Evaluation of Standard Beam Delivery Devices in Proton Radiosurgery

Purpose: To evaluate the use of standard apertures and range shifters for the treatment of brain metastasis in proton stereotactic radiosurgery.

Materials and Methods: Nine patients with localized brain metastasis who had been previously treated using our intracranial proton stereotactic radiosurgery procedure (ie, with a custom aperture and bolus) were randomly selected from our patient cohort. The custom aperture and bolus treatment plans were used as the standard of care in this case and comparative treatment plans using the standard aperture and range shifter concept were generated. Gantry/table angle and the number of treatment beams were optimized as part of this study to evaluate the ability of the standard aperture/range shifter system to deliver a comparable treatment to the patient. Conformity index, homogeneity index, isodose volumes, and integral dose were all evaluated to determine the degree of conformity of the plans created and for comparison to the custom aperture/bolus treatment modality.

Results: The generated treatment plans demonstrated that the standard aperture and range shifter combination could be used to produce comparable conformity indices and isodose volumes to the custom aperture/bolus case in eight of the nine patients studied. A comparative conformity index was achieved in two patients by optimizing the angles of the 3 treatment beams, whereas, in the other cases, additional beams (1 or 2) were required. Additionally, this system exhibited efficiency gains of 60% to 90% over the custom aperture bolus system in reducing the time necessary for treatment planning, device manufacture, and quality assurance.

Conclusion: This work demonstrated that the largely spherical shape of brain metastases make this target well suited to an application of standard apertures while additionally providing efficiency gains in device manufacture and quality assurance for treatment.