Planning target volume density impact on treatment planning for lung stereotactic body radiation therapy.

Background: To evaluate the impact of the planning target volume (PTV) density on treatment planning for lung Stereotactic Body Radiation Therapy (SBRT).

Material And Methods: The PTV coverage was analyzed in two groups of 40 lung SBRT patients. One group had PTV density <0.5 g/cm, while the other group had PTV density >0.5 g/cm. The treatments were planned in Pinnacle 9.10, using the collapsed cone convolution (CCC) algorithm. The prescribed dose was 60 Gy to the PTV in 4-8 fractions. Respecting constraint for the PTV coverage (D98% > 95%), we compared changes in the isodose line prescription, the number of monitor units (MU), maximum dose (), irradiated volume covered with 30 Gy (), and the optimization planning volume (OPV).

Results: For the same median values of the PTV coverage (98.3%), the differences are presented with median values between lower and higher density than 0.5 g/cm. The isodose line prescription was 83 90% ( < 0.0001), the MUs were 2294 1655 MU ( < 0.0001), was 74.26 68.09 Gy ( < 0.0001), was 117.03 104.81 cc ( = 0.04), and OPV was 28.48 39.35 cc ( < 0.001). By overriding the ITV density to 0.8 g/cm, the isodose line prescription decreases. The and MUs decrease by 7%, by 34%, and OPV by 70%.

Conclusion: To obtain similar PTV coverage for PTV which is <0.5 g/cm, a larger margin irradiating a large OPV was used. More MUs and a higher maximum dose were delivered. For the PTV density of ≤0.36 g/cm overriding is recommended to reduce the dose and irradiated volume.