Target Coverage Improvement With Dose Matching in Carbon-Ion Radiation Therapy for Pancreatic Cancer.

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Carbon-ion radiation therapy (CIRT) offers sharp dose distribution but is susceptible to positioning inaccuracies.
• Interfractional tumor motion in pancreatic CIRT can reduce tumor dose, posing challenges for adequate margin expansion due to nearby organs at risk.
• Online adaptive radiation therapy (ART) addresses motion but faces equipment and time constraints in CIRT.

Purpose of the Study:

• To evaluate the feasibility and effectiveness of dose matching (DM) as a more convenient alternative to ART for pancreatic CIRT.
• To assess DM's ability to improve tumor dose coverage despite interfractional motion.

Main Methods:

• A 3D search for optimal isocenters was performed around the initial target matching (TM) isocenter using in-room CT images.
• Fractional dose distributions were calculated for each potential isocenter, identifying the dose matching (DM) isocenter that maximized clinical target volume (CTV) V95%.
• Variations in CTV V95% and organ-at-risk (OAR) doses were compared between bone matching (BM), TM, and DM.

Main Results:

• Dose matching (DM) significantly improved CTV V95% coverage, with median variations of -0.36%, compared to -1.39% for TM and -2.18% for BM.
• Organ-at-risk (OAR) doses remained within acceptable limits in the DM group.
• Toxicity was comparable between DM and BM, as maximum OAR dose variations were similar.

Conclusions:

• Dose matching (DM) effectively improves CTV V95% in pancreatic CIRT while respecting OAR dose constraints.
• Proper implementation of DM requires consideration of treatment efficacy and efficiency.
• Optimizing target coverage necessitates judicious application of TM, DM, and ART based on specific treatment sites.