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Medical Physics / Volume 39 / Issue 1 / RADIATION THERAPY PHYSICS

Med. Phys. 39, 237 (2012); http://dx.doi.org/10.1118/1.3668059 (9 pages)

Biological-based optimization and volumetric modulated arc therapy delivery for stereotactic body radiation therapy

Quentin Diot, Brian Kavanagh, and Moyed Miften

Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado 80045

Robert Timmerman

Department of Radiation Oncology, University of Texas Southwestern Medical School, Dallas, Texas 75390

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(Received 15 June 2011; accepted 19 November 2011; revised 17 November 2011; published online 20 December 2011)

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Purpose: To describe biological-based optimization and Monte Carlo (MC) dose calculation-based treatment planning for volumetric modulated arc therapy (VMAT) delivery of stereotactic body radiation therapy (SBRT) in lung, liver, and prostate patients.
Methods: Optimization strategies and VMAT planning parameters using a biological-based optimization MC planning system were analyzed for 24 SBRT patients. Patients received a median dose of 45 Gy [range, 34–54 Gy] for lung tumors in 1–5 fxs and a median dose of 52 Gy [range, 48–60 Gy] for liver tumors in 3–6 fxs. Prostate patients received a fractional dose of 10 Gy in 5 fxs. Biological-cost functions were used for plan optimization, and its dosimetric quality was evaluated using the conformity index (CI), the conformation number (CN), the ratio of the volume receiving 50% of the prescription dose over the planning target volume (Rx/PTV50). The quality and efficiency of the delivery were assessed according to measured quality assurance (QA) passing rates and delivery times. For each disease site, one patient was replanned using physical cost function and compared to the corresponding biological plan.
Results: Median CI, CN, and Rx/PTV50 for all 24 patients were 1.13 (1.02–1.28), 0.79 (0.70–0.88), and 5.3 (3.1–10.8), respectively. The median delivery rate for all patients was 410 MU/min with a maximum possible rate of 480 MU/min (85%). Median QA passing rate was 96.7%, and it did not significantly vary with the tumor site.
Conclusions: VMAT delivery of SBRT plans optimized using biological-motivated cost-functions result in highly conformal dose distributions. Plans offer shorter treatment-time benefits and provide efficient dose delivery without compromising the plan conformity for tumors in the prostate, lung, and liver, thereby improving patient comfort and clinical throughput. The short delivery times minimize the risk of patient setup and intrafraction motion errors often associated with long SBRT treatment delivery times.

© 2012 American Association of Physicists in Medicine

ACKNOWLEDGMENT

Partially supported by the DOD PC061629 and Elekta.

Article Outline

  1. INTRODUCTION
  2. METHODS AND MATERIALS
  3. RESULTS
  4. DISCUSSION
    1. Delivery times
    2. Passing rates
    3. Conformity
    4. Planning using biological optimization and Monte Carlo dose calculation
    5. Biological vs physical optimization
  5. CONCLUSIONS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3668059

KEYWORDS and PACS

Keywords

biological organs, dosimetry, liver, lung, Monte Carlo methods, radiation therapy, tumours, VMAT, SBRT, lung, liver, prostate, biological-based optimization

PACS

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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Figures (8) Tables (3)

Figures (click on thumbnails to view enlargements)

FIG.1
QA Passing rate as a function of the average number of MU/segment for 60 biological-based VMAT plans including the 24 SBRT plans (square) of the study.

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FIG.2
CI, CN, and Rx/PTV50 as a function of the maximum dose to the target in percentage of the prescription dose.

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FIG.3
Dose distribution for a VMAT SBRT prostate plan (patient 5) with axial (top), coronal (left), and sagittal (right) views. Isodose lines shown are 112%, 105%, 100%, 80%, 60%, and 40% of the prescription dose. The dose distribution avoids the bladder, the urethra, and the rectum.

FIG.3 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.4
Dose distribution for a VMAT SBRT lung plan (patient 14) with axial (top), coronal (left), and sagittal (right) views. Isodose lines shown are 112%, 105%, 100%, 80%, 60%, and 40% of the prescription dose. The high and intermediate dose distributions avoid the stomach, the heart, and the esophagus.

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FIG.5
Dose distribution for a VMAT SBRT liver plan (patient 17) with axial (top), coronal (left), and sagittal (right) views. Isodose lines shown are 112%, 105%, 100%, 80%, 60%, and 40% of the prescription dose.

FIG.5 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.6
Comparison of biological-based and physical plans for prostate patient 5.

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FIG.7
Comparison of biological-based and physical plans for lung patient 14.

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FIG.8
Comparison of biological-based and physical plans for liver patient 17.

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Tables

Table I. Delivery parameters for biological-based VMAT SBRT plans.

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Table II. Treatments duration, QA passing rates, and conformation numbers.

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Table III. Relevant cost functions for each disease sites with the biological parameters used for three different patients that were replanned using physical constraints. The resulting EUD for the biological-based plan and the physical plan are also reported.

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