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S987
ESTRO 36 2017
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requires a dose limitation in healthy organs at risk
(contralateral lung, heart, spine)
Our
objectives
were:
-- To evaluate the mean dose (Dm) received by the
contralateral lung in SBRT for thoracic lesions.
-- To analyze if PTV volume and/or total dose (TD) are
related to the Dm achieved
in the contralateral lung.
Material and Methods
A total of 26 pulmonary lesions treated with SBRT were
evaluated. Simulation was performed with CT 4D
respiratory gating and customized immobilization devices.
PTV was designed with an isotropic margin of 0.5 cm from
the GTV. Treatment was delivered with Linear Accelerator
( CLINAC, Varian), and verification done with internal
fiducial markers surrogates.
Results
Total Dose (TD) (Gy): range 20 – 45 Gy. Most cases (18;
69%) received a TD of
45Gy.
Dose/fraction: range 10-20 Gy/fr. The most frequent
fractionation was 15 Gy (20; 77%).
PTV volumen (cc): range between 10.18 - 99.33cc, with a
mean: 36.14cc ; median:
26.65cc
Healthy lung Dm (Gy): range 0.23 - 9.8 Gy; mean: 1.75Gy;
median: 1.25Gy
The increase in PTV volume did not associate an increase
in the average dose to the contralateral lung. Fig 1
An increase in total dose not involved an associated
increase in the dose to the healthy lung. Fig. 2
Conclusion
The Mean Dose received by the contralateral healthy lung
is
minimal.
No relationship was found between the increase in total
dose and increased in contralateral lung Dmean
No relationship was found between the volume of PTV and
Dmean reached in contralateral
lung
The parameters PTV and TD do not appear to relate to the
dose received to the contralateral
lung.
We can conclude that SBRT technique can be applied
safely largely preserving the healthy lung.
EP-1829 Dose delivery accuracy in total body
irradiation delivered with Step and Shoot IMRT
T. Berlon
1
, L. Specht
1
, P.M. Petersen
1
, L.S. Fog
1
1
Rigshospitalet, Clinic of Oncology- Department of
Radiotheraphy, Copenhagen, Denmark
Purpose or Objective
In total body irradiation (TBI) delivered with step and
shoot IMRT (SS IMRT), the dose conformity is considerably
improved compared with the more widely used TBI
delivered with open fields. This conformity is achieved
through the use of multiple fields defined by multileaf
collimators (MLCs). We aim to quantify the accuracy with
which TBI patients treated at our clinic were positioned,
and to determine the effect any positioning errors may
have had on the delivered dose.
Material and Methods
Images acquired as a routine part of the patient treatment
with the Theraview ™ (Theraview Technology, Leuden,
The Netherlands) imaging system were used to determine
the positioning shift in the cranio-caudal direction.
Images for 11 consecutive patients, each receiving 6
fractions, were analysed and the shifts recorded (figure
1). For 3 of the patients, only images for 5 of the 6
fractions
were
available.
The plans were then recalculated implementing the shifts
using the algorithm used for the clinical plans (Eclipse ™,
Varian Medical Systems, Palo Alto, AAA algorithm, v 13.6).
The mean and maximum doses for the lungs, kidneys,
brain and the (body-lungs-5mm) structure were extracted
and the difference between the planned and the
recalculated
doses
determined.Results
The mean doses change by a maximum of 0.6% (lungs), 0.6
(kidneys), 0.5% (brain) and 0.2% (body-lungs-5mm). The
greatest difference between the maximum doses are 8.0%
(lungs), 4.8% (kidneys), 2.6% (brain) and 12.0% (bodylungs-
5mm).
The standard deviation of the difference between the
calculated and recalculated doses are greater for the
maximum doses than the mean doses (figure 2). Given that
the minimum and maximum doses for SS TBI are typically
in the range 90-110% of the prescribed dose, the
differences in maximum dose should lead to care
being
taken when positioning patients for SS TBI.
Conclusion
Patient positioning for a total of 63 fractions of SS TBI is
such that the mean delivered doses differs from the
planned by less than 0.6%. However, the maximum doses