Characteristics of Radiotherapy Trials Compared With Other Oncological Clinical Trials in the Past 10 Years

Importance: Modern precision radiotherapy is an innovative and effective treatment of cancer, yet it is unclear how radiotherapy trials are affected by expanding targeted and immune therapies and declining National Institutes of Health funding.

Objective: To analyze and compare the characteristics of radiotherapy trials with other oncological trials registered on ClinicalTrials.gov.

Design, Setting, And Participants: This is a cross-sectional analysis of trials registered on ClinicalTrials.gov between June 1, 2007, and May 8, 2017. Records of all 243 758 clinical studies registered by May 8, 2017, were downloaded, but only 25 907 interventional oncological trials registered between June 1, 2007, and May 8, 2017, and whose primary purpose was "treatment" were included in the final analysis. Trials were categorized according to cancer type and other registration information.

Main Outcomes And Measures: Characteristics of radiotherapy trials were compared with characteristics of other oncological trials. Chronological shifts in radiotherapy trials were also analyzed.

Results: Of the 25 907 trials selected, 1378 (5.3%) were radiotherapy trials and 24 529 (94.7%) were other oncological studies. The number of radiotherapy trials increased gradually from 94 (June 1, 2007, through May 31, 2008) to 192 (June 1, 2015, through May 31, 2016). Radiotherapy trials were less likely than other oncological studies to be registered before participant enrollment (763 of 1370 [55.7%] vs 16 105 of 24 434 [65.9%]; P < .001), to be blinded (45 of 1378 [3.3%] vs 2784 of 24 529 [11.3%]; P < .001), or to involve multiple geographic regions (2.4% vs 9.5%; P < .001), but they were more likely to be phase 2 to 3 (773 of 1124 [68.8%] vs 12 910 of 22 300 [57.9%]; P < .001) and to have a data-monitoring committee (839 of 1264 [66.4%] vs 11 728 of 21 060 [55.7%]; P < .001). Only a minority of radiotherapy trials were industry sponsored, which was significantly lower than for other oncological trials (80 of 1378 [5.8%] vs 10 651 of 24 529 [43.4%]; P < .001; adjusted odds ratio, 0.08; 95% CI, 0.06-0.10). The number of National Institutes of Health-sponsored radiotherapy trials decreased from 80 of 544 trials (14.7%) from 2007 to 2012 to 72 of 834 trials (8.6%) from 2012 to 2017 (P < .001). Radiotherapy trials with a sample size of more than 100 patients decreased from 155 of 543 trials (28.5%) from 2007 to 2012 to 157 of 833 trials (18.8%) from 2012 to 2017 (P < .001).

Conclusions And Relevance: The limited number of and the scarcity of funding for radiotherapy trials is concerning given the integral role of radiotherapy in the clinical management of patients with cancer worldwide. A multidisciplinary collaboration to promote and fund more radiotherapy research is warranted.