Program Information

A Realistic Breathing Phantom of the Thorax for Testing New Motion Mitigation Techniques with Scanning Proton Therapy

R Perrin

R Perrin¹*, M Peroni¹ , K Bernatowicz¹ , M Zakova¹ , A Knopf¹ , S Safai¹ , T Parkel² , A Lomax¹ , (1) Paul Scherrer Institut, Psi-villigen, Aargau, (2) CSEM, Swiss Centre of Electronics and Microtechnology, Landquart, Graubunden

Presentations

SU-D-BRE-1 Sunday 2:05PM - 3:00PM Room: Ballroom E

Purpose:
A prototype breathing phantom (named LuCa) has been developed which simulates the anatomy and motion of a patient thorax.In this work, we describe the results of the first commissioning tests with LuCa.

Methods:
The phantom provides a close representation of the human thorax. The lungs,contained within a tissue-equivalent ribcage and skin,are made from a polymer foam,which is inflated and deflated using a custom-made ventilator. A tumor is simulated using a wooden ball with cutplanes for placing GafChromic films. The ventilator,controlled with Labview software,simulates a full range of breathing motion types.
Commissioning tests were performed to assess its performance using imaging (CT and radiographic) and film dosimetry as follows:i)maximum Tumor excursion at acceptable pressure ranges, ii)tumor Motion repeatability between breathing periods,iii)reproducibility between measurement days,iv)tumor-to-surface motion correlation and v)reproducibility of film positioning in phantom.

Results:
The phantom can generate repeatable motion patterns with sin⁴,sin,breath-hold (tumor amplitude repeatability <0.5mm over 10min),aswell as patient-specific motion types. Maximum excursions of the tumor are 20mm and 14mm for the large and small tumor inserts respectively. Amplitude reproducibility (Coefficient of Variation) averaged at 16% for the workable pressure range over 2 months. Good correlation between tumor and surface motion was found with R²=0.92. Reproducibility of film positioning within the thorax was within 0.9mm, and maximum 3° error from the coronal plane. Film measurements revealed that the film repositioning error yields relative errors in the mean dose over the planned target volume (PTV) of up to 2.5% and 4.5% for films at the center and on the edge of the PTV respectively.

Conclusion:
Commissioning tests have shown that the LuCa phantom can produce tumor motion with excellent repeatability. However,a poorer performance in reproducibility of tumor amplitude for a given peak pressure week-to-week. Film set-up reproducibility is adequate for detection of dosimetric errors resulting from motion of >3%.

Funding Support, Disclosures, and Conflict of Interest: This work is funded by Swiss National Fund Grants 320030_127569 and 320030_1493942-1


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