ESTRO 2024 - Abstract Book

S1675

Clinical - Lung

ESTRO 2024

1 Stanford University School of Medicine, Radiation Oncology, Stanford, USA. 2 University of Washington, Radiation Oncology, Seattle, USA. 3 Hokkaido University, Radiation Oncology, Hokkaido, Japan. 4 Stanford Cancer Institute, Stanford Cancer Institute, Stanford, USA. 5 University of Sydney, Radiation Oncology, Sydney, Australia. 6 University of California San Diego, Radiation Medicine and Applied Sciences, La Jolla, USA

Purpose/Objective:

Single fraction SABR is a safe, effective, and efficient approach for non-central thoracic tumors 1 . Whether tumor location adjacent to the chest wall (CW) should be a contraindication for single-fraction treatment is debatable. Although CW pain is generally low-grade and self-limited, mitigating toxicity through understanding radiation dose response is a worthwhile, patient-centered goal. The purpose of this study is to evaluate the incidence and grade of CW pain among patients treated on a prospective clinical trial and to evaluate the dose-volume-response relationship to inform treatment planning and risk prediction.

Material/Methods:

This study is a secondary analysis of the international prospective non-randomized iSABR trial which evaluated a ‘personalized’ dosing strategy to lung SABR (iSABR) (NCT01463423) 2 based on tumor size and location. Patients with a non-central, non-colorectal histology, tumor less than 10 cc in volume were treated with 25 Gy in a single fraction. CW pain was prospectively collected and graded based on the CTCAE version 4. Cumulative incidence for CW pain was estimated using the Kaplan-Meier method. Log-rank test was used to search for metrics predictive of toxicity. Dose-response modeling was performed using a logistic model with maximum likelihood method utilized for parameter fitting. Likelihood ratio test was used to assess significance of the dose-response slope 3,4 .

Results:

We evaluated 99 patients from the iSABR that were treated with 25 Gy in a single fraction. Of these, 67.7% had overlap of the planning target volumes (PTV) with the CW. There was a total of 22 CW pain events, including five grade 2 or higher events and zero grade 3 or higher events. The metrics most highly correlated with a toxicity event were the volume receiving at least 10.8 Gy (V10.8 Gy ) and the dose to the hottest 2 cc (D2cc). The D2cc and V10.8 Gy associated with a 20% rate of CW pain were 17.4 Gy and 28 cc, respectively. Patients that met the D2cc (36.6% vs. 3.7%, p = 0.003) and V10.8 Gy (40.0% vs. 8.1%, p < 0.01) constraints had a significantly lower incidence of CW pain at 3 years compared to those that did not. Similarly, in a subset analysis of patients with the PTV overlapping or adjacent to the chest wall, rates of chest wall pain were significantly lower when the D2cc (36.6% vs. 4.0%, p < 0.01) and V10.8 Gy (40.0% vs. 8.6%, p = 0.011) constraints were met.

Conclusion:

For small, peripheral tumors, single fraction SABR is associated with modest rates of CW pain which are low-grade in nature including for targets that are adjacent to or overlapping the CW. The D2cc and V10.8 Gy are highly correlated with CW pain and can be used to guide constraints and estimate risk.