P05.31 Plan quality of stereotactic radiosurgery in a multicenter phase III randomized trial in patients with 4 up to 10 brain metastases
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ABSTRACT: Abstract Background Stereotactic radiosurgery is a promising treatment option for patients with multiple brain metastases (BM). A multicenter randomized phase III trial (NCT02353000) is ongoing in patients with 4 up to 10 BM to determine the palliative value of SRS compared to whole brain radiotherapy (WBRT). Optimal SRS plan quality is essential to minimize the risk of radionecrosis (RN) and thereby maintenance of quality of life. This study evaluates the possible differences in the plan quality of the participating radiotherapy centers. Material and Methods An anonymized planning-CT with three BM scenarios was sent to the participating centers to contour targets and make clinical SRS treatment plans. The first, second, and third scenario consisted of 7, 5, and 10 BM, 1x21 Gy, 1x18Gy, and 1x18Gy respectively. Planning Target Volume coverage should be V100?99%. The maximum allowed gross tumor volume (GTV) to PTV margin was 2 mm. To assess SRS plan quality, the primary endpoint for this study was the Paddick gradient index (ratio of the volume of half the prescription isodose to the volume of the prescription isodose). Several secondary endpoints were calculated, such as the V12Gy of the largest BM (e.g. volume of healthy brain tissue which received 12 Gy or more). For all the endpoints the median and corresponding range were calculated. Results Data was available for nine centers for the first two scenarios and for eight centers for the third scenario. Eight centers used Volumetric Modulated Arc Therapy (VMAT) as their SRS technique and one center Cyberknife. Only once center used three fractions instead of a single fraction SRS. In the three scenario’s, the median Paddick gradient ranged from 3.5 up to 4.6, the poorest Paddick gradient index from 5.9 up to 7.4 and the optimal Paddick gradient index from 2.6 up to 3.1. Also variation was seen on other endpoints, such as the V12Gy of the largest BM. Conclusion Clinical relevant variation is seen in SRS plan quality in the participating centers, expressed by the variation in the Paddick gradient index, V12 Gy and the mean PTV dose. A Paddick gradient of less than 3.0 generally reflects a favorable SRS plan quality. Centers are encouraged to further optimize SRS plan quality.
SUBMITTER: Hartgerink D
PROVIDER: S-EPMC6144076 | biostudies-literature | 2018 Sep
REPOSITORIES: biostudies-literature
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