Clinical implementation of respiratory‐gated spot‐scanning proton therapy: An efficiency analysis of active motion management

Abstract

Purpose The aim of this work is to describe the clinical implementation of respiratory‐gated spot‐scanning proton therapy (SSPT) for the treatment of thoracic and abdominal moving targets. The experience of our institution is summarized, from initial acceptance and commissioning tests to the development of standard clinical operating procedures for simulation, motion assessment, motion mitigation, treatment planning, and gated SSPT treatment delivery. Materials and methods A custom respiratory gating interface incorporating the Real‐Time Position Management System (RPM, Varian Medical Systems, Inc., Palo Alto, CA, USA) was developed in‐house for our synchrotron‐based delivery system. To assess gating performance, a motion phantom and radiochromic films were used to compare gated vs nongated delivery. Site‐specific treatment planning protocols and conservative motion cutoffs were developed, allowing for free‐breathing (FB), breath‐holding (BH), or phase‐gating (Ph‐G). Room usage efficiency of BH and Ph‐G treatments was retrospectively evaluated using beam delivery data retrieved from our record and verify system and DICOM files from patient‐specific quality assurance (QA) procedures. Results More than 70 patients were treated using active motion management between the launch of our motion mitigation program in October 2015 and the end date of data collection of this study in January 2018. During acceptance procedures, we found that overall system latency is clinically‐suitable for Ph‐G. Regarding room usage efficiency, the average number of energy layers delivered per minute was <10 for Ph‐G, 10‐15 for BH and ≥15 for FB, making Ph‐G the slowest treatment modality. When comparing to continuous delivery measured during pretreatment QA procedures, the median values of BH treatment time were extended from 6.6 to 9.3 min (+48%). Ph‐G treatments were extended from 7.3 to 13.0 min (+82%). Conclusions Active motion management has been crucial to the overall success of our SSPT program. Nevertheless, our conservative approach has come with an efficiency cost that is more noticeable in Ph‐G treatments and should be considered in decision‐making.

Managing treatment-related uncertainties in proton beam radiotherapy for gastrointestinal cancers

“…Active motion management commonly includes breath holding (BH) and the use of abdominal compression (AC), both of which have been shown to be effective for reducing breathing motion in GI cancers (32)(33)(34)(35). BH requires patient compliance and results in decreased delivery efficiency (36).…”

The emerging role of proton therapy for esophagus cancer

“…For PBS-PBT specifically, several techniques have been utilized to minimize dosimetric plan degradation due to motion interplay. Repainting strategies, such as a maximum monitor-unit threshold-based isolayered repainting technique, have been commonly used to better disperse delivered proton spots across the breathing cycle and thereby dampen dosimetric heterogeneity (44)(45)(46)(47)(48)(49)(50).…”

“…To summarize, incorporation of motion management techniques for esophageal treatments should facilitate development of PBT plans which are appropriately robust to diaphragmatic motion and target interplay effects. However, motion management comes with costs, e.g., clinicians must anticipate the potential for introduction of additional uncertainties, increased technical and process complexity, and overall practice efficiency decreases associated with extending the treatment delivery time (46). Verification CT scans should be performed periodically during the treatment course to evaluate for inter-fraction anatomic or setup changes.…”

Dose-response of deformable radiochromic dosimeters for spot scanning proton therapy

“…Regions near the lung are dealt with using e.g. breath-hold techniques in combination with image based monitoring [1] , while approaches such as respiratory gating and tumour tracking are also being explored [2] , [3] , [4] , [5] .…”