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More advantaged socioeconomic status (SES) has been repeatedly associated with better cancer outcomes, even in clinical trial settings with strict protocol-directed care. Separately, prolongation of overall treatment time in radiation therapy (RT) is known to be associated with inferior outcomes in selected cancers. In this study, we aim to evaluate any association of SES with prolongation of overall RT treatment time in a cohort of lung cancer patients treated with curative intent daily fractionated RT.

This is a retrospective study in a single Australian institution, which runs a metropolitan facility and a regional facility. The maximal ideal treatment time was computed based on number of prescribed RT fractions, considering non-treatment on weekends. Actual total treatment time was calculated based on documented RT start- and end-date. Treatment prolongation was defined as excess number of days beyond the maximal ideal treatment time. SES was derived from patients’ residential postcode using the Socio-Economic Indexes for Area (SEIFA) index for Relative Socio-Economic Disadvantage based on the Australian Bureau of Statistics data, and further subdivided into quintiles based on the state of Victoria's general population. Multivariate logistic regressions were used to evaluate factors associated with treatment prolongation, including: age at RT, sex, SES, ECOG performance status, use of concurrent chemotherapy, metropolitan or regional facility, and year of RT.

From 2000 to 2020, 507 patients received 562 courses of RT. Of these, there was treatment prolongation in 307 (55%) courses of RT. The median RT prolongation was two days (range: 1-15). Patients from lowest SES quintiles were more likely to have treatment prolongation compared to patients from highest SES quintiles (71% vs. 46%, P<0.001). Patients treated in the regional facility were more likely to have treatment prolongation, compared to patients treated in metropolitan facility (67% vs. 45%, P<0.001). In multivariate analyses, SES, treatment facility and year of treatment were independently associated with treatment prolongation. Patients from the third SES quintile were 52% (95%CI=4-76%, P=0.04) less likely to have treatment prolongation than patients from the lowest SES quintile. Patients treated in the regional facility were three times (95%CI=1.6-5.4, P<0.001) more likely to have treatment prolongation than patients treated in the metropolitan facility. Patients treated in 2016-2020 were 58% (95%CI=21-77%, P=0.007) less likely to have treatment prolongation compared to patients treated in 2001-2005.

Our single institution study suggested that SES and those treated in the regional facility were more likely to have treatment prolongation. More resources should be put into supporting patients from lower SES and regional RT facilities to ensure timely completion of RT.