Treatment planning for multicatheter interstitial brachytherapy of breast cancer – from Paris system to anatomy-based inverse planning

Abstract

In the last decades, treatment planning for multicatheter interstitial breast brachytherapy has evolved considerably from fluoroscopy-based 2D to anatomy-based 3D planning. To plan the right positions of the catheters, ultrasound or computed tomography (CT) imaging can be used, but the treatment plan is always based on postimplant CT images. With CT imaging, the 3D target volume can be defined more precisely and delineation of the organs at risk volumes is also possible. Consequently, parameters calculated from dose-volume histogram can be used for quantitative plan evaluation. The catheter reconstruction is also easier and faster on CT images compared to X-ray films. In high dose rate brachytherapy, using a stepping source, a number of forward dose optimization methods (manual, geometrical, on dose points, graphical) are available to shape the dose distribution to the target volume, and these influence dose homogeneities to different extent. Currently, inverse optimization algorithms offer new possibilities to improve dose distributions further considering the requirements for dose coverage, dose homogeneity, and dose to organs at risk simultaneously and automatically. In this article, the evolvement of treatment planning for interstitial breast implants is reviewed, different forward optimization methods are discussed, and dose-volume parameters used for quantitative plan evaluation are described. Finally, some questions of the inverse optimization method are investigated and initial experiences of the authors are presented.

Does inverse planning improve plan quality in interstitial high-dose-rate breast brachytherapy?

“…The classical dosimetry systems are based on LDR sources. With the stepping source technique, those systems can be simulated using uniform source dwell times [2,3,34]. However, after any optimization technique, the dwell times will be non-uniform, occasionally with large fluctuation.…”

“…Furthermore, the introduction of cross-sectional imaging and 3D target volume definition in BT required new planning approaches. Forward optimization is now regularly used for BT planning, and the most accepted methods are the geometrical (GO) and graphical optimi-zations (GRO), which can provide clinically acceptable dose distributions for breast implants [1,2,3,4]. During GO, there is no need for defining dose points, because dwell positions themselves serve as reference dose points for optimization.…”

“…Competing plans were assessed and compared with dose-volume parameters, such as relative volumes receiving a percentage of PD (e.g., V 100 , V 90 , V 50 ) and relative doses in percentage of the PD to small absolute volumes (e.g., D 0.1cm3 , D 1cm3 ). Since the skin and ribs were not delineated as whole organs, the V 5 for skin and the V 50 for ribs were given as absolute value in cm 3 . The dose homogeneity was described by the DNR (dose non-uniformity ratio) and the conformality with COIN (conformity index).…”

Image guided high-dose-rate brachytherapy versus volumetric modulated arc therapy for head and neck cancer: A comparative analysis of dosimetry for target volume and organs at risk

“…After catheter reconstruction, treatment plans were made with geometrical optimization, complemented with graphical optimization by adjusting the isodose line in order to appropriately cover the PTV by the prescribed dose (PD) and keep the doses to OARs as low as possible. 13 Our aim was to obtain less than 0.40 for the dose non-uniformity ratio (DNR), the ratio of volumes receiving 1.5 times the PD and those receiving the PD, (V 150 /V 100 ). At our institute the fractionation schedule was 15 x 3 Gy (45 Gy) for IGBT alone and 7 x 3 Gy (21 Gy) for IGBT after 50 Gy EBRT.…”

Case report of a dose-volume histogram analysis of rib fracture after accelerated partial breast irradiation: interim analysis of a Japanese prospective multi-institutional feasibility study

“…The skin (5 mm thickness from the surface) and chest wall were excluded from the target volume. In numerous planning methods [ 14 ], we used the Paris dose calculation system with manual modifications. The prescribed doses were 36 Gy per six fractions in 3 days, with an interval of 6 hours between two fractions on the same day.…”