Sequencing sector fields

1. A method for optimizing a treatment plan for a patient for a gamma radiation therapy system, the system comprising a radiation therapy unit having a fixed radiation focus point, wherein a collimator of said therapy system is provided with a plurality of collimator passage inlets directing radiation emanating from radioactive sources of a source carrier arrangement of the therapy system to said focus point, said collimator having a plurality of sectors and wherein each sector has a number of states of collimator passage diameters which can be individually adjusted to change a spatial dose distribution surrounding the focus point, said method comprising the steps of:

determining a set of shots to be delivered to a plurality of isocenter positions within a target volume of a patient during a treatment session;

determining a beam-on time for each respective sector and state for each isocenter during which radiation is to be delivered based on the treatment plan; and

for each isocenter position, grouping sectors and states of respective sector in accordance with predetermined rules with respect to beam-on times for respective states of the sectors,

wherein sectors and respective states are aggregated for simultaneous delivery of radiation during a predetermined period of time, and wherein the predetermined rules comprise selecting the longest beam-on time for each state of a respective sector for an aggregated simultaneous delivery of radiation and wherein the predetermined period of time for simultaneous delivery of radiation is determined to be the minimum beam-on time for a state of a sector of the aggregated sectors.

2. The method according to claim 1 , further comprising the steps of:

checking whether the minimum beam-on time for a state of a sector of the aggregated sectors is zero;

setting the sector having a zero beam-on time to be blocked, wherein the sector is blocked for delivery of radiation; and

selecting the shortest non-zero beam-on time as the period of time for delivery of radiation.

3. The method according to claim 2 , further comprising the step of excluding a set of sectors and respective states aggregated for a simultaneous delivery of radiation during a predetermined period of time from delivery if said predetermined period of time is below a predetermined threshold.

4. The method according to claim 1 , further comprising the step of excluding a set of sectors and respective states aggregated for a simultaneous delivery of radiation during a predetermined period of time from delivery if said predetermined period of time is below a predetermined threshold.

5. A sector planning module for a gamma radiation therapy system, the system comprising a radiation therapy unit having a fixed radiation focus point, wherein a collimator of said therapy system is provided with a plurality of collimator passage inlets directing radiation emanating from radioactive sources of a source carrier arrangement of the therapy system to said focus point, said collimator having a plurality of sectors and wherein each sector has a number of states of collimator passage diameters which can be individually adjusted to change a spatial dose distribution surrounding the focus point, said sector planning module comprising:

a dose distribution module adapted to obtain information of a set of shots to be delivered to a plurality of isocenter positions within a target volume of a patient during a treatment session, and of a beam-on time for each respective sector and state for each isocenter during which radiation is to be delivered based on the treatment plan; and

an aggregation module adapted to, for each isocenter position, group sectors and states of respective sector in accordance with predetermined rules with respect to beam-on times for respective states of the sectors,

wherein sectors and respective states are aggregated for simultaneous delivery of radiation during a predetermined period of time and wherein the predetermined rules comprise to select the longest beam-on time for each state of a respective sector for an aggregated simultaneous delivery of radiation and wherein the predetermined period of time for simultaneous delivery of radiation is determined to be the minimum beam-on time for a state of a sector of the aggregated sectors.

6. The sector planning module according to claim 5 , whether said aggregation module is adapted to:

check whether the minimum beam-on time for a state of a sector of the aggregated sectors is zero;

set the sector having a zero beam-on time to be blocked, wherein the sector is blocked for delivery of radiation; and

select the shortest non-zero beam-on time as the period of time for delivery of radiation.

7. The sector planning module according to claim 6 , wherein said aggregation module is adapted to exclude a set of sectors and respective states aggregated for a simultaneous delivery of radiation during a predetermined period of time from delivery if said predetermined period of time is below a predetermined threshold.

8. The sector planning module according to claim 5 , wherein said aggregation module is adapted to exclude a set of sectors and respective states aggregated for a simultaneous delivery of radiation during a predetermined period of time from delivery if said predetermined period of time is below a predetermined threshold.