ESTRO 38 Abstract book

S1116 ESTRO 38

Of these IBS is the most widely used in staging and initial management decisions. Often decisions regarding treatment are based on changes in ALP and PSA in the absence of radiological information. We present preliminary data from a Phase II trial exploring the use of Radium-223 (Ra-223) in combination with prostate and pelvic radiotherapy post docetaxel in a metastatic castration sensitive prostate cancer (mCSPC) (> 3 bone metastases, no lymph node or visceral disease T4N0/1M1b). Material and Methods Twenty-eight metastatic castration sensitive prostate cancer (mCSPC) patients were treated with monthly injections of radium-223 along with castration therapy and Volumetric Modulated Arc Therapy (VMAT) to the prostate and pelvic lymph nodes. Fifteen of the eligible mCSPC patients had baseline bone scans and treatment follow-up bone scans (during and post-treatment) available for automated aBSI analysis. The EXINI aBSI software programmed was used to retrospectively analyse the IBS and generate the aBSI value. Alkaline phosphatase (ALP) and Prostate Specific Antigen (PSA) values were collected. Results Fifteen patients had at least 2 pre and post Ra-223 IBS available for analysis. All 15 patients had a reduction or stability in the aBSI reading. There was a median reduction of 71.5% (-350-88.9%) in the aBSI with a number of patients having almost complete resolution of quantifiable disease on bone scan as evidenced in Figure 1. All 15 patients included had a reduction in ALP from Cycle 1 to Cycle 6 with treatment, median reduction from cycle 1 90 (65- 236) to cycle 6 59 (37-165). Over a median follow up period of 25.9 months the median overall survival and progression free survival have not yet been reached.

Electronic Poster: Physics track:Imaging acquisition and processing

EP-2033 Impact of CBCT roll rotation artifact on adaptive online cranial SRS of multiple targets J. Casals Farran 1 , J.F. Calvo-Ortega 1 , S. Moragues Femenia 1 , C. Laosa 1 1 Hospital Quirónsalud Barcelona, Radiotherapy, Barcelona, Spain Purpose or Objective Roll artifacts up to 1° in CBCT scans have been described in the literature for the Varian OBI system [Phys Med Biol. 2013 Feb 21;58(4):1059-73]. Our aim is to investigate the dosimetric impact of this artifact on cranial SRS planning using an online adaptive procedure developed by our group [Med Dosim. 2013 Autumn;38(3):291-7]. Material and Methods A Varian Clinac 2100 CD equipped with an OBI system was used. After placing a phantom (Easy Cube phantom, Scanditronix……) on the treatment couch, 2 CBCT scans (CCW and CW directions) were acquired with the SRS protocol used for our CBCT-based SRS procedure. Proper leveling of the phantom was done before CBCT imaging by using a digital level with ± 0.1° accuracy (Smart Tool, M- D Building Products), and it was not moved between both scans. The differences between both CBCT scans were analyzed and the roll error observed in the axial reconstructed images was measured. Ten (10) independent measurements for each acquisition direction (CCW and CW) were performed to know the roll error inherent to the CBCT images ( Ɵ ). We randomly selected 10 cases of multiple brain metastases planned with a single isocenter. For each one, the CBCT scan acquired during patient setup (CBCTref) was corrected by applying a rotation of - Ɵ ° to the axial planes (CBCTcorr). A single-isocenter reference plan was calculated over the CBCTref (Plan_ref), and then was also re-calculated over the generated CBTCcorr scan (Plan_corr). Both plans were compared in order to know the dosimetric impact of these rotations in the target coverage (D99%) when the uncorrected CBCTref scan is used for adaptive SRS planning. Differences in D99% were given respect to the prescription dose (PD) of each target: [D99%@Plan_corr – D99%@Plan_ref]/PD. Results Average roll errors of 0.3° (range: 0.1° to 0.4°) and 0.5° (range: 0.3° to 0.8°) were found for the CCW and CW- CBCT acquisitions, respectively. Target coverage differences (mean ± SD) of -1.0% ± 1.1% and -2.9%± 2.1% were found for the CCW and CW-CBCT acquisitions, respectively. Conclusion Roll artifacts of less than 0.5° were detected in the CCW- CBCT direction acquisition. A negligible dosimetric impact (~1%) in the target coverage whether the CCW-CBCT scan is used for adaptive SRS planning. Only the CCW acquisition direction was selected for our SRS online procedure. EP-2034 Evaluation of a web-based software for "Winston-Lutz" test analysis J.F. Calvo Ortega 1 , M. Hermida-López 2 , S. Moragues Femenia 1 , J. Casals 1 1 Hospital Quirónsalud Barcelona, Radiotherapy, Barcelona, Spain ; 2 Hospital Universitario Valle de Hebrón, Servicio de Física y Protección Radiológica, Barcelona, Spain Purpose or Objective The popular "Winston-Lutz (WL)" test is a well established procedure to check the congruency between the center of a target to be irradiated and the radiation linac isocenter.

Conclusion aBSI allows quantitative measurement of response to bone targeted therapies. It is more standardised, readily available and more economically sustainable than other modalities as a post therapeutic monitoring tool in bony metastatic setting. It’s use in the castration sensitive prostate cancer setting with Ra-223 has not been previously documented, two-thirds of the patients in this study have prolonged reductions in aBSI in excess of 2 years post commencement of LHRHa. Further comparison with wbMRI in this study will allow comparison of response and prognostic information.