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

• Published in: International journal of radiation oncology, biology, physics Vol. 54; no. 1; pp. 229 - 236
• Main Authors: Tarnawski, Rafal, Fowler, Jack, Skladowski, Krzysztof, Świerniak, Andrzej, Suwiński, Rafal, Maciejewski, Boguslaw, Wygoda, Andrzej
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.09.2002; Elsevier
• Subjects: Biological and medical sciences; Cell Division; Head and Neck Neoplasms - pathology; Head and Neck Neoplasms - radiotherapy; Head-and-neck cancers; Humans; Medical sciences; Otorhinolaryngology (head neck, general aspects and miscellaneous); Otorhinolaryngology. Stomatology; Probability; Radiation therapy and radiosensitizing agent; Retrospective Studies; Time Factors; Treatment gap; Treatment with physical agents; Treatment. General aspects; Tumor repopulation; Tumors; Treatment gap; Tumor repopulation; Head-and-neck cancers; Human; Cell proliferation; Theoretical model; Cohort study; Head and neck; ENT disease; Kinetics; Malignant tumor; Radiotherapy; Waiting time; Time variation; Tumor cell
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/S0360-3016(02)02936-X

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.