ESTRO 36 Abstract Book

S512 ESTRO 36 2017 _______________________________________________________________________________________________

of this phenomenon, encouraging them to adhere to appropriate PSA surveillance and avoiding unnecessary and repetitive PSA measurements, biopsies and premature or inappropriate initiation of salvage therapy during PSAb.

Poster: Brachytherapy: Gynaecolgy

PO-0933 Urethral dose in cervical image guided brachytherapy K. MacLennan 1 , M. Zahra 2 , W. Keough 2 1 NHS Lothian, ST6, Edinburgh, United Kingdom 2 NHS Lothian, Edinburgh Cancer Centre, Edinburgh, United Kingdom Purpose or Objective Urethral dose is not currently included in the recommendations for the dose constraints for organs at risk (OARs). However, combined external beam and HDR cervical brachytherapy can result in significant urinary toxicity. We investigated the urethral dosimetry for patients treated with HDR brachytherapy. Material and Methods Retrospective audit of 117 patients undergoing cervical brachytherapy for cervical cancer in the Edinburgh Cancer Centre between 2010-2015. Patients were treated with 45Gy/25 fractions EBRT followed by 3 fractions of CT- guided HDR brachytherapy with a ring and tandem aiming for D90 between 80-85Gy. The urethra and peri-urethral tissues were retrospectively contoured 1cm inferiorly from bladder neck or to the axial slice corresponding to the metal connector of ring and tandem device (whichever most inferior). Dose volume histograms were used to determine the urethral D2cc and expressed as 2Gy equivalent (EQD2) using an a/b ratio of 3. A combined EQD2 dose for external beam and HDR treatment was calculated. Data was also collected on the length and angle of the tandem applicator and a paired T-test with 0.05 significance level was used to assess the effect of the angle or tandem length on the urethral dose. Results 117 patients aged 21-84. A 30º applicator angle was used in 12% cases, 45º in 67%, 60º in 21% patients. A 6 cm applicator was used in 68% patients; 4cm in 32% patients.7 patients had a single fraction of HDR brachytherapy and converted to a CT planned phase 2 with external beam radiotherapy. Excluding the phase 2 patients, median combined dose to HRCTV was 84.03 Gy and to the urethral d2cc was 50.7Gy (range: 44.8- 173.9Gy) Comparing the maximum EQD2 to 2cm 3 urethra from the fractionated treatment by applicator angle and length; Tandem Applicator Angle 30º Tandem 45º Tandem 60º Tandem

Conclusion Five-year clinical outcome of MR-guided HDR-BT boost is encouraging, providing excellent disease control and lack of serious late side effects. A slight decline in long-term urinary QoL was observed. PO-0932 Prostate-specific Antigen bounce in patients treated with 125I prostate brachytherapy: Keep calm A. Pires 1 , D. Moreira 1 , C. Castro 1 , A. Oliveira 1 , J. Oliveira 2 , L. Trigo 3 1 Instituto Português de Oncologia do Porto Francisco Gentil- EPE, Radioncology, Porto, Portugal 2 Instituto Português de Oncologia do Porto Francisco Gentil- EPE, Urology, Porto, Portugal 3 Instituto Português de Oncologia do Porto Francisco Gentil- EPE, Brachytherapy, Porto, Portugal Purpose or Objective Permanent low-dose-rate brachytherapy (BT) with 125 I is an established curative modality for the treatment of localized prostate cancer. After treatment, prostate- specific antigen (PSA) level may fluctuate and temporarily increase without a clear reason. This phenomenon is called “PSA bounce” (PSAb) and often causes anxiety in patient and physician. Our aim was to analyse the kinetics of PSA in our patients and the association between PSA bounce and the long term disease outcome after prostate BT with 125 I. Material and Methods We analysed 134 patients treated with 125 I implantation monotherapy between 2004 and 2006 in a single institution. All patients had tumour stage T1-T2cN0M0, Gleason score ≤ 7 and follow-up time was ≥ 9 years. Patients who received neo-adjuvant hormone therapy were excluded. PSAb was defined as a rise beyound 0.2 ng/ml the initial PSA nadir with a subsequent decline to or below the initial nadir without treatment. Biochemical failure (BF) was determined using the Phoenix definition (nadir +2 ng/mL). Associations between PSAb and the various pre and post-treatment factors were assessed with logistic regression analysis, the association between a PSAb and BF was examined with the log-rank test and the Mann-Whitney U test was applied to test for difference in the time to a PSA rise between PSAb and BF patients. Results PSAb occurred in 53 (39,8%) patients with a median time to bounce of 18,8 months. Only 7 (13,2%) patients with PSAb developed BF, in contrast to 12 (15%) patients without previous bounce (p = 0,084). Among the pre and post-treatment factors, only younger age predicted a PSAb on a multivariate analysis (p = 0.049). PSA levels during the bounce reached levels as high as 8,85 ng/mL in this cohort. BF occurred in 19 patients (14,4%). The 9-year overall survival rate was 83,6%, the 9-year disease-specific survival was 95,8% and the rate of survival at 9-year freedom from BF was higher than 90%. Conclusion PSAb is a common finding in our population and is associated with a lower rate of subsequent BF. Patients should be advised for the eventual PSAb after permanent 125 I prostate BT. Those who experience a PSAb are more likely to be younger. The physicians involved in patients follow-up after prostate BT should also be aware

Median 3.262 Gy (range 0.76- 23.67) Median 6.89 Gy (range 2.14- 52.81)

Maximum EQD2 per fraction to 2cm 3 urethra Total EQD2 2cm 3 urethra 3 fractions HDR BT

Median 3.63 Gy (range 0.70- 60.98)

Median 1.52 Gy (range 0.94-4.90)

Median 8.07 Gy (range 1.82- 130.75)

Median 3.59 Gy (range 1.59-12.30)

T test for angle (30º vs 45º, 45º vs 60º and 60º vs 45º) suggested a difference in urethral dose using a 30º applicator, with a tendency for lower urethral D2cc with a 30º angle. (30 vs 45 p = 0.002 and 30 vs 60 p = 0.04). There was no difference in urethral dose per HDR fraction according to applicator length (t-test, p = 0.54). Conclusion