Product Development of Intensity Modulation for Bolus Electron Conformal Therapy

项目总结/文摘

Project Summary/Abstract Electron beam therapy (EBT) using 6-20 MeV beams provides effective radiation treatment for superficial cancers (depth<6 cm). As many as 20% of radiotherapy patients (166,000 in USA annually) are eligible for electron therapy for some portion of their treatment, making it the second most used external beam modality. As many as 10% of these electron patients (16,600 annually) could benefit from bolus electron conformal therapy (ECT), a technique conforming the dose distribution (distal 90% isodose surface) to the targeted cancer volume while protecting surrounding healthy tissue from acute and long-term adverse effects of radiation, aligning with the agency mission to improve cancer treatment quality. Currently, radiation oncologists are limited in the use of bolus ECT because of dose heterogeneity (as great as 30%) in the targeted cancer volume due to multiple Coulomb scattering from the irregular proximal bolus surface. This Phase I application proposes to research and develop electron intensity modulation technology (planning software and delivery device), which when integrated with existing bolus ECT technology, can eliminate the dose heterogeneity problem, i.e., deliver a more uniform dose distribution (10% dose spread) to the targeted cancer volume. Availability of the proposed product, intensity modulated bolus ECT, should not only greatly improve current treatments of superficial cancers using electron radiotherapy (bolus ECT or otherwise), but in some cases provide an improved alternative to other radiation modalities (e.g. volumetric arc therapy or intensity modulated radio-therapy) by having (1) decreased chance of secondary cancers, (2) equally high chance of cancer control, and (3) equally low chance of acute normal tissue complications. The proposed delivery technology is an intensity modulator plate, which consists of a matrix of small-diameter, cylindrical island blocks imbedded in a low-density slab attached to the beam-defining, collimating insert. The magnitude of the intensity modulation is related to the fraction of beam area covered by the island blocks in a small overlying region. By properly varying the diameter and/or separation of these island blocks, electron scatter in air should result in a smoothly varying intensity pattern on the patient and/or bolus that restores the dose uniformity in the cancer target volume when using bolus ECT. Phase I goals will be to demonstrate proof of principle by (1) incorporating intensity modulation into the existing BolusECT software product, including a method for ‘segmenting’ the intensity pattern into an appropriate matrix of island blocks, (2) validating that the planning software modeling the island blocks produces expected results for select patient sites, and (3) validating delivery of the planned intensity modulated BolusECT beams by demonstrating agreement between delivered (measured) and planned (calculated) dose distributions in water.