MO-A-BRB-01: Non-Coplanar Rotational Therapy by Using High Efficient Unflattened Beams

The rapid dose fall-off from treatment target to the adjacent critical organs has been the Holy Grail for radiotherapy treatment planning. The modern treatment delivery technologies to address such goal include volumetric modulated rotational therapy, non-coplanar EVIRT beams and the use of unflattened beams to reduce the penumbra area. In this lecture, the integration of above techniques will be presented to achieve the goal of a sharp gradient dose around the target and also the discussion of middle to low dose volumes. Use of volumetric modulated rotational therapy by multiple non-coplanar arcs is an idea treatment modality to focus the high dose in the target area while spreading the low dose to even larger volume to reduce the middle range dose to surrounding critical organs. This is especially important for SBRT treatment plans since the fraction dose is much higher than the traditional fraction schema. The challenges we face today are 1. the gantry-couch (patient) collision issue for non-coplanar beam angles, 2. the treatment delivery efficiency due to multiple arc rotations and 3. the massive inverse optimization computation for multiple rotational arcs can be resource intensive and time consuming for treatment plan systems. It might not be easy to resolve all the challenges at one time. However, the high efficient unflattened beam can certainly improve the delivery speed by reducing the beam- on time and this, again, is essential to SBRT patients with high fractional dose. In this lecture, the non-coplanar rotational therapy treatment planning techniques will be presented and be evaluated by using comformality index, gradient index as well as dose volume histogram comparison. The differences in treatment delivery time will be tabulated and compared. At the end, the high-medium-low dose volumes will be illustrated with radiobiological models for the philosophy of sun tanned versus sun burned.

1. Understand treatment plan and dose gradient advantages of using non- coplanar rotational therapy 2. Understand potential delivery efficiency by using unflattened beams for multiple non-coplanar rotational beams 3. Understand sun tanned versus sun burned: the low dose volume and integrated dose.