ESTRO 2021 Abstract Book

S1346

ESTRO 2021

Conclusion Signal‐to‐MU ratio was almost found as linear from 2 MU to 1000 MU and there was negligible over-response of the EPID signal in image #1 compared to image #2 during the use of iViewDose in-vivo dosimetry system in clinical practice.

PO-1625 Evaluation of digital linac log data for patient-specific VMAT quality assurance F. U'wais 1 , H. M Zin 1 , Y. Radzi 2 , N.N. Rizan 3

1 Universiti Sains Malaysia, Advanced Medical and Dental Institute, Penang, Malaysia; 2 Universiti Sains Malaysia, Physics Department , Penang, Malaysia; 3 Gleneagles Hospital , Radiotherapy Department, Penang, Malaysia Purpose or Objective An accurate and efficient patient-specific quality assurance (QA) method is highly desired for the advanced radiotherapy delivery techniques such as volumetric arc radiotherapy (VMAT). The techniques involve delivery of complex treatment parameters including the dynamic movement of the multi-leaf collimators (MLC). This study aims to evaluate the use of digital linac log data for the VMAT QA. Materials and Methods The treatment log data for an Elekta Synergy linac was recorded using the service graphing tool on the linac control computer. VMAT treatment plans were delivered from the linac and all the dynamic treatment parameters including monitor unit (MU), MLC position and speed, collimator angle were recorded in real-time using the service graphing tool. The recorded raw data were extracted and analysed for discrepancy between the log and planned data using algorithms written in MATLAB (MathWorks, Natick, MA). The gamma pass rate of the fluence delivered, calculated using the treatment parameters logged was compared to the Octavius1500 (PTW, Freiburg, Germany) 2D ion chamber array that was measured during the pretreatment dose verification measurements. Results Our results demonstrated that the digital log data can track MLC leaves and that position errors of the dynamic MLC motion can be detected with an accuracy of 1.0 mm at speeds ranging from 3.04 to 3.4 cm/s. Evaluation of the measured dose distribution for VMAT delivery using digital log data was shown to agree well with planned dose distribution measured in 2D detector array, with an average gamma pass rate of 92% at 3%/3mm. Gamma pass rate from the log data was higher than the 2D array detector, with an increase ratio up to 7.99%. and the range of variation within 1.3 to 7.3. Log data obtained gamma pass rate superior than 97.5% while 2D array within 91.5%. Conclusion The digital linac log data provides the basis to an essential high resolution real-time verification tool, useful in accessing accurate delivery of complex high energy radiation to the tumor and ultimately to achieve better cure rates for cancer patients. We concluded that the method under investigation may be used interchangeably for routine patient specific QA. PO-1626 Dosimetric comparison: VMAT based CSI in Ring gantry Halcyon and Cantilever linear accelerator B. Sarkar 1 , S.S. Biswal 2 , T. Shahid 3 , M. Gazi 1 , J. Bhattacharya 3 , T. Ghosh 4 , S. Roy Chowdhury 5 , A. De 3 , S. Mitra 5 , A. Mishra 6 , S. Mandal 7 , K. George 5 , P. Soren 8 , M. Mukherjee 5 , L.N. Biswas 3 , J. Akhtar 9 , P. Chatterjee 10 , G. Indira 5 , P. Ch. Sekhar 5 , A. Samanta 5 , R. Raj 5 , S. Goswami 5 , A. Paul 5 , S. Sengupta 5 , R. Bhaskar 11 , A. Pradhan 12 , A. Manikandan 13 , K. Appunu 5 1 Apollo Hospitals , Radiation Oncology, KOLKATA, India; 2 Apollo Hospitals, , Radiation Oncology, KOLKATA, India; 3 Apollo Hospitals , Radiation Oncology, Kolkata, India; 4 Apollo Hospitals, Radiation Oncology , KOLKATA, India; 5 Apollo Hospitals, Radiation Oncology, Kolkata, India; 6 Apollo Hospitals, radiation Oncology, Kolkata, India; 7 Apollo Hospitals, Radiation Oncology, KOLKATA, India; 8 Apollo Hospitals , radiation oncology, Kolkata, India; 9 Apollo Hospitals, Radiation Onoclogy, Kolkata, India; 10 Apollo JHospitals, radiation Oncology, Kolkata, India; 11 Apollo Hospitals, Radiation oncology, Kolkata, India; 12 GLA University, Mathematics, Mathura, India; 13 Apollo proton Cancer Centre, medical Physics, Chennai, India Purpose or Objective This study aim to compare the dosimetric characteristics of the Craniospinal irradiation (CSI) between ring gantry Halcyon [E] (HA) and C-Arm Novalis Tx (NT) linear accelerators (LA).