Effect of gap length and position on results of treatment of cancer of the larynx in Scotland by radiotherapy: a linear quadratic analysis.
OBJECTIVE
This paper reports on the analysis of the effect of the length and position of unplanned gaps in radiotherapy treatment schedules.


METHODS
Data from an audit of the treatment of carcinoma of the larynx are used. They represent all newly diagnosed cases of glottic node-negative carcinoma of the larynx between 1986 and 1990, inclusive, in Scotland that were referred to one of the five Scottish Oncology Centres for primary radical radiotherapy treatment. The end-points are local control of cancer of the larynx in 5 years and the length of the disease-free period. The local control rates at > or =5 years, Pc were analyzed by log linear models and Cox proportional hazard models were used to model the disease-free period.


RESULTS
Unplanned gaps in treatment are associated with poorer local control rates and an increased hazard of a local recurrence through their effect on extending the treatment time. A gap of 1 day is potentially damaging but the greatest effect is at treatment extensions of 3 or more days, where the hazard of a failure of local control is increased by a factor of 1.75 (95% confidence interval 1.20-2.55) compared to no gap. The time factor for the actual time was imprecisely estimated at 2.7 Gy/day with a standard error of 13.2 Gy/day. Among those cases who had exactly one gap resulting in a treatment extension of 1 day, there is no evidence that gap position influences local control (P = 0.17). The treatment extension as a result of the gap is more important than the position of the gap in the schedule.


CONCLUSIONS
Gaps in the treatment schedule have a detrimental effect on the disease-free period. A gap has a slightly greater effect than an increase in the prescribed treatment time. Any gap in treatment is potentially damaging. The position of the gap in the schedule was shown to be not important.
Beatson Oncology Centre, West Glasgow Hospitals University Trust, UK.
A G
AG
Robertson
C
C
Robertson
C
C
Perone
K
K
Clarke
J
J
Dewar
M H
MH
Elia
D
D
Hurman
R H
RH
MacDougall
H M
HM
Yosef
D001071:Appointments and Schedules; D002277:Carcinoma / Q000473:pathology / Q000532:radiotherapy*; D016001:Confidence Intervals; D018572:Disease-Free Survival; D019583:Dose Fractionation, Radiation; D005500:Follow-Up Studies; D006801:Humans; D007822:Laryngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D016014:Linear Models; D016015:Logistic Models; D008485:Medical Audit; D009364:Neoplasm Recurrence, Local / Q000473:pathology; D009367:Neoplasm Staging; D016016:Proportional Hazards Models; D012606:Scotland; D016019:Survival Analysis; D013997:Time Factors; D016896:Treatment Outcome