Anticancer research · 2026
Inter-fractional Variation of Linear Energy Transfer Profiles During Carbon-ion Radiotherapy for Pancreatic Cancer.
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Yoshimatsu Yukihiko, Oike Takahiro, Sakai Makoto, Miyasaka Yuhei, Yoshida Hanae, Ohno Tatsuya
Аннотация
BACKGROUND/AIM: In carbon-ion radiotherapy (CIRT), a low dose-averaged linear energy transfer (LETd) within the tumor has been suggested as a potential unfavorable prognostic factor for local recurrence. However, inter-fractional variations in LETd during daily CIRT sessions remain unelucidated. This study aimed to investigate inter-fractional variations in LETd profiles during CIRT for pancreatic cancer.
PATIENTS AND METHODS: Seven patients with locally advanced pancreatic cancer treated with CIRT were retrospectively analyzed. Treatment plans delivering 55.2 Gy (relative biological effectiveness) in 12 fractions were generated based on computed tomography (CT) images (Plan-CT). For each CIRT session, in-room CT images were acquired immediately after irradiation and referred to as Daily-CT; all 12 series of images were deformably registered to the Plan-CT. LETd parameters (L98%, L95%, L50%, and L2%) for target volumes were compared between Plan-CT and Daily-CT (LX% was defined as the minimum LETd delivered to X% of the target volume).
RESULTS: The L50% and L2% values for the planning target volumes were significantly lower on Daily-CT than on Plan-CT, although the differences were modest. Meanwhile, no significant differences were observed for L98% and L95%. One patient exhibited a consistent decrease in LETd on Daily-CT across all LETd parameters and target volumes examined. For this patient, increased bowel gas within the beam path was observed during daily sessions, which caused a distal shift of the LETd distribution, which then reduced LETd coverage of the target volumes.
CONCLUSION: During CIRT for pancreatic cancer, inter-fractional variations in LETd profiles may be more pronounced at larger target volumes and at lower LX% values. Although the variations were modest in most cases, inter-fractional changes in bowel gas within the beam path are a potential risk factor for reduced LETd coverage.
PATIENTS AND METHODS: Seven patients with locally advanced pancreatic cancer treated with CIRT were retrospectively analyzed. Treatment plans delivering 55.2 Gy (relative biological effectiveness) in 12 fractions were generated based on computed tomography (CT) images (Plan-CT). For each CIRT session, in-room CT images were acquired immediately after irradiation and referred to as Daily-CT; all 12 series of images were deformably registered to the Plan-CT. LETd parameters (L98%, L95%, L50%, and L2%) for target volumes were compared between Plan-CT and Daily-CT (LX% was defined as the minimum LETd delivered to X% of the target volume).
RESULTS: The L50% and L2% values for the planning target volumes were significantly lower on Daily-CT than on Plan-CT, although the differences were modest. Meanwhile, no significant differences were observed for L98% and L95%. One patient exhibited a consistent decrease in LETd on Daily-CT across all LETd parameters and target volumes examined. For this patient, increased bowel gas within the beam path was observed during daily sessions, which caused a distal shift of the LETd distribution, which then reduced LETd coverage of the target volumes.
CONCLUSION: During CIRT for pancreatic cancer, inter-fractional variations in LETd profiles may be more pronounced at larger target volumes and at lower LX% values. Although the variations were modest in most cases, inter-fractional changes in bowel gas within the beam path are a potential risk factor for reduced LETd coverage.