Dosimetric verification of the dose distribution in pulsed dose rate brachytherapy

Abstract

Background

Pulsed dose rate (PDR) brachytherapy is clinically used as an irradiation technique. It combines the physical advantages of high-dose-rate (HDR) technology (isodose optimization, planning flexibility and radiation safety) with the radiobiological advantages of low-dose-rate (LDR) brachytherapy [1,2]. The single radioactive stepping source moves through all the implanted catheters during each pulse. The source is enclosed in a capsule 2.5 mm long with a diameter of 1.1 mm [3]. The resulting isodoses can be optimized by modulating the dwell time of the source as a function of its trajectory within the implanted volume.

Aim

The aim of this study was the dosimetric verification (in-phantom) of doses calculated with the Plato treatment planning system (TPS) by using GafChromic films and thermoluminescent detectors (TL) in PDR brachytherapy.

Materials/Methods

Absorbed doses at chosen points were measured with TL detectors, while dose distributions were measured with GafChromic films. Dose measurements were made at 14 reference points in a specially designed, tissue equivalent phantom. The prescribed doses were compared with the measured doses. A fusion of two dose distributions was made. The image read from the dosimetric film after its digitalization was fused with the one received from TPS. Qualitative analysis of this fusion was performed.

Results

Wilcoxon test and sign test (dependent samples) were used to compare the doses calculated with those measured with TL detectors. The statistical comparison of doses calculated and measured revealed differences in the range of – 14.7% to 12.6%. These results fitted well with the results of qualitative analysis made using images’ fusion made for calculated and measured dose distributions.

Conclusions

Both quantitative and qualitative analysis proved the correctness of the calculation algorithms used by the Plato planning system in a phantom study for PDR brachytherapy.