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Phys Med. 2013 Mar;29(2):171-7. doi: 10.1016/j.ejmp.2012.01.004. Epub 2012 Feb 18.

Dosimetric verification of a high dose rate brachytherapy treatment planning system in homogeneous and heterogeneous media.

Author information

1
Department of Radiology, Himalayan Institute of Medical Sciences, HIHT University, C-I-5, HIHT Campus, Swami Ram Nagar, P.O. Doiwala, Jolly Grant, Dehradun, Uttarakhand 248140, India. uniyal.satish@rediffmail.com

Abstract

OBJECTIVES:

To verify the dosimetric accuracy of treatment plans in high dose rate (HDR) brachytherapy by using Gafchromic EBT2 film and to demonstrate the adequacy of dose calculations of a commercial treatment planning system (TPS) in a heterogeneous medium.

METHODS:

Absorbed doses at chosen points in anatomically different tissue equivalent phantoms were measured using Gafchromic EBT2 film. In one case, tandem ovoid brachytherapy was performed in a homogeneous cervix phantom, whereas in the other, organ heterogeneities were introduced in a phantom to replicate the upper thorax for esophageal brachytherapy treatment. A commercially available TPS was used to perform treatment planning in each case and the EBT2 films were irradiated with the HDR Ir-192 brachytherapy source.

RESULTS:

Film measurements in the cervix phantom were found to agree with the TPS calculated values within 3% in the clinically relevant volume. In the thorax phantom, the presence of surrounding heterogeneities was not seen to affect the dose distribution in the volume being treated, whereas, a little dose perturbation was observed at the lung surface. Doses to the spinal cord and to the sternum bone were overestimated and underestimated by 14.6% and 16.5% respectively by the TPS relative to the film measurements. At the trachea wall facing the esophagus, a dose reduction of 10% was noticed in the measurements.

CONCLUSIONS:

The dose calculation accuracy of the TPS was confirmed in homogeneous medium, whereas, it was proved inadequate to produce correct dosimetric results in conditions of tissue heterogeneity.

PMID:
22342220
DOI:
10.1016/j.ejmp.2012.01.004
[Indexed for MEDLINE]

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