ESTRO 37 Abstract book

ESTRO 37

S564

System v15.5 [Varian Medical Systems, Palo Alto, CA, USA] with 4-Pi and HyperArc. HyperArc is a non-coplanar SRS planning and treatment solution, available in Eclipse v15.5. These plans were then further optimised with Trade-Off exploration. Trade-Offs is the multi-criteria optimisation planning method, available in Eclipse v15.5. The cohort of patients included one 5 lesion case, one 4 lesion case, four 3 lesions cases and four 2 lesions cases. All plans were optimized using standard objectives to meet constraints based on SRS guidelines. All plans were normalized to 99% of the highest prescription target volume (primary target volume) receiving 100% of the prescribed dose. Additional Trade-Off optimization was applied to the 4Pi and HyperArc plans to determine if any further sparing of healthy brain or OARs could be achieved. Plan quality was evaluated by; volume of the brain receiving 4Gy(V4Gy), volume of brain receiving 12Gy(V12Gy), mean dose to brain, OAR doses and deviation from PTV prescription. Results For non-primary volumes, the deviation from prescription was reduced with HyperArc in comparison to 4-Pi, 2.6% to 7.3% (p=0.006). Trade-Off exploration reduced the deviation with 4-Pi to 4.4% but was not statistically significant (p=0.06), Trade-Off exploration with HyperArc increased this deviation to 4% (p=0.002). V4Gy and V12Gy to brain was reduced in all 10 cases when planning with HyperArc in comparison to 4-Pi (p=0.008 and p=0.01, respectively). The average reduction in V4Gy was 145cc and for V12Gy 6.3cc. The largest improvement is found in the 5 and 4 lesion cases. The addition of Trade-Off exploration to 4-Pi significantly reduced V4Gy (p=0.002) but was borderline significant in reducing V12Gy (p=0.05). There was no significant change in brain dose with the addition of Trade-Offs to HyperArc. The only significant change in OAR dose was in D0.5cc to Brainstem and D0.2cc to optic pathway which was increased when planning with 4-Pi alone. There was no significant improvement with HyperArc Trade-Offs in comparison to HyperArc alone although dose to optic pathway was reduced in 7 of 10 cases. Conclusion HyperArc planning provides significant improvements in PTV coverage, dose to healthy brain and OAR doses in comparison to 4-Pi. The addition of Trade-Off exploration to 4-Pi provides significant improvements in plan quality although not comparable to HyperArc. HyperArc is particularly beneficial for multi lesion cases. Trade- Off exploration of HyperArc plans can confer planning advantages in individual site specific cases to at risk OARs but provides no general improvement in dose to normal brain. PO-1010 A crowd-knowledge-based analysis of DVHs in SBRT: first steps towards a national virtual audit A. Savini 1 , M. Fusella 1 , M. Esposito 1 , C. Carbonini 1 , S. Clemente 1 , C. Fiandra 1 , C. Garibaldi 1 , F. Giglioli 1 , C. Marino 1 , E. Moretti 1 , S. Russo 1 , L. Strigari 1 , S. Strolin 1 , C. Talamonti 1 , E. Villaggi 1 , M. Stasi 1 , P. Mancosu 1 1 SBRT Working Group, AIFM - Italian Association of Medical Physics, Italy, Italy Purpose or Objective Currently, most of the multicenter analyses on treatment planning rely on selected data extraction from the dose volume histogram (DVH) of each plan. Different treatment planning systems employ different algorithms

Table 1 shows an overview of the patient-specific QA results for the first patients. In 90% of patient plans the local γAS was above 97,7%. The IC point measurements agreed with calculations within 3% except for a single lung IMRT case (+4.1%).

The delivery time of VMAT plans (2-3 arcs) was on average 1 min. 33 sec. while for IMRT (9 fields) it took about 2 min. 37 sec. on average. Conclusion The novel Halcyon™ system showed fast treatment delivery of VMAT and IMRT with good dosimetric agreement between the measured and calculated dose using the pre-configured beam model in the TPS for a wide range of treatment sites. PO-1009 Plan comparison of non-coplanar VMAT, HyperArc and multi-criteria optimization for radiosurgery. P. Houston 1 , S. Currie 1 1 Beatson West of Scotland Cancer Centre, Radiotherapy, GLASGOW, United Kingdom Purpose or Objective To evaluate the plan quality of 4 modern stereotactic radiosurgery (SRS) treatment methods. The methods investigated are 4-arc non-coplanar VMAT(4-Pi); with and without multi-criteria optimisation (Trade-Offs) and HyperArc; with and without Trade-Offs. Material and Methods Ten patients, single fraction, multiple cranial metastases cases were planned using the Eclipse Treatment Planning