Image-guided radiotherapy of the prostate using daily CBCT: the feasibility and likely benefit of implementing a margin reduction

Maund, Isabella; Benson, Richard; Fairfoul, J.; Cook, J. Taylor; Huddart, Robert; Poynter, A.

doi:10.1259/bjr.20140459

Cited by 59 publications

(42 citation statements)

References 47 publications

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“…Although the planning margins for prostate interfraction variation have been widely studied, previous publications 15 , 16 , 17 , 18 used kV‐CBCT or MVCT that displayed worse image quality than that of planning CTs. For prostate treatment, because the prostate moves independently of the pelvic bones, soft tissue alignment is necessary.…”

Section: Discussionmentioning

confidence: 99%

Using daily diagnostic quality images to validate planning margins for prostate interfractional variations

Vassil

Godley

et al. 2016

J Applied Clin Med Phys

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The purpose of this study is to use the same diagnostic‐quality verification and planning CTs to validate planning margin account for residual interfractional variations with image‐guided soft tissue alignment of the prostate. For nine prostate cancer patients treated with IMRT to 78 Gy in 39 fractions, daily verification CT‐on‐rails images of the first seven and last seven fractions false(n=126false) were retrospectively selected for this study. On these images, prostate, bladder, and rectum were delineated by the same attending physician. Clinical plans were created with a margin of 8 mm except for 5 mm posteriorly, referred to as 8/5 mm. Three additional plans were created for each patient with the margins of 6/4 mm, 4/2 mm, and 2 mm uniform. These plans were subsequently applied to daily images and radiation doses were recalculated. The isocenters of these plans were placed according to clinical online shifts, which were based on soft tissue alignment to the prostate. Retrospective offline shifts by aligning prostate contours were compared to online shifts. The resultant daily target dose was analyzed using D99, the percentage of the prescription dose received by 99% of CTV. The percent of bladder volume receiving 65 Gy false(normalV65Gyfalse) and rectum normalV70Gy were also analyzed. After interfractional correction, using CTV normalD99>97%% criteria, 8/5 mm, 6/4 mm, 4/2 mm, and 2 mm planning margins met the CTV dose coverage in 95%, 91%, 65%, and 53% of the 126 fractions with online shifts, and 99%, 98%, 85%, and 68% with offline shifts. The rectum normalV70Gy and bladder normalV65Gy were significantly decreased at each level of margin reduction (p<0.05). With daily diagnostic quality imaging‐guidance, the interfractional planning margin may be reduced from 8/5 mm to 6/4 mm. The residual interfractional uncertainties most likely stem from prostate rotation and deformation.PACS number(s): 87.53.‐j

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Section: Discussionmentioning

confidence: 99%

Using daily diagnostic quality images to validate planning margins for prostate interfractional variations

Vassil

Godley

et al. 2016

J Applied Clin Med Phys

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“…The mechanical accuracy and intrafraction tracking capabilities of the CyberKnife would allow smaller PTV margins and, as a consequence, would necessarily result in lower dose to the surrounding tissue and reduced treatment time than is presented here. For example, Maund et al (33) find the probability for rectal toxicity greater than grade 2 decreases from 2.1% to 1.4% for a reduction of PTV margin reduction of 5 mm to 3 mm. We chose to use the same PTVs for the CK-MLC plans to focus on the capabilities of the treatment machine and planning system and not on the benefits derived from reduced margins.…”

Section: Discussionmentioning

confidence: 99%

Investigating the clinical advantages of a robotic linac equipped with a multileaf collimator in the treatment of brain and prostate cancer patients

McGuinness

Gottschalk

Lessard

et al. 2015

J Applied Clin Med Phys

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The purpose of this study was to evaluate the performance of a commercially available CyberKnife system with a multileaf collimator (CK-MLC) for stereotactic body radiotherapy (SBRT) and standard fractionated intensity-modulated radiotherapy (IMRT) applications. Ten prostate and ten intracranial cases were planned for the CK-MLC. Half of these cases were compared with clinically approved SBRT plans generated for the CyberKnife with circular collimators, and the other half were compared with clinically approved standard fractionated IMRT plans generated for conventional linacs. The plans were compared on target coverage, conformity, homogeneity, dose to organs at risk (OAR), low dose to the surrounding tissue, total monitor units (MU), and treatment time. CK-MLC plans generated for the SBRT cases achieved more homogeneous dose to the target than the CK plans with the circular collimators, for equivalent coverage, conformity, and dose to OARs. Total monitor units were reduced by 40% to 70% and treatment time was reduced by half. The CK-MLC plans generated for the standard fractionated cases achieved prescription isodose lines between 86% and 93%, which was 2%-3% below the plans generated for conventional linacs. Compared to standard IMRT plans, the total MU were up to three times greater for the prostate (whole pelvis) plans and up to 1.4 times greater for the intracranial plans. Average treatment time was 25 min for the whole pelvis plans and 19 min for the intracranial cases. The CK-MLC system provides significant improvements in treatment time and target homogeneity compared to the CK system with circular collimators, while maintaining high conformity and dose sparing to critical organs. Standard fractionated plans for large target volumes (> 100 cm 3 ) were generated that achieved high prescription isodose levels. The CK-MLC system provides more efficient SRS and SBRT treatments and, in select clinical cases, might be a potential alternative for standard fractionated treatments.

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“…1 In addition to acquiring high quality two-dimensionally planar radiographs and fluoroscopy images, OBIs are capable of generating volumetric cone beam CT (CBCT) images of a patient's internal anatomy, 2 enabling more accurate positioning of patients prior to their treatment. 3 Due to their acquisition arrangement, the three-dimensional (3D) CBCT images generated by OBIs are of inferior quality compared to the planning CTs (pCTs), generated by diagnostic CT scanners used to plan a patient's radiotherapy treatment. 4 However, there have been a number of studies investigating the accuracy of treatment planning dose calculations performed using CBCT images and potential methods to improve observed limitations in their calculation accuracy.…”

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confidence: 99%

An evaluation of techniques for dose calculation on cone beam computed tomography

Giacometti

King

Agnew

et al. 2019

The British Journal of Radiology

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Objective: To assess the accuracy and efficiency of four different techniques, thus determining the optimum method for recalculating dose on cone beam CT (CBCT) images acquired during radiotherapy treatments. Methods: Four established techniques were investigated and their accuracy assessed via dose calculations: (1) applying a standard planning CT (pCT) calibration curve, (2) applying a CBCT site-specific calibration curve, (3) performing a density override and (4) using deformable registration. Each technique was applied to 15 patients receiving volumetric modulated arc therapy to one of three treatment sites, head and neck, lung and prostate. Differences between pCT and CBCT recalculations were determined with dose volume histogram metrics and 2.0%/0.1 mm gamma analysis using the pCT dose distribution as a reference. Results: Dose volume histogram analysis indicated that all techniques yielded differences from expected results between 0.0 and 2.3% for both target volumes and organs at risk. With volumetric gamma analysis, the dose recalculation on deformed images yielded the highest pass-rates. The median pass-rate ranges at 50% threshold were 99.6–99.9%, 94.6–96.0%, and 94.8.0-96.0% for prostate, head and neck and lung patients, respectively. Conclusion: Deformable registration, HU override and site-specific calibration curves were all identified as dosimetrically accurate and efficient methods for dose calculation on CBCT images. Advances in knowledge: With the increasing adoption of CBCT, this study provides clinical radiotherapy departments with invaluable information regarding the comparison of dose reconstruction methods, enabling a more accurate representation of a patient’s treatment. It can also integrate studies in which CBCT is used in image-guided radiation therapy and for adaptive radiotherapy planning processes.

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Image-guided radiotherapy of the prostate using daily CBCT: the feasibility and likely benefit of implementing a margin reduction

Cited by 59 publications

References 47 publications

Using daily diagnostic quality images to validate planning margins for prostate interfractional variations

Using daily diagnostic quality images to validate planning margins for prostate interfractional variations

Investigating the clinical advantages of a robotic linac equipped with a multileaf collimator in the treatment of brain and prostate cancer patients

An evaluation of techniques for dose calculation on cone beam computed tomography

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