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S291

ESTRO 36 2017

_______________________________________________________________________________________________

needed to study the impact of the combination on overall

survival and PFS.

PV-0551 PSMA PET/CT vs MRI for GTV delineation in

prostate cancer: a comparison with histology

C. Zamboglou

1

, V. Drendel

2

, C.A. Jilg

3

, H.C. Rischke

1

, B.

Teresa I.

4

, T. Krauss

5

, M. Werner

2

, M. Bock

6

, M. Langer

5

,

P.T. Meyer

4

, A.L. Grosu

1

1

Medical Center - University of Freiburg, Department of

Radiation Oncology, Freiburg, Germany

2

Medical Center - University of Freiburg, Department of

Pathology, Freiburg, Germany

3

Medical Center - University of Freiburg, Department of

Urology, Freiburg, Germany

4

Medical Center - University of Freiburg, Department of

Nuclear Medicine, Freiburg, Germany

5

Medical Center - University of Freiburg, Department of

Radiology, Freiburg, Germany

6

Medical Center - University of Freiburg, Department of

Radiology- Medical Physics Division, Freiburg, Germany

Purpose or Objective

The exact delineation of the intraprostatic tumour burden

is crucial for treatment planning in primary prostate

cancer (PCa). We compared

68

Ga-HBED-CC-PSMA PET/CT

with multiparametric MRI (mpMRI) for gross tumour

delineation in patients with primary PCa based on slice by

slice correlation with histopathological reference

material.

Material and Methods

Patients with histopathologically proven primary PCa

underwent

68

Ga-HBED-CC-PSMA PET/CT (n=10) and MRI

(n=7) followed by radical prostatectomy. Resected

prostates were scanned by ex-vivo CT using a special

localizer and prepared for histopathology in a customized

cutting device. Invasive PCa was delineated on a HE

stained histologic tissue slide and matched to ex-vivo CT

to obtain gross tumor volume (GTV-)histo. Ex-vivo CT

including GTV-histo and MRI data were matched to in-vivo

CT(PET). Consensus contours based on MRI (GTV-MRI),

PSMA PET (GTV-PET) or the combination of both (GTV-

union/-intersection) were delineated. In each in-vivo CT

slice the prostate was separated into 4 equal segments

(total 340 segements) and sensitivity and specificity for

PSMA PET and mpMRI were assessed by comparison with

histological reference material. Furthermore, the spatial

overlap with GTV-histo was measured. In the case of

multifocal PCa (4/7 patients), SUV values (PSMA PET) and

b-values (diffusion weighted MRI) were obtained for each

lesion.

Results

GTV-histo was detected in 225 of 340 segments (66%).

Sensitivity and specificity for GTV-PET, GTV-MRI, GTV-

union and GTV-intersection were 75% and 87%, 70% and

82%, 82% and 67%, 55% and 99%, respectively. GTV-histo

had on average the highest overlap with GTV-union

(57±22%), which was significantly higher than overlap with

GTV-MRI (p=0.016) and GTV-PET (p=0.016), respectively.

In every patient with multifocal PCa there was one lesion

which had both the highest SUV and the highest b-value

(mean and max), which was always the largest lesion in

histology.

Conclusion

68

Ga-HBED-CC-PSMA PET/CT and mpMRI showed high

sensitivity and specificity in detection of primary PCa. The

combination of both methods performed even better in

terms of sensitivity (GTV-union) and specificity (GTV-

intersection). A good spatial overlap with GTV-histo was

observed for PSMA PET/CT and mpMRI alone which was

significantly improved by GTV-union. Further studies are

warranted to analyse the impact of these preliminary

findings for therapeutic (focal therapy) strategies in

primary PCa.

PV-0552 Urethra-sparing SBRT for prostate cancer:

acute toxicity results from a randomized phase II trial

T. Zilli

1

, S. Jorcano

2

, S. Bral

3

, C. Rubio

4

, A. Bruynzeel

5

, A.

Oliveira

6

, U. Abacioglu

7

, H. Minn

8

, Z. Symon

9

, R.

Miralbell

1,2

1

Hôpitaux Universitaires de Genève, Radiation Oncology,

Geneva, Switzerland

2

Teknon Oncologic Institute, Radiation Oncology,

Barcelona, Spain

3

Onze-Lieve-Vrouwziekenhuis, Radiation Oncology, Aalst,

Belgium

4

Hospital Universitario Sanchinarro, Radiation Oncology,

Madrid, Spain

5

VU University Medical Center, Radiation-Oncology,

Amsterdam, The Netherlands

6

Portuguese Institut of Oncology, Radiation Oncology,

Porto, Portugal

7

Neolife Medical Center, Radiation Oncology, Istanbul,

Turkey

8

University Hospital Turku, Radiation Oncology, Turku,

Finland

9

Sheba Medical Center, Radiation Oncology, Ramat Gan,

Israel

Purpose or Objective

To present the acute toxicity results from a prospective

multicenter phase II randomized trial of short or

protracted urethra-sparing stereotactic body radiotherapy

(SBRT) for localized prostate cancer (PCa).

Material and Methods

From 08/2012 to 12/2015, 170 patients (pts) from nine

European centers with cT1c-3a N0 M0 PCa and a low risk

of nodal involvement (≤20%, according to Roach et al.)

were recruited and randomized according to two different

overall treatment time (OTT) schedules: either 9 days

(arm A, 84 pts), or 28 days, once-a-week, the same week-

day (arm B, 86 pts). The prescribed dose was 36.25 Gy in

5 fractions of 7.25 Gy to the prostate ± seminal vesicles in

both arms. The prostatic urethra, with a surrounding

margin of 3 mm, received a lesser dose of 5 x 6.5 Gy = 32.5

Gy. All patients were treated either with a VMAT or IMRT

technique under stereotactic conditions using Novalis

linacs and ExacTrac image-guided technology.

Genitourinary (GU) and gastrointestinal (GI) toxicity

(CTCAE v4.0 grading scale), IPSS, and QoL scores (EORTC

QLQ-PR25) were assessed at baseline, at the 5

th

fraction

(5fx), and 12

th

weeks (12W) since SBRT start.

Results

82 (median age 70 years) and 83 (median age 69 years)

pts, respectively, from arms A and B, were retained for

this analysis. Low-, intermediate-, and high-risk

presentation was respectively 22%, 63%, and 15% (arm A)

and 22%, 64%, and 14% (arm B). A 6-months androgen

deprivation was used in 44% and 45% of the pts in arm A

and B, respectively. The toxicity stopping rule of the study

during the first 3-months was never activated. In both

arms, Grade 1 GI toxicity increased from baseline to 5fx

(from 19.5% to 38% and from 23% to 32% for arms A and B,

respectively) returning back to baseline by W12

(18% for

Arm A and 25% for Arm B). Only 2 cases of grade 2 GI

toxicity (2.5%) were observed at 5fx in arm A. Grade 2 GU

toxicity rates at baseline, 5fx, and W12 were 2%, 17%, and

11% vs. 5%, 19% and 6% in arms A and B, respectively

(mainly moderate irritative and voiding symptoms). Only

one grade 3 GU toxicity was observed at W12 in arm B

(desobstructive TURP in a patient with a preexisting

history of acute urinary retention). Median IPSS scores at

the same endpoints were 6, 10, and 6 vs. 6, 10, and 7 for

arms A and B, respectively, with similar IPSS-based QoL

rates at baseline and W12 (80% of pts satisfied). No

changes in EORTC QLQ-PR25 scores for GU, GI, and sexual

domains were observed in both arms between baseline and

W12.