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. 2002 Sep 1;54(1):229-36.
doi: 10.1016/s0360-3016(02)02936-x.

How fast is repopulation of tumor cells during the treatment gap?

Rafal Tarnawski  1 , Jack Fowler, Krzysztof Skladowski, Andrzej Swierniak, Rafal Suwiński, Boguslaw Maciejewski, Andrzej Wygoda
Affiliations

How fast is repopulation of tumor cells during the treatment gap?

Rafal Tarnawski et al. Int J Radiat Oncol Biol Phys. .

Abstract

Purpose/objective: Our goal was to analyze the repopulation of surviving tumor cells during a treatment gap in radiotherapy for head-and-neck cancer.

Methods and materials: 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.

Conclusion: 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.

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