Static device for use in radiotherapy treatment and design method for such a device

A method of designing a compensating device for use in ion-based radiotherapy treatment delivery, the device including a substantially disk-shaped structure including on one side of the disk a plurality of elongate elements, the method comprising the steps of:

• a. obtaining a pencil beam scanning initial treatment plan, wherein the initial treatment plan is optimized with respect to one or more of:
• Physical dose, Relative Biological Effective dose, and Linear Energy Transfer objectives;
• b. obtaining characteristics of an actual treatment plan, the actual treatment plan comprising at least one beam to be used for treating the patient;
• c. determining at least one parameter, the parameter being characteristic of the desired energy modulation of the actual treatment plan, by performing a dose calculation of the initial treatment plan;
• d. based on the at least one parameter, computing a shape for each of the plurality of elongate elements to modulate the dose of the delivery beam to mimic the dose of the initial treatment plan per beam;
• e. re-optimizing the actual treatment plan, wherein the re-optimization uses a single energy layer and takes into account the compensating device, to produce a final treatment plan to be used in delivery to the patient;
• f. adjusting the shape of one or more of the elongate elements, based on the results of the re-optimizing;
• and
• g. iterating steps e and f until the final treatment plan and the geometry of the compensating device remain stable between successive iterations.