ESTRO 36 Abstract Book

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S455 ESTRO 36 2017
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increase of lung damage up to a certain threshold (60 Gy),
before adopting an asymptotic relationship. Patient
response in the linear fitting was heterogeneous with a
greater than 3 fold difference found in the IQR. These
findings may aid in post-treatment response assessment
and toxicity modeling in NSCLC patients undergoing
escalated dosing regimens.
PO-0848 Predictors of patient-reported incontinence
after prostate cancer RT: results from a cohort study
C. Cozzarini1, N. Bedini2, E. Garibaldi3, D. Balestrini 4, P.
Franco 5, G. Girelli6, I. Improta7, F. Palorini8, V.
Vavassori9, T. Rancati8, R. Valdagni 2,8, C. Fiorino7
1 San Raffaele Scientific Institute, Radiotherapy, Milano,
Italy
2 Fondazione IRCCS Istituto Nazionale dei Tumori,
Radiation Oncology 1, Milano, Italy
3 Istituto di Candiolo- Fondazione del Piemonte per
l'Oncologia IRCCS, Radiotherapy, Candiolo, Italy
4 Ospedale Bellaria, Radiotherapy, Bologna, Italy
5 Ospedale Regionale U.Parini-AUSL Valle d’Aosta,
Radiotherapy, Aosta, Italy
6 Ospedale ASL9, Radiotherapy, Ivrea, Italy
7 San Raffaele Scientific Institute, Medical Physics,
Milano, Italy
8 Fondazione IRCCS Istituto Nazionale dei Tumori,
Prostate Cancer Program, Milano, Italy
9 Cliniche Gavazzeni-Humanitas, Radiotherapy, Bergamo,
Italy
Purpose or Objective
To assess clinical and dose factors affecting the incidence
of patient-reported urinary incontinence (INC) at three
years after radical radiotherapy (RT) for prostate cancer
of a large group of patients enrolled in a prospective,
multi-centric trial in the period 2010-2014.
Material and Methods
Enrolled patients were treated in seven Institutions at
different prescribed doses with conventional (74-80 Gy at
1.8-2 Gy/fr, CONV) or moderately hypo-fractionated RT
(65-75.2 Gy at 2.2-2.7 Gy/fr, HYPO) in 5 fractions/week.
Several clinical factors were collected for each patient:
comorbidities, drugs, hormone therapies, previous
surgeries, smoking, alcohol, age, and body mass index. In
addition, the prescribed 2Gy equivalent dose (EQD2) was
considered by applying an alpha-beta ratio of 0.8, 3 and
5Gy, according to values recently reported in the
literature. INC was evaluated through the International
Consultation on Incontinence Modular Questionnaire short
form (ICIQ) filled in by the patients at start/end of RT and
every 6 months until 5 years of follow up. In the current
analysis, patients with ICIQ available at 30 and/or 36
months were considered (n=298;); the incidence of INC at
3 years was defined as the occurrence of an ICIQ value >12
at least once between 6 and 36 months. Univariable and
backward multivariable logistic analyses were performed
to build a predictive model.
Results
In total, 298 patients had the required minimum follow-
up; patients with baseline ICIQ>12 (n=3) were excluded
restricting the analysis to 295 patients (CONV: 149; HYPO:
146, 86% treated with IMRT). The median number per
patients of completed questionnaires was 5 (range: 2-6):
the incidence of ICIQ>12 was 5.1% (n=15) with a
prevalence at 30/36 months equal to 4.1%. Main predictors
at univariable analysis were age (p=0.01,OR=1.19),
baseline ICIQ>0 (p=0.056, OR=2.9), previous TURP
(p=0.04, OR=3.8) and EQD2 (p=0.003-0.02, OR=1.12-1.17
depending on alpha-beta). EQD2 calculated with alpha-
beta=0.8Gy showed the best performances in terms of
calibration plot and p-value and was included in the multi-
variable analysis. Final results suggested a two-variable
model including EQD2 (p=0.005,OR=1.13; 95%CI:1.04-1.24)
and age (p=0.011,OR=1.19; 95%CI:1.04-1.37); the model
showed good performances in terms of goodness of fit
(H&L test, p=0.55) and calibration plot (slope:1.02,
R2=0.92). In Figure, the risk of 3-year INC vs EQD2 (alpha-
beta=0.8Gy) is shown with the calibration plot of the final
two-variable model. The validity of the model was
confirmed in the HYPO subgroup.
Conclusion
The incidence of patient-reported 3-year INC after high-
dose RT for prostate cancer dramatically depends on the
prescribed dose (EQD2) and, secondarily, on the age of
patients. A previously suggested low alpha-beta value
(0.8Gy) for late INC resulted in a significantly better
calibrated model, consistently with a high sensitivity of
late I NC to fractionation.
PO-0849 Trismus after chemoradiation in head & neck
cancer: relation with medial pterygoid and masseter
dose
O. Hamming-Vrieze1, S. Kraaijenga2, S. Verheijen 1, M.
Jonker 1, L. Van der Molen2, J. Van de Kamer1, M. Van de
Brekel2, W. Heemsbergen1
1Netherlands Cancer Institute Antoni van Leeuwenhoek
Hospital, Radiation Oncology, Amsterdam, The
Netherlands
2Netherlands Cancer Institute Antoni van Leeuwenhoek
Hospital, Head and Neck Surgery, Amsterdam, The
Netherlands
Purpose or Objective
Reduced maximal mouth opening (MMO) is a serious side
effect that can occur after chemoradiation (CRT) in head
& neck patients. Recent studies showed dose-effect
relationships with both the ipsilateral masseter muscle