Compensators: An alternative IMRT delivery technique

Abstract

Six years of experience in compensator-IMRT clinical implementation is presented. An inverse planning dose optimization algorithm was used to generate intensity modulation maps, which were delivered via either the compensator or segmental MLC IMRT techniques. The in-house developed compensator-IMRT technique is presented with the focus on several design issues. The dosimetry of the delivery techniques was analyzed for several clinical cases. The treatment time for both delivery techniques on Siemens accelerators was retrospectively analyzed based on the electronic treatment record in LANTIS for 95 patients. We found that the compensator technique consistently took noticeably less time for treatments of equal number of fields compared to the segmental technique. The compensator technique also produced treatment dosimetry that was closer to the ideal IMRT treatment with no technical limitations in comparison to the segmental MLC technique. The typical time needed to fabricate a compensator was 13 minutes, 3 minutes of which was manual processing. More than 80% of the ~700 compensators evaluated had a maximum deviation of less than 5% from the calculation in intensity profile. 72% of the patient treatment dosimetry measurements for 340 patients have an error of no more than 5%. The pros and cons of different IMRT compensator material are also discussed. Our experience shows that the compensator-IMRT technique offers robustness, excellent intensity modulation resolution, high treatment delivery efficiency, simple fabrication and QA procedures, and the flexibility to be used on any teletherapy unit.