Hypofractionated Stereotactic Body Radiation Therapy With Simultaneous Integrated Boost and Simultaneous Integrated Protection in Pancreatic Ductal Adenocarcinoma.

AIMS: To evaluate the safety and feasibility of stereotactic body radiation therapy (SBRT) with simultaneous integrated boost (SIB) and simultaneous integrated protection (SIP) in borderline resectable and locally advanced pancreatic ductal adenocarcinoma. MATERIALS AND METHODS: Patients receiving SBRT following induction chemotherapy from January 2017 to December 2018 were included in this observational analysis. SBRT was delivered in five consecutive daily fractions by administering 30 Gy to the planning target volume while simultaneously delivering a 50 Gy SIB to the tumour-vessel interface. SIP was created by lowering the dose to 25 Gy on the overlap area between the planning target volume and the planning organ at risk volume. The primary end point was acute and late gastrointestinal grade ≥3 toxicity. Secondary end points were freedom from local progression, overall survival and progression-free survival (PFS). RESULTS: Fifty-nine consecutive patients (27 borderline resectable and 32 locally advanced) were included. Fifty-eight patients (98.3%) completed the SBRT planned treatment and 35 patients (59.4%) received surgical resection following SBRT. No acute or late grade ≥3 SBRT-related adverse events were observed. The median follow-up time was 15.1 months in the overall cohort and 18.1 months in censored patients. One- and 2-year freedom from local progression rates were 85% and 80% versus 79.7% and 60.6% in resected and unresected patients, respectively (P = 0.33). The median overall survival and PFS were 30.2 months and 19 months from diagnosis and 19.1 months and 10.7 months from SBRT in the entire cohort. Resected patients had improved 2-year overall survival rates (72.5% versus 49%, P = 0.012) and median PFS (13 months versus 5 months; P < 0.001) relative to unresected patients. There was no survival difference between borderline resectable and locally advanced patients. CONCLUSIONS: SBRT with SIB/SIP had an excellent toxicity profile and could be administered safely on pancreatic ductal adenocarcinoma patients, even in a total neoadjuvant setting.

SU-E-J-168: 4D-PET for Target Volume Delineation in Respiratory-Gated Radiation Therapy.

PURPOSE: To find an optimized workflow for the use of respiratory-gated PET (4D-PET) in target volume delineation of tumors subject to respiratory-gated radiation therapy. METHODS: 15 patients with lung (11) and pancreas (4) tumors who had FDG-PET-CT for target delineation prior to EBRT were studied. Patients were selected among the group that showed respiratory-induced tumor motion 〉5mm. 4D-PET was performed by means of a Philips Gemini BigBore scanner, using the Varian RPM gating system. An identical system was available at the linac for treatment. The breathing cycle was equally divided in 4 phases, according to a previous study. Since planning was made on a single CT-phase, no ITV was explicitly built from the set of phases. The BTV was identified with SUV=2.2 threshold and the PTV was obtained expanding the BTV by 8mm(S-I), 5mm(A-P) and 3mm(L-R) to account for residual motion and setup errors. The most advantageous CT-phase for treatment planning was then identified by simulating plans on each phase and analyzing the resulting DVHs of OARs (lung, trachea, oesophagus, spinal cord, left ventricle). RESULTS: The observed maximum range of motion was 5.5mm(L-R), 12.3mm(A-P) and 19.2mm(S-I). The standard deviation of the BTV volume in the 4 phases ranged from 6% to 13.7%. V20 (lung) ranged 7.1%-15.2% in inspiration and 7.8%-18.6% in expiration. The mean dose to the oesophagus ranged 0.1-2.2Gy in inspiration and 1.4-2.0Gy in expiration. In general, the dose to OARs was smaller when planning on a single phase than on the overall, respiratory-uncontrolled volume (p-value〈0.05). CONCLUSIONS: The BTV volume was almost constant between phases, confirming that the motion might be described by 4 phases. There was no obvious choice of the optimal phase for treatment planning, suggesting patient-by-patient studies. However, planning and delivery on one phase consistently allowed dose sparing to be obtained compared to non-gated techniques.

Radiation dose saving through the use of cone-beam CT in hearing-impaired patients.

PURPOSE: Bionic ear implants provide a solution for deafness. Patients treated with these hearing devices are often children who require close follow-up with frequent functional and radiological examinations; in particular, multislice computed tomography (MSCT). Dental volumetric cone-beam CT (CBCT) has been reported as a reliable technique for acquiring images of the temporal bone while delivering low radiation doses and containing costs. The aim of this study was to assess, in terms of radiation dose and image quality, the possibility of using CBCT as an alternative to MSCT in patients with bionic ear implants. MATERIALS AND METHODS: One hundred patients (mean age 26 years, range 7-43) with Vibrant SoundBridge implants on the round window underwent follow-up: 85 with CBCT and 15 with MSCT. We measured the average tissue-absorbed doses during both MSCT and CBCT scans. Each scan was focused on the temporal bone with the smallest field of view and a low-dose protocol. In order to estimate image quality, we obtained data about slice thickness, high- and low-contrast resolution, uniformity and noise by using an AAPM CT performance phantom. RESULTS: Although the CBCT images were qualitatively inferior to those of MSCT, they were sufficiently diagnostic to allow evaluation of the position of the implants. The effective dose of MSCT was almost three times higher than that of CBCT. CONCLUSIONS: Owing to low radiation dose and sufficient image quality, CBCT could be considered an adequate technique for postoperative imaging and follow-up of patients with bionic ear implants.