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. 2023 Jul 22;9(1):101317.
doi: 10.1016/j.adro.2023.101317. eCollection 2024 Jan.

High-Linear Energy Transfer Irradiation in Clinical Carbon-Ion Beam With the Linear Energy Transfer Painting Technique for Patients With Head and Neck Cancer

Ryosuke Kohno  1   2 , Masashi Koto  3 , Hiroaki Ikawa  3 , Sung Hyun Lee  4 , Kana Sato  5 , Mitsuyasu Hashimoto  2 , Taku Inaniwa  1 , Toshiyuki Shirai  1
Affiliations

High-Linear Energy Transfer Irradiation in Clinical Carbon-Ion Beam With the Linear Energy Transfer Painting Technique for Patients With Head and Neck Cancer

Ryosuke Kohno et al. Adv Radiat Oncol. .

Abstract

Purpose: Dose-averaged linear energy transfer (LETd) is one of the important factors in determining clinical outcomes for carbon-ion radiation therapy. Innovative LET painting (LP) has been developed as an advanced form of conventional intensity modulated carbon-ion radiation therapy (IMIT) at the QST Hospital. The study had 2 motivations: to increase the minimum LETd (LETdmin) and to improve uniformity of the LETd distribution within the gross tumor volume (GTV) by using LP treatment plans for patients with head and neck cancer while maintaining the relative biologic effectiveness (RBE)-weighted dose coverage within the planning tumor volume (PTV) the same as in the conventional IMIT plan.

Methods and materials: The LP treatment plans were designed with the in-house treatment planning system. For the plans, LETd constraints and LETdmin, goal-LETd, and maximum-LETd (LETdmax) constraints for the GTV were added to the conventional dose constraints in the IMIT prescription. For 13 patients with head and neck cancer, the RBE-weighted dose to 90% (D90) and 50% (D50) of the PTV and the LETdmin, mean (LETdmean), and LETdmax values within the GTV in the LP plans were evaluated by comparing them with those in the conventional IMIT plans.

Results: The LP for 13 patients with head and neck cancer could keep D90s and D50s for the PTV within 1.0% of those by the conventional IMIT. Among the 13 patients, the mean LETdmin of the LP plans for the GTV was 59.2 ± 7.9 keV/μm, whereas that of the IMIT plans was 45.9 ± 6.0 keV/μm. The LP increased the LETdmin to 8 to 24 keV/μm for the GTV compared with IMIT.

Conclusions: While maintaining the dose coverage to the PTV as comparable to that for IMIT, the LP increased the mean LETdmin to 13.2 keV/μm for the GTV. For a GTV up to 170 cm3, LETd > 44 keV/μm could be achieved using LP, which according to previous studies was associated with lower recurrence. In addition, the LP method delivered more uniform LETd distributions compared with IMIT.

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Figures

Figure 1
Figure 1
PTV D90 of IMIT and LP (L = 45, 55, 65, 75, 85, 95, and 105) for patients 1 to 13; 100% was defined as the prescribed dose Gy (RBE). Abbreviations: D90 = percentage of dose to 90%; IMIT = intensity modulated carbon-ion radiation therapy; LP = linear energy transfer painting; PTV = planning tumor volume; RBE = relative biologic effectiveness.
Figure 2
Figure 2
Relative biologic effectiveness–weighted dose distributions of (a) intensity modulated carbon-ion radiation therapy and (b) linear energy transfer painting.
Figure 3
Figure 3
Dose-averaged linear energy transfer distribution of (a) intensity modulated carbon-ion radiation therapy and (b) linear energy transfer painting.
Figure 4
Figure 4
LETdmin, LETdmean, and LETdmax of the IMIT and LP versus GTV size (Volume) for 13 patients with head and neck cancer. The dotted line is a linear fitting function obtained from the LETdmin results of the LP and given as LETdmin keV/μm = –0.139 keV/μm/cm3 × V + 67.8 keV/μm. Abbreviations: GTV = gross tumor volume; IMIT = intensity modulated carbon-ion radiation therapy; LET = linear energy transfer; LETdmax = maximum dose-averaged LET; LETdmean = mean dose-averaged LET; LETdmin = minimum dose-averaged LET; LP = LET painting.
Figure 5
Figure 5
Box plots of (a) the maximum RBE-weighted dose and (b) the LETdmax to stem, chiasma, and optic nerves for the IMIT and LP for 13 patients with head and neck cancer.
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