Compensators: An alternative IMRT delivery technique

Sha Xiao Chang,Katharin M Deschesne,Elizabeth P Miller,Julian G Rosenman,Timothy J Cullip

doi:10.1120/jacmp.2021.25274

Abstract

Seven years of experience in compensator intensity-modulated radiotherapy (IMRT) clinical implementation are presented. An inverse planning dose optimization algorithm was used to generate intensity modulation maps, which were delivered via either the compensator or segmental multileaf collimator (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 treatment of equal numbers of fields compared to the segmental technique. The typical time needed to fabricate a compensator was 13 min, 3 min of which was manual processing. More than 80% of the approximately 700 compensators evaluated had a maximum deviation of less than 5% from the calculation in intensity profile. Seventy-two percent 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 materials are also discussed. Our experience shows that the compensator-IMRT technique offers robustness, excellent intensity modulation resolution, high treatment delivery efficiency, simple fabrication and quality assurance (QA) procedures, and the flexibility to be used in any teletherapy unit. PACS numbers: 87.53Mr, 87.53Tf

Highlights

The most common techniques today for delivering IMRT treatments on linear accelerators use multileaf collimators (MLCs).(1) The obvious benefit of the MLC-based intensitymodulated radiotherapy (IMRT) techniques is treatment delivery automation
The treatment delivery time is often considerably extended, and concerns about radiation contamination of the prolonged beam-on time are raised.[9]. The often highly irregularly shaped MLC segment fields pose challenges to dose and monitor units (MUs) calculation.[14]. The dynamics of intensity map production by the MLC-IMRT techniques might interfere with the dynamics of patient organ motion when it is considered for treatment planning.[15]
In our years of practice of using both compensator and MLC-based IMRT delivery techniques, we have found that the IM map quality assurance (QA) quality of compensator-IMRT treatments is not inferior to that of the segmental MLC-IMRT treatments

Summary

Introduction

The most common techniques today for delivering IMRT treatments on linear accelerators use multileaf collimators (MLCs).(1) The obvious benefit of the MLC-based intensitymodulated radiotherapy (IMRT) techniques is treatment delivery automation. Years of clinical application have shown that the increased technical and mechanical complexity of MLC-IMRT techniques weakens the benefit gained by automation. MLC-based IMRT techniques have shown several drawbacks in clinical application.[2,3,4,5,6,7,8,9,10,11,12,13] For instance, the total monitor units (MUs) required for a segmental MLCIMRT treatment are often much higher than that of the corresponding nonintensity modulated treatment. The treatment delivery time is often considerably extended, and concerns about radiation contamination of the prolonged beam-on time are raised.[9] The often highly irregularly shaped MLC segment fields pose challenges to dose and MU calculation.[14] The dynamics of intensity map production by the MLC-IMRT techniques might interfere with the dynamics of patient organ motion when it is considered for treatment planning.[15]

Methods

Results

Discussion

Conclusion