EP-1747: Assessment of PTV margins accounting for prostate intrafraction motion in SBRT with online IGRT

Magli, A.; Malisan, M.R.; Fontanella, Chiara Giulia; Crespi, Michele; Guernieri, M.; Titone, F.; Sacco, Clara; Moretti, E.; Foti, C.

doi:10.1016/s0167-8140(16)32998-x

Cited by 3 publications

(10 citation statements)

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“…If we assume 1-2 mm margins are necessary for systematic errors related to contouring and machine performance (33)(34)(35), then the minimum PTV margins required in the absence of frequent intra-fractional monitoring and correction would be 2.9-3.9 mm LR, 3.7-4.7 mm SI, and 4.1-5.1 mm AP. The fact that a greater posterior margin is necessary is practically relevant, as many contemporary SBRT protocols allow for smaller posterior margins (5,(36)(37)(38)(39). For instance, in the landmark PACE-B trial, margins were 4-5 mm non-posteriorly and 3-5 mm posteriorly (5).…”

Section: Discussionmentioning

confidence: 99%

Clinical Assessment of Prostate Displacement and Planning Target Volume Margins for Stereotactic Body Radiotherapy of Prostate Cancer

et al. 2020

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Purpose: To assess the optimal planning target volume (PTV) margins for stereotactic body radiotherapy (SBRT) of prostate cancer based on inter-and intra-fractional prostate motion determined from daily image guidance. Methods and Materials: Two hundred and five patients who were enrolled on two prospective studies of SBRT (8 Gy × 5 fractions) for localized prostate cancer treated at a single institution between 2012 and 2017 had complete inter-and intra-fractional shift data available. All patients had scheduled kilovoltage planar imaging during SBRT with rigid registration to intraprostatic fiducials prior to each of four half-arcs delivered per fraction, as well as cone beam CT verification of anatomy prior to each fraction. Inter-and intra-fractional shift data were obtained to estimate the required PTV margins based on the classic van Herk formula. Inter-and intra-fractional motion were compared between patients with and without severe toxicities using the independent two-sample Wilcoxon test. Results: The margins required to account for inter-fractional motion were estimated to be 0.99, 1.52, and 1.45 cm in lateral (LR), longitudinal (SI), and vertical (AP) directions, respectively. The margins required to account for intra-fractional motion were estimated to be 0.19, 0.27, and 0.31 cm in LR, SI and AP directions, respectively. Large intra-fractional shifts were mostly observed in the SI and AP directions, with 2.0 and 5.4% of patients experiencing average intra-fractional motion >3 mm in the SI and AP directions, respectively, compared with none experiencing mean shifts >3 mm in the LR direction. Six patients experienced grade 3 gastrointestinal or genitourinary toxicity. There were no significant differences in mean inter-or intra-fractional motion in any of the cardinal directions compared to patients without severe toxicity (inter-fractional p = 0.46-0.99, intra-fractional p = 0.10-0.84). Levin-Epstein et al. Prostate Displacement and SBRT Margins Conclusion: The inter-and intra-fractional margins estimated from this study are in line with prior reported values. Intra-fractional prostate motion was generally small with larger margins required for the SI and AP directions, notably just slightly exceeding the commonly used 3 mm posterior PTV margin even with realignment between half-arcs. Development of severe toxicity was not significantly associated with the degree of inter-or intra-fractional motion.

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Section: Discussionmentioning

confidence: 99%

Clinical Assessment of Prostate Displacement and Planning Target Volume Margins for Stereotactic Body Radiotherapy of Prostate Cancer

et al. 2020

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“…In the PACE‐B trial, 12.8% and 86% of SBRT cases used less than 3‐mm and 3∼5‐mm posterior margins, respectively 1 . Additionally, margins of 3 mm were considered applicable for treatment times between 5 and 10 min 21,28 in IGRT with online correction. Magli et al 21 .…”

Section: Discussionmentioning

confidence: 99%

“…of SBRT cases used less than 3-mm and 3∼5-mm posterior margins, respectively. 1 Additionally, margins of 3 mm were considered applicable for treatment times between 5 and 10 min 21,28 in IGRT with online correction. Magli et al 21 observed a significant correlation between the intrafraction displacement of the prostate and the elapsed treatment time.…”

Section: Discussionmentioning

confidence: 99%

Assessment of planning target volume margins in 1.5 T magnetic resonance‐guided stereotactic body radiation therapy for localized prostate cancer

Yang

Yuan

Poon

et al. 2022

Precision Radiation Oncology

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Objective:We aimed to determine the planning target volume margins applicable to magnetic resonance-guided stereotactic body radiation therapy (MRgSBRT) of localized prostate cancer on a 1.5 T MR-Linac.Methods: A total of 10 patients with low-to intermediate-risk prostate cancer were retrospectively enrolled. All patients received five-fraction MRgSBRT treatments, and underwent daily endorectal ballooning and bladder control. Five patients were implanted with the hydrogel rectal spacer. Three MR scans at each fraction were acquired to evaluate the intrafractional prostate motion. The required planning target volume margin was determined using the van Herk margin recipe based on direct MR-MR prostate registration. The set-up margin for localization using bony anatomy was also estimated. Results:The mean and standard deviation of translational displacement in left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions were -0.3 ± 0.7, 2.0 ± 1.5, and 1.4 ± 1.1 mm, respectively. Planning target volume margins over the MRgSBRT fraction duration were 2.8 (LR), 5.3 (SI), and 3.9 mm (AP). Set-up margins were estimated to 2.6 (LR), 3.3 (SI), and 3.3 mm (AP). Prostate motion increased considerably with treatment duration. Adapt-to-position had smaller intrafractional motions than adapt-to-shape. The rectal spacer insignificantly (p > 0.1) reduced the prostate motion in SI and AP. Conclusion:Online workflow efficiency enhancement and intrafractional motion monitoring are vital for planning target volume margin reduction and precision enhancement in MRgSBRT.

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“…If the lymph node portion of that PTV is already compromised at the beginning of the treatment, then misalignments have the potential worsen within the fraction 7 . There are several potential solutions: deformable registration with inter‐faction adaptive treatments, improvements to bladder filling protocol to total reduce motion, and an expansion of target margins in the most active regions of misalignment 11–14 . At our clinic we have adopted asymmetric margin expansions for the CTV to better account for the motion 15 .…”

Section: Discussionmentioning

confidence: 99%

“…7 There are several potential solutions: deformable registration with inter-faction adaptive treatments, improvements to bladder filling protocol to total reduce motion, and an expansion of target margins in the most active regions of misalignment. [11][12][13][14] At our clinic we have adopted asymmetric margin expansions for the CTV to better account for the motion. 15 In addition, CBCT scans are acquired in the daily set-up process for the first 25 to facilitate improved lymph node alignment.…”

Section: C | Prospective Solutionsmentioning

confidence: 99%

Impact of prostate focused alignment on planned pelvic lymph node dose

Kilian-Meneghin

Kumaraswamy

2021

J Applied Clin Med Phys

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EP-1747: Assessment of PTV margins accounting for prostate intrafraction motion in SBRT with online IGRT

Cited by 3 publications

References 0 publications

Clinical Assessment of Prostate Displacement and Planning Target Volume Margins for Stereotactic Body Radiotherapy of Prostate Cancer

Clinical Assessment of Prostate Displacement and Planning Target Volume Margins for Stereotactic Body Radiotherapy of Prostate Cancer

Assessment of planning target volume margins in 1.5 T magnetic resonance‐guided stereotactic body radiation therapy for localized prostate cancer

Impact of prostate focused alignment on planned pelvic lymph node dose

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