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Implenting Dosimetric Quality Index in Lattice Radiotherapy Treatments

M Banos-capilla*, J Lago-martin, J Bea-gilabert, L Ros-garcia, L Larrea-rabassa, E Lopez-munoz, P Antonini, V Gonzalez-vidal, M Berenguer, Hospital Vithas NISA Virgen del Consuelo ValenciaES,

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
To implement Lattice Radiotherapy Treatment (LTR) establishing a dosimetry quality criteria
LTR consists on administration of a near maximum dose (V2%) from 15Gy to 18Gy in a single fraction over at least 5 points distributed inside of GTV, concomitant with PTV treatment delivered in standard fractionation.
Treatment planning and reporting need to establish some specific volumes of interest:
LTV (Lattice Tumor Volume): structure where the overdose volume is located.
VTV (Vertex Tumor Volume): set of 1cm diameter spheres placed inside LTV and separated by 2.5cm to 3.0 cm
VV (Valley Volume): subtraction of LTV-VTV.
A theoretical study of the dose distribution has been carried out analyzing the impact of vertices distance and the dose prescribed to PTV.

Methods:
A node structure has been defined following diamond crystal lattices with adjacent center distance from 20 to 35mm. Each node serves as the center to generate a 1cm diameter sphere that constitutes the VTV. These templates can be automatically imported over the LTV by means a RTPS automatic routine.

Results:
Different lattice node distance and PTV Dose combinations dose have been calculated and as a result we have settled the planning objectives and the treatment quality metric:
The Vertex Index (VI), defined as the ratio D50%/D2% must be >0.75 in VTV
V8Gy <30% of VV
V5Gy<50% of PTV
In VTV 1% To achieve the dosimetric objectives, keeping PTV dose between 2 and 3Gy, the vertices separation must be between 25mm and 30mm. Once we established these parameters in a phantom we applied quality criteria in real patients.

Conclusion:
According to the degree of modulation achieved by the treatment unit, the geometric distribution of the vertices must be analyzed prior to settle LTR technique. This gradient dose schedules requires elevated modulation dosimetry that must be prior verified with high-resolution detection systems.

Download ePoster [PDF]

Funding Support, Disclosures, and Conflict of Interest: Travelling costs support by BIOTERRA

Keywords

Treatment Techniques, Intensity Modulation, Inverse Planning

Taxonomy

TH- External Beam- Photons: Development (new technology and techniques)

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