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S71
ESTRO 36
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Purpose or Objective
Results from a Bayesian-randomized trial on intensity
modulated radiotherapy (IMRT) vs. passively scattered 3D
proton therapy (3DPT) show no significant difference in
protocol failure (i.e., either grade>=3 radiation
pneumonitis (RP) or local recurrence within 12 months).
We intend to analyze the differences in dose distribution
between modalities, relations between dosimetric
parameters and radiation-induced toxicities. The
objective is to identify dosimetric constraints that would
limit normal tissue complications in future trials.
Material and Methods
We analyzed 149 (57 3DPT, 92 IMRT) randomized trial
patients. DVH parameters for 3DPT and IMRT treatment
plans were compared for lung, esophagus, and heart. To
measure the predictive value of high- and low-dose
parameters for toxicity in lungs and esophagus, we fitted
V5 and V50Gy to RP and grade>=3 radiation esophagitis
(RE). Heart dose data was missing for 5 IMRT patients.
Results
RP and RE are not significantly different between
modalities (p>0.1, two-tailed Wilcoxon rank-sum test).
The difference between mean doses planned for IMRT and
3DPT plans was tested: Lung V5, V50, V60, V70Gy (in %),
esophageal V5Gy, and heart V5, V10Gy are significantly
different (p<0.005, two-tailed Wilcoxon rank-sum test).
The significant esophageal and heart dose parameters are
smaller for 3DPT, lung V5Gy is smaller, while lung
V50,V60,V70Gy are larger.
3DPT plan V5 and V50Gy are computed for each OAR and
compared to the respective median values of IMRT plans.
The percentage of 3DPT plans with V5Gy below or equal
to the IMRT median and V50Gy above the IMRT median are
reported:
<=V5Gy IMRT Median
>V50Gy IMRT Median
3DPT
Lung
0.93
0.68
Esophagus
0.67
0.49
Heart
0.93
0.54
3DPT plans yield smaller low dose regions in all three
OARs. However, 3DPT yields larger high dose regions in the
lungs.
To assess the relationship between low/high dose regions
and toxicity, V5 and V50Gy of lung and heart were fitted
to RP, esophageal V5 and V50Gy were fitted to RE:
There appears to be a stronger relationship between
toxicity and high dose regions in the affected OAR. Heart
doses have a weaker relationship with RP.
Conclusion
Tucker et al. (2013) showed that high dose regions in lung
tissue in lung IMRT have a pronounced effect on toxicity.
This is also observable in this trial cohort of IMRT and 3DPT
patients. In order to reduce toxicities, high dose regions
in normal tissues need to be reduced. 3DPT reduces low
dose regions significantly in all three OARs but high doses
regions are significantly higher in the lungs. Future
investigations should focus on stricter high dose
constraints for 3DPT plans. If such constraints are not
achievable due to penumbral and scattering
characteristics of protons and the usage of passive
scattering techniques, intensity modulated proton therapy
should be considered.
Joint Symposium: ESTRO-JASTRO: Oligometastatic
disease
SP-0145 Biological rationale and clinical evidence
P. Ost
1
1
University Hospital Ghent, Gent, Belgium
In 1995, Hellman and Weichselbaum hypoth esized that
the number and location of the metastases are an
important prognostic factor reflecting the metastatic
phenotype and hence prognosis of the cancer patient.
They suggested this based on the historical observation
that some metastatic patients have a durable survival in
case their limited metastases are surgically removed. For
these cases, they proposed the term oligometastases,
suggesting that eradicating oligometastases with
metastasis-directed therapy (MDT) would have the
potential to improve survival. This hypothesis would shift
the paradigm for oligometastatic patients from a
palliative to a potentially curable disease. Recent data in
several solid tumors support the notion that patients with
oligometastatic disease have a more favorable prognosis
as compared to their counterparts and that these different
phenotypes probably require a different therapeutic
approach. Clinical data indicate that the number of
patients with oligometastatic disease receiving aggressive
treatment is increasing rapidly. We will discuss the key
evidence supporting or refuting the existence of an
oligometastatic state.
SP-0146 Oligometastatic disease: Radiophysics
implementation and pitfalls
D. Verellen
1
1
GZA- Ziekenhuizen - St. Augustinus Iridium
Kankernetwerk Antwerpen, Radiotherapy, Wilrijk,
Belgium
As clinical evidence in favor of SBRT for treatment of
oligometastatic disease increases, SBRT proves to be a
safe and effective treatment modality to achieve local
control and delay progression, which in turn also
postpones the need for further treatment. Basically SBRT
refers to a high-dose-per-fraction-high-precision
technique and the mainstream adaptation of SBRT is the
result of combined developments in image guided motion
management, treatment planning and delivery. This
presentation will cover some of the main issues related to
clinical implementation of SBRT and quality assurance. A
critical overview will be provided comparing dedicated
equipment against mainstream technology. The different
treatment modalities will be benchmarked allowing to
assess an appropriate balance between technological
needs and patient compliance. As the efficacy of SBRT in
the management of the oligometastic state increases, the
need for treatment of multiple metastases and re-
irradiation requires extra attention. In this presentation,
some of the issues related to dose accumulation for this
particularly challenging situation will also be highlighted.
SP-0147 Interpretation and management of
oligometastases
H. Onishi
1
1
Yamanashi University, Department of Radiology, Chuo,
Japan
All of cancer state with metastases is judged as stage IV
even if the number of metastases is only one. However, it
has been known that some of patients with a limited
number of metastatic lesions regions have a good
prognosis by a locally radical therapy combined with
systemic chemotherapy, and the disease state was named
“oligometastases” by Hellman in 1995. In addition, a
limited disease state of oligometastases with primary