Lynsey Hamlett
Townsville Hospital Cancer Centre
Advanced ROMP

Marcus Powers
Medical physicist
Townsville cancer centre

Michael Roche
Registrar
Townsville cancer centre

David Wood
Radiation Therapist
N/A

Louis Fourie
Director of Physics
Townsville Cancer Centre

Introduction

The Townville Hospital, QLD, is validating Elekta’s commercially available Advanced Collapsed Cone Engine (ACE©) these are the preliminary findings.

Method

Following AAPM report TG-186[1], reference plans were calculated using TG-43 for both level 1 and level 2 plan conditions.

For level 1 testing three plans; single dwell; two dwell; and an eight dwell circular arrangement were produced in a water equivalent cube phantom.

Level 2 testing used the test plans available from the AAPM/ESTRO/ABG working group registry (WGR) [2]. This introduced non water equivalent phantom materials. Finally complex ‘HDR prostate type’ CT plans using titanium catheters with 16 catheters and 205 dwell positions, 20 catheters and 205 dwells and 12 catheters and 137 dwells were investigated.

Each plan was recalculated using ACE© standard accuracy and ACE© high accuracy and compared to the TG-43 reference plans. Plans were compared both visually using the ‘Analyse’ module in Oncentra, using point doses and for the prostate type plans comparision via dose volume histogram (DVH).

Results

Level 1 results were similar to those published by Yunzhi Ma et al [3], dose differences were seen on the single dwell plan in regions of low dose positioned on the longitudinal axis i.e. passing through the source axis.

Level 2 plan results using the WGR data showed some small differences between the ACE© TG-186 calculations and the WDR data, these were visible on the dose wash comparison.

For the prostate plan using titanium catheters variation was visible(Figure 1) and enough to effect the plan quality i.e Urethra D10% reduced from 114.98% to 112.08% (DVH Figure 2).

The TG-186 accuracy modes showed negligible difference for the clinical plans, calculation times ranged from 10mins for standard to 120mins for high.

Conclusion

ACE© calculation algorithm produces dose distributions within water equivalent reference phantoms similar to TG-43. The results of the prostate plans suggest that titanium needles potentially introduce a variation in the dose distribution which could effect plan quality. Further work aims to investigate more clinical sites and to benchmark ACE© using Monte Carlo modelling.

References

[1] Beaulieu L et al(2012) Report of the Task Group 186 on model-based dose calculation methods in brachytherapy beyond the TG-43 formalism Med. Phys. 39 (10) 6208-36

[2] AAPM/ESTRO/ABG Brachytherapy Working Group

[3] Ma Y et al Validation of the Oncentra Brachy Advanced Collapsed Cone Engine for a commercial Ir192 source using heterogeneous geometries. Brachytherapy 14 (2015) 939-952


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