ESTRO 36 Abstract Book

S422

ESTRO 36

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plaques with radiochromic film, and all of them use

specifically machined plastic phantoms. We aimed to

develop a practical experimental method for measuring

the absolute absorbed dose distributions in water

produced by

106

Ru/

106

Rh plaques using the EBT3

radiochromic film.

Material and Methods

Two experimental setups were developed to measure dose

planes (1) perpendicular to the symmetry axis of the

plaque at 5 mm from the intersection of the symmetry axis

with the concave plaque surface, and (2) containing the

symmetry axis of the plaques (PDD planes). Both, the

plaque and the film, were immersed in water. The

required materials are easily affordable by a medical

physics department without the need of specifically

machined solid phantoms. The setups were tested

measuring dose distributions from one CCA and two CCX

plaques. Dose distributions were obtained from the

irradiated films using the triple-channel dosimetry

algorithm implemented in the FilmQA 2015 software. The

measured dose distributions were compared with the

results of Monte Carlo simulations run with the PENELOPE

code, and with published data.

Results

The measured absolute dose rates agreed with the values

quoted in the calibration certificates of the plaques within

the experimental uncertainty, with typical differences

below 5%. The relative standard uncertainties obtained

were of 3.8% for dose distributions measured at planes

perpendicular to the symmetry axis at 5 mm from the

surface of the plaque, and of 7.4% for planes containing

the symmetry axis. These values are comparable to those

reported by other authors using plastic phantoms, but

avoiding the uncertainties associated to the conversion

from dose–to–plastic to dose–to–water. A good agreement

was obtained between measurements and simulations,

improving upon published data (see figures for data of

depth-dose curves, and lateral profiles at 5 mm from the

surface of the plaque, for the CCX plaques).

Conclusion

We developed a practical experimental method to

measure with the EBT3 radiochromic film the dose

distributions in water produced by

106

Ru/

106

Rh ophthalmic

plaques. The obtained results were of similar or better

quality than those obtained using solid phantoms. These

setups may ease the quality assurance procedures to the

users of these plaques.

PO-0794 Comprehensive quality assurance test for high

precision teletherapy

S. Wegener

, A. Spiering

, O.A. Sauer

University Hospital, Radiation Oncology, Würzburg,

Germany

Purpose or Objective

Modern radiation therapy aims to minimize negative side

effects on healthy tissue by tailoring the dose distribution

as accurately as possible to each individual tumor. This

leads to a progressively increasing complexity of the

treatment plans and demands a very high precision of all

involved components. Even small errors can significantly

compromise treatment techniques which require such an

extensive precision as stereotactic radiation therapy. A

suitable quality management for such techniques should

include a regular end-to-end test that closely mimics the

entire procedure of the actual patient treatment while

being able to reliably detect a variety of possible errors