Purpose: Whole-lung radiation therapy possess a unique challenge for treatment planning due to the size of the target, the proximity of the organs at risk (OARs) and the high radiosensitivity of the lungs. The purpose of this work is to propose a novel field arrangement for whole-lung radiation therapy to maximize OAR sparing.
Methods: A 19 year old with metastatic synovial sarcoma was simulated using 4DCT and prescribed 15 Gy in 10 fractions to total lung using VMAT. The internal target volume (ITV) was defined from MinIP including all lung tissue and primary disease, with the planning target volume (PTV) created from ITV with a 1 cm margin. Beam isocenter was placed between the lungs at approximately midplane. Two arcs with 90 degree collimation and asymmetric jaws were used to maximize heart blocking while keeping X jaw field sizes to less than 15 cm. An additional two arcs with +/- 5 degree collimator rotations were added with asymmetric jaws to provide field overlap while also maintaining X jaw fields size less than 15 cm. Plan was optimized for a TrueBeam linac using 6MV photons and air cavity correction. In-vivo transit dosimetry was recorded using the EPID and analyzed with SunNuclear PerFraction.
Results: ITV coverage was V100%=99.3%, with ITV+5mm receiving V100%=98.9% and PTV D95%=97.6%. The PTV mean dose was 101.7%, with V105% below 2%, and Dmax=108%. The mean dose to the heart was 8.38 Gy with V10Gy=37.3%. The mean doses to the esophagus, liver, and kidneys were 8.91, 7.97 Gy, and 2.28 Gy respectively. The maximum dose to the spinal cord was 13.91 Gy. All fractions passed (>95%) in-vivo dosimetry 2D gamma analysis at 3%/2mm indicating accurate delivery.
Conclusion: An optimized field arrangement and isocenter placement allows for excellent coverage of whole-lung RT without compromising mediastinal OAR sparing.
Treatment Planning, Lung, Transit Dosimetry
TH- External Beam- Photons: treatment planning/virtual clinical studies