Transition from Paris dosimetry system to 3D image-guided planning in interstitial breast brachytherapy

Abstract

PurposeThe purpose of this study is to evaluate our first experience with 3D image-guided breast brachytherapy and to compare dose distribution parameters between Paris dosimetry system (PDS) and image-based plans.Material and methodsFirst 49 breast cancer patients treated with 3D high-dose-rate interstitial brachytherapy as a boost were selected for the study. Every patient underwent computed tomography, and the planning target volume (PTV) and organs at risk (OAR) were outlined. Two treatment plans were created for every patient. First, based on a Paris dosimetry system (PDS), and the second one, imaged-based plan with graphical optimization (OPT). The reference isodose in PDS implants was 85%, whereas in OPT plans the isodose was chosen to obtain proper target coverage. Dose and volume parameters (D90, D100, V90, V100), doses at OARs, total reference air kerma (TRAK), and quality assurance parameters: dose nonuniformity ratio (DNR), dose homogeneity index (DHI), and conformity index (COIN) were used for a comparison of both plans.ResultsThe mean number of catheters was 7 but the mean for 20 first patients was 5 and almost 9 for the next 29 patients. The mean value of prescribed isodose for OPT plans was 73%. The mean D90 was 88.2% and 105.8%, the D100 was 59.8% and 75.7%, the VPTV90 was 88.6% and 98.1%, the VPTV100 was 79.9% and 98.9%, and the TRAK was 0.00375 Gym–1 and 0.00439 Gym–1 for the PDS and OPT plans, respectively. The mean DNR was 0.29 and 0.42, the DHI was 0.71 and 0.58, and the COIN was 0.68 and 0.76, respectively.ConclusionsThe target coverage in image-guided plans (OPT) was significantly higher than in PDS plans but the dose homogeneity was worse. Also, the value of TRAK increased because of change of prescribing isodose. The learning curve slightly affected our results.

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.…”

External beam boost versus interstitial high-dose-rate brachytherapy boost in the adjuvant radiotherapy following breast-conserving therapy in early-stage breast cancer: a dosimetric comparison

“…Long-term risks to ribs have scarcely been documented. There is one study that published dosimetric data on the rib with a HDR-BT boost [ 31 ]. In that study, the most exposed rib received 24.5% of the prescribed dose.…”

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

“…The classical Paris dosimetry system can be imitated by using uniform dwell times in all dwell positions, which means no optimization is applied. In that case, the dose distribution is always homogeneous, but the conformality will not be optimal [ 18 ]. The target volume can be covered by the prescription isodose surface adequately, but relatively large volume of normal tissue will be unnecessarily irradiated by the prescription dose (PD).…”