Planning Strategy to Optimize the Dose-Averaged LET Distribution in Large Pelvic Sarcomas/Chordomas Treated with Carbon-Ion Radiotherapy

Author:

Nachankar Ankita12,Schafasand Mansure134ORCID,Carlino Antonio1,Hug Eugen1,Stock Markus14,Góra Joanna1,Fossati Piero15

Affiliation:

1. MedAustron Ion Therapy Center, 2700 Wiener Neustadt, Austria

2. ACMIT Gmbh, 2700 Wiener Neustadt, Austria

3. Department of Radiation Oncology, Medical University of Vienna, 1090 Wien, Austria

4. Division Medical Physics, Karl Landsteiner University of Health Sciences, 3500 Krems an der Donau, Austria

5. Division Radiation Oncology, Karl Landsteiner University of Health Sciences, 3500 Krems an der Donau, Austria

Abstract

To improve outcomes in large sarcomas/chordomas treated with CIRT, there has been recent interest in LET optimization. We evaluated 22 pelvic sarcoma/chordoma patients treated with CIRT [large: HD-CTV ≥ 250 cm3 (n = 9), small: HD-CTV < 250 cm3 (n = 13)], DRBE|LEM-I = 73.6 (70.4–73.6) Gy (RBE)/16 fractions, using the local effect model-I (LEM-I) optimization and modified-microdosimetric kinetic model (mMKM) recomputation. We observed that to improve high-LETd distribution in large tumors, at least 27 cm3 (low-LETd region) of HD-CTV should receive LETd of ≥33 keV/µm (p < 0.05). Hence, LETd optimization using ‘distal patching’ was explored in a treatment planning setting (not implemented clinically yet). Distal-patching structures were created to stop beams 1–2 cm beyond the HD-PTV-midplane. These plans were reoptimized and DRBE|LEM-I, DRBE|mMKM, and LETd were recomputed. Distal patching increased (a) LETd50% in HD-CTV (from 38 ± 3.4 keV/µm to 47 ± 8.1 keV/µm), (b) LETdmin in low-LETd regions of the HD-CTV (from 32 ± 2.3 keV/µm to 36.2 ± 3.6 keV/µm), (c) the GTV fraction receiving LETd of ≥50 keV/µm, (from <10% to >50%) and (d) the high-LETd component in the central region of the GTV, without significant compromise in DRBE distribution. However, distal patching is sensitive to setup/range uncertainties, and efforts to ascertain robustness are underway, before routine clinical implementation.

Funder

Austrian Center for Medical Innovation and Technology (ACMIT) Gmbh

Publisher

MDPI AG

Subject

Cancer Research,Oncology

Reference57 articles.

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