28 Primary and secondary liver malignancies

Primary and secondary liver malignancies

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 15/07/2022

inserted through each angiography sheath during removal, sealing the puncture tract [2]. Patient preparation Interstitial brachytherapy is typically performed under local anaesthesia and conscious sedation (e.g. midazolam [0.5 mg up to 2.5 mg stepwise, patient-specific] and fentanyl [50-75 µg up to 200 µg stepwise, patient-specific]). Premedication with antiemetics (e.g. ondansetron 8 mg i.v. and dexamethasone 8 mg i.v., directly before catheter insertion) is recommended. To enhance patient comfort during catheter placement, treatment planning, treatment application, and catheter removal, a urethral catheter may be placed. Vital monitoring (non-invasive blood pressure, heart rate, oxygenation and ECG) is essential during the entire treatment. The patient should be positioned carefully in order to have the best possible access to the tumour. Typically, a supine setup with both arms elevated above the head is chosen. When identifying possible puncture tracts, the required length of the puncture tracts should be considered as well as the proximity to possible structures at risk (e.g. arteries, ribs, bowel, lung). Patient comfort is of utmost importance, as the patient must remain in this position for possibly several hours to ensure unchanged patient anatomy and to prevent catheter dislocation. The patient has to remain in this position for the entire duration of the treatment until catheter removal. During catheter placement, the interventional radiologist usually stands on the right side of the patient (see figure 4). Access for the application of sedative-analgesic medications is extended to the back of the CT gantry, which allows adjustments even during the intervention. Due to the respiration depressant effect of analgesics and sedatives, the patient is usually supplied with oxygen peri- and post-intervention (nasal tube). Preplanning Prior to actual catheter placement, it may be useful to generate a pre-plan to assess the optimal catheter position for full dose coverage and OAR sparing. Based on available diagnostic 3D-imaging, the PTV and OAR are delineated and a proposal for the number and placement of catheters can be developed in close collaboration with the medical physicist and the radiation oncologist or interventional radiologist, who will perform the implant. Ideally, the catheters should be arranged in parallel, as this configuration provides good and reproducible dose coverage of the PTV. However, this is not practical in most cases, since practically accessible catheter trajectories are limited and avoidance of OARs should be prioritized. With some experience, the pre-planning steps can be omitted in standard cases, but will remain helpful in complex target lesions. Catheter placement The catheters should be implanted by a trained radiation oncologist or interventional radiologist.The intervention is always conducted under sterile conditions. The catheters are usually implanted under CT-fluoroscopic guidance. However, some centres also have the possibility to perform the procedure in an open bore MRI, which presupposes the availability of MR-compatible materials. Ultrasound-guided implantation is rarely used, however it is a very good option where staff are trained in this approach. For 3D treatment planning, a subsequent simulationCT orMRI is required. The brachytherapy catheter is sealed at the tip and usually has a millimetre scale, which is helpful for correct positioning within the angiography sheath. The brachytherapy catheters are then numbered to allow the catheters to be reconstructed correctly later. Adhesive skin badges are helpful for this purpose and can

be attached to the brachytherapy catheter in a way that the final position within the angiography sheath is also marked and that a shift of the brachytherapy catheter relative to the angiography sheath is prevented. The angiography sheath should be sutured to the skin of the patient for fixation (see Figure 5). It is important, that the brachytherapy catheters are always inserted to a depth that is at least equal or exceeds the length of the angiography sheath within the liver, as the angiography sheath is radiopaque and the exact position of the brachytherapy catheter tip would not be visible on CT imaging for catheter reconstruction if it was located within the angiography sheath. The number of catheters depends on the size and shape of the tumour. Irregularly shaped and larger tumours require more catheters in order to adequately cover the target with the prescribed dose and to ensure good sparing of healthy liver tissue and adjacent organs at risk. Another method, favoured by some radiation oncologists is the direct puncture technique. Here, plastic catheters and steel obturators are used. However, this technique does not allow sealing of the puncture tract after catheter removal [51]. Furthermore, if a catheter position correction is required in cases where it was not adequately implanted, the direct puncture technique causes more trauma compared to a needle rearrangement using the Seldinger technique. After catheter placement, simulation imaging (planning CT/MR) is performed. In case of a planning CT, the use of contrast agent should be considered. The image set is then transferred to the treatment planning system (TPS). A maximum slice thickness of 2 mm is preferable, in order to achieve precise target volume delineation and catheter position definition. After target delineation, the next step is the reconstruction of the catheters in the TPS. This can be done already before the target structure and OAR delineation, or even simultaneously if the TPS provides such functionality.The planning goal is to achieve a robust, high quality treatment plan in a short time, in order to minimize the overall treatment time (from catheter implantation to catheter removal) for improved patient comfort. Each catheter must be correctly identified and reconstructed and the first dwell position in each catheter must be marked. If imaging reference markers (e.g. CT markers of known length) are used inside the catheters, in order to define a reference position, it should be noted that the positional uncertainty of the dwell positions tends to increase with increasing distance from this reference position. Additionally, a smaller catheter curvature radius increases the systematic offset of the dwell positions due to slackness of the source inside the catheter. This effect is usually small in HDR liver brachytherapy due to large curvature radii. After catheter reconstruction, all reconstructed catheters should be checked for plausibility, e.g. via visual inspection of a 3D rendering of the catheters.The 3Dmodel should show a smooth shape of the catheters without any kinks. It may be helpful to have a schematic drawing of how the catheters exit through the skin of the patient. In addition, if catheter insertion is performed using the Seldinger technique, the excess end of the brachytherapy catheter from the angiography sheath should be measured outside the patient as a second validation (see Figure 6). Using this information, the internal excess of the brachytherapy 9. TREATMENT PLANNING