Lane R. Rosen, MD
Radiation therapy, a foundation of cancer treatment for decades, remains fertile for continued technological innovation that can improve patient outcomes. Some of the newest technologies, however, may be practical for only the largest institutions. For example, particle-based radiation therapy—specifically, proton therapy—has generated lots of buzz, but the majority of radiation oncology practices lack the financial resources and expertise needed to purchase and operate the equipment for this. Fortunately, the continued evolution of legacy technologies enables clinicians to offer excellent patient care. Advancements in stereotactic body radiation therapy (SBRT) and image-guided radiation therapy (IGRT) exemplify how radiation oncologists can deliver excellent outcomes using familiar tools that are already widely deployed.
A critical challenge in radiation oncology is effectively destroying cancer cells while minimizing damage to nearby healthy tissue. This is similar to the challenges associated with the use of chemotherapy agents that disrupt mechanisms that are present in both malignant and nonmalignant cells. Medical oncologists increasingly rely on targeted chemotherapies to increase cytotoxic effects within cancer cells while minimizing them in normal cells. Similarly, radiation oncologists can utilize SBRT and IGRT to deliver high doses of precisely targeted radiation.
SBRT focuses multiple radiation beams on a defined target area. Although the dose along any given beam path is relatively low, the dose at the focal point where the beams converge is sufficient to cause cell death. Recent advances in SBRT technology have increased the precision and accuracy with which radiation doses can be targeted. The now-standard use of smaller, more dynamic multileaf collimators allows the radiotherapy beams to better conform to the 3-D structure of the tumor, increasing delivery of radiation within the tumor while protecting healthy tissue from exposure.
IGRT has undergone a similar evolution. Computed tomography (CT) has improved the localization of tumors from surrounding tissue with more detailed 3-D images and 4-D images that demonstrate target motion over time. Continued improvements have also been made to magnetic resonance imaging (MRI) technologies, which are increasingly integrated into radiotherapy departments. Compared with CT scans, MRI technologies make it possible to more accurately discriminate between tumors and adjacent soft tissues. MRI-guided linear accelerators will be the ultimate marriage of these advances and are already under clinical evaluation.
Combining SBRT with IGRT allows better visualization of the target area and more precise delivery of radiation to the target, increasing our ability to precisely eliminate tumor cells with little to no effect on normal tissue. As the volume of healthy tissue in a field decreases, we are able to shorten treatment courses while delivering tumoricidal doses. This concept of hypofractionation, or the delivery of higher doses in fewer sessions, is changing how we treat patients who have a variety of cancers.
The Willis-Knighton Health System in Shreveport, Louisiana, first adopted IMRT in 1998. It was 1 of the first 5 centers in the United States to use IGRT in 2003 and is currently among a select few centers with an MRI simulator dedicated to planning radiation therapy. We have continually upgraded our systems for both technologies, allowing us to offer patients hypofractionated regimens that can reduce treatment times while maintaining excellent safety and tolerability profiles. For more than 12 years, patients with breast cancer treated at our center typically underwent 6.5 weeks of radiation therapy. Today, using the Versa HD image-guided linear accelerator from Elekta, patients with breast cancer often receive hypofractionated regimens that allow them to complete their treatment in only 4 weeks. Similarly, for more than 10 years, most patients with lung cancer at our center received radiation therapy over 6 weeks. Now, in select cases, we can treat some patients with lung cancer safely in only 2 or 3 weeks.
Today’s precise SBRT and IGRT technologies also enable the use of radiation to complement cytotoxic and targeted agents in the treatment of limited systemic disease. More effective management of metastatic lesions through the use of hypofractionated radiation therapy may extend survival even for patients who have not achieved complete remission.
A growing body of data supports the use of hypofractionated regimens in several common cancer indications, including breast, lung, and prostate. In February 2017, the International Journal of Radiation Oncology • Biology • Physics
published a commentary calling for the use of hypofractionated regimens for prostate cancer that can be administered over just 4 or 5 weeks, compared with the current standard regimen administered over 9 weeks.