Alpha DaRT source activity confirmation using a reentrant well-type ionization chamber

Area of Science:

• Nuclear Medicine
• Radiation Oncology
• Medical Physics

Background:

• Alpha-emitting radionuclides offer precise cancer therapy due to high linear energy transfer and limited tissue penetration.
• Diffusing Alpha-emitters Radiation Therapy (Alpha DaRT) utilizes Radium-224 (Ra-224) sources implanted directly into tumors.
• Alpha DaRT has shown promise in preclinical and clinical trials for various cancers.

Purpose of the Study:

• Develop reliable methods for verifying Alpha DaRT source activity before treatment to ensure accurate radiation delivery.
• Establish a protocol for assessing Ra-224 source activity within Alpha DaRT applicators using gamma emissions, as direct alpha particle measurement is impractical.
• Provide a practical method for quality assurance that detects errors without compromising applicator sterility.

Main Methods:

• Ra-224 Alpha DaRT sources in sterile Flex and Needle applicators were assessed.
• Source activity was verified using a high-purity germanium (HPGe) detector.
• Calibration factors were established using an IVB1000 well-type ionization chamber, with measurements corrected for environmental factors.

Main Results:

• HPGe measurements confirmed vendor-stated activities.
• Average calibration coefficients were determined for Flex (233 ± 3 kBq/pA) and Needle (597 ± 7 kBq/pA) applicators.
• Quality assurance on 26 Flex applicators showed a mean difference of 1.1 ± 5.8% compared to vendor-stated activity.

Conclusions:

• A reentrant well-type ionization chamber is effective for pre-treatment quality assurance of Ra-224 Alpha DaRT applicators.
• This method allows for verification of vendor-stated activity while maintaining applicator sterility.
• The established protocol supports accurate and consistent radiation delivery in Alpha DaRT treatments.