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ESTRO 36
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Results
All planning goals have been achieved as per TG119 report
shown in figure-1. At high dose point measurement mean
dose differences averaged over different techniques
(IMRT/VMAT) planned with different energies for all test
cases was 0.002±0.020, and corresponding confidence
limit (mean + 1.96σ i.e. σ stand for standard deviation)
was 0.041. At low dose point measurement mean dose
averaged over different techniques planned with different
energies for all test cases was -0.004±0.021, and
corresponding confidence limit was 0.045. For planar dose
measurement gamma passing rate averaged over all test
cases was 99.40%±0.40 for 3%/3mm criteria and
97.82%±0.13 for 2%/2mm criteria respectively. Present
work overall confidence limit (100-mean + 1.96σ i.e. σ
stand for standard deviation) for composite planar dose
measurement was 1.38(i.e., 98.62% passing) for 3%/3mm
and 2.45(i.e., 97.55% passing) for 2%/2mm criteria.
Gamma analysis results for a representative measurement
are shown in figure-2.
Conclusion
Planning and delivery of IMRT/VMAT has been validated
using TG119 report. Local institutional confidence limits
were established which can be used as baseline for future
patient specific quality assurance.
EP-1499 Additional dose of Image Guided Radiation
Therapy in Pediatric Patients
J. Topczewska-Bruns
1
, T. Filipowski
1
, D. Hempel
1
, B.
Pancewicz-Janczuk
2
, R. Chrenowicz
2
, D. Kazberuk
1
, A.
Szmigiel-Trzcinska
1
, E. Rozkowska
1
1
Comprehensive Cancer Center, Department of
Radiotherapy, Bialystok, Poland
2
Comprehensive Cancer Center, Department of Physics,
Bialystok, Poland
Purpose or Objective
Kilovoltage cone beam computed tomography (kV CBCT)
imaging improves the accuracy of radiation therapy.
However, an extra radiation dose is delivered to cancer
patients. Instead of default scanning protocol used for
adults we prepared individual presets for children
undergoing radiotherapy in our Department. The aim of
the study was to evaluate additional dose delivered to the
pediatric patients being treated according to local
protocol for IGRT.
Material and Methods
10 children, aged 2-6 years with different type of
neoplasms were
treated in supine position on linear
accelerator (Elekta Synergy) equipped with kV CBCT (XVI
v.4.2.) The pretreatment position was evaluated
according to our protocol on day 1,2,3 and once in a week
thereafter. The individual presets for pediatric patients
were prepared for different types of neoplasms and
localization of the irradiated area For dose calculation
delivered by use of kv CBCT the phantom PMMA 20x20x12
and 16x16x16 with CT chamber TM30009 (PTW) with
Unidos (PTW) was used.
Results
The modification of IGRT protocols for children includes
changes in the acquisition parameters such as
frequency, beam energy, voltage, rotational degree,
gantry speed, size of field of view, filter with good
quality of images (examples of images from the date
obtained by collecting of kV CBCT will be presented on the
poster) . The following presets were prepared (Tab.1).The
additional dose deliverd to the pediatric patients depends
on the number of fractions when the CBCT was
performed. Our local protocol for usage of kV CBCT results
in delivering of additional dose of 2,52mGy (4 fr. in
protocol A) or 2,92mGy (4 fr. in protocol B) for elective
brain irradiation in ALL, 3,55 mGy (5 fr. protocol F)
for left sided nephroblastoma 3,4 mGy (5 fr. protocol D)
or 3,8mGy (5 fr. protocol C) for right
sided nephroblastoma, 17,6 mGy (8 fr. protocol E) for RMS
in pelvis and 3,45 mGy (5 fr. protocol G) for LGL.
Conclusion
The additional doses of kV CBCT depends on the type of
presets used in procedure and number of fractions with
IGRT during all treatment. The modified presets enable
reducing exposure to irradiation so that IGRT – associated
doses seems to be clinically acceptable. However the
children’s anthropomorphic phantom is needed to further
evaluate exposure of normal healthy tissue to irradiation
during colleting the date for IGRT.