To gate or not to gate - dosimetric evaluation comparing Gated vs. ITV-based methodologies in stereotactic ablative body radiotherapy SABR treatment of lung cancerReport as inadecuate




To gate or not to gate - dosimetric evaluation comparing Gated vs. ITV-based methodologies in stereotactic ablative body radiotherapy SABR treatment of lung cancer - Download this document for free, or read online. Document in PDF available to download.

Radiation Oncology

, 11:125

Radiation Physics

Abstract

BackgroundTo compare retrospectively generated gated plans to conventional internal target volume ITV-based plans and to evaluate whether gated radiotherapy provides clinically relevant dosimetric improvements to organs-at-risk OARs.

MethodsEvaluation was performed of 150 stereotactic ablative radiotherapy treatment plans delivered to 128 early-stage T1-T3 <5 cm NSCLC patients. To generate gated plans, original ITV-based plans were re-optimized and re-calculated on the end-exhale phase and using gated planning target volumes PTV. Gated and ITV-based plans were produced for 3 × 18 Gy and 4 × 12 Gy fractionation regimens. Dose differences between gated and ITV-based plans were analyzed as a function of both three-dimensional motion and tumor volume. OARs were analyzed using RTOG and AAPM dose constraints.

ResultsDifferences between gated and ITV-based plans for all OAR indices were largest for the 3 × 18 Gy regimen. For this regimen, MLD differences calculated by subtracting the gated values from the ITV-based values ITV vs. Gated were 0.10 ± 0.56 Gy for peripheral island N = 57, 0.16 ± 0.64 Gy for peripheral lung-wall seated N = 57, and 0.10 ± 0.64 Gy for central tumors N = 36. Variations in V20 were similarly low, with the greatest differences occurring in peripheral tumors 0.20 ± 1.17 %. Additionally, average differences in 2Gy-equivalence between ITV and gated lung indices fell well below clinical tolerance values for all fractionation regimens, with no clinically meaningful differences observed from the 4 × 12 Gy regimen and rarely for the 3 × 18 Gy regimen <2 % of cases. Dosimetric differences between gated and ITV-based methods did generally increase with increasing tumor motion and decreasing tumor volume. Dose to ribs and bronchial tree were slightly higher in gated plans compared to ITV-based plans and slightly lower for esophagus, heart, spinal cord, and trachea.

ConclusionsAnalysis of 150 SABR-based lung cancer treatment plans did not show a substantial benefit for the gating regimen when compared to ITV-based treatment plans. Small benefits were observed only for the largest tumor motion exceeding 2 cm and the high dose treatment regimen 3 × 18 Gy, though these benefits did not appear to be clinically relevant.

KeywordsSABR Gating ITV-based planning Treatment planning AbbreviationsAAPMAmerican Association of Physicists in Medicine

CTVClinical target volume

GTVGross tumor volume

IMRTIntensity modulated radiation therapy

ITVInternal target volume

MLDMean lung dose

NSCLCNon small cell lung cancer

OAROrgan at risk

PTVPlanning target volume

PTVgatePlanning target volume for gating

RTOGRadiation Therapy Oncology Group

SABRStereotactic ablative body radiotherapy

V20Percent volume receiving 20 Gy

VMATVolume modulated arc therapy

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Author: Joshua Kim - Qixue Wu - Bo Zhao - Ning Wen - Munther Ajlouni - Benjamin Movsas - Indrin J. Chetty

Source: https://link.springer.com/







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