M Goss*, M Trombetta, V Eisen, V Demartino, Allegheny Health Network, Pittsburgh, PA

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  M Goss

PO-GePV-T-317 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To compare dose metrics between tangent-breast plans calculated with Collapsed Cone (CC) and Monte Carlo (MC) algorithms.

Methods: 13 clinically-treated patients, whose plans had been calculated using the CC algorithm, were identified. These plans were copied and recalculated using MC. Various dose metrics were compared for targets and OARs, as well as the time necessary to perform each calculation. Special consideration was given to V105%, which is increasingly used as a predictor of skin toxicity and plan quality. Finally, both the CC and MC plans for four of the patients were delivered onto a phantom used to analyze quality assurance pass rate. The values were also compared.

Results: Metrics such as Planning target volume (PTV) D95% and V95% showed a variation of 3% or less between the CC and MC plans, while the PTV V100% and Ipsilateral Lung V20Gy showed slightly higher variations. Finally, the PTV V105% showed the highest variation, of up to a 593% increase after being recalculated with MC. The time necessary to perform calculations was longer for each CC plan than for the same plan that had been recalculated using MC. Also, QA pass rates using 2%2mm as well as 3%3mm gamma criteria for each CC plan were lower than for the same plan that had been recalculated using MC.

Conclusion: Our study showed that it is highly likely that PTV V105% values are in reality significantly higher than the values presented when the Collapsed Cone dose calculation algorithm is used in planning. Because this metric is often used as a benchmark for acceptability of plan quality and a predictor of toxicity, and because computational power and associated calculation time for Monte Carlo is no longer prohibitive, we can suggest that Monte Carlo be used as the standard dose calculation algorithm for tangent breast planning.

Keywords

Breast, Monte Carlo, Collapsed Cone Superposition

Taxonomy

TH- External Beam- Photons: treatment planning/virtual clinical studies

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