ESTRO 36 Abstract Book

S517 ESTRO 36 _______________________________________________________________________________________________

Conclusion There is little existing data guiding urethral dose constraint but study in peri-urethral cancer has demonstrated a higher risk of urethral toxicity in patients with a urethral EQD2 of >85Gy. Our median EQD2 was below this level but with a wide range, indicating the degree of adaptation using image guidance. Given the poor correlation of applicator angle and length with dose to OARs choice of applicator should remain dictated by the patients’ anatomy. PO-0934 Brachytherapy as part of the conservative treatment for primary and recurrent vulvar carcinoma C. Chargari 1,2 , P. Castelnau-Marchand 1 , A. Escande 1 , I. Dumas 1 , R. Mazeron 1 , P. Maroun 1 , E. Bentivegna 3 , S. Gouy 3 , A. Cavalcanti 3 , P. Morice 3 , C. Haie-Meder 1 1 Gustave Roussy Cancer Campus, Brachytherapy unit- Radiation oncology, Villejuif, France 2 French Military Health Services Academy, French Military Health Services Academy, Paris, France 3 Gustave Roussy Cancer Campus, Department of Surgery, Villejuif, France Purpose or Objective There are only scarce data on the place of brachytherapy (BT) for treatment of vulvar carcinoma. Our institutional experience of interstitial BT for vulvar carcinoma patients is reported. Material and Methods Clinical records of patients receiving low-dose rate (LDR) or pulsed-dose rate (PDR) BT as part of the primary treatment for primary/recurrent vulvar squamous cell carcinoma or as part of adjuvant treatment between 2000 and 2015 were included. Patients, tumors and treatments characteristics as well as clinical outcome were examined. Results A total of 26 patients treated with BT were identified. BT was delivered as part of primary intent treatment for locally advanced/recurrent cancer in 11 patients, and as part of adjuvant treatment in 15 patients. Median age at time of BT was 63 years (range: 41 – 88 years). PDR and LDR were used in 15 patients and 11 patients, respectively. BT was performed as a boost to the tumour bed following EBRT (n=13) or as only irradiation modality (n=13). Total median dose at the level of primary tumor was 60 GyEQD2 (range: 55 – 60 GyEQD2). With mean follow-up of 41 months (range: 5 months – 11.3 years), 11 patients experienced tumour relapse. Ten patients experienced local relapse as first event, associated with synchronous extra-vulvar events in 8/10 patients. Three- year estimated disease-free survival and overall survival rates were 57% (95%CI: 45–69%) and 81% (95%CI: 72-90%). All toxicities were grade 2 or less. Conclusion Interstitial BT used as part of the primary or adjuvant treatment of vulvar carcinoma is feasible with a satisfactory toxicity profile. Prognosis remains however, dismal, with a high frequency of local and distant failures in patients with locally advanced tumors. PO-0935 Modeling to compensate for intra-fractional bladder dose variations in gynecological brachytherapy Z. Siavashpour 1 , R. Jaberi 2 , M.R. Aghamiri 1 , C. Kirisits 3 1 Shahid Beheshti University, Medical Radiation Engineering, Tehran, Iran Islamic Republic of 2 Tehran University of Medical Sciences, Radiotherapy, Tehran, Iran Islamic Republic of 3 Comprehensive Cancer Center- Medical University of Vienna, Department of Radiotherapy and Oncology, Vienna, Austria Purpose or Objective Proposing a model to compensate for intra-fractional bladder dose variations during gynecological (GYN) brachytherapy.

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

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).