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  5. Impact of Incorporating Accurate Density of Lung During Treatment Planning for Non-Small Cell Lung Cancer (NSCLC) Using SBRT with Different Dose Computation Algorithms and ICRU-83 Reporting Standards

Impact of Incorporating Accurate Density of Lung During Treatment Planning for Non-Small Cell Lung Cancer (NSCLC) Using SBRT with Different Dose Computation Algorithms and ICRU-83 Reporting Standards

H Malhotra*, D Mohatt , A Singh , J Gomez , Roswell Park Cancer Institute, Buffalo, NY

Presentations

(Tuesday, 7/31/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 4

Purpose: A large percentage of clinical data for lung cancer, treated by SBRT, has been determined without incorporating the lung density. While new clinical protocols are demanding incorporation of heterogeneity corrections, new computation algorithms are proposing specification of dose in medium rather than in muscle.

Methods: The treatment plans of 118 patients with heterogeneities off were retrospectively computed with same parameters including MUs but utilizing actual lung density using 2 dose computation algorithms viz. AAA (dose to muscle) algorithm and Acuros-XB (dose to water) algorithm on Eclipse treatment planning system. Actual dose computed to the tumor and various OARs were then compared with clinical plans. Various dosimetric indices from ICRU-83 were also compared.

Results: Analysis of 118 patients reveals that with heterogeneity corrections applied, the dose received by 95% of the planning target volume (PTV), decreased from 100.4±1.6% to 99.0±4.2% (AAA) and to 95.4±5.1% (Acuros-XB). Similarly, the maximum dose received by any point ≥2 cm from the PTV changed from 51.6±6.7% (heterogeneity off) to 53.8±7.6% and 51.7±6.8% with AAA & Acuros-XB, respectively. The volume outside of the PTV receiving greater than 105% of the prescribed dose was 1.69±1.87 cm3 without heterogeneity corrections; however, this value increased to 2.48±2.49 cm3 with AAA and decreased to 1.11±1.20 cm3 with Acuros-XB. Homogeneity index (HI) increased from 0.17±0.02 (heterogeneity off) to 0.24±0.03 (AAA algorithm) and 0.26±0.04 (Acuros-XB). The maximum dose received by the spinal cord increased from 3.01±2.03 Gy to 3.50±2.34 Gy (AAA) and 3.33±2.13 Gy (Acuros-XB). Lung V20 changed from 1.25 ± 0.88% to 1.32 ± 0.97% (AAA) and 1.85 ± 1.33% (Acuros-XB).

Conclusion: Numerical values of standard lung SBRT parameters are not only different with heterogeneity applied but are also sufficiently different between AAA and Acuros-XB to merit consideration of changes in dosimetric planning coverage parameters & OAR doses.

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