Department of Radiation Oncology, Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson University Hospital, Philadelphia, PA 19107

Results:
For the 5 cases examined, there was no appreciable difference in the DVHs for the two planning methods. Dose inhomogeneity (determined as the maximum dose minus the dose covering 95% of the PTV divided by this dose) averaged 20%, demonstrating the increase that occurs for targets with invaginations that surround critical structures. On the average, for the type of invaginated target investigated here, the 75 field segments needed for a forward generated plan increased by 40% to 105 total segments for an inverse plan. Additionally, the forward technique delivered approximately 35% of the dose at each gantry position through an unmodulated conformal portal while no simple conformal field was evident for any of the inverse planning portals.