Irradiation System for HIMAC.

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Therapy

Background:

• Carbon radiotherapy clinical trials commenced in 1994 at the Heavy Ion Medical Accelerator of Chiba (HIMAC).
• Early trials focused on establishing uniform dose delivery using broad beam techniques and spread-out Bragg peaks (SOBP).

Purpose of the Study:

• To detail the technical advancements and methodologies employed in carbon radiotherapy clinical trials.
• To highlight innovations for precise dose delivery, including managing moving targets and protecting adjacent normal tissues.

Main Methods:

• Utilized a broad beam method with wobbler magnets and scatterers to achieve a uniform 20 cm diameter field at the isocenter.
• Employed a bar ridge filter to modulate beam energy, creating a flat biological dose SOBP considering varying Linear Energy Transfer (LET).
• Implemented respiration-gated irradiation for moving organs (lung, liver) and a layer-stacking method with a multi-leaf collimator for precise target conformity.

Main Results:

• Achieved a highly uniform dose field (+/- 2.5%) with a maximum SOBP width of 15 cm.
• Respiration gating successfully reduced treatment margins for moving targets.
• Layer-stacking with multi-leaf collimator enabled precise dose sculpting for large volume cancers.

Conclusions:

• Carbon radiotherapy systems at HIMAC have demonstrated stable and reliable operation since 1994.
• Advanced techniques like respiration gating and layer-stacking have significantly improved treatment precision and normal tissue sparing.
• The established methods are effective for treating various cancers, including large volume bone and soft-tissue malignancies.