Intraoperative HDR Brachytherapy: Present and Future

Radiotherapy is one of the most effective modalities in cancer treatment, and can be applied either by external beam radiotherapy or by brachytherapy. Brachytherapy is a treatment modality in which tumors are irradiated by positioning radioactive sources very close to or in the tumor volume. The use of (fractionated) HDR and PDR brachytherapy has increased dramatically. In chapter 2 the techniques and results of fractionated HDR and PDR brachytherapy for head and neck cancer are presented. HDR/PDR brachytherapy is usually performed with single stepping source afterloaders, containing a small Iridium-192 source, enabling optimization of the dose distribution by optimization of the dwell times over all dwell positions in the implant. In chapter 3 the effects of geometric optimization on the dose distribution of interstitial volume implants have been studied in terms of the irradia¬ted volume, the dose uniformity, and the choice of the reference dose. The results of anatomy based inverse planning in HDR prostate implants are evaluated in chapter 4. An Integrated Brachytherapy Unit (IBU), i.e. a shielded operating room with an HDR afterloader and a dedicated brachytherapy localiser, connected to a treatment planning computer, was established at the Erasmus MC – Daniel Den Hoed Cancer Center. This set-up enables integration of the entire brachy¬therapy procedure, i.e. implantation, implant reconstruction, dose planning and delivery in a single session. In chapter 5 the reconstruction accuracy of this dedicated localiser has been evaluated by simulations and by measurements using phantoms representing clinical relevant implant geometries. When converting to on-line planning by importing the fluoroscopy images directly in the planning computer the image distortions present in fluoroscopy images should be eliminated. In chapter 6, the accuracy of on-line planning in the IBU using dedicated image distortion correction algorithms has been evaluated. The availability of an HDR afterloader in the IBU enables the use of intraoperative brachytherapy (IOBT). IOBT is applied using a 5 mm thick flexible intraoperative template (FIT). To reduce the procedure time, treatment planning is performed using standard plans, that neglect the curvature of the FIT. In chapter 7 we have calculated the individual treatment plan, based on the real geometry of the FIT, and the dose at clips placed during surgery, of 32 patients with locally advanced rectal tumors treated this way. In chapter 8 the technique and results, in terms of local failure and survival, of IOBT for patients with locally advanced or recurrent rectal cancer are discussed. A taskgroup on quality assurance (QA) of brachytherapy systems of the Netherlands Commission on Radiation Dosimetry was established to develop nation wide accepted guidelines for QA in brachytherapy. The taskgroup investigated the accuracy of brachytherapy treatments in 33 radiotherapy institutions in The Netherlands and Belgium, by determining the accuracy of implant reconstruction and dose delivery (chapter 9). In chapter 10 the practice of brachytherapy QA in The Netherlands and Belgium was evaluated and compared with international recommendations. The determination of the reference air kerma rate for Iridium-192 sources and the related uncertainty are discussed in chapter 11. In chapter 12 the presented set-up for HDR (intraoperative) brachytherapy is discussed in some more detail and future perspectives are presented.

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