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Dosimetric impact of uncorrected systematic yaw rotation in VMAT for peripheral lung SABR.

ABSTRACT: Aim:This study aimed to evaluate the dosimetric impact of uncorrected yaw rotational error on both target coverage and OAR dose metrics in this patient population. Background:Rotational set up errors can be difficult to correct in lung VMAT SABR treatments, and may lead to a change in planned dose distributions. Materials and methods:We retrospectively applied systematic yaw rotational errors in 1° degree increments up to -5° and +5° degrees in 16 VMAT SABR plans. The impact on PTV and OARs (oesophagus, spinal canal, heart, airway, chest wall, brachial plexus, lung) was evaluated using a variety of dose metrics. Changes were assessed in relation to percentage deviation from approved planned dose at 0 degrees. Results:Target coverage was largely unaffected with the largest mean and maximum percentage difference being 1.4% and 6% respectively to PTV D98% at +5 degrees yaw.Impact on OARs was varied. Minimal impact was observed in oesophagus, spinal canal, chest wall or lung dose metrics. Larger variations were observed in the heart, airway and brachial plexus. The largest mean and maximum percentage differences being 20.77% and 311% respectively at -5 degrees yaw to airway D0.1cc, however, the clinical impact was negligible as these variations were observed in metrics with minimal initial doses. Conclusions:No clinically unacceptable changes to dose metrics were observed in this patient cohort but large percentage deviations from approved dose metrics in OARs were noted. OARs with associated PRV structures appear more robust to uncorrected rotational error.

SUBMITTER: Barrett S

PROVIDER: S-EPMC6731354 | biostudies-literature | 2019 Nov-Dec

REPOSITORIES: biostudies-literature

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Dosimetric impact of uncorrected systematic yaw rotation in VMAT for peripheral lung SABR.

Barrett Sarah S Thirion Pierre P Harper Dean D Simpkin Andrew J AJ Leech Michelle M Hickey Kim K Ryan Laoise L Marignol Laure L

Reports of practical oncology and radiotherapy : journal of Greatpoland Cancer Center in Poznan and Polish Society of Radiation Oncology 20190904 6

<h4>Aim</h4>This study aimed to evaluate the dosimetric impact of uncorrected yaw rotational error on both target coverage and OAR dose metrics in this patient population.<h4>Background</h4>Rotational set up errors can be difficult to correct in lung VMAT SABR treatments, and may lead to a change in planned dose distributions.<h4>Materials and methods</h4>We retrospectively applied systematic yaw rotational errors in 1° degree increments up to -5° and +5° degrees in 16 VMAT SABR plans. The impac ...[more]

PMID: 31516398

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Project description:Volumetric-modulated arc therapy (VMAT) is emerging as a leading technology in treating early-stage, non-small cell lung cancer (NSCLC) with stereotactic ablative radiotherapy (SABR). However, two other modalities capable of deliver-ing intensity-modulated radiation therapy (IMRT) include fixed-beam and helical TomoTherapy (HT). This study aims to provide an extensive dosimetric compari-son among these various IMRT techniques for treating early-stage NSCLC with SABR. Ten early-stage NSCLC patients were retrospectively optimized using three fixed-beam techniques via nine to eleven beams (high and low modulation step-and-shoot (SS), and sliding window (SW)), two VMAT techniques via two partial arcs (SmartArc (SA) and RapidArc (RA)), and three HT techniques via three different fan beam widths (1 cm, 2.5 cm, and 5 cm) for 80 plans total. Fixed-beam and VMAT plans were generated using flattening filter-free beams. SS and SA, HT treatment plans, and SW and RA were optimized using Pinnacle v9.1, Tomoplan v.3.1.1, and Eclipse (Acuros XB v11.3 algorithm), respectively. Dose-volume histogram statistics, dose conformality, and treatment delivery efficiency were analyzed. VMAT treatment plans achieved significantly lower values for contralat-eral lung V5Gy (p ? 0.05) compared to the HT plans, and significantly lower mean lung dose (p < 0.006) compared to HT 5 cm treatment plans. In the comparison between the VMAT techniques, a significant reduction in the total monitor units (p = 0.05) was found in the SA plans, while a significant decrease was observed in the dose falloff parameter, D2cm, (p = 0.05), for the RA treatments. The maximum cord dose was significantly reduced (p = 0.017) in grouped RA&SA plans com-pared to SS. Estimated treatment time was significantly higher for HT and fixed-beam plans compared to RA&SA (p < 0.001). Although, a significant difference was not observed in the RA vs. SA (p = 0.393). RA&SA outperformed HT in all parameters measured. Despite an increase in dose to the heart and bronchus, this study demonstrates that VMAT is dosimetrically advantageous in treating early-stage NSCLC with SABR compared to fixed-beam, while providing significantly shorter treatment times.

Project description:BackgroundDuring prostate stereotactic body radiation therapy (SBRT), prostate tumor translational motion may deteriorate the planned dose distribution. Most of the major advances in motion management to date have focused on correcting this one aspect of the tumor motion, translation. However, large prostate rotation up to 30° has been measured. As the technological innovation evolves toward delivering increasingly precise radiotherapy, it is important to quantify the clinical benefit of translational and rotational motion correction over translational motion correction alone.PurposeThe purpose of this work was to quantify the dosimetric impact of intrafractional dynamic rotation of the prostate measured with a six degrees-of-freedom tumor motion monitoring technology.MethodsThe delivered dose was reconstructed including (a) translational and rotational motion and (b) only translational motion of the tumor for 32 prostate cancer patients recruited on a 5-fraction prostate SBRT clinical trial. Patients on the trial received 7.25 Gy in a treatment fraction. A 5 mm clinical target volume (CTV) to planning target volume (PTV) margin was applied in all directions except the posterior direction where a 3 mm expansion was used. Prostate intrafractional translational motion was managed using a gating strategy, and any translation above the gating threshold was corrected by applying an equivalent couch shift. The residual translational motion is denoted as Tres$T_{res}$ . Prostate intrafractional rotational motion Runcorr$R_{uncorr}$ was recorded but not corrected. The dose differences from the planned dose due to Tres$T_{res}$ + Runcorr$R_{uncorr}$ , ΔD( Tres$T_{res}$ + Runcorr$R_{uncorr}$ ) and due to Tres$T_{res}$ alone, ΔD( Tres$T_{res}$ ), were then determined for CTV D98, PTV D95, bladder V6Gy, and rectum V6Gy. The residual dose error due to uncorrected rotation, Runcorr$R_{uncorr}$ was then quantified: ΔDResidual$\Delta D_{Residual}$ = ΔD( Tres$T_{res}$ + Runcorr$R_{uncorr}$ ) - ΔD( Tres${T}_{\textit{res}}$ ).ResultsFractional data analysis shows that the dose differences from the plan (both ΔD( Tres$T_{res}$ + Runcorr$R_{uncorr}$ ) and ΔD( Tres$T_{res}$ )) for CTV D98 was less than 5% in all treatment fractions. ΔD( Tres$T_{res}$ + Runcorr$R_{uncorr}$ ) was larger than 5% in one fraction for PTV D95, in one fraction for bladder V6Gy, and in five fractions for rectum V6Gy. Uncorrected rotation, Runcorr$R_{uncorr}$ induced residual dose error, ΔDResidual$\Delta D_{Residual}$ , resulted in less dose to CTV and PTV in 43% and 59% treatment fractions, respectively, and more dose to bladder and rectum in 51% and 53% treatment fractions, respectively. The cumulative dose over five fractions, ∑D( Tres$T_{res}$ + Runcorr$R_{uncorr}$ ) and ∑D( Tres$T_{res}$ ), was always within 5% of the planned dose for all four structures for every patient.ConclusionsThe dosimetric impact of tumor rotation on a large prostate cancer patient cohort was quantified in this study. These results suggest that the standard 3-5 mm CTV-PTV margin was sufficient to account for the intrafraction prostate rotation observed for this cohort of patients, provided an appropriate gating threshold was applied to correct for translational motion. Residual dose errors due to uncorrected prostate rotation were small in magnitude, which may be corrected using different treatment adaptation strategies to further improve the dosimetric accuracy.

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Dataset Information

Dosimetric impact of uncorrected systematic yaw rotation in VMAT for peripheral lung SABR.

Publications

Dosimetric impact of uncorrected systematic yaw rotation in VMAT for peripheral lung SABR.

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