Cattani, F.

Ferrari, A.M.

Mastella, E.

Orecchia, R.

Piperno, G.

Rondi, E.

Rozza, D.

Strata, E.

Vigorito, S.

Elsevier - Publisher Connector 

3rd ESTRO Forum 2015                                                                                                                                         S415 
 
 
 
Conclusions: Results of this study suggest that a matching 
between our two gantries seems feasible, thus potentially 
allowing for a significant time saving in both TPS 
commissioning and clinical operations. We will test additional 
clinical indications to see whether the results of this study 
apply to all relevant treatment scenarios.  
 
PO-0823  
Evaluation of the accuracy of Cyberknife tumor tracking 
using gafchromic EBT3 films 
E. Mastella1, S. Vigorito1, E. Rondi1, F. Cattani1, G. Piperno1, 
A.M. Ferrari1, D. Rozza1, E. Strata1, R. Orecchia1 
1European Institute of Oncology, Radiotherapy, Milan, Italy  
 
Purpose/Objective: The purpose of this study was to 
evaluate the accuracy of the Cyberknife tumor tracking 
system with gafchromic EBT3 films and triple-channel film 
dosimetry. 
Materials and Methods: The CT scan of the Easy Cube 
Phantom (Sun Nuclear, FL) was acquired with the clinical 
parameters used for Cyberknife patients. The Easy Cube 
Phantom was mounted on the ET Gating Phantom (Brainlab, 
GE), which can move along the superior-inferior axis of the 
patient to simulate the respiratory motion of a lung tumor. A 
gafchromic EBT3 film was positioned between two slabs of 
the Easy Cube while a PinPoint ionization chamber was 
placed in an appropriate insert. 8 fiducial markers were 
inserted into the Easy Cube for the treatment set-up and for 
the tracking. 
The synchrony tracking method was used for the template QA 
plan: the patient's plan was recalculated on the Easy Cube 
phantom and centred in the sensitive volume of the 
ionization chamber. The dose distributions were calculated 
with Ray-Tracing algorithm.  
The EBT3 films were calibrated with a 6 MV linear 
accelerator (Trilogy, Varian), from 0 to 15 Gy. 
A total of 8 patients were evaluated statically (no motion of 
the ET Gating Phantom) and in different dynamic conditions 
(e.g. motion amplitude from 10 to 25 mm), for a total of 40 
cases.  
The films were scanned using an Epson 10000XL scanner 
(transmission mode, 48-bit colour, 96 dpi resolution) and the 
planar dose distributions were built with the multichannel 
film analysis performed by the FilmQA Pro software (Ashland, 
NJ). 
Calculated and measured planar dose distributions were 
compared with the gamma analysis method, both in static 
and in dynamic irradiation conditions. The local gamma 
passing rates (%GP) were evaluated using three difference 
acceptance criteria: 3% 3mm threshold (TH) = 10%, 2% 2mm 
TH = 20% and 2% 1mm TH = 50%.  
PinPoint absolute dose measurements were also compared 
with the TPS doses, calculated in the sensitive volume of the 
chamber. 
Results: The percentage of treatments passing the gamma 
analysis (95% of dose points that comply the acceptance 
criteria) was 100% for all the three criteria. The %GP ± SD 
were 99.8 ± 0.2 for the 3% 3mm criteria, 95.8 ± 2.0 for the 2% 
2mm and 97.2 ± 1.2 for the 2% 1mm criteria. No significant 
differences were found between the static and the dynamic 
cases. The percentage differences between calculated and 
measured PinPoint dose range from -1.0 to 7.5 with a mean 
value of 4.0 ± 2.8. 
Conclusions: Preliminary results obtained with EBT3 
gafchromic films and the triple-channel analysis show an 
excellent agreement between calculated and measured dose 
distributions in all the cases. First of all, we can definitely 
assert that this is an efficient method for pretreatment 
patient-specific QA. Furthermore, no significant differences 
were found between the static cases and the different 
motion conditions, confirming the validity of this method to 
evaluate the accuracy of Cyberknife tumor tracking system.  
 
PO-0824   
Influence of the biological target volume modeling on 
ionization cluster-size distributions using Geant4-DNA 
M. Bueno1, R. Schulte2, S. Meylan1, C. Villagrasa1 
1Institut de Radioprotection et de Sûreté Nucléaire, 
Dosimetrie SDE/LDRI, Fontenay aux Roses, France  
2Loma Linda University Medical Center, Radiation Medicine, 
Loma Linda, USA  
 
Purpose/Objective: The aim of this study was to evaluate 
the influence of the geometrical detail of description of the 
biological target volume on the topology of ionization 
clusters induced by protons and alpha particles of different 
energies using Geant4-DNA. A simplified geometry would 
have the advantage of speeding up calculations but may lead 
to inaccurate results compared to a detailed DNA model. 
Materials and Methods: Two geometrical descriptions of the 
biological target volume at the level of a single chromatin 
fiber containing 18·103 base pairs (bp) have been considered 
for the Monte Carlo calculations. The detailed geometry 
(GeomHist) included a realistic molecular description of the 
DNA double helix (2.3 nm diameter) wrapped around 
cylindrical histones. Based on the assumption that relevant 


PO-0823: Evaluation of the accuracy of Cyberknife tumor tracking using gafchromic EBT3 films 

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PO-0823: Evaluation of the accuracy of Cyberknife tumor tracking using gafchromic EBT3 films

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