The low-LET radiation contribution to the tumor dose in diffusing alpha-emitters radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Medicine

Background:

• Diffusing alpha-emitters Radiation Therapy (Alpha DaRT) utilizes interstitial sources of Radium-224 (Ra) to treat solid tumors.
• Alpha DaRT releases short-lived progeny that emit alpha particles and other radiation, creating a localized high-dose region.

Purpose of the Study:

• To quantify the electron and photon dose from diffusing and surface-bound atoms in Alpha DaRT.
• To evaluate the low-linear energy transfer (LET) contribution to tumor dose and cell survival.
• To demonstrate the sparing of surrounding healthy tissues.

Main Methods:

• Calculated low-LET dose using EGSnrc and FLUKA Monte Carlo codes.
• Compared line-source approximation with full simulations including atom diffusion.
• Analyzed scenarios with varying diffusion and leakage, and applied superposition for multi-source lattices.

Main Results:

• Minimal low-LET dose between sources in a hexagonal lattice (3 $$ Ci/cm $$ Ra, 4 mm spacing) was $$ Gy, dominated by beta contribution.
• Low-LET dose dropped below 5 Gy at 1 mm from the lattice edge.
• The low-LET dose reduced tumor cell survival by a factor of $$ .

Conclusions:

• Low-LET dose in Alpha DaRT can be accurately modeled with Monte Carlo techniques and leakage corrections.
• For 3 $$ Ci/cm $$ Ra sources, low-LET dose reduces tumor cell survival by up to two orders of magnitude.
• Increasing source activity could elevate the low-LET dose to therapeutic levels, potentially enabling wider lattice spacing.