Prostate Intrafraction Translation Margins for Real-Time Monitoring and Correction Strategies

Litzenberg, Dale W.; Balter, James M.; Hadley, Scott; Hamstra, Daniel A.; Willoughby, Twyla R.; Kupelian, Patrick A.; Djemil, T.; Mahadevan, A.; Jani, Shirish; Weinstein, G.; Solberg, T.D.; Enke, Charles Arthur; Levine, L.; Sandler, Howard M.

doi:10.1155/2012/130579

Cited by 18 publications

(13 citation statements)

References 15 publications

(22 reference statements)

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“…Prostate motion and its impact on margins and delivered dose distributions in radiotherapy are well studied. [2][3][4][5][6][7] Dynamic multileaf collimator (DMLC) tracking is a method to compensate for intrafraction target motion by real-time adaption of the MLC aperture to the targets movement. [8][9][10][11][12][13][14][15][16][17] Other methods of motion compensation, not covered in this study, include beam gating, moving the source, and couch tracking.…”

Section: Introductionmentioning

confidence: 99%

The impact of leaf width and plan complexity on DMLC tracking of prostate intensity modulated arc therapy

et al. 2013

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Purpose: Intensity modulated arc therapy (IMAT) is commonly used to treat prostate cancer. The purpose of this study was to evaluate the impact of leaf width and plan complexity on dynamic multileaf collimator (DMLC) tracking for prostate motion management during IMAT treatments. Methods: Prostate IMAT plans were delivered with either a high-definition MLC (HDMLC) or a Millennium MLC (M-MLC) (0.25 and 0.50 cm central leaf width, respectively), with and without DMLC tracking, to a dosimetric phantom that reproduced four prostate motion traces. The plan complexity was varied by applying leaf position constraints during plan optimization. A subset of the M-MLC plans was converted for delivery with the HDMLC, isolating the effect of the different leaf widths. The gamma index was used for evaluation. Tracking errors caused by target localization, leaf fitting, and leaf adjustment were analyzed. Results: The gamma pass rate was significantly improved with DMLC tracking compared to no tracking (p < 0.001). With DMLC tracking, the average gamma index pass rate was 98.6% (range 94.8%-100%) with the HDMLC and 98.1% (range 95.4%-99.7%) with the M-MLC, using 3%, 3 mm criteria and the planned dose as reference. The corresponding pass rates without tracking were 87.6% (range 76.2%-94.7%) and 91.1% (range 81.4%-97.6%), respectively. Decreased plan complexity improved the pass rate when static target measurements were used as reference, but not with the planned dose as reference. The main cause of tracking errors was leaf fitting errors, which were decreased by 42% by halving the leaf width. Conclusions: DMLC tracking successfully compensated for the prostate motion. The finer leaf width of the HDMLC improved the tracking accuracy compared to the M-MLC. The tracking improvement with limited plan complexity was small and not discernible when using the planned dose as reference.

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Section: Introductionmentioning

confidence: 99%

The impact of leaf width and plan complexity on DMLC tracking of prostate intensity modulated arc therapy

et al. 2013

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“…CBCT data sets were available for 432 fractions from 22 patients with a median (range) of 20 (16)(17)(18)(19)(20)(21)(22) CBCT per patient. Fifty (10%) of the 482 planned CBCT scans were unusable due to image quality or data capture failure (e.g.…”

Section: Resultsmentioning

confidence: 99%

Geographical miss of the prostate during image-guided radiotherapy with a 6-mm posterior expansion margin

et al. 2016

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IntroductionOur department commonly uses a planning target volume (PTV) expansion of 6 mm posterior and 1 cm in all other directions when treating prostate cancer patients with image‐guided radiotherapy (IGRT). This study aimed to test the adequacy of this PTV expansion by assessing geographical miss of the prostate on post‐treatment cone‐beam CT (CBCT) and identify those at risk of geographical miss.MethodsTwenty‐two prostate cancer patients receiving IGRT with implanted fiducial markers underwent daily pre‐treatment orthogonal kV imaging followed by a post‐treatment CBCT for a total of 432 fractions. The prostate was outlined on all CBCTs. For each imaging set, the volume of geographic miss was measured by subtracting the PTV from the planning CT and prostate volume on the post‐treatment CBCT.ResultsThe prostate volume moved outside the PTV by >0.01 cc in 9% of fractions (39/432). This occurred in 13 (59%) of 22 patients. Large prostates >40 cc and >50 cc had significantly more geographical miss events (both P < 0.001). Changes in rectal filling appear to be responsible for prostate motion/deformation in 82% (32/39) of fractions.ConclusionsOur analysis suggests that, despite IGRT, prostate PTV margins are not adequate in some patients, particularly those with large prostates. PTV margins may be reduced in some other patients. Prostate rotation and deformation play an important role in setting margins and may not always be represented accurately by fiducial marker displacements. Individualised and adaptive margins for prostate cancer patients should be a priority for future research.

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“…Both of the studies used radiofrequency beacons for localization and real-time tracking of gantry SBRT. The University of Michigan study contended that when using Calypso to monitor intrafraction translation and rotation, one could safely reduce the PTV to gain a toxicity-profile advantage without the sacrifice of disease control 56. The two gantry-SBRT studies that did not use radiofrequency beacons – Madsen et al and Loblaw et al – had larger PTV margins of 4–5 mm in all directions 8,9.…”

Section: Theoretical Benefits Of Robotic Arm Vs Gantry Sbrtmentioning

confidence: 99%

A comparison of robotic arm versus gantry linear accelerator stereotactic body radiation therapy for prostate cancer

Avkshtol¹,

Lango²,

Hayes³

et al. 2016

RRU

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Prostate cancer is the most prevalent cancer diagnosed in men in the United States besides skin cancer. Stereotactic body radiation therapy (SBRT; 6–15 Gy per fraction, up to 45 minutes per fraction, delivered in five fractions or less, over the course of approximately 2 weeks) is emerging as a popular treatment option for prostate cancer. The American Society for Radiation Oncology now recognizes SBRT for select low- and intermediate-risk prostate cancer patients. SBRT grew from the notion that high doses of radiation typical of brachytherapy could be delivered noninvasively using modern external-beam radiation therapy planning and delivery methods. SBRT is most commonly delivered using either a traditional gantry-mounted linear accelerator or a robotic arm-mounted linear accelerator. In this systematic review article, we compare and contrast the current clinical evidence supporting a gantry vs robotic arm SBRT for prostate cancer. The data for SBRT show encouraging and comparable results in terms of freedom from biochemical failure (>90% for low and intermediate risk at 5–7 years) and acute and late toxicity (<6% grade 3–4 late toxicities). Other outcomes (eg, overall and cancer-specific mortality) cannot be compared, given the indolent course of low-risk prostate cancer. At this time, neither SBRT device is recommended over the other for all patients; however, gantry-based SBRT machines have the abilities of treating larger volumes with conventional fractionation, shorter treatment time per fraction (~15 minutes for gantry vs ~45 minutes for robotic arm), and the ability to achieve better plans among obese patients (since they are able to use energies >6 MV). Finally, SBRT (particularly on a gantry) may also be more cost-effective than conventionally fractionated external-beam radiation therapy. Randomized controlled trials of SBRT using both technologies are underway.

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Prostate Intrafraction Translation Margins for Real-Time Monitoring and Correction Strategies

Cited by 18 publications

References 15 publications

The impact of leaf width and plan complexity on DMLC tracking of prostate intensity modulated arc therapy

The impact of leaf width and plan complexity on DMLC tracking of prostate intensity modulated arc therapy

Geographical miss of the prostate during image-guided radiotherapy with a 6-mm posterior expansion margin

A comparison of robotic arm versus gantry linear accelerator stereotactic body radiation therapy for prostate cancer

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