How fast is repopulation of tumor cells during the treatment gap?
OBJECTIVE
Our goal was to analyze the repopulation of surviving tumor cells during a treatment gap in radiotherapy for head-and-neck cancer.


METHODS
Clinical material is based on the records of 1502 patients treated by radiotherapy alone in Maria Sklodowska-Curie Memorial Institute in Gliwice during the period between1980 and 1989. All patients had histologically confirmed squamous cell carcinoma of the larynx or pharynx. The mean gap duration was 9 days. Only 10% of patients were treated without gaps. The dose per fraction was in the range of 1.5 to 2.5 Gy. Patient data were fitted directly to the mixed linear-quadratic model using maximum-likelihood estimation. Tumor stage or tumor localization was introduced into the equation as a categorical variable. Tumor proliferation was estimated by dividing the treatment gaps into three groups: the first 2 weeks, second 2 weeks, and the period after 4 weeks of irradiation.


RESULTS
Tumor control probability was significantly correlated with radiation dose, tumor progression (according to TNM), overall treatment time, and gap duration. Laryngeal cancers had a better prognosis than cancers of the oro- and nasopharynx. Significant tumor repopulation was found after the first 2 weeks of radiotherapy. During the treatment gap, the proliferation rate was equal to 0.75 Gy/day. During the days with irradiation, repopulation was slower and equal to 0.2 Gy/day.


CONCLUSIONS
The repopulation of tumor cells is faster during a gap than during the normal days of irradiation. Accelerated repopulation probably starts soon after 2 weeks of irradiation.
Center of Oncology, Maria Sklodowska-Curie Memorial Institute Gliwice, Wyd. Armii Krajowej 15 44-101, Gliwice, Poland. tarnawski@io.gliwice.pl
Rafal
R
Tarnawski
Jack
J
Fowler
Krzysztof
K
Skladowski
Andrzej
A
Swierniak
Rafal
R
Suwiński
Boguslaw
B
Maciejewski
Andrzej
A
Wygoda
D002455:Cell Division; D006258:Head and Neck Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D011336:Probability; D012189:Retrospective Studies; D013997:Time Factors