Beam selection for stereotactic ablative radiotherapy using Cyberknife with multileaf collimation

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Highlights

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A fast optimisation framework is used to create IMRT SABR plans for Cyberknife.
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The value of the Cyberknife multileaf collimator is investigated.
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A beam selection algorithm is used to determine a subset of beam orientations.
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Fifteen selected beams are sufficient to create high-quality treatment plans.
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Treatment time is minimised using this approach.

Abstract

The Cyberknife system (Accuray Inc., Sunnyvale, CA) enables radiotherapy using stereotactic ablative body radiotherapy (SABR) with a large number of non-coplanar beam orientations. Recently, a multileaf collimator has also been available to allow flexibility in field shaping. This work aims to evaluate the quality of treatment plans obtainable with the multileaf collimator. Specifically, the aim is to find a subset of beam orientations from a predetermined set of candidate directions, such that the treatment quality is maintained but the treatment time is reduced. An evolutionary algorithm is used to successively refine a randomly selected starting set of beam orientations. By using an efficient computational framework, clinically useful solutions can be found in several hours. It is found that 15 beam orientations are able to provide treatment quality which approaches that of the candidate beam set of 110 beam orientations, but with approximately half of the estimated treatment time. Choice of an efficient subset of beam orientations offers the possibility to improve the patient experience and maximise the number of patients treated.

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Most cited references 34

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iCycle: Integrated, multicriterial beam angle, and profile optimization for generation of coplanar and noncoplanar IMRT plans.

Pascal R M Storchi, Peter W J Voet, B J M Heijmen … (2012)

To introduce iCycle, a novel algorithm for integrated, multicriterial optimization of beam angles, and intensity modulated radiotherapy (IMRT) profiles. A multicriterial plan optimization with iCycle is based on a prescription called wish-list, containing hard constraints and objectives with ascribed priorities. Priorities are ordinal parameters used for relative importance ranking of the objectives. The higher an objective priority is, the higher the probability that the corresponding objective will be met. Beam directions are selected from an input set of candidate directions. Input sets can be restricted, e.g., to allow only generation of coplanar plans, or to avoid collisions between patient/couch and the gantry in a noncoplanar setup. Obtaining clinically feasible calculation times was an important design criterium for development of iCycle. This could be realized by sequentially adding beams to the treatment plan in an iterative procedure. Each iteration loop starts with selection of the optimal direction to be added. Then, a Pareto-optimal IMRT plan is generated for the (fixed) beam setup that includes all so far selected directions, using a previously published algorithm for multicriterial optimization of fluence profiles for a fixed beam arrangement Breedveld et al. [Phys. Med. Biol. 54, 7199-7209 (2009)]. To select the next direction, each not yet selected candidate direction is temporarily added to the plan and an optimization problem, derived from the Lagrangian obtained from the just performed optimization for establishing the Pareto-optimal plan, is solved. For each patient, a single one-beam, two-beam, three-beam, etc. Pareto-optimal plan is generated until addition of beams does no longer result in significant plan quality improvement. Plan generation with iCycle is fully automated. Performance and characteristics of iCycle are demonstrated by generating plans for a maxillary sinus case, a cervical cancer patient, and a liver patient treated with SBRT. Plans generated with beam angle optimization did better meet the clinical goals than equiangular or manually selected configurations. For the maxillary sinus and liver cases, significant improvements for noncoplanar setups were seen. The cervix case showed that also in IMRT with coplanar setups, beam angle optimization with iCycle may improve plan quality. Computation times for coplanar plans were around 1-2 h and for noncoplanar plans 4-7 h, depending on the number of beams and the complexity of the site. Integrated beam angle and profile optimization with iCycle may result in significant improvements in treatment plan quality. Due to automation, the plan generation workload is minimal. Clinical application has started.

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Monte Carlo simulated corrections for beam commissioning measurements with circular and MLC shaped fields on the CyberKnife M6 System: a study including diode, microchamber, point scintillator, and synthetic microdiamond detectors.

P Francescon, W Kilby, J Noll … (2017)

Monte Carlo simulation was used to calculate correction factors for output factor (OF), percentage depth-dose (PDD), and off-axis ratio (OAR) measurements with the CyberKnife M6 System. These include the first such data for the InCise MLC. Simulated detectors include diodes, air-filled microchambers, a synthetic microdiamond detector, and point scintillator. Individual perturbation factors were also evaluated. OF corrections show similar trends to previous studies. With a 5 mm fixed collimator the diode correction to convert a measured OF to the corresponding point dose ratio varies between -6.1% and -3.5% for the diode models evaluated, while in a 7.6 mm × 7.7 mm MLC field these are -4.5% to -1.8%. The corresponding microchamber corrections are +9.9% to +10.7% and +3.5% to +4.0%. The microdiamond corrections have a maximum of -1.4% for the 7.5 mm and 10 mm collimators. The scintillator corrections are 15%, reducing to d max were <2% for all detectors except IBA Razor where a maximum 4% correction was observed at 300 mm depth. OAR corrections were smaller inside the field than outside. At the beam edge microchamber OAR corrections were up to 15%, mainly caused by density perturbations, which blurs the measured penumbra. With larger beams and depths, PTW and IBA diode corrections outside the beam were up to 20% while the Edge detector needed smaller corrections although these did vary with orientation. These effects are most noticeable for large field size and depth, where they are dominated by fluence and stopping power perturbations. The microdiamond OAR corrections were <3% outside the beam. This paper provides OF corrections that can be used for commissioning new CyberKnife M6 Systems and retrospectively checking estimated corrections used previously. We recommend the PDD and OAR corrections are used to guide detector selection and inform the evaluation of results rather than to explicitly correct measurements.

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Virtual HDR CyberKnife SBRT for Localized Prostatic Carcinoma: 5-Year Disease-Free Survival and Toxicity Observations

Donald Blake Fuller, John Naitoh, George Mardirossian (2014)

Purpose: Prostate stereotactic body radiotherapy (SBRT) may substantially recapitulate the dose distribution of high-dose-rate (HDR) brachytherapy, representing an externally delivered “Virtual HDR” treatment method. Herein, we present 5-year outcomes from a cohort of consecutively treated virtual HDR SBRT prostate cancer patients. Methods: Seventy-nine patients were treated from 2006 to 2009, 40 low-risk, and 39 intermediate-risk, under IRB-approved clinical trial, to 38 Gy in four fractions. The planning target volume (PTV) included prostate plus a 2-mm volume expansion in all directions, with selective use of a 5-mm prostate-to-PTV expansion and proximal seminal vesicle coverage in intermediate-risk patients, to better cover potential extraprostatic disease; rectal PTV margin reduced to zero in all cases. The prescription dose covered >95% of the PTV (V100 ≥95%), with a minimum 150% PTV dose escalation to create “HDR-like” PTV dose distribution. Results: Median pre-SBRT PSA level of 5.6 ng/mL decreased to 0.05 ng/mL 5 years out and 0.02 ng/mL 6 years out. At least one PSA bounce was seen in 55 patients (70%) but only 3 of them subsequently relapsed, biochemical-relapse-free survival was 100 and 92% for low-risk and intermediate-risk patients, respectively, by ASTRO definition (98 and 92% by Phoenix definition). Local relapse did not occur, distant metastasis-free survival was 100 and 95% by risk-group, and disease-specific survival was 100%. Acute and late grade 2 GU toxicity incidence was 10 and 9%, respectively; with 6% late grade 3 GU toxicity. Acute urinary retention did not occur. Acute and late grade 2 GI toxicity was 0 and 1%, respectively, with no grade 3 or higher toxicity. Of patient’s potent pre-SBRT, 65% remained so at 5 years. Conclusion: Virtual HDR prostate SBRT creates a very low PSA nadir, a high rate of 5-year disease-free survival and an acceptable toxicity incidence, with results closely resembling those reported post-HDR brachytherapy.

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Author and article information

Contributors

James L. Bedford

Journal

Journal ID (nlm-ta): Med Eng Phys

Journal ID (iso-abbrev): Med Eng Phys

Title: Medical Engineering & Physics

Publisher: Butterworth-Heinemann

ISSN (Print): 1350-4533

ISSN (Electronic): 1873-4030

Publication date PMC-release: 1 February 2019

Publication date (Print): February 2019

Volume: 64

Pages: 28-36

Affiliations

[0001]Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London SM2 5PT, UK

Author notes

[* ]Corresponding author. james.bedford@ 123456icr.ac.uk

Article

Publisher ID: S1350-4533(18)30180-2

DOI: 10.1016/j.medengphy.2018.12.011

PMC ID: 6358634

PubMed ID: 30579786

SO-VID: e4890e79-5b8d-4051-8026-f7030c90df99

License:

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

History

Date received : 19 December 2017

Date revision received : 14 August 2018

Date accepted : 12 December 2018

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Beam selection for stereotactic ablative radiotherapy using Cyberknife with multileaf collimation

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Most cited references 34

iCycle: Integrated, multicriterial beam angle, and profile optimization for generation of coplanar and noncoplanar IMRT plans.

Monte Carlo simulated corrections for beam commissioning measurements with circular and MLC shaped fields on the CyberKnife M6 System: a study including diode, microchamber, point scintillator, and synthetic microdiamond detectors.

Virtual HDR CyberKnife SBRT for Localized Prostatic Carcinoma: 5-Year Disease-Free Survival and Toxicity Observations

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