Abstract book - ESTRO meets Asia

S50 ESTRO meets Asia 2018

G. Biasi 1 , M. Carolan 2 , A. Rosenfeld 1 , M. Petasecca 1 1 University of Wollongong, Centre For Medical Radiation Physics, Wollongong NSW, Australia 2 Wollongong Hospital, Illawarra Cancer Care Centre, Wollongong, Australia Purpose or Objective VMAT is a rotational radiotherapy technique involving the simultaneous modulation of dose rate (DR) and gantry speed (GS) and continuous MLC reshaping of the radiation field. For a successful plan delivery, the three dynamic components must demonstrate consistent synchronization. A new system known as DUO, is used to evaluate the accuracy of the DR and GS during VMAT delivery and provide an independent measurement of the MLC leaf speed. Material and Methods The high-resolution dosimeter (DUO) features two orthogonal arrays of silicon diodes with 200µm centre-to- centre pixel distance. DUO is synchronized to an inclinometer and inserted in the accessory tray of the LINAC head of a Varian TrueBeam operating at 10 MV using FFF modality. Three VMAT tests (Customer Acceptance Plan (CAP), Spokes, Error introduction) were designed to evaluate the machine synchronization of DR and GS during arc delivery. The sensitivity of the dosimeter in detecting deviations in the dynamic components was also verified. Furthermore, the MLC leaf speed was quantitatively evaluated using a sweeping window technique with two nominal leaf speeds of 2.50 and 1.87 cm.s -1 . These QA tests are based upon the NCS Code of Practice for VMAT QA and measurements were compared to the Varian Dynalog files. Results The CAP test was performed with three different GSs (0.5, 1.5 and 6 °s-1) and four DRs (0, 35, 595 and 795 MU/min). A 1% variation in the DR was observed between Dynalog data and measurements performed using the DUO dosimeter. The GS was found to be within 3% of the Dynalog data, however, large discrepancies were observed during the transition from high to low DR delivery. The spokes test based on a previous study published by Van Esch was used to evaluate the machine behavior during extreme variations of DR (0 to 1200 MU/min) and GS (0.5 to 6 °.s -1 ). The average DR measured by DUO was 1148.64±16.17 MU/min across all the spokes; in comparison to Dynalog with an average of 1153.81±1.01 MU/min. The DUO/inclinometer system measured GS that varied between 0.48 ± 0.07 and 5.96 ± 0.12 °.s -1 in the high and low DR regions, respectively. The errors introduced in the VMAT plan caused a deviation in the rotational speed (0.77 °.s -1 with error versus 0.50 °.s -1 without error) measured by DUO and Dynalog. The average MLC leaf speeds measured was 2.57±0.51 cm.s -1 , and 1.84 ±0.8 cm.s -1 which are within experimental uncertainty of the Dynalog data of 2.48±0.15 cm.s -1 and 1.86 ±0.23 cm.s -1 . Conclusion The reliability of DUO as a dosimetric QA device was evaluated for VMAT delivery upon Varian LINAC, using 10MV FFF modality to satisfy the requirements of the NCS Code of Practice report 24 for VMAT QA. The system proved its capability in the accurate reconstruction of the dose rate and gantry speed and evaluation of the MLC leaf speed and its sensitivity to systematic errors. The system offers a reliable, efficient and independent method to perform the VMAT QA procedures and avoid the need for multiple detectors. PV-126 MAGICA gel dosimeter: An instrument to measure the dose enhancement factor by Bismuth nanoparticles S. Shoobkolaei 1 , N. Riyahi alam 1 , A. Shabestani Monfared 2 1 Tehran University of Medical Sciences Radiation On,

Department of medical physics, Tehran, Iran Islamic Republic of 2 Babol University of Medical Sciences, Department of Biophysics and Biochemistry- Cellular and Molecular Biology Research Centre, Babol, Iran Islamic Republic of Nanoparticles embedded in polymer gels dosimeter is the Common method for estimation of nanoparticle dose enhancement. MAGICA gel dosimeter is modified magic gel by added agarose, access more stability, dynamic range, reproducibility and increasing stiffness. Bismuth-based nanoparticles by high atomic number and electron density are a promising and more capable candidate for dose enhancement studies. Bismuth is usual CT contrast agent but also behaves as a Radioenhancer. This study intends to indicate the dose enhancement factor of BiNPs in MAGICA gel dosimeter irradiated by megavoltage range energy. Material and Methods Synthesized Bi nanoparticles with sizes around the 20 nm and 0.1mM concentration Loaded to Fabricated MAGICA Gel dosimeter and irradiated with 6 MV X-rays beams from a linear accelerator for dose-response readout, Gels were imaged using a 1.5 T MRI. Results The results have shown that the MAGICA polymer gel dose response in the dose range of 0 to 1000 cGy is linear. The mean absorbed doses in the presence of 0.1mM BiNPs in MAGICA gel were 13.8% higher than the corresponding Values without the BiNPs under the 6 MV X-rays beams Conclusion Finally, these results demonstrate the potential applicability of bismuth nanoparticles to amplify radiation in megavoltage radiation therapy for treatment using. additionally, MAGICA gel dosimeter is suitable tools for verification & estimation of dose enhancing. PV-127 Impact of radiotherapy on ovarian function in ovarian transposition of cervical cancer patents S. Lu 1 , L. Yin 2 , J. Wang 1 , W. Hu 1 , G. Ke 2 1 Fudan University Shanghai Cancer Center, Department of Radiation Oncology, Shanghai, China 2 Fudan University Shanghai Cancer Center, Department of Gynecologic Oncology, Shanghai, China Abstract Withdrawn Purpose or Objective To investigate the impact of radidothery on ovarian function for ovarian transposition of cervical cancer patients Material and Methods This retrospective study have enrolled 98 cervical cancer patients who received radical hysterectomy and ovarian transposition before radiotherapy from April 2011 to December 2016 in Fudan University Shanghai Cancer Center. The age was ranged from 24 to 49 years. According to the International Federation of Gynecology and Obstetrics (FIGO) 2009 Criteria, clinical staging of tumors was Ib 1 ~IIb. Postoperative adjuvant intensity-modulated radiation therapy (IMRT) were recommended for all patients with high-risk pathological factors. Ten patients received IMRT with no limitation on radiation dose to ovaries, and 88 patients underwent IMRT with dose constrain (maximum dose is 7Gy and mean dose is 5Gy) to ovaries, of which 41 patients received unilateral ovary limitation, 47 patients received bilateral ovaries limitation. All patients were followed up about sex hormone levels (E2, follicle stimulating hormone [FSH],) one year after completion of their radiotherapy. The influence of ovarian maximum dose, ovarian mean dose Abstract withdrawn Purpose or Objective