Large anatomical changes in head-and-neck cancers - A dosimetric comparison of online and offline adaptive proton therapy

Mislav Bobić; Arthur Lalonde; Konrad P Nesteruk; Hoyeon Lee; Lena Nenoff; Bram L Gorissen; Alejandro Bertolet; Paul M Busse; Annie W Chan; Brian A Winey; Gregory C Sharp; Joost M Verburg; Antony J Lomax; Harald Paganetti

doi:10.1016/j.ctro.2023.100625

Large anatomical changes in head-and-neck cancers - A dosimetric comparison of online and offline adaptive proton therapy

Clin Transl Radiat Oncol. 2023 Mar 31:40:100625. doi: 10.1016/j.ctro.2023.100625. eCollection 2023 May.

Authors

Affiliations

¹ Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
² Department of Physics, ETH Zurich, Switzerland.
³ Stanley Center for Psychiatric Research, Broad Institute of Harvard and MIT, Cambridge, MA, USA.
⁴ Paul Scherrer Institute, Villigen, Switzerland.

Abstract

Purpose: This work evaluates an online adaptive (OA) workflow for head-and-neck (H&N) intensity-modulated proton therapy (IMPT) and compares it with full offline replanning (FOR) in patients with large anatomical changes.

Methods: IMPT treatment plans are created retrospectively for a cohort of eight H&N cancer patients that previously required replanning during the course of treatment due to large anatomical changes. Daily cone-beam CTs (CBCT) are acquired and corrected for scatter, resulting in 253 analyzed fractions. To simulate the FOR workflow, nominal plans are created on the planning-CT and delivered until a repeated-CT is acquired; at this point, a new plan is created on the repeated-CT. To simulate the OA workflow, nominal plans are created on the planning-CT and adapted at each fraction using a simple beamlet weight-tuning technique. Dose distributions are calculated on the CBCTs with Monte Carlo for both delivery methods. The total treatment dose is accumulated on the planning-CT.

Results: Daily OA improved target coverage compared to FOR despite using smaller target margins. In the high-risk CTV, the median D₉₈ degradation was 1.1 % and 2.1 % for OA and FOR, respectively. In the low-risk CTV, the same metrics yield 1.3 % and 5.2 % for OA and FOR, respectively. Smaller setup margins of OA reduced the dose to all OARs, which was most relevant for the parotid glands.

Conclusion: Daily OA can maintain prescription doses and constraints over the course of fractionated treatment, even in cases of large anatomical changes, reducing the necessity for manual replanning in H&N IMPT.