OC-0522 Characterising dose changes due to unplanned gas cavities in Magnetic Resonance guided Radiotherapy

J. Shortall, E. Vasquez Osorio, A. Green, R. Chuter, A. McWilliam, K. Kirkby, R. Mackay, M. Van Herk
2019 Radiotherapy and Oncology  
HERO trial protocol was created in which approximately equal points were allocated to target dosimetry including conformity index (CI), and to OAR dosimetry. Where applicable, progressive scoring was used; for example, participants received a minimum score for meeting trial protocol and increasing points when OAR dose was reduced further below protocol. In addition to dosimetry metrics, delivery parameters including treatment plan geometry, delivery time and monitor units were analysed for the
more » ... op 50 plans. Results A total of 160 plans were submitted from 28 countries. Treatment devices included linacs, CyberKnife (CK), GammaKnife (GK), TomoTherapy and particle therapy. The majority of plans were VMAT (101), followed by GK (20), CK (16) and IMRT (7) (Figure 1 ). The median score was 124.8 (out of 150) and maximum was 146.2, achieved with CK. The top 50 plans scored 134.5-146.2. Of these, VMAT/IMRT plans had superior CI100% compared with CK and GK, however VMAT was inferior to IMRT, CK and GK for CI50%. IMRT achieved lower normal brain receiving 12 Gy compared with VMAT, CK and GK (Figure 2 ). It should be noted that GK PTV margin in practice may be lower than for linac plans. For all techniques, all top 50 plans had at least 125% target maximum dose. Top 50 linac plan score was independent of monitor units, but all had at least three couch angles. Median VMAT delivery time was 14 minutes, compared with 25, 120 and 169 minutes for IMRT, CK and GK respectively (Figure 2 ). Figure 1: Waterfall plot of plan scores for the top 50 plans with delivery or planning technique denoted by colour Figure 2: (a) 100% CI (b) 50% CI (c) volume of normal brain receiving 12 Gy and (d) delivery time for IMRT, VMAT, GammaKnife and Cyberknife in the top 50 scoring plans Conclusion In this international multi-metastases SRS planning competition, similar plan quality was achieved with across various SRS delivery systems. There was a vast range in delivery time required between different SRS delivery systems. This study did not however collect planning and QA time, or QA results, for which large variations between systems may be present. OC-0522 Characterising dose changes due to unplanned gas cavities in Magnetic Resonance guided Radiotherapy
doi:10.1016/s0167-8140(19)30942-9 fatcat:635cux65qfbl7gbzvrs22i2wl4