Tumor Motion Management in Radiotherapy Using 4D-MRI

Respiration-induced patient motion has become a major obstacle for achieving high-precision
radiotherapy of cancers especially in the thorax and upper abdomen. As the target is
continuously moving, an additional margin has to be added to the clinical target volume to
compensate for the uncertainty in the tumor and organ motion, causing toxicity to the normal
tissue and limiting the dose delivered to the target. To account for the tumor motion,
surrogate tracking methods are commonly used in clinics during radiotherapy. However, the
relationship between the surrogate and tumor motion is hard to generalize as it depends on
individual patients, tumor location, treatment fractions, and sometimes shows complex
patterns or transient, unpredictable changes. Hence, there is an urgent need to better
scrutinize the current surrogate-based motion management strategies. Moreover, the most
robust motion management strategy for the given patient should be determined in the
pre-treatment setting but the investigators currently lack a sufficient tool to provide this
information.

4D-CT is typically used to characterize the tumor motion over the course of the
radiotherapy. However, 4D-CT is an oversimplified snapshot representation of a
single-breathing cycle with low soft tissue contrast while imparting a considerable amount
of radiation dose to the patient. Consequently, the limitations of 4D-CT prevent
applicability in acquiring information over timescales that represent a treatment session.
MRI is highly advantageous as it is non-ionizing and provides excellent soft tissue
contrast. Although real-time 3D dynamic MRI is limited by low image quality and temporal
resolution, 2D dynamic MRI techniques have high fidelity and spatio-temporal resolution
requisite for real-time tracking of the moving target. Furthermore, a respiration-correlated
4D-MRI can be reconstructed from multi-slice 2D dynamic MR images, enabling volumetric image
processing and analysis. Therefore, 4D-MRI is an attractive solution to address breathing
motion and tumor tracking obstacles in radiotherapy.

The main goal of this research is to characterize patient-specific respiration-induced tumor
and surrogate motion to evaluate the accuracy and effectiveness of the surrogate-based
motion management strategies currently used in clinics. Specifically, the investigators
hypothesize that dynamic MRI obtained over a temporal duration consistent with radiotherapy
treatments will provide spatio-temporal information of both the tumor and surrogate, and
therefore can serve as a means to assess the quality of the tumor motion tracking with the
surrogate. To test their hypothesis, the investigators specifically propose to 1) track and
characterize the tumor and surrogate motion with 4D-MRI and 2) evaluate surrogate-based
motion tracking in a cohort of patients with thoracic tumors.

External and internal surrogate-based strategies commonly used in clinics have not been
appropriately validated. With the increasing adaptation of these surrogate methods for
motion management, the proposed research addresses these urgent issues in clinical
radiotherapy while providing a means to achieve patient-specific motion management.

Inclusion Criteria:

- Histologically-confirmed primary lung cancer (non-small cell OR small cell)

- Plan to undergo external radiation treatment of lung cancer

Exclusion Criteria:

- Patients who cannot undergo MRIs.

- Patients who have a cardiac device or other electronic or metal implant