Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science


Epidemiology and Biostatistics


Louie, Alexander


Sunnybrook Health Sciences Centre

2nd Supervisor

Zaric, Greg



The phase II randomized study SABR-COMET demonstrated that in cancer patients with 1-5 oligometastatic lesions, stereotactic ablative radiotherapy (SABR) was associated with an improvement in both progression-free survival and overall survival compared to standard of care (SoC). SABR, however, is associated with higher costs and treatment-related toxicity. The objective of this study was to assess the cost-effectiveness of SABR versus SoC in patients with oligometastatic disease.

A time-dependent Markov model with five health states was constructed from the Canadian health care system perspective. Utility values and transition probabilities were derived from the SABR-COMET trial. Costs were obtained from the published literature. A willingness-to-pay threshold of $100,000/quality adjusted life year (QALY) was used.

SABR was cost-effective in the base case, at an incremental cost-effectiveness ratio of $37,157/ QALY gained over a lifetime horizon, as compared to the SoC. Therefore, administering SABR is cost-effective for patients with 1-5 oligometastatic lesions compared to SoC.

Summary for Lay Audience

Historically, cancer that has spread beyond its origin, a state known as metastatic disease, is treated with medications such as chemotherapy that go throughout the body. Radiotherapy, as a form of local treatment, has been traditionally used to palliative symptoms. Two major developments have resulted in a paradigm change. First, there is an increasing appreciation of the concept of oligometastatic cancer, whereby, patients with a limited number of metastases have been observed to have an improved prognosis. Secondly, the recent phase II SABR-COMET trial demonstrated that stereotactic ablative radiotherapy (SABR) delivering a high dose of radiation precisely, can improve cancer control and potential survival for patients with oligometastatic cancers.

SABR is associated with more treatment-related side effects and requires more health resources. It is unknown whether the additional cost is justified by the potential health benefit gained from SABR. Therefore, this study aims to assess the cost-effectiveness of adding SABR to the standard of care (SoC) in these patients, from the perspective of the Canadian health care system.

We developed a Markov model simulating a cohort of hypothetical patients based on the SABR-COMET trial. The model took considerations of survival, cancer progression, treatment-related side effects, utilities (indicators of quality of life), and medical care costs. The model reported the incremental cost-effectiveness ratio (ICER) of SABR, which is defined by the difference in cost divided by the difference in quality-adjusted life years (QALYs) comparing the two treatment approaches.

Our model predicted that SABR+SoC was cost-effective compared to SoC, with an ICER of $37,157/QALY. This is below the commonly accepted willingness-to-pay threshold of $100,000/QALY, which represents an estimate of what a consumer of health care might be willing to pay for the health benefit given other competing demands on that consumer's resources. The robustness of our findings was assessed via sensitivity analysis (SA) by varying parameters over plausible ranges individually (deterministic one-way SA) and simultaneously (probabilistic SA). Based on extensive testing, we conclude that the findings of this model are robust.

In conclusion, SABR+SoC is cost-effective compared to SoC for patients with oligometastatic cancer from the Canadian health care perspective.