Abstract book - ESTRO meets Asia

S111 ESTRO meets Asia 2018

PO-271 Comparison of IMRT plans designed on Varian and Elekta Linac in different esophageal cancer R. Zhang 1 , W. Bai 2 , Q. Zhang 1 , J. Wang 1 , Z. Jing 1 , Q. Ren 1 1 Fourth Hospital of Hebei Medical University, Radiotherapy, Sijiazhuang- Hebei, China Purpose or Objective The dose parameters affecting the dose distribution and projection of the target area mainly include such factors as nose scattering, penumbra, leakage and transmission of the linear accelerator. Different linear accelerator manufacturers have different types of head structures to achieve intensity-modulated radiation therapy(see Figure1).The structure and performance parameters of the linear accelerator head are the important factors influencing the treatment of the patients, to compare and analyze the characteristics of static intensity modulated radiotherapy(IMRT) plans designed on Varian(V-IMRT) and Elekta(E-IMRT) Linac in different esophageal cancer(EC), exploring advantages and disadvantages of different vendor Linac, thus can be better serve for clinical. 2 Fourth Hospital of Hebei Medical University, Radiation Oncology, Sijiazhuang- Hebei, China

carried out for every CBCT. Total 180 CBCT were available for review. When required, Offline ART planning done in all cases Results There were 13 cases of Brain, 36 of Head and Neck, 22 of Thorax, 10 of abdomen and 29 of pelvis. Total 68 (37%) adaptive events were observed out of 180 available CBCT, 44 in H&N, 10 in Thorax and 14 in Pelvis. PTV (mostly PTV- LN) reduction was done in all adaptive events of H&N cases, because of weight loss and tumor shrinkage. PTV reduction was done in thorax cases because the tumor shrinkage was leading to the increase in overlapping lung volume [Fig 1, 2]. In pelvis, major discrepancy was observed because of organ motion; especially rectal filling and PTV modulation was carried out in all adaptive events. No adaptation was done in cases of Abdomen. In 78 % of cases, 1 st ART plan was made during 12 – 15 fraction, and in 66 % of cases, 2 nd ART planning done during 22-25 fraction. Minor DVH changes seen for OAR’s, especially cumulative dose to spinal cord and lung were lower after adaptation.

Material and Methods Forty patients with EC were selected, including 10 cases located in the cervical, upper, middle and the lower thorax, respectively. Two IMRT plans were generated with the Oncentra planning system: in Elekta Synergy™ and Varian 23EX Linac, prescription dose of 60Gy in 30 fractions to the planning target volume (PTV). The dose volume histogram parameters of PTV and the organs at risk (OAR) such as lungs, spinal cord and heart were examined, and additional monitor units (MU), treatment time, homogeneity index (HI) and conformity index (CI) comparisons were performed. Results All the V-IMRT and E-IMRT plans can satisfy the clinical dosimetry requirements. The doses to PTV, HI and OAR in E-IMRT were not statistically different in comparison with V-IMRT , with the following exceptions: in cervical, upper and lower thoracic EC the PTV's CI ,were better in E-IMRT than in V-IMRT (0.73±0.036 vs. 0.646±0.039, 0.72±0.078 vs. 0.68±0.08, 0.742±0.0722 vs. 0.702±.082, P=0.004,0.02, 0.05), while in middle thorax EC V-IMRT PTV's D2, D50 and PTV-average were better than E-IMRT (6469.8±107.2cGy vs. 6522.2±92.5cGy, 6252.5±62.5cGy vs. 6289.3±66.5cGy, 6248.2±67.9cGy vs. 6288.8±62.7cGy, P = 0.038, 0.009, 0.006). Treatment time were significantly decreased in V- IMRT as against E-IMRT in the cervical, upper and the

Conclusion Co registration of CBCT to planning CT for ART is helpful for volume modification, required due to anatomical changes and tumor regression during long course radiotherapy. It corrects the deficiencies in the simulation process which further improve the conformity of the delivered plan and reduces normal tissue dose by treating a smaller target volume. Efficient workflows are required to enable frequent adaptive intervention. ART increase the precision of radiotherapy and thus have the potential to increase the therapeutic window which has to be investigated in future studies.

PO-270

Optimal treatment planning conditions for SABR treatments of spinal and lung tumours

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