Abstract

SBRT is increasingly utilized in liver tumor treatment. MRI-guided RT allows for real-time MRI tracking during therapy. Liver tumors are often poorly visualized and most contrast agents are transient. Gadoxetate may allow for sustained tumor visualization. Here, we report on the first use of gadoxetate during real-time MRI-guided SBRT.

Purpose

This work describes a commercial treatment planning system, its technical features, and its capabilities for creating 60Co intensity modulated radiation therapy (IMRT) treatment plans for a magnetic resonance image guidance radiation therapy (MR-IGRT) system.

Methods and Materials

The ViewRay treatment planning system (Oakwood Village, OH) was used to create 60Co IMRT treatment plans for 33 cancer patients with disease in the abdominal, pelvic, thorax, and head and neck regions using physician-specified patient-specific target coverage and organ at risk (OAR) objectives. Backup plans using a third-party linear accelerator (linac)-based planning system were also created. Plans were evaluated by attending physicians and approved for treatment. The 60Co and linac plans were compared by evaluating conformity numbers (CN) with 100% and 95% of prescription reference doses and heterogeneity indices (HI) for planning target volumes (PTVs) and maximum, mean, and dose-volume histogram (DVH) values for OARs.

Results

All 60Co IMRT plans achieved PTV coverage and OAR sparing that were similar to linac plans. PTV conformity for 60Co was within <1% and 3% of linac plans for 100% and 95% prescription reference isodoses, respectively, and heteroge- neity was on average 4% greater. Comparisons of OAR mean dose showed generally better sparing with linac plans in the low-dose range <20 Gy, but comparable sparing or organs with mean doses >20 Gy. The mean doses for all 60Co plan OARs were within clinical tolerances.

Conclusions

A commercial 60Co MR-IGRT device can produce highly conformal IMRT treatment plans similar in quality to linac IMRT for a variety of disease sites. Additional work is in progress to evaluate the clinical benefit of other novel features of this MR-IGRT system.

Abstract

A device for MRI-guided radiation therapy (MR-IGRT) that uses cobalt-60 sources to deliver intensity modulated radiation therapy is now commercially available. We investigated the performance of the treatment planning and delivery system against the benchmark recommended by the American Association of Physicists in Medicine (AAPM) Task Group 119 for IMRT commissioning and demonstrated that the device plans and delivers IMRT treatments within recommended confidence limits and with similar accuracy as linac IMRT.

Abstract

A description of the first commercially available magnetic resonance imaging (MRI)–guided radiation therapy (RT) system is provided. The system consists of a split 0.35-T MR scanner straddling 3 60Co heads mounted on a ring gantry, each head equipped with independent doubly focused multileaf collimators. The MR and RT systems share a common isocenter, enabling simultaneous and continuous MRI during RT delivery. An on-couch adaptive RT treatment-planning system and integrated MRI-guided RT control system allow for rapid adaptive planning and beam delivery control based on the visualization of soft tissues. Treatment of patients with this system commenced at Washington University in January 2014.

Abstract

ViewRay, a novel technology providing soft-tissue imaging during radiotherapy is investigated for treatment planning capabilities assessing treatment plan dose homogeneity and conformity compared with linear accelerator plans. ViewRay offers both adaptive radiotherapy and image guidance. The combination of cobalt-60 (Co-60) with 0.35 Tesla magnetic resonance imaging (MRI) allows for magnetic resonance (MR)-guided intensity-modulated radiation therapy (IMRT) delivery with multiple beams. This study investigated head and neck, lung, and prostate treatment plans to understand what is possible on ViewRay to narrow focus toward sites with optimal dosimetry. The goal is not to provide a rigorous assessment of planning capabilities, but rather a first order demonstration of ViewRay planning abilities. Images, structure sets, points, and dose from treatment plans created in Pinnacle for patients in our clinic were imported into ViewRay. The same objectives were used to assess plan quality and all critical structures were treated as similarly as possible. Homogeneity index (HI), conformity index (CI), and volume receiving <20% of prescription dose (DRx) were calculated to assess the plans. The 95% confidence intervals were recorded for all measurements and presented with the associated bars in graphs. The homogeneity index (D5/D95) had a 1-5% inhomogeneity increase for head and neck, 3-8% for lung, and 4-16% for prostate. CI revealed a modest conformity increase for lung. The volume receiving 20% of the prescription dose increased 2-8% for head and neck and up to 4% for lung and prostate. Overall, for head and neck Co-60 ViewRay treatments planned with its Monte Carlo treatment planning software were comparable with 6 MV plans computed with convolution superposition algorithm on Pinnacle treatment planning system.