Online Adaptive Radiation Therapy: Implementation of a New Process of Care

Abstract

Onboard magnetic resonance imaging (MRI) guided radiotherapy is now clinically available in nine centers in the world. This technology has facilitated the clinical implementation of online adaptive radiotherapy (OART), or the ability to alter the daily treatment plan based on tumor and anatomical changes in real-time while the patient is on the treatment table. However, due to the time sensitive nature of OART, implementation in a large and busy clinic has many potential obstacles as well as patient-related safety considerations. In this work, we have described the implementation of this new process of care in the Department of Radiation Oncology at the University of California, Los Angeles (UCLA). We describe the rationale, the initial challenges such as treatment time considerations, technical issues during the process of re-contouring, re-optimization, quality assurance, as well as our current solutions to overcome these challenges. In addition, we describe the implementation of a coverage system with a physician of the day as well as online planners (physicists or dosimetrists) to oversee each OART treatment with patient-specific 'hand-off' directives from the patient's treating physician. The purpose of this effort is to streamline the process without compromising treatment quality and patient safety. As more MRI-guided radiotherapy programs come online, we hope that our experience can facilitate successful adoption of OART in a way that maximally benefits the patient.

Keywords: mri; on-line adaptive radiotherapy.

Figure 1. Communication forms.

Templated communication forms for covering physician (A) and physicist (B).

Figure 2. Adaptive re-contouring.

In this case, deformably propagated contours on the bladder wall distal to the target were not corrected because the un-contoured portion was expected and confirmed to receive less than 20 Gy. The dark green line indicates the 20 Gy isodose contour. The red line indicates the planning target volume contour. The light green line indicates the small bowel contour. The orange line indicates the rectum contour. The yellow line indicates the bladder contour.

Figure 3. Challenging pancreatic stereotactic body radiotherapy (SBRT).

A challenging pancreatic SBRT case treated adaptively. The 40 Gy prescription isodose line is shown in red, and the 20 Gy isodose line is shown in green. In the initial plan (A), the kidney was not weighted in the optimization, but received less than tolerance dose. During the first adaptive fraction (B), a change in the bowel near the target caused the optimizer to turn a beam on through the kidney. Subsequently, an optimization weight was added to the kidney, which improved the dosimetry (C) at the expense of increased planning time.

Figure 4. Bixel minute ratio.

Bixel-minute ratio (A) and target contour volume ratio (B) in 40 adapted fractions. Variations in target structure volume resulted from increased and decreased to target volume margins based on physician judgement and proximity to dose limiting structures.