Abstract book - ESTRO meets Asia

S119 ESTRO meets Asia 2018

Results We found that different ID influenced the LC data by less than 1%, however, higher ID increased the risk of RIP, CWP and RIRF by up to 4.1%, 2.7% and 4.8% in the four FS. For patients suffered from high risk of RIP, CWP or RIRF, higher ID increased the median risk of RIP, CWP and RIRF by up to 11.0%, 10.4% and 6.9%, respectively. Conclusion Different ID principally affects the risk of RIP, CWP and RIRF whereas have slight impact on LC. Greater influence is observed for patients with high risk of RIP, CWP or RIRF. PO-288 The effect of segment number on plan quality of IMRT 1 Cancer Hospital of Shantou University Medical College, Department of Radiation Oncology, Shantou, China Purpose or Objective To investigate the effect of segment number (SN) on plan quality of intensity-modulated radiation therapy (IMRT) for upper thoracic esophageal carcinoma (UTEC) patients. Material and Methods CT datasets of 15 UTEC patients were enrolled. Three groups of IMRT plans in which the SN were set to 64 (G1 Group), 115 (G2 group) and 166 (G3 group) were designed. The dose was prescribed at 64 Gy in 32 fractions for the target volume. Three groups of plans were compared in terms of conformity index (CI), homogeneity index (HI), organ-at-risk (OAR) sparing, monitor units (MUs) and treatment time (TT). Results We found that the G1 Group plans obtained significantly higher mean dose (Dmean), D2 and HI but lower CI for the target than the other two groups (P<0.05). The G1 Group plans showed slight reduction of V30 (%) for the lungs than the G3 group plans, but V10 (%) and V20 (%) for the G1 Group were slightly increased than the G2 group plans (P<0.05). The maximum dose (Dmax) to the spinal cord and heart among the three groups were comparable (P>0.05). The G1 Group plans resulted in up to 3.4% MUs and 7.6% TT reduction. Conclusion The dosimetric study demonstrates that reduction in SN to 64 was feasible for achieving comparable OARs sparing while remarkably reducing the MUs and shortening the TT. PO-289 Study of total skin electron therapy dosimetry using different detectors C. Tambe 1 , S. Mishra 2 , S. Kale 1 , R.R. Upreti 1 , R. Kinhikar 1 , D. Deshpande 1 1 Tata Memorial Hospital, Medical Physics, Mumbai, India 2 Dr. B Borooah Cancer Institute, Medical Physics Unit- Dept. of Radiation Oncology, Guwahati, India Purpose or Objective The aim of this project is to review the dosimetry of TSET following AAPM TG-30 report and using TLDs and Radiochromic films. Material and Methods A Varian Truebeam LINAC with 6 MeV HDTSe - mode for TSET having a dose rate of 2500 MU/min was used in this study. A wooden frame was specially designed for patient treatment with a slot to fix Perspex sheet as scatterer/degrader of dimension of 110 cm × 195 cm × 2 mm. The dose measurement is done at a distance of 26 cm from the degrader. Target to skin distance is kept at 463- cm. Beam energy, depth dose and Profile measurements were done using parallel plate chamber PPC05 and in Solid water phantom (SWP). Verification of depth dose was done by sandwiching a Radiochromic film in SWP. Profiles were verified using Thermoluminescence dosimeter (TLD) for upper thoracic esophageal carcinoma W.Z. Zhang 1 , B.T. Huang 1 ,J.Y. Lu 1 ,X. Peng 1

with wax bolus for buildup. Angle of tilt was determined geometrically by superimposing 2 vertical profiles using FWHM and verified dosimetrically. PDD for the 6 dual field was determined by placing a film in a cylindrical wax phantom (WP). Absolute dose measurement was done at the calibration point (at Umbilicus height) using Roos chamber according to TG-30 and TRS-398 recommendations. MUs were delivered to get the prescribed dose for a single dual field to the WP with TLDs attached in 3 positions 60˚ apart with appropriate buildup. The same was verified in a body phantom. Treatment skin dose was calculated by exposing the WP to 6 dual fields with TLDs placed in all 6 positions and film wrapped around it with 1.5 mm buildup. Results A Single TSET field has a mean energy of 4.2 MeV, most probable energy of 5 MeV at surface and X ray contamination of 1.5%. Uniformity for a single field in the central 160 cm × 60 cm region is 30% vertically and 5% horizontally which is below the recommended guidelines. To improve uniformity, the use of dual field becomes necessary. Angle of tilt calculated graphically, measured with TLD and determined dosimetrically are 15.5˚, 16˚ and 17 ˚ respectively. However in comparison with other beam angles, at 17˚ tilt angle the best uniformity of 2% is obtained and hence considered appropriate. The characteristics for both single and dual field are identical, both having dmax at 8 mm. Due to contribution of other beams the dmax for 6 dual field is 1.2 mm. Measured absolute dose at Calibration point using dual field is 0.038cGy/MU. For a planned dose of 1.2 Gy for a single dual field, the measured dose was 1.1 Gy. For prescribed Treatment skin dose of 3.6 Gy for 6 dual field, the measured dose was 2.92 Gy. This variation is due to uncertainty involved in the technique and needs to be explained to Physician in determining prescription dose. The ratio of Treatment Skin dose to Calibration point dose (B factor) was found to be 2.65 which is within the range specified in TG. Conclusion The result shows a better dose uniformity along the patient height and these results can be used for patient treatment. PO-290 Quality Assurance of External Beam RT at Khwaja Yunus Ali Medical College& Hospital in Bangladesh M.N. Sharmin 1 , M.S. Rahman 2 , M.A. Bari 1 1 Khwaja Yunus Ali Medical College and Hospital- Cancer Center, Radiation Oncology, Enayetpur-Sirajgong, Bangladesh 2 Secondary Standard Dosimetry Laboratory- Institute of Nuclear Science and Technology- Bangladesh Atomic Ener gy Commission- Savar- Dhaka-1349- Bangladesh, Secondary Standard Dosimetry Laboratory, Dhaka, Bangladesh Purpose or Objective Radiotherapy is the leading mechanism for the treatment of cancer patients. The outcome of the radiotherapy is highly dependent on how precisely the dose is delivered to the tumor that should not be exceed ±5% of the prescribed dose including all types of uncertainties involved in the treatment procedure such as dosimetry, treatment planning and dose stability of the treatment unit etc. The outcome of the radiotherapy is highly dependent on how precisely the dose is delivered to the tumor. The present study is aimed for comprehensive Quality Assurance program of two medical linear accelerators Elekta Synergy, which are operated in the past several years at the Cancer Center of KhwajaYunus Ali Medical College and Hospital, a leading oncology center in Bangladesh.