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  4. Dosmetric Considerations in Incorporating Accurate Lung Density for Non-Small-Cell Lung Cancer (NSCLS) Using SBRT with Different Dose Computation Algorithms and Changes From Dose Calibration (dose-To-Muscle) to (dose-To-Water) Methodologies

Dosmetric Considerations in Incorporating Accurate Lung Density for Non-Small-Cell Lung Cancer (NSCLS) Using SBRT with Different Dose Computation Algorithms and Changes From Dose Calibration (dose-To-Muscle) to (dose-To-Water) Methodologies

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

Presentations

(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: The differences in the dose computation algorithms for lung SBRT protocols needs to be studied so that clinical protocols can adjust the dose specification in a clinic before migrating either from heterogeneity off computations to heterogeneity ON as well as the changes expected from migrating from specification of dose in medium rather than in muscle.

Methods: SBRT lung treatment plans of 255 patients (M/F 125/130) with heterogeneities off were recomputed with same parameters including MUs but utilizing CT HU values using 2 dose computation algorithms viz. AAA (dose to muscle) algorithm and Acuros-XB (dose to water) algorithm on Eclipse treatment planning system. Computed dose to the tumor and various OARs were then compared with clinical plans. ICRU-83 dosimetric indices were also compared.

Results: When heterogeneity corrections were applied, the dose received by 95% of the planning target volume (PTV), decreased from 100.3±0.8% to 99.3±4.5% (AAA) and to 99±6% (Acuros-XB). The maximum dose received by any point ≥2 cm from the PTV changed from 52.5±6.6% (heterogeneity off) to 56±7.5% and 56.4±8.5% with AAA & Acuros-XB, respectively. The volume outside of the PTV receiving greater than 105% of the prescribed dose was 2.0±2.7 cm3 (heterogeneity off); however, this value increased to 3.2±3.9 cm3 with AAA and decreased to 3.4±4.1 cm3 with Acuros-XB. Homogeneity index (HI) increased from 0.2±0.0 (heterogeneity off) to 0.3±0.1 (AAA algorithm) and 0.3±0.1 (Acuros-XB). Similarly, maximum spinal cord dose increased from 5.8±4.3 Gy to 6.9±4.9 Gy (AAA) and 6.7±4.8 Gy (Acuros-XB). Lung V20 changed from 2.8 ± 2.1% to 3.1 ±2.4% (AAA) and 3.1 ± 2.4% (Acuros-XB).

Conclusion: The change between AAA and AcurosXB is minor compared to the change between heterogeneity correction off to AAA. It is unlikely that any significant changes will be required to current dose limits in transitioning from AAA to AcurosXB.

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