ESTRO 36 Abstract Book

S995 ESTRO 36 _______________________________________________________________________________________________

To assess the accuracy of the immobilization devices, we immobilized the CIRS Radiosurgery Head Phantom with hidden target by BoS cast and headring, respectively. Then we implemented the imaging guidance by using bony structure. Compare to the localization method, the CIRS Radiosurgery Head Phantom with hidden target was immobilized by headring followed by implementation of the imaging guided process using bony structure and fiducial markers, respectively. The overall couch shifts were performed by the radiation therapists, the deviation with respect to the proton isocenter was measured by using the hidden target with paired t-test and 3D vector . Results For BoS cast and headring, the deviations (mm) were 0.54±0.68 and 0.48±0.28 (p ＝ 0.412) in right-left (RL), 0.22±0.28 and -0.11±0.34 (p ＝ 0.186) in superior-inferior (SI), -0.30±0.11 and -0.15±0.22 (p ＝ 0.167) in anterior- posterior (AP) directions, and 0.85±0.42 and 0.60±0.32 (p ＝ 0.017) in 3D vector, respectively. For the imaging- guided localization method, the deviations (mm) of bony structure and fiducial markers were -0.29±0.65 and 0.19±0.34 (p ＝ 0.002) in RL, -0.14±0.53 and 0.01±0.12 (p ＝ 0.126) in SI, -0.01±0.42 and 0.10±0.25 (p ＝ 0.219) in AP directions, and 0.84±0.48 and 0.41±0.23 (p ＝ 0.004) in 3D vector, respectively. Conclusion Translational deviations were not statistically significant between the immobilization methods or imaging-guided landmarks. However, there were significant differences in 3D vector. The results of our study demonstrated that headring and fiducial markers can achieve good accuracy for brain cancer in proton stereotactic radiosurgery (P- SRS). EP-1814 Is AIO belly board device advantageous in all irradiated rectal cancer patients? D. Hempel 1 , J. Mandrosz 1 , J. Topczewska-Bruns 1 , D. Kazberuk 1 , A. Szmigiel-Trzcińska 1 , R. Maksim 1 , M. Konopka-Filippow 1 , T. Filipowski 1 , M.Z. Wojtukiewicz 2 , E. Sierko 2 1 Comprehensive Cancer Center, Department of Radiotherapy, Białystok, Poland 2 Comprehensive Cancer Center, Department of Clinical Oncology, Białystok, Poland Purpose or Objective A prospective study was undertaken to compare prone on flat table position vs on 'All in one” belly board device (AIO BBD) by assessment of patients’ preferences, irradiated small bowel and bladder volume (SB-V, B-V) as well as setup accuracy in rectal cancer patients (RCPs). Material and Methods Material and methods: Fifteen RCPs scheduled to irradiation on pelvic area (preoperative, n = 11 and postoperative, n = 4) were scanned twice: in prone on flat table and prone on AIO BBD position. Patients were asked to complete an institution-developed questionnaire concerning their perception of the positioning. Using 3D planning system the dose-volume histograms (DVHs) for SB and B were compared in two treatment plans. Setup accuracy of bony anatomy and pelvic organs were analyzed in MV-portals and X-ray volume imaging (XVI) procedures, respectively for on AIO BBD – positioned patients (n = 14). Results AIO BBD was accepted as immobilization method by majority of RCPs and provided better DVHs for SB than prone on flat table position. The setup reproducibility was good, within tolerance limit for patients with BMI ≤ 29 kg/m 2 . However, two patients with obesity regarded AIO BBD as uncomfortable and they presented mean setup shifts out of tolerance limit in Y axis – 5.9 mm. The another

obese patient was disqualified from irradiation on AIO BBD due to more beneficial DVH for SB in prone on flat table position . Conclusion The AIO BBD should be recommended as immobilization method in RCPs with BMI ≤ 29 kg/m 2 . Immobilization of obese patients on AIO BBD may be uncomfortable for them, cause worse dose-volume distribution in SB and /or result in unacceptable setup shifts. EP-1815 Technical aspects and setup irradiation of rats using a clinical accelerator V. SACCO 1 , A. Viale 1 , B. Noris Chiorda 1 , C. Sini 2 , G. Salvadori 1 , C. Fiorino 2 , N. Di Muzio 1 , C. Cozzarini 1 1 Nuova Fondazione Centro San Raffaele, Radiotherapy, Milano, Italy 2 Nuova Fondazione Centro San Raffaele, Medical Physics, Milano, Italy Purpose or Objective A preclinical study having the aim to test the possible hormone protective role on radio-induced inflammation of the bladder wall has been conceived in our centre using a rat model. This kind of application usually requires a dedicated microlinac to deliver radiotherapy to small animals. However, this device is not available in our hospital. The purpose of this study is to set up a system allowing to irradiate rats by a clinical accelerator, with a positioning system that ensures the reproducibility of the treatment. Material and Methods Eight male rats were surgically catheterized, anesthetized, immobilized within small containers in plastic material, and positioned on the clinical accelerator bed (RapidArc® - Varian Medical Systems). The isocentre was placed on the abdomen of the animals, with a source- to-skin distance (SSD) of 100 cm. A kilovoltage cone-beam CT was acquired in order to image the bladder, previously filled by injecting Gastrografin. The treatment field was defined by assigning an expansion of 3 mm to the bladder on the coronal projection of the cone-beam CT. After positioning of a bolus of 1 cm on the abdomen of the animals, a single fraction of 20 Gy was delivered with 6 MV photons. A single fraction treatment was decided to avoid the need of repeated irradiations that would complicate organisation issues.

Results The animals were successfully treated and well tolerated radiotherapy, being alive after 6 months of irradiation. The shift difference between the cone beam CT reconstruction and the manual correction of the radiotherapist was calculated. The values measured in the group of animals were expressed in three dimensional shifts (along X,Y,Z IEC coordinates, in cm), as mean values ± standard deviations: X = -0.13 ±0.10; Y = 0.13±0.08; Z= 0.13±0.12.