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      Multiple energy extraction reduces beam delivery time for a synchrotron-based proton spot-scanning system

      research-article
      Author(s): , PhD, , PhD, , MD, , PhD, , PhD, , MD, , PhD, , PhD *
      Publication date (Electronic):
      Journal: Advances in Radiation Oncology
      Publisher: Elsevier

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          Abstract

          Purpose

          Multiple energy extraction (MEE) is a technology that was recently introduced by Hitachi for its spot-scanning proton treatment system, which allows multiple energies to be delivered in a single synchrotron spill. The purpose of this paper is to investigate how much beam delivery time (BDT) can be reduced with MEE compared with single energy extraction (SEE), in which one energy is delivered per spill.

          Methods and Materials

          A recently developed model based on BDT measurements of our synchrotron's delivery performance was used to compute BDT. The total BDT for 2694 beam deliveries in a cohort of 79 patients treated at our institution was computed in both SEE and 9 MEE configurations to determine BDT reduction. The cohort BDT reduction was also calculated for hypothetical accelerators with increased deliverable charge and compared with the results of our current delivery system.

          Results

          A vendor-provided MEE configuration with 4 energy layers per spill reduced the total BDT on average by 35% (41 seconds) compared with SEE, with up to 65% BDT reduction for individual fields. Adding an MEE layer reduced the total BDT by <1% of SEE BDT. However, improving charge recapture efficiency increased BDT savings by up to 42% of SEE BDT.

          Conclusions

          The MEE delivery technique reduced the total BDT by 35%. Increasing the charge per spill and charge recapture efficiency is necessary to further reduce BDT and thereby take full advantage of our MEE system's potential to improve treatment delivery efficiency and operational throughput.

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          Treatment planning and verification of proton therapy using spot scanning: initial experiences.

          Jorn Verwey, Alessandra Bolsi, Beate Timmermann … (2004)
          Since the end of 1996, we have treated more than 160 patients at PSI using spot-scanned protons. The range of indications treated has been quite wide and includes, in the head region, base-of-skull sarcomas, low-grade gliomas, meningiomas, and para-nasal sinus tumors. In addition, we have treated bone sarcomas in the neck and trunk--mainly in the sacral area--as well as prostate cases and some soft tissue sarcomas. PTV volumes for our treated cases are in the range 20-4500 ml, indicating the flexibility of the spot scanning system for treating lesions of all types and sizes. The number of fields per applied plan ranges from between 1 and 4, with a mean of just under 3 beams per plan, and the number of fluence modulated Bragg peaks delivered per field has ranged from 200 to 45 000. With the current delivery rate of roughly 3000 Bragg peaks per minute, this translates into delivery times per field of between a few seconds to 20-25 min. Bragg peak weight analysis of these spots has shown that over all fields, only about 10% of delivered spots have a weight of more than 10% of the maximum in any given field, indicating that there is some scope for optimizing the number of spots delivered per field. Field specific dosimetry shows that these treatments can be delivered accurately and precisely to within +/-1 mm (1 SD) orthogonal to the field direction and to within 1.5 mm in range. With our current delivery system the mean widths of delivered pencil beams at the Bragg peak is about 8 mm (sigma) for all energies, indicating that this is an area where some improvements can be made. In addition, an analysis of the spot weights and energies of individual Bragg peaks shows a relatively broad spread of low and high weighted Bragg peaks over all energy steps, indicating that there is at best only a limited relationship between pencil beam weighting and depth of penetration. This latter observation may have some consequences when considering strategies for fast re-scanning on second generation scanning gantries.
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            Commissioning of the discrete spot scanning proton beam delivery system at the University of Texas M.D. Anderson Cancer Center, Proton Therapy Center, Houston.

            Uwe Titt, Narayan Sahoo, Bijan Arjomandy … (2009)
            To describe a summary of the clinical commissioning of the discrete spot scanning proton beam at the Proton Therapy Center, Houston (PTC-H). Discrete spot scanning system is composed of a delivery system (Hitachi ProBeat), an electronic medical record (Mosaiq V 1.5), and a treatment planning system (TPS) (Eclipse V 8.1). Discrete proton pencil beams (spots) are used to deposit dose spot by spot and layer by layer for the proton distal ranges spanning from 4.0 to 30.6 g/cm2 and over a maximum scan area at the isocenter of 30 x 30 cm2. An arbitrarily chosen reference calibration condition has been selected to define the monitor units (MUs). Using radiochromic film and ion chambers, the authors have measured spot positions, the spot sizes in air, depth dose curves, and profiles for proton beams with various energies in water, and studied the linearity of the dose monitors. In addition to dosimetric measurements and TPS modeling, significant efforts were spent in testing information flow and recovery of the delivery system from treatment interruptions. The main dose monitors have been adjusted such that a specific amount of charge is collected in the monitor chamber corresponding to a single MU, following the IAEA TRS 398 protocol under a specific reference condition. The dose monitor calibration method is based on the absolute dose per MU, which is equivalent to the absolute dose per particle, the approach used by other scanning beam institutions. The full width at half maximum for the spot size in air varies from approximately 1.2 cm for 221.8 MeV to 3.4 cm for 72.5 MeV. The measured versus requested 90% depth dose in water agrees to within 1 mm over ranges of 4.0-30.6 cm. The beam delivery interlocks perform as expected, guarantying the safe and accurate delivery of the planned dose. The dosimetric parameters of the discrete spot scanning proton beam have been measured as part of the clinical commissioning program, and the machine is found to function in a safe manner, making it suitable for patient treatment.
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              Interplay effects in proton scanning for lung: a 4D Monte Carlo study assessing the impact of tumor and beam delivery parameters.

              S Dowdell, C Grassberger, G C Sharp … (2013)
              Relative motion between a tumor and a scanning proton beam results in a degradation of the dose distribution (interplay effect). This study investigates the relationship between beam scanning parameters and the interplay effect, with the goal of finding parameters that minimize interplay. 4D Monte Carlo simulations of pencil beam scanning proton therapy treatments were performed using the 4DCT geometry of five lung cancer patients of varying tumor size (50.4-167.1 cc) and motion amplitude (2.9-30.1 mm). Treatments were planned assuming delivery in 35 × 2.5 Gy(RBE) fractions. The spot size, time to change the beam energy (τes), time required for magnet settling (τss), initial breathing phase, spot spacing, scanning direction, scanning speed, beam current and patient breathing period were varied for each of the five patients. Simulations were performed for a single fraction and an approximation of conventional fractionation. For the patients considered, the interplay effect could not be predicted using the superior-inferior motion amplitude alone. Larger spot sizes (σ ~ 9-16 mm) were less susceptible to interplay, giving an equivalent uniform dose (EUD) of 99.0 ± 4.4% (1 standard deviation) in a single fraction compared to 86.1 ± 13.1% for smaller spots (σ ~ 2-4 mm). The smaller spot sizes gave EUD values as low as 65.3% of the prescription dose in a single fraction. Reducing the spot spacing improved the target dose homogeneity. The initial breathing phase can have a significant effect on the interplay, particularly for shorter delivery times. No clear benefit was evident when scanning either parallel or perpendicular to the predominant axis of motion. Longer breathing periods decreased the EUD. In general, longer delivery times led to lower interplay effects. Conventional fractionation showed significant improvement in terms of interplay, giving a EUD of at least 84.7% and 100.0% of the prescription dose for the small and larger spot sizes respectively. The interplay effect is highly patient specific, depending on the motion amplitude, tumor location and the delivery parameters. Large degradations of the dose distribution in a single fraction were observed, but improved significantly using conventional fractionation.
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                Author and article information

                Contributors
                Jiajian Shen
                Journal
                Journal ID (nlm-ta): Adv Radiat Oncol
                Journal ID (iso-abbrev): Adv Radiat Oncol
                Title: Advances in Radiation Oncology
                Publisher: Elsevier
                ISSN (Electronic): 2452-1094
                Publication date PMC-release: 23 February 2018
                Publication date Collection: Jul-Sep 2018
                Publication date (Electronic): 23 February 2018
                Volume: 3
                Issue: 3
                Pages: 412-420
                Affiliations
                Department of Radiation Oncology, Mayo Clinic, Phoenix, Arizona
                Author notes
                [* ]Corresponding author. Mayo Clinic Arizona, Phoenix, AZ 85054. Shen.Jiajian@ 123456mayo.edu
                Article
                Publisher ID: S2452-1094(18)30031-9
                DOI: 10.1016/j.adro.2018.02.006
                PMC ID: 6127977
                PubMed ID: 30197942
                SO-VID: 59d93551-0d6e-43b0-9d26-70e169128552
                Copyright © © 2018 The Authors
                License:

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

                History
                Date received : 20 December 2017
                Date accepted : 13 February 2018
                Categories
                Subject: Physics Contribution

                Data availability:

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