Inverse planning with HIPO

HIPO stands for Hybrid Inverse Planning & Optimization and has two main functionalities, as mentioned by its name: inverse planning and inverse optimization.  The inverse planning functionality enables the automatic placement of a specific number of catheters, defined by the user, in such a way that all selected objectives are realised in the most effective way. When the placement of catheters is fixed, HIPO is used for the optimization of the dose distribution. It is a unique tool for inverse planning & optimization in HDR prostate treatment which makes the intra-operative preplanning of a prostate implant effective and user-independent.

Taking into account all selected objectives and dose limits, HIPO starts with an initial placement of catheters. This placement is adapted to the patient's anatomy. The fast dose optimization algorithm adapts the catheter position on the spot in order to achieve the implant setup that best realizes all objectives. For each catheter configuration HIPO runs a dose optimization algorithm and evaluates the 3D dose distribution. This way enables the realisation of all possible clinical scenarios. Based on the results of the optimization for each catheter set-up HIPO selects the one that fits to the user-selected dosimetry objectives.

The user can propose an initial catheter placement and ask HIPO for improvement. The user may also define catheters that are to be used in any case and ask HIPO for the most appropriate additional catheter(s). At any moment the user may decide to stop HIPO and intervene by introducing changes. In that case, HIPO will reallocate the most efficient implant positions.

The first commercial release of HIPO was launched with Nucletron's Oncentra Prostate  version 3.0 in 2007. One year later, in 2008, a new version of HIPO  was  released with Oncentra GYN, adapted to the needs of gyneacological treatment planning.

Dose optimization with HIPO (DVHO)

If the catheters have already been placed, HIPO can be used to optimize the dose distribution using its dose optimization engine (also known as DVHO in Oncentra Prostate version 3.0 and 3.1). This dose optimization engine is a unique implementation of DVH-based inverse optimization technology.  In addition to target volume (CTV or PTV) several GTV’s (CTV3) and several organs at risk can be considered simultaneously.

For the target volume(s) a dose-window is defined: the low and high dose limit. A high dose limit is considered for each of the organs at risk.

Typical cases of plans with 12-14 catheters can be optimized within 2-3 seconds. The speed of HIPO dose optimizer enables interactive optimization. 

An example of dose optimization using HIPO in a prostate live plan. First the optimization settings and the volumes are demonstrated, then the button "Optimize" is pressed and within seconds the optimized plan is available. The DVH and the isodoses are demonstrated after the optimization.

Dwell time gradient restriction filter

HIPO offers a dwell time gradient restriction filter in order to account for clinical constraints within the catheters. In other words, high values of this filter are expected to produce solutions with smooth changes of dwell times/weights along each catheter and prevent solutions with dominating source dwell positions. The dwell time gradient restriction acts practically as a dose modulation restriction filter. This enables the creation of better security in the delivery dose distributions without having to compromise to the optimization performance.

HIPO is the only commercial inverse dose optimization tool in brachytherapy offering this functionality.

An example of the effect of the gradient restriction: On the left, no restriction is used (zero gradient factor) and two areas wtih dominating dwell positions are shown. On the right, the gradient restriction takes its maximum value and the dominating positions have been replaced by a smooth and distributed contribution to the dose by the dwell positions.