Plaque Therapy and Scatter Dose Using {sup 252}Cf Sources

Conference · Sun Nov 12 04:00:00 EST 2000

OSTI ID:786882

Rivard, Mark J; Mahajan, Anita

As melanomas are radioresistant to conventional low-linear energy transfer (LET) radiations such as photons and electrons, {sup 252}Cf (high-LET due to neutrons) may offer more promising clinical results. Although {sup 252}Cf also emits photons and electrons, the majority of absorbed dose is imparted by the high-LET radiation. This study examines the impact of scattering material on the neutron dose distributions for {sup 252}Cf plaque therapy (used to treat surface lesions like melanoma). Neutrons were transported through a 10-cm-diam water phantom with a thickness of either 5 or 10 cm using the MCNP radiation transport code. The phantom was surrounded by vacuum; the {sup 252}Cf neutron energy spectrum was modeled as a Maxwellian distribution; and the source was a bare point positioned at 1.0, 0.5, or {epsilon} above or below the water/vacuum interface. These source positions were chosen to mimic the case where a plaque locates the source either above the skin's surface, e.g., 2{pi} scattering geometry, or if layers of tissue-equivalent bolus materials were placed atop the implant to provide radiation backscatter, 4{pi} geometry. Differences between the 2{pi} and 4{pi} geometries were maximized closest to the source and for source positions farthest from the water/vacuum interface. Therefore, the maximum radiation dose (closest to the {sup 252}Cf source) may be minimized by not including scattering material for plaque therapy. However, for nonrelativistic, elastic scattering for protons by neutrons, the proton range increases with neutron energy. This result was expected since the neutron energy spectrum degrades at increasing depth and the proportion of fast neutron dose to total dose is maximized closest to the source in the 2{pi} geometry. Future studies will examine this effect as a function of neutron energy, will consider synergy with the low-LET {sup 252}Cf dose component and include experimental measurements, and will assess this technique to possibly improve in vivo dose distributions.

• Research Organization: Tufts New England Medical Center, Boston, MA (US)
• Sponsoring Organization: none (US)
• OSTI ID: 786882
• Report Number(s): none; ISSN 0003-018X; CODEN TANSAO; ISSN 0003-018X; CODEN TANSAO
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
CALIFORNIUM 252
COMPUTERIZED SIMULATION
FAST NEUTRONS
IN VIVO
IRRADIATION PROCEDURES
M CODES
MELANOMAS
NEUTRON THERAPY
PHANTOMS
PLAQUE
PLAQUE FORMATION
RADIATION DOSE DISTRIBUTIONS
RADIATION TRANSPORT
SCATTERING
SPATIAL DOSE DISTRIBUTIONS