ESTRO 2020 Abstract book

S737 ESTRO 2020

Therapy System, P235, Japan), as shown in Fig. 1. The irradiation energy of the proton beam was set as 100 MeV. The dose range from 0 Gy to 6 Gy and three-dose rates, 20, 40, and 80 MU/min were used for studying the dose- response curve and dose rate dependence effect. The PDD distribution and Bragg peak position of the NIPAM gel dosimeter were also studied.

to the German Cooperative Group (GCG) and Numeric Rating Scale (NRS) at the beginning of RT and during follow- up, the adverse effects of irradiation, duration of pain relief, further treatment and necessity of analgesics use. Results The mean duration of follow-up was 5 years [range 4–6 years]. Among them, 58% of patients (n= 32) complained about pain for months and 42% for years before RT. Nearly all patients ( 90%, n= 49) had taken analgesics and (84%, n= 46) had undergone physiotherapy. 64 % (n= 35) of patients reported pain relief and walking possibility improvement at the end of RT. Median NRS score was 5 points lower at the end of RT than before (50% pain reduction). Some patients reported pain relief after 0,5 to 6 months from the end of RT. Duration of pain relief was in range from 10 to 64 months. No radiation toxicity or secondary malignancies were observed during the follow- up. Conclusion Low-dose radiotherapy for Painful Heel Spur Syndrome is an effective method providing a long-lasting pain relief without significant toxicity and secondary malignances. PO-1306 Pilot study: Characteristics of N-isopropyl acrylamide polymer gel dosimetry with proton beam E. Huang 1 , K. Juan 1 , J. Lan 1 , Y. Juan 2 , P. Juang 1 , C. Yao 3 , Y. Chang 4 1 Kaohsiung Chang Gung Memorial Hospital, Department of Radiation Oncology, Kaohsiung, Taiwan ; 2 China Medical University, Department of Master Program for Biomedical Engineering / School of Chinese Medicine, Taichung, Taiwan ; 3 China Medical University, Department of Biomedical Imaging and Radiological Science, Taichung, Taiwan ; 4 Feng Chia University, Department of Aerospace and System Engineering, Taichung, Taiwan Purpose or Objective In Taiwan, the second proton center has started to operate for one year since 2018. The number of patients for proton therapy increased gradually these years in Taiwan. The advantage of proton therapy is to make more conformal therapy shape fitted to the tumor, and to give high energy deposition density close to the target tumor. Accordingly, the three-dimensional (3D) dose verification is more important for proton therapy. This is a pilot study to investigate the basic characteristics of the N-isopropyl acrylamide (NIPAM) polymer gel dosimetry. The percentage depth dose (PDD) distribution and dose rates dependence of the NIPAM gel dosimetry were discussed in the current study. Material and Methods The N-isopropyl acrylamide (NIPAM) polymer gel dosimeter is a kind of polymer gel dosimeters (PGDs). It can record 3D dose distribution and it has high sensitivity and linearity. Although some previous studies have used gel dosimeters for clinical research, however, the performance of the NIPAM gel dosimeter for proton therapy is not very clear. In the current study, the cylindrical acrylic el phantom of 10 cm in diameter, 10 cm in height, and 3 mm in thickness was used. The gel recipes, i.e., 5% gelatin (300 Bloom Type A,Sigma-Aldrich), 5% NIPAM (97% pure; Wako, Osaka, Japan), 3% N,N-methylene bisacrylamide (Bis), and 5mM tetrakis (hydroxymethyl) phosphonium chloride (THPC) was used for gel preparation. We adopted a self-developed parallel beam optical computed tomography (Optical-CT) as the readout tool for the gel phantom. The NIPAM gel was filled into the acrylic phantoms and was irradiated with the proton beam (“Sumitomo” Proton Poster: Physics track: Basic dosimetry and phantom and detector development

Results The results showed that the PDD distribution was consistent with TPS and the dose difference between the measured dose and TPS was lower than 7% at the beam entrance region before the Bragg peak (1 to 6 cm depth), as shown in Fig. 2. At the Bragg peak position, the dose was 4% underestimation as compared with TPS. And the results showed that there was no dose rate dependence for the NIPAM polymer gel dosimeter with proton therapy.

Conclusion We conclude that the NIPAM polymer gel dosimeter has superior performance for proton beam and it showed high potential for proton therapy in clinic. More characteristics of NIPAM gel dosimetry and various treatment plan of the tumor will be performed for dose verification in the future. PO-1307 IPEM Code of Practice for high-energy photon dosimetry based on the NPL dose calibration service D. Eaton 1 , G. Bass 2 , P. Booker 3 , J. Byrne 4 , S. Duane 2 , J. Frame 5 , M. Grattan 6 , R. Thomas 2 , N. Thorp 3 , A. Nisbet 7 1 Guy's and St Thomas' NHS Foundation Trust, Medical Physics, LONDON, United Kingdom ; 2 National Physical Laboratory, Medical Physics, Teddington, United Kingdom ; 3 Royal Preston Hospital, Rosemere Cancer Centre, Preston, United Kingdom ; 4 Northern Centre for Cancer Care, Radiotherapy Physics, Newcastle, United Kingdom ; 5 Western General Hospital, Edinburgh Cancer