A. Van Mourik

EP-1577: A robust method to minimize geometric table rotational errors in stereotactic radiotherapy

S731 ________________________________________________________________________________ coverage and the conformity due to the dental implant for nasopharyngeal cancer(NPC) group (implant outside the PTV ).However, for the Non-NPC group (implant inside the PTV), a large discrepancy was obtained in all PTV parameters. There were statistically sig. differences(P<0.05) in PTVmax, PTVmean, Conformation Number and volume covered with 70Gy(V70Gy) among models.A large portion of PTV was underdosed.For the stainless steel, the V70Gy is below 70%, which is 25% poorer when compared with AAA plans. In the phantom study, ionization chamber and film measurements supported the dose perturbations by AXB. Using a 3% and 3mm criteria Gamma analysis, passing rate was between 95.0% and 99.7% demonstrating that AXB was in agreement with measurements in different models.

EP-1680: Treatment planning of stereotactic radiosurgery for single brain metastases: impact of leaf width

ESTRO 35 2016 _____________________________________________________________________________________________________ Results: The mean GTV volumes ranged from 149.44 to 526.53 cc. VMAT plans show good results in comparison with 3DCRT in both conformity index (0.81±0.09 Vs 0.68±0.07 respectively, p-value of 0.009), and heterogeneity index (0.11±0.03 Vs 0.14±0.02, p value= 0.042). Furthermore, minimum doses to PTV in VMAT plans are higher than 3DCRT plans (57±1.22 Vs 55.1±0.86, p value= 0.001). In risk structures, the lung volume receiving 10Gy, 20Gy and 30Gy were reduced in VMAT plans (with relative reduction of 2.27%, p=0.002; 4.87%, p=0.001; 11.8% respectively). Mean lung dose was also reduced ( 15 Vs 17.69 ) but not statistically significant. V30 of the heart was reduced compared to 3DCRT (7.53±6.2 10.43±6.8 with p value of 0.051). The maximum dose of esophagus with VMAT was 47.7 Vs 48.69 with 3D CRT ( not statistically significant). Moreover, D 50 of the esophagus was less with VMAT ( 19.94 Vs 23.63) with p value of 0.22. Regarding monitor units, the mean values were ( 461.40±124.42 Vs 227.90±13.52) for VMAT and 3D CRT respectively.