Methodologies and tools for proton beam design for lung tumors

Purpose: Proton beams can potentially increase the dose delivered to lung t umors without increasing the dose to critical normal tissues because proton s can be stopped before encountering the normal tissues. This potential can only be realized if tissue motion and planning uncertainties are correctly included during planning. This study evaluated several planning strategies to determine which method best provides adequate tumor coverage, minimal n ormal tissue irradiation, and simplicity of use. Methods and Materials: Proton beam treatment plans were generated using one or more of three different planning strategies. These strategies included designing apertures and boluses to the PTV, apertures to the PTV and boluse s to the CTV, and aperture and bolus to the CTV. Results: The planning target volume as specified in ICRU Report 50 can be u sed only to design the lateral margins of beams, because the distal and pro ximal margins resulting from CT number uncertainty, beam range uncertainty, tissue motions, and setup uncertainties, are different than the lateral ma rgins resulting from these same factors. The best strategy for target cover age with the planning tools available overirradiated some normal tissues un necessarily. The available tools also made the planning of lung tumors diff icult. Conclusions: This study demonstrated that inclusion of target motion and se tup uncertainties into a plan should be performed in the beam design step i nstead of creating new targets. New computerized treatment planning system tools suggested by this study will ease planning, facilitate abandonment of the PTV concept, improve conformance of the dose distribution to the targe t, and improve conformal avoidance of critical normal tissues. (C) 2001 Els evier Science Inc.