ESTRO 2020 Abstract book

S969 ESTRO 2020

Radiotherapy treatment planning scans were acquired before radiotherapy and after 4 weeks of radiotherapy (40Gy/20#). Initial radiotherapy plan (OPLAN70/35) was generated for the entire 7 week course of radiotherapy and implemented. Beam configuration of initial plan was superimposed on the interim planning scan and a hybrid plan (HYBRID30/15) generated. Adaptive re-planning (RPLAN30/15) base on interim planning scan was done and dose distribution of target and OARs was compared with and without re-planning. Anatomical and dosimetric changes in target and OARs after 4 weeks of radiotherapy were compared. Statistical data was analyzed using SPSS Statistics 23.0; SPSS Inc., Chicago, IL, USA. Paired t-test or wilcoxon signed-rank test was used for comparing between each plan and a p-value<0.05 was considered statistically significant. Correlation between dosimetric and anatomical factors was studied. Results Significant percentage decrease in primary site, gross nodes and parotids was noted after 4 weeks of radiotherapy (p<0.05). No significant difference between the OPLAN30/15 and HYBRID30/15 (planned and actual delivered) radiotherapy doses to target volume were seen (p>0.05) for remaining 3 weeks radiotherapy. Hybrid plan showed an increase in delivered dose to ipsilateral and contralateral parotid glands (p<0.05). Tumor shrinkage and weight loss led to medial shift in centre of mass (COM) of parotid glands (Mean medial shift 3.8cm) which correlated significantly with weight loss. Adaptive re- planning mid-treatment reduced the dose to OARs (Spinal cord and parotid glands) (p<0.05) and improved treatment plan homogeneity. Conclusion Mid-treatment CT simulation and adaptive re-planning after 4 weeks of radiotherapy improves target volume coverage and provides greater normal tissue sparing. PO-1671 Accuracy of proton beam range detection using J-PET system - a simulation study J. Baran 1 , J. Gajewski 1 , M. Garbacz 1 , M. Pawlik- Niedźwiecka 1 , P. Moskal 2 , A. Ruciński 1 1 Institute of Nuclear Physics PAN, Proton Radiotherapy Group, Krakow, Poland ; 2 Jagiellonian University, Faculty of Physics- Astronomy and Applied Computer Science, Kraków, Poland Purpose or Objective One of the emerging issues of charged particle therapy is an in-vivo beam range verification. Among various methods introduced so far, the positron emission tomography (PET) is one of the possible solutions. PET enables measurement of the β+ activity produced within the patient body during proton beam therapy (PBT) which could be correlated with the beam range. Recently, a new, affordable, easily reconfigurable, lightweight, modular, plastic scintillator based PET technology (J-PET) was developed. The aim of this study is to quantify the sensitivity of the J-PET technology to detect proton beam range variations. Material and Methods A single J-PET module consists of thirteen 50 cm long scintillator strips. Back-to-back annihilation photons produce light pulses in a strip that are propagated to the strip edges and converted to electrical signals with silicon photomultipliers read-out by fast, on-board, front-end electronics. GATE Monte Carlo simulations of 10^8 primary protons irradiating a PMMA phantom at seven energies differing in the proton range of 1 mm were performed. Signal in discretized J-PET detector of annihilation gammas resulting from β+ emitters produced by the proton beam was scored for different geometrical configurations (Fig. 1). A list-mode TOF-MLEM reconstruction (5 iterations with 500ps TOF resolution), incorporating random, scatter, attenuation and normalization corrections using CASToR software were performed with 2.5mm^3 isotropic reconstruction grid.

PO-1670 Dosimetric and Volumetric impact of Intensity Modulated Adaptive Radiotherapy in Head Neck Cancer S. Mitra 1 , A. Dewan 2 , S. Aggarwal 3 , I. Singh Wahi 3 , S. Barik 4 , K. Dobriyal 5 , J. Mukhee 5 , A.K. Dewan 6 1 Rajiv Gandhi Cancer Institute & Research Centre, Senior Consultant Radiation Oncologist, Rohini- Delhi, India ; 2 Rajiv Gandhi Cancer Institute & Research Centre, Consultant Radiation Oncologist, Rohini- Delhi, India ; 3 Rajiv Gandhi Cancer Institute & Research Centre, Attending Consultant Radiation Oncologist, Rohini- Delhi, India ; 4 Rajiv Gandhi Cancer Institute & Research Centre, Senior Resident Radiation Oncologist, Rohini- Delhi, India ; 5 Rajiv Gandhi Cancer Institute & Research Centre, Resident Radiation Oncologist, Rohini- Delhi, India ; 6 Rajiv Gandhi Cancer Institute & Research Centre, Director Surgical Oncologist, Rohini- Delhi, India Purpose or Objective Intensity modulated Radiotherapy (IMRT) in locally advanced head and neck cancer (LAHNC) lead to significant anatomical changes including rapid shrinkage of primary and nodes, weight loss etc. Aim of the present study was to evaluate its impact on treatment dosimetry and compare the dose distribution with and without Between January’2014 to December’2016, hundred patients with LAHNC treated with concurrent chemoradiation were enrolled in a prospective study conducted at tertiary care centre in North India. adaptive re-planning. Material and Methods