Development and evaluation of an automated EPTN-consensus based organ at risk atlas in the brain on MRI.

BACKGROUND AND PURPOSE: During radiotherapy treatment planning, avoidance of organs at risk (OARs) is important. An international consensus-based delineation guideline was recently published with 34 OARs in the brain. We developed an MR-based OAR autosegmentation atlas and evaluated its performance compared to manual delineation. MATERIALS AND METHODS: Anonymized cerebral T1-weighted MR scans (voxel size 0.9 × 0.9 × 0.9 mm3) were available. OARs were manually delineated according to international consensus. Fifty MR scans were used to develop the autosegmentation atlas in a commercially available treatment planning system (Raystation®). The performance of this atlas was tested on another 40 MR scans by automatically delineating 34 OARs, as defined by the 2018 EPTN consensus. Spatial overlap between manual and automated delineations was determined by calculating the Dice similarity coefficient (DSC). Two radiation oncologists determined the quality of each automatically delineated OAR. The time needed to delineate all OARs manually or to adjust automatically delineated OARs was determined. RESULTS: DSC was ≥ 0.75 in 31 (91 %) out of 34 automated OAR delineations. Delineations were rated by radiation oncologists as excellent or good in 29 (85 %) out 34 OAR delineations, while 4 were rated fair (12 %) and 1 was rated poor (3 %). Interobserver agreement between the radiation oncologists ranged from 77-100 % per OAR. The time to manually delineate all OARs was 88.5 minutes, while the time needed to adjust automatically delineated OARs was 15.8 minutes. CONCLUSION: Autosegmentation of OARs enables high-quality contouring within a limited time. Accurate OAR delineation helps to define OAR constraints to mitigate serious complications and helps with the development of NTCP models.

Stereotactic body radiation therapy for oligometastases to the lung: a phase 2 study.

PURPOSE: To assess, in a phase 2 study, the efficacy and toxicity of stereotactic body radiation therapy for oligometastases to the lung in inoperable patients. METHODS AND MATERIALS: Patients with lung metastases were included in this study if (1) the primary tumor was controlled; (2) patients were ineligible for or refused surgery and chemotherapy; and (3) patients had 5 or fewer metastatic lesions in no more than 2 organs. Large peripheral tumors were treated with a dose of 60 Gy (3 fractions), small peripheral tumors with 30 Gy (1 fraction), central tumors received 60 Gy (5 fractions), and mediastinal tumors or tumors close to the esophagus received 56 Gy (7 fractions). RESULTS: Thirty patients with 57 metastatic lung tumors from various primary cancers were analyzed. The median follow-up was 36 months (range, 4-60 months). At 2 years, local control for the 11 central tumors was 100%, for the 23 peripheral tumors treated to 60 Gy it was 91%, and for the 23 tumors treated in a single 30-Gy fraction it was 74% (P=.13). This resulted in an overall local control rate at 1 year of 79%, with a 2-sided 80% confidence interval of 67% to 87%. Because the hypothesized value of 70% lies within the confidence interval, we cannot reject the hypothesis that the true local control rate at 1 year is ≤70%, and therefore we did not achieve the goal of the study: an actuarial local control of the treated lung lesions at 1 year of 90%. The 4-year overall survival rate was 38%. Grade 3 acute toxicity occurred in 5 patients. Three patients complained of chronic grade 3 toxicity, including pain, fatigue, and pneumonitis, and 3 patients had rib fractures. CONCLUSIONS: The local control was promising, and the 4-year overall survival rate was 38%. The treatment was well tolerated, even for central lesions.