ESTRO 36 Abstract Book

S511 ESTRO 36 2017 _______________________________________________________________________________________________

17/19 procedures from MRI1 to MRI2 and in 13/18 procedures from MRI1 to MRI3. Concordance between scoring by photo and MRI was found in 24/37procedures. Average needle migration was 2.9 ± 1.6 mm for anterior needles and 3.6 ± 1.5 mm for posterior needles (students t-test, p=0.08) Conclusion Needle migration was of acceptable magnitude measured from MRI1 to MRI2, but of considerable magnitude from MRI1 to MRI3. Insufficient concordance between scoring by photo and MRI indicates that visual inspection is inadequate for evaluating implant stability. A likely explanation for the lack of concordance between for photos and MRI is the developing oedema following needle insertion. PO-0930 CT to TRUS based Prostate HDR: what is the optimal dosimetric margin to use? F. Lacroix 1 , M. Lavallée 1 , E. Vigneault 1 , W. Foster 1 , A.G. Martin 1 1 Centre Hospitalier Universitaire de Québec- L'Hôtel- Dieu de Québec, Department of radio-oncology, Quebec, Canada Purpose or Objective The contouring volume variability resulting from delineating the target with Computed Tomography (CT) or Transrectal Ultrasound (TRUS) results in a 30 to 50% increase in volume when contouring a prostate on CT versus TRUS due to the poor soft tissue contrast of CT. This may have a significant dosimetric impact when moving from a CT to a TRUS based prostate high-dose rate (HDR) brachytherapy planning as the treated volumes are susceptible to differ significantly. This study aims at determining the proper dosimetric margin to apply when going from CT to TRUS based planning in order to compensate for this volume difference. By doing so, we aim to treat the same volume of prostatic tissue in CT or TRUS and insure a constancy in quality of care for prostate cancer patients treated with HDR. Material and Methods Twenty-seven prostate cancer patients were given a 15Gy HDR boost using a TRUS-based catheter insertion and planning approach. A 2 mm isotropic dosimetric margin was used for the TRUS planning. An average of 17 catheters were implanted. Without moving patients still under general anesthesia, a CT on rails located inside the operating room was used to image the pelvis. Three experienced radiation oncologists specialized in brachytherapy delineated the prostate on the resulting CT images and an offline, independent CT based planning was performed. A 1 mm isotropic dosimetric margin was used in CT planning. The prostate volume, 15Gy volume and V100 of the prostate were then collected and compared for the US and CT based plans. Results The average prostate, 15Gy volumes and V100 are presented in table 1. Table 1: Average prostate volume, 15Gy volume and V100 for TRUS and CT based planning Modality Average prostate volume (CC) Average 15 Gy volume (CC) V100 (100%) TRUS 38.0 50.2 96.3 CT 44.3 54.2 96.0 The average TRUS volume is 16.5% smaller than the average CT volume. When using a 2 mm dosimetric margin, the volume receiving 15Gy is smaller by 8% in TRUS compared to CT based planning. The V100 are almost identical with both modalities. The standard deviation on the TRUS prostate volume is slightly lower (10.6) than on CT (11.2). Conclusion

Our study shows an average systematic 16% smaller prostate volume on TRUS compared to CT. This differs from the 30 to 50% smaller volumes on TRUS reported in the literature. This discrepancy is probably due to the presence of catheters implanted under TRUS guidance in CT based planning which means that catheters are inserted under TRUS guidance in both planning modalities. These catheters act as fiducial markers to delimit the prostate capsule transversely on CT. The residual 16% volume variation is largely due to the uncertainty in identifying the prostate apex. A 2.8 mm isotropic dosimetric margin should be used in order to treat comparable volumes in TRUS compared to CT based planning. PO-0931 Clinical outcome and quality of life after MRI- guided HDR boost for prostate cancer. F. Lakosi 1 , A. Miovecz 1 , G. Antal 1 , J. Pall 2 , D. Nagy 3 , M. Csima 4 , J. Hadjiev 1 , I. Rep a 1 , G. Toller 1 1 Kaposvar University, Radiotherapy, Kaposva r, Hungary 2 Csolnoky Ferenc Hospital, Radiotherapy, Veszprem, Hungary 3 Kaposi Mor Teaching Hospital, Urology, Kaposvar, Hungary 4 Kaposvar University, Faculty of Pedagogy, Kaposvar, Hungary Purpose or Objective To analyze 5-year clinical outcome and quality of life (QoL) after MR-guided high-dose-rate brachytherapy (HDR-BT) combined with 3D conformal external beam Fifty-two patients with intermediate (IR) (n=22) to high- risk (HR) (n=30, 18 T3 diseases) localized prostate cancer were treated with 46-60 Gy of 3D EBRT preceded and/or followed by a single dose of 8-10 Gy MR-guided HDR-BT. Template reconstruction, trajectory planning, image guidance, contouring and treatment planning were exclusively based on MR images. Ninety-six percent of the patients received androgen deprivation. Biochemical relapse–free survival (bRFS, Phoenix definition), local relapse-free survival (LRFS), distant metastasis-free survival (DMFS), cancer-specific survival (CCS) and overall survival (OS) were analyzed actuarially. Morbidity were scored using CTCAEv4.0, while patients self-reported urinary and bowel QoL was measured with the Expanded Prostate Cancer Index Composite (EPIC) instrument and International Prostate Symptom Score (IPSS) at baseline and at regular intervals up to 6 years. Results Median follow-up time was 73 (range:13-103) months. The crude/5-year actuarial rates of bRFS, LRFS, DMFS, CSS and OS were 94/97.4 %, 98/100 %, 96/97 %, 100/100 % and 92/91 %, respectively. Two distant failures occurred in HR group, while one local recurrence in IR group. The main urinary toxicity was dysuria, which were Gr. 2 in 24/52 cases, including 9 patients with alfa blocker use at baseline. There were 3 urinary strictures including one Gr. 3 event. Late GI morbidity was mild, representing Gr. 1 diarrhea (10/51), Gr. 1 urgency (9/51), Gr. 2 proctitis (1/52) and Gr. 2 fecal incontinence (1/52), respectively. A significant decline in urinary domain was observed within the first 3 months, which mostly recovered by 6 months, thereafter declined progressively (p>0.05) and remained stable from 4th years follow up (p>0.05) (Figure). A similar trend was seen for bowel QoL, where a significant decline occured within the first 3 months that subsequently returned to nearly baseline level within 6 months, however, in contrast to urinary functions remained stable over time (p>0.05). The evolution of IPPS scores showed the same pattern as EPIC urinary scores. radiotherapy (3D-EBRT). Material and Methods