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

Abstract

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: 5 × 5 Gy with an integrated boost to the tumor core of 5 × 10 Gy or 10 × 3 Gy with a boost of 10 × 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.

Therapeutic In Situ Cancer Vaccine Using Pulsed Stereotactic Body Radiotherapy—A Translational Model

“…Also, in certain situations, partial volume treatment, targeting selectively the hypoxic segment of bulky tumors [ 84 ]; lattice therapy with a three-dimensional spatially arranged high-dose volume inside the tumor [ 95 ]; tumor core volume boosting [ 96 ]; multi-shell integrated boost techniques [ 97 ]; and other novel unconventional RT techniques [ 98 ] can be exercised as options for large tumors or those with a resistant residual volume after initial fractions/sessions. High-linear-energy-transfer (LET) radiation techniques, like the use of proton and carbon ions, have higher immunogenicity, increased stem cell clearance capability, improved immunological memory, and a higher sensitivity to hypoxia cancer cells [ 99 ].…”