Oncology therapies employing radioactive seeds

1. A radioactive seed for use in oncology therapy, the radioactive seed comprising:

a radioactive material including at least one radioisotope; and

a biodegradable host in which the radioactive material is disposed, the biodegradable host configured to biodegrade over a therapy time period when implanted in an oncology subject;

wherein the radioactive material defines a radioactive core and the biodegradable host defines a biodegradable encapsulant surrounding the radioactive core;

wherein the biodegradable encapsulant is absorbing for at least one type of radiation emitted by the radioactive material to control the radiation versus time delivered to the oncology subject by radiation absorption that varies with time as the biodegradable encapsulant degrades over the therapy time period when implanted in the oncology subject;

wherein the at least one radioisotope has a half life that is shorter than a time period for the biodegradable host to biodegrade when implanted in the oncology subject, the half life of the at least one radioisotope respective to the time period for the biodegradable host to biodegrade being effective for the biodegradable host to hold the radioactive material in place at a target location in the oncology subject for the therapy time period, after which biodegradation of the biodegradable host releases the radioactive material; and

wherein the radioactive seed is configured by the biodegradable encapsulant to have radiation output at a time of implantation that is lower than a peak radiation output that occurs at a time after the time of implantation.

2. The radioactive seed as set forth in claim 1 , wherein the biodegradable encapsulant comprises a plurality of concentric biodegradable encapsulant layers at least one of which is partially absorbing for at least one type of radiation emitted by the radioactive material.

3. The radioactive seed as set forth in claim 1 , wherein the radioactive material includes a beta emitting radioisotope.

4. A radioactive seed for use in oncology therapy, the radioactive seed comprising:

a radioactive material including at least one radioisotope; and

a biodegradable host in which the radioactive material is disposed, the biodegradable host configured to biodegrade over a therapy time period when implanted in an oncology subject;

wherein the radioactive material defines a radioactive core and the biodegradable host defines a biodegradable encapsulant surrounding the radioactive core;

wherein the biodegradable encapsulant is absorbing for at least one type of radiation emitted by the radioactive material to control the radiation versus time delivered to the oncology subject by radiation absorption that varies with time as the biodegradable encapsulant degrades over the therapy time period when implanted in the oncology subject;

wherein the at least one radioisotope has a half life that is substantially shorter than a time period for the biodegradable host to biodegrade when implanted in the oncology subject;

wherein the radioactive seed is configured to deliver radiation versus time R out (t)=R(t)T(t) to the oncology subject from a time of implantation t=0 of where:

the radioactive core is configured to output radiation R(t)=R o exp(−t/τ) from the time of implantation t=0 where R o is an initial output of the at least one type of radiation emitted by the radioactive core at t=0 and τ is a time constant corresponding to the half-life of the radioactive material; and

the biodegradable encapsulant is configured to exhibit transmission T(t) proportional to exp(−α·d(t)) from the time of implantation t=0 where α is an attenuation coefficient of the biodegradable host and d(t) is an aggregate thickness of the biodegradable encapsulant with d(t) decreasing over time after the time of implantation t=0 due to biodegradation of the biodegradable encapsulant; and

wherein the radioactive seed is configured by the biodegradable encapsulant to have radiation output R o at a time of implantation that is lower than a peak of the radiation output R out (t)=R(t)T(t) that occurs at a time after the time of implantation.

5. A radioactive seed for use in oncology therapy, the radioactive seed comprising:

a radioactive material including at least one radioisotope; and

a biodegradable host in which the radioactive material is disposed, the biodegradable host configured to biodegrade over a therapy time period when implanted in an oncology subject;

wherein the radioactive material defines a radioactive core and is not distributed in the biodegradable host, and the biodegradable host defines a biodegradable encapsulant surrounding the radioactive core;

wherein the biodegradable encapsulant is absorbing for at least one type of radiation emitted by the radioactive material to control the radiation versus time delivered to the oncology subject by radiation absorption that varies with time as the biodegradable encapsulant degrades over the therapy time period when implanted in the oncology subject; and

wherein the radioactive seed is configured to deliver initial radiation R o to the oncology subject at a time of implantation and peak radiation greater than the initial radiation R o at a peak time later than the time of implantation, wherein the peak time is configured by the half-life of the radioisotope and the initial thickness of the biodegradable encapsulant.

6. The radioactive seed of claim 5 wherein the radioactive material includes a plurality of different oncologically therapeutic radioisotopes having half-lives configured to control a radiation versus time profile of oncologically therapeutic radiation emitted by the radioactive material.

7. The radioactive seed as set forth in claim 6 , wherein the plurality of different oncologically therapeutic radioisotopes includes a beta emitting oncologically therapeutic radioisotope.

8. The radioactive seed as set forth in claim 6 , wherein the plurality of different oncologically therapeutic radioisotopes includes a gamma-emitting oncologically therapeutic radioisotope and a beta-emitting oncologically therapeutic radioisotope.

9. The radioactive seed as set forth in claim 6 , wherein the radioactive material defines a radioactive core and the host material defines an encapsulant surrounding the radioactive core.

10. The radioactive seed as set forth in claim 9 , wherein the radioactive core includes:

a central core including a first oncologically therapeutic radioisotope of the plurality of different oncologically therapeutic radioisotopes; and

an outer core concentrically surrounding the central core and including a second oncologically therapeutic radioisotope of the plurality of different oncologically therapeutic radioisotopes.

11. The radioactive seed as set forth in claim 10 , wherein the first oncologically therapeutic radioisotope is a gamma-emitting radioisotope and the second oncologically therapeutic radioisotope is a beta-emitting radioisotope.

12. An oncology therapy method comprising implanting a radioactive seed as set forth claim 5 in an oncology subject, wherein the implanted radioactive seed delivers oncologically therapeutic radiation to the oncology subject in accord with the radiation versus time profile of oncologically therapeutic radiation emitted by the radioactive seed.