SU-E-T-506: Dosimetric Study for Shallow-Seated Tumor Using Passive/active Scanning Proton Beam

Area of Science:

• Medical Physics
• Radiation Oncology
• Proton Therapy

Background:

• Superficial lesions pose treatment challenges in radiation oncology.
• Spot scanning proton beam therapy offers precise dose delivery.
• Optimizing beam configurations for superficial targets is crucial for minimizing dose to surrounding healthy tissues.

Purpose of the Study:

• To evaluate the feasibility of using a single spot scanning proton beam for treating superficial lesions.
• To compare the efficacy and safety of a single spot scanning beam with a pre-absorber against conventional single and multi-beam techniques.

Main Methods:

• A cylindrical phantom with a simulated superficial target (0.5-4cm depth) was used.
• Three treatment plans were generated: single uniform scanning beam, single spot scanning beam with pre-absorber, and a five-beam spot scanning plan.
• Geant4 Monte Carlo simulations were employed to design the pre-absorber for the spot scanning beam.

Main Results:

• All plans achieved comparable target dose coverage (within 2.4%).
• The single spot scanning beam with a pre-absorber demonstrated superior conformity (index 1.04) and a narrow lateral penumbra (0.73 cm), comparable to the uniform beam.
• This approach also reduced skin dose and mean normal tissue dose compared to the multi-beam plan.

Conclusions:

• A single spot scanning proton beam, when combined with a properly designed pre-absorber, is a viable option for treating superficial lesions.
• This technique provides excellent target coverage and effective normal tissue sparing.
• It presents a promising alternative to more complex multi-beam configurations for superficial target treatments.