Abstract book - ESTRO meets Asia

S11 ESTRO meets Asia 2018

Results 49 patients with LBC, age between 29-79, were studied from January 2018 to April 2018. Of 49 patients, 42 (87.5%) patients underwent ABC CT simulation and treatment. 1 (2.1%) patient underwent ABC CT Simulation but did not attend RT. 5 (10.4%) patients could not tolerate the use of ABC device. Inter fractionation reproducibility was evaluated on the first day of RT and mid RT using portal images in comparison with digitally reconstructed radiographs. Of the 42 patients who received radiation therapy using ABC, 8 (19.0%) patients required isocenter shifts while 38 (81.0%) patients did not require isocenter shift on first day of RT (Fig.1). 6 (14.0%) patients required isocenter shift and 36 (86.0%) patients did not require isocenter shift mid RT (Fig.2). 29 (69.0%) of 42 patients did not require isocenter shifts during the entire course of RT.

1 Hong Kong Sanatorium & Hospital, Radiotherapy, Happy Valley, Hong Kong SAR China 2 Sheffield Hallam University, Faculty of Health and Wellbeing, Sheffield, United Kingdom Purpose or Objective The purpose of this study was to dosimetrically compare TomoDirect, TomoHelical, and Linac-based 3D-conformal radiotherapy (3DCRT) for craniospinal irradiation (CSI) in the treatment of medulloblastoma. Material and Methods Five CSI patients were retrospectively replanned with Linac-3DCRT, TomoHelical, TomoDirect-3DCRT, and TomoDirect-intensity-modulated radiotherapy (IMRT) using a standardized planning protocol. CSI dose of 36Gy in 20 fractions was prescribed to the planning target volume (PTV). Lateral opposing cranial fields and a direct posterior spinal field arrangement was used for Linac- 3DCRT and TomoDirect plans. Slice-by-slice isodose distributions and dose-volume histograms (DVHs) were compared for all plans. Furthermore, conformation number (CN), homogeneity index (HI), non-target integral dose (NTID), organs-at-risk (OAR) D max , D mean , V 5Gy , V 10Gy , V 20Gy , and V 30Gy and treatment times were compared. Results TomoHelical achieved the best PTV homogeneity and plan conformity compared with Linac-3DCRT, TomoDirect- 3DCRT and TomoDirect-IMRT (HI of 3.6% vs. 20.9%, 8.7% and 9.4%, CN of 0.83 vs 0.42, 0.44 and 0.47 respectively). Qualitative analysis of isodose distributions supported these findings (Figure 1). In contrast, TomoDirect-IMRT achieved the lowest NTID compared with TomoDirect- 3DCRT, TomoHelical and Linac-3DCRT (141J vs. 151J, 181J and 250J), indicating the least biological damage to non- PTV normal tissues. DVH analysis showed that sparing of the lungs was best achieved with TomoDirect planning. TomoHelical plans achieved the lowest D max in all organs except the breasts, and the lowest D mean for OARs, except in the mandible, lungs, breasts, liver, kidneys, bowels, and non-target body, where both TomoDirect methods triumphed (Figure 2). Linac plans resulted in the highest OAR D mean in all cases except for of the breasts. Lastly, beam-on time was longest for TomoHelical treatments, followed by TomoDirect-IMRT, TomoDirect-3DCRT, and Linac-3DCRT (19.7±3.3min, 15.0±3.9min, 12.2±3.2min, and 1.3±0.4min respectively).

Conclusion The ABC device is well tolerated by 87.5% of the patients where 69.0% of the patients did not require isocenter shifts throughout the entire course of RT. Extending the usage of ABC device to all LBC patients would likely provide unequivocal benefit in reducing lung and heart dose. These preliminary findings support the need for further research in this area. PV-027 Dosimetric comparison of craniospinal Irradiation by TomoDirect, TomoHelical and 3D conventional RT S.W.S. Tsang 1 , G. Chiu 1 , J.T.L. Wong 1 , M. Collins 2

Figure 1 . Sample dose distributions for one pediatric patient. Isodose lines of 115%, 110%, 107%, 100%, 95%, 90%, 80%, 70%, 50%, and 30% of the prescribed dose are