yasuda
M
M
Fukuda
S
S
Inuyama
Y
Y
Miyasaka
K
K
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D009364:Neoplasm Recurrence, Local / Q000473:pathology; D009367:Neoplasm Staging; D010306:Parotid Gland / Q000473:pathology; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015996:Survival Rate; D014057:Tomography, X-Ray Computed; D014987:Xerostomia / Q000209:etiology / Q000517:prevention & control*