Evaluating which plan quality metrics are appropriate for use in lung SBRT

Yaparpalvi, Ravindra; Garg, Madhur; Shen, Jin; Bodner, William; Mynampati, D; Gafar, Aleiya; Kuo, Hsiang-Chi; Basavatia, Amar; Ohri, Nitin; Hong, Linda

doi:10.1259/bjr.20170393

Cited by 16 publications

(17 citation statements)

References 32 publications

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“…This concept is similar to the acceptance of dose heterogeneity within the GTV in other forms of SBRT. 8 , 14 Past SBRT trials, even with 3 and 1 fraction regimens have shown that duodenum, small bowel, and stomach constraints of V20 < 30 cc, V35 < 1 cc, and maximum dose <40 Gy are safe and well tolerated Table 2 .…”

Section: Discussionmentioning

confidence: 99%

Dose escalation for locally advanced pancreatic cancer: How high can we go?

Colbert

Rebueno

Moningi

et al. 2018

Advances in Radiation Oncology

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PurposeThere are limited treatment options for locally advanced, unresectable pancreatic cancer (LAPC) and no likelihood of cure without surgery. Radiation offers an option for local control, but radiation dose has previously been limited by nearby bowel toxicity. Advances in on-board imaging and treatment planning may allow for dose escalation not previously feasible and improve local control. In preparation for development of clinical trials of dose escalation in LAPC, we undertook a dosimetric study to determine the maximum possible dose escalation while maintaining known normal tissue constraints.Methods and MaterialsTwenty patients treated at our institution with either SBRT or dose-escalated hypofractionated IMRT (DE-IMRT) were re-planned using dose escalated SBRT to 70 Gy in 5 fractions to the GTV and 40 Gy in 5 fractions to the PTV. Standard accepted organ at risk (OAR) constraints were used for planning. Descriptive statistics were generated for homogeneity, conformality, OAR's and GTV/PTV.ResultsMean iGTV coverage by 50 Gy was 91% (±0.07%), by 60 Gy was 61.3% (±0.08%) and by 70 Gy was 24.4% (±0.05%). Maximum PTV coverage by 70 Gy was 33%. Maximum PTV coverage by 60 Gy was 77.5%. The following organ at risk (OAR) constraints were achieved for 90% of generated plans: Duodenum V20 < 30 cc, V30 < 3 cc, V35 < 1 cc; Small Bowel V20 < 15 cc, V30 < 1 cc, V35 < 0.1 cc; Stomach V20 < 20 cc, V30 < 2 cc, V35 < 1 cc. V40 < 0.5 cc was achieved for all OAR.ConclusionsDose escalation to 60 Gy is dosimetrically feasible with adequate GTV coverage. The identified constraints for OAR's will be used in ongoing clinical trials.

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Section: Discussionmentioning

confidence: 99%

Dose escalation for locally advanced pancreatic cancer: How high can we go?

Colbert

Rebueno

Moningi

et al. 2018

Advances in Radiation Oncology

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“…The RTOG protocol 9 provides guidance for acceptable values for R50% as function of the PTV volume measurement. Other RTOGdefined quantities used to assess SBRT plan quality are D2cm 7 (maximum Dose 2 cm from the PTV in any direction), V105% 9 When considering the PTV dose heterogeneity there are three metrics available: ICRU HI, 9 RTOG HI, 11 and PTV mean dose (PTV D av ). The ICRU HI, RTOG HI, and PTV D av are defined, respectively, as follows:…”

Section: Introductionmentioning

confidence: 99%

A physically meaningful relationship between R50% and PTV surface area in lung SBRT

Desai

Cordrey

Johnson

2020

J Applied Clin Med Phys

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Purpose We propose a novel understanding of two characteristics of the planning target volume (PTV) that affect the intermediate‐dose spill in lung stereotactic body radiation therapy (SBRT) as measured by R50%. This phantom model research investigates two characteristics of the PTV that have a marked effect on the value of R50%: the mean dose deposited within the PTV (Dav) and the surface area of the PTV (SAPTV). Methods Using a phantom model provided by a CT of the IROC Thorax‐Lung Phantom® (IROC Houston QA Center, Houston, TX) and Eclipse® Treatment Planning System (Varian Medical Systems, Palo Alto, CA), we investigate the two characteristics for spherical and cylindrical PTVs. A total of 135 plans with tightly controlled PTV characteristics are employed. A lower bound for R50% (R50%min∆r) is derived and clearly establishes a relationship between R50% and SAPTV that has not been fully appreciated previously. Results The study of PTV Dav revealed a local minimum for R50% as a function of the PTV Dav at Dav ≈ 110% of Rx dose. As PTV Dav increases above this local minimum, R50% increases; while for PTV Dav less than this local minimum, the R50% value also increases. The study of PTV surface area (SAPTV) demonstrated that as the SAPTV increases, the R50% increases if the PTV volume stays the same. The SAPTV result is predicted by the theoretical investigation that yields the R50% lower bound, R50%min∆r. Conclusions This research has identified two characteristics of the PTV that have a marked influence on R50%: PTV Dav and SAPTV. These characteristics have not been clearly articulated in the vast body of previous research in SBRT. These results could help explain plans that cannot meet the RTOG criteria for R50%. With further development, these concepts could be extended to provide additional guidance for creating acceptable SBRT plans.

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“…Tolerances from the RTOG trial 0813, also used in the RTOG trial 0915 [15] have also been adopted internationally, however these tolerances are based on the use of 3D conformal (3D-CRT) co-planar or non-coplanar SBRT techniques, potentially calculated with Type-A algorithms, which does not reflect the techniques currently routinely used for lung SBRT [16] . The need for updating RTOG guidance has been raised in more recent publications that reviewed dose conformity in co-planar [17] , [18] , [19] , [20] , [21] or non-coplanar [22] IMRT or volumetric modulated arc therapy (VMAT) lung SBRT plans. Recommendations for plan quality metrics in other body sites are scarce; the PACE trial protocol referencing the ASTRO report [23] , that the volume ratio of the planning target volume (PTV) D 95% to the PTV should be less than 1.2.…”

Section: Introductionmentioning

confidence: 99%

Multi-center evaluation of dose conformity in stereotactic body radiotherapy

Lee

Dean

Patel

et al. 2019

Physics and Imaging in Radiation Oncology

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Background and purpose: Stereotactic body radiotherapy (SBRT) is an emerging technique for treating oligometastases, but limited data is available on what plan quality is achievable for a range of modalities and clinical sites. Methods: SBRT plans for lung, spine, bone, adrenal, liver and node sites from 17 participating centers were reviewed. Centers used various delivery techniques including static and rotational intensity-modulation and multiple non-coplanar beams. Plans were split into lung and other body sites and evaluated with different plan quality metrics, including two which are independent of target coverage; "prescription dose spillage" (PDS) and "modified gradient index" (MGI). These were compared to constraints from the ROSEL and RTOG 0813 clinical trials. Results: Planning target volume (PTV) coverage was compromised (PTV V100% < 90%) in 29% of patient plans in order to meet organ-at-risk (OAR) tolerances, supporting the use of plan quality metrics which are independent of target coverage. Both lung (n = 48) and other body (n = 99) site PDS values agreed well with ROSEL constraints on dose spillage, but RTOG 0813 values were too high to detect sub-optimal plans. MGI values for lung plans were mis-matched to both sets of previous constraints, with ROSEL values too high and RTOG 0813 values too low. MGI values were lower for other body plans as expected, though this was only statistically significant for PTV volumes < 20 cm 3. Conclusions: Updated guidance for lung and other body site SBRT plan quality using the PDS and MGI metrics is presented.

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Evaluating which plan quality metrics are appropriate for use in lung SBRT

Cited by 16 publications

References 32 publications

Dose escalation for locally advanced pancreatic cancer: How high can we go?

Dose escalation for locally advanced pancreatic cancer: How high can we go?

A physically meaningful relationship between R50% and PTV surface area in lung SBRT

Multi-center evaluation of dose conformity in stereotactic body radiotherapy

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