The tumor core boost study: A feasibility study of radical dose escalation to the central part of large tumors with an integrated boost in the palliative treatment setting.

PURPOSE: For patients with large tumors palliative radiotherapy often is the only local treatment option. To prevent toxicity the administered doses are low. Dose escalation to the tumor could be an option to better smyptom control and prolong local control rates. In this prospective study we used a very pragmatic approach with a simultaneously integrated boost (SIB) to an almost geometrically defined tumor core to achieve this. The primary endpoint was to demonstrate feasibility. METHOD: Patients with solid tumors > 4 cm in diameter of different histologies were eligible in this single arm, prospective, multi-institutional clinical feasibility trial with two treatment concepts: 5â€¯× 5 Gy with an integrated boost to the tumor core of 5â€¯× 10 Gy or 10â€¯× 3 Gy with a boost of 10â€¯× 6 Gy. The objective of dose escalation in this study was to deliver a minimum dose of 150% of the prescribed dose to the gross tumor volume (GTV) tumor core and to reach a maximum of at least 200% in the tumor core. RESULTS: In all, 21 patients at three study sites were recruited between January 2019 and November 2020 and were almost evenly spread (9 to 12) between the two concepts. The treated planning target volumes (PTV) averaged 389.42 cm3 (range 49.4-1179.6 cm3). The corresponding core volumes were 72.85 cm3 on average (range 4.21-338.3 cm3). Dose escalation to the tumor core with mean doses of 167.7-207.7% related to the nonboost prescribed isodose led to PTV mean doses of 120.5-163.3%. Treatment delivery and short-term follow-up was successful in all patients. CONCLUSIONS: Palliative radiotherapy with SIB to the tumor core seems to be a feasible and well-tolerated treatment concept for large tumors. The applied high doses of up to 50 Gy in 5 fractions (or 60 Gy in 10 fractions) did not cause unexpected side effects in the 42 day follow-up period. Further research is needed for more information on efficacy and long-term toxicity.

Automatic image segmentation based on synthetic tissue model for delineating organs at risk in spinal metastasis treatment planning.

PURPOSE: One of the main goals in software solutions for treatment planning is to automatize delineation of organs at risk (OARs). In this pilot feasibility study a clinical validation was made of computed tomography (CT)-based extracranial auto-segmentation (AS) using the Brainlab Anatomical Mapping tool (AM). METHODS: The delineation of nine extracranial OARs (lungs, kidneys, trachea, heart, liver, spinal cord, esophagus) from clinical datasets of 24 treated patients was retrospectively evaluated. Manual delineation of OARs was conducted in clinical routine and compared with AS datasets using AM. The Dice similarity coefficient (DSC) and maximum Hausdorff distance (HD) were used as statistical and geometrical measurements, respectively. Additionally, all AS structures were validated using a subjective qualitative scoring system. RESULTS: All patient datasets investigated were successfully processed with the evaluated AS software. For the left lung (0.97 ± 0.03), right lung (0.97 ± 0.05), left kidney (0.91 ± 0.07), and trachea (0.93 ± 0.04), the DSC was high with low variability. The DSC scores of other organs (right kidney, heart, liver, spinal cord), except the esophagus, ranged between 0.7 and 0.9. The calculated HD values yielded comparable results. Qualitative assessment showed a general acceptance in more than 85% of AS OARs-except for the esophagus. CONCLUSIONS: The Brainlab AM software is ready for clinical use in most of the OARs evaluated in the thoracic and abdominal region. The software generates highly conformal structure sets compared to manual contouring. The current study design needs revision for further research.