ESTRO 36 Abstract Book

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S16 ESTRO 36 2017
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The Film, TLD, Alanine, and ion-chamber measurements
showed a similar delivered dose (10 Gy), regardless of the
dose rate setting. The TLD measurements in the brain of
the sacrificed mouse verified that the prescribed 10 Gy
dose was delivered to the mouse brain, for a 10 Gy in 1.8
µs and a 0.1 Gy/s dose rate delivery (10.06 and 9.90 ±
8.2%, k = 2, respectively). Our results showed spatial
memory preservation in mice after 10 Gy WBI delivered in
a single 1.8 µs electron pulse, whereas 10 Gy WBI
delivered with a dose rate similar to what is
conventionally used in radiotherapy (0.1 Gy/s) impaired
mice mid-term spatial memory. Using systematic dose rate
escalation, 100 Gy/s was found to be the lower limit for
full preservation of spatial memory functions after 10 Gy
WBI.
Conclusion
This study shows for the first time that normal brain tissue
toxicities after WBI can be reduced with increased dose
rate. Spatial memory is preserved after WBI with mean
dose rates above 100 Gy/s, whereas 10 Gy WBI at a
conventional radiotherapy dose rate (0.1 Gy/s) totally
impairs spatial memory. This radiobiological advantage,
together with other practical considerations that benefit
from rapid radiotherapy treatment delivery, such as
minimizing intra-fractional motion, increased patient
comfort, and improved treatment efficiency, makes Flash-
RT a promising treatment modality.
OC-0040 Validation of prospective electronic toxicity
registration to audit dose constraints
T.M. Janssen1, A. Dikstaal 1, M. Kwint1, S. Marshall1, A.L.
Wolf1, J. Knegjens 1, L. Moonen1, J. Belderbos1, J.J.
Sonke1, M. Verheij1, C. Van Vliet-Vroegindeweij 1
1 Netherlands Cancer Institute Antoni van Leeuwenhoek
Hospital, Radiotherapy, Amsterdam, The Netherlands
Purpose or Objective
In 2012 we started with the prospective, electronic
registration by the treating physician of all grade ≥2
toxicities (CTCAE v4.0) for all patients irradiated at our
department. Simultaneously we set up an infrastructure
to couple this data to dose and treatment parameters. The
aim of this work is to assess the validity of the data and to
show the feasibility of such an infrastructure to audit
toxicity prediction models and dose constraints in daily
clinical practice.
Material and Methods
As a showcase we consider the relation between the
esophagus V50Gy and grade ≥2 esophagitis in locally
advanced NSCLC patients receiving concurrent
chemoradiotherapy (CCRT; 24 x 2.75Gy, daily 6mg/m 2
cisplatin). Clinically we use V50Gy<50% as a dose
constraint based on a previously developed NTCP model
[1]. The applicability of this model to current clinical
practice is not evident since dose criteria changed after
publication and patients currently receive intravenous
pre-hydration (1L, NaCl 0.9%) which was shown to
decrease esophagitis
[2]. For all CCRT patients (excluding adaptive RT and re-
irradiations) treated in 2014/2015, the planned V50Gy and
the registered esophagitis ≥grade 2 were retrieved.
Furthermore, a single observer retrospectively scored
toxicity, based on the electronic health records.
We calculated the incidence of grade ≥2 esophagitis per
V50Gy and compared this with the expected incidence
based upon the model by Kwint et al. using a χ2 test. ROC
analysis was performed to assess the predictive value of
V50Gy.
Results
For 82 patients, 558 consultations were performed.
Median follow up was 3.5 months and grade ≥2 esophagitis
was prospectively (retrospectively) scored for 41 (46)
patients. For 74 patients, retrospective and prospective
scoring was identical and for 3 patients esophagitis was
scored in both cases, but grades differed.
A comparison of the observed and predicted grade ≥2
esophagitis is shown in Figure 1a. The prospective
(retrospective) observed incidence of grade ≥2 esophagitis
was 50% (56%) while the model predicts 54%. Neither
registrations differ from the model prediction
(prospective p=0.78 , retrospective p= 0.91 ). ROC analysis
(figure 1b) of prospective registrations result in an area
under the curve of 0.71.
Conclusion
Retrospective and prospective toxicity registration
showed overlap in 90% of cases. Moreover, the observed
dose-effect of grade ≥2 esophagitis was almost identical
to the NTCP model. This implies 1) that the V50Gy
accurately predicts toxicity for our current treatment
protocol and 2) that our prospective toxicity registration
results in valid data. Esophagitis incidence was expected
to decrease due to pre-hydration. While this discrepancy
requires further investigation, it does show that the
electronic toxicity registration and connection to dose
parameters appears to be a valuable tool to audit the
applicability of dose constraints in daily clinical practice.
[1] Kwint et al. IJROBP 2012
[2] Uyterlinde et al. R&O 2014
OC-0041 Predictors of asymptomatic radiation
induced vascular damage to infradiaphragmatic vessels
L. Cella1, R. Liuzzi1, P. Romanelli2, M. Conson2, V.
D'Avino1, M. Ottaviano3, V. Damiano3, G. Palmieri 3, R.
Pacelli 2, M. Mancini1
1Institute of Biostructure and Bioimaging-CNR, National
Council of Research, Napoli, Italy
2Federico II University School of Medicine, Department of
Advanced Biomedical Sciences, Napoli, Italy
3Federico II University School of Medicine, Centro
Riferimento Tumori Rari Regione Campania, Napoli, Italy
Purpose or Objective
Blood vessels may be damaged by radiation exposure and
radiation therapy (RT) may have a negative impact on the
vascular system by promoting accelerated atherosclerotic
vascular complications. Aim of the present study is to
identify predictors of asymptomatic radiation-induced
abdominal atherosclerosis in patients affected by