الفهرس 
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Abstract
The present study was designed to study the effect of radiotherapy interruptions in the treatment of breast cancer.174 female breast cancer patients were received PORT with the linear accelerator.The patients were categorized according to the duration of treatment interruptions : group A had 45 patients who had no treatment interruption, group B had 87 patients with treatment interruptions of 7 days or less, group C had 26 patients with treatment interruptions of at least 8 days but not more than 14 days, and group D had 16 patients with treatment interruptions of 15 days or more. We determined the treatment outcome (OS&LRC rates) from the follow-up (FU) of the patients, as the patient still survived or died, and recurrence till the time of investigation occurred or not, and were estimated with the Kaplan-Meier (K-M) method and Logrank test, respectively.The results showed a decrease in LRC rate in the groups with radiotherapy treatment interruption B, C, and D by 15 % (P=0.019, a significant value). Then surviving fraction (SF) and tumor control probability (TCP) were calculated, and the curves of the relationships between (SF&OTT) and (TCP&OTT) were showed, which confirmed the detrimental effect of unscheduled gap or interruption during radiotherapy fractions on the treatment outcome.Also data on patients of host- and treatment-related factors were collected, and the influence of these factors on LRC and OS rates was evaluated with a Chi-square test.Finally, we recommended that during postoperative hypofractionated irradiation of breast cancer (40 Gy/15 fractions/3weeks) interruptions should be avoided and if they are inevitable, they should not be prolonged more than two days, as they will adversely affect the treatment outcome (LRC rate).