A recent study highlights the potential of a novel approach to treat lung cancers located near critical structures. Researchers at GenesisCare UK have explored the use of stereotactic MR-guided adaptive radiotherapy (SMART) as a promising alternative for patients with centrally located lung tumors.
Standard treatment for non-small cell lung cancer (NSCLC) typically involves stereotactic ablative body radiotherapy (SABR), which delivers high doses of radiation over a limited number of sessions. While this method can effectively control tumors, the proximity of these cancers to vital organs poses a significant risk of severe radiation toxicity.
For ultracentral lung lesions, defined as tumors that are adjacent to or overlap with critical structures like the proximal bronchial tree, esophagus, or pulmonary vessels, the application of SABR can be especially challenging. The study published in Advances in Radiation Oncology indicates that SMART-based SABR may provide a safer and more effective solution for these complex cases.
SMART employs high-quality MR scans for real-time imaging, enabling precise tracking of soft tissue and automated adjustments of the radiation beam. This method allows for daily adaptations to treatment plans, accommodating changes in tumor size and position relative to surrounding organs. The use of real-time imaging facilitates treatment during breath-hold, which reduces the need for larger planning target volume (PTV) margins and enhances the precision of the radiation delivery.
The research team conducted a study involving 11 patients with 18 ultracentral lesions, primarily those diagnosed with oligometastatic or olioprogressive disease. Patients underwent five to eight treatment sessions, with a median dose of 40 Gy. The study aimed to assess the incidence of SABR-related toxicities and found that SMART treatments significantly reduced both the PTV volume and its overlap with critical organs when compared to conventional SABR.
Results indicated that the median PTV for SMART was notably smaller at 10.1 cc, compared to 30.4 cc for conventional SABR. Furthermore, the overlap with organs-at-risk was reduced to 0.85 cc for SMART, significantly less than the 4.7 cc observed with traditional methods. The rates of acute and late grade 1-2 toxicities were recorded at 54% and 18%, respectively, with no occurrences of severe grade 3-5 toxicities, showcasing the increased safety of the SMART approach.
At the median follow-up of 28 months, the outcomes were encouraging, with two-thirds of patients still alive and 93% showing no local progression at 12 months. The median progression-free survival was reported at 5.8 months, while median overall survival reached 20 months.
The researchers acknowledge the short duration of follow-up and the possibility of late toxicities emerging over time. However, they are optimistic that SMART will gain recognition as a viable treatment option for patients facing ultracentral NSCLC lesions. They concluded that their analysis of hypofractionated SMART treatments, combined with daily online adaptations, achieved local control comparable to that of conventional SABR but with a significantly safer toxicity profile.
Despite being an emerging treatment not yet widely available, SMART-based SABR could represent a significant advancement in care for patients with challenging lung tumors. The ongoing phase 1 clinical trial, SUNSET, further explores the safety and efficacy of stereotactic radiation therapy for ultracentral NSCLC tumors, aiming to refine treatment protocols and improve patient outcomes.
