D Baldassari*, C Esquivel, L Patton, A Tipton, T Roberts, Texas Oncology San Antonio, San Antonio, TX

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  D Baldassari

PO-GePV-T-229 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: Assess the use of a novel automated software in the treatment planning system to evaluate hypofractionated plans using conventional constraints.

Methods: Eighteen Eclipse(v15.5) hypofractionated treatment plans of varying sites and dose per fraction regimens were retrospectively reviewed using Radformation’s plan check software, ClearCheck(v1.67). The hypofractionated doses were compared to conventional 2Gy constraints using Equivalent-Dose(EQD2) formula, EQD2=TD[(d+α/β)/(2+α/β)], where the α/β=2. Within each treatment plan, EQD2 doses from ClearCheck were evaluated for soundness, accuracy, and consistency.

Results: Variation in values of EQD2 doses determined by ClearCheck, compared to calculated values for the 18 plans, ranged between ±0.1cGy. Software-reported values demonstrated accuracy in the calculation itself and consistency amongst plans. In one plan, hypofractionated doses were within the defined objectives in ClearCheck. Subsequent conversion to the EQD2 however, indicates values just slightly in excess of the tolerances in ClearCheck for two critical structures. In theory, EQD2 values should be greater than the doses from the hypofractionated treatment plan. Invalid EQD2 values were observed for structures that were receiving doses less than 2Gy per fraction.

Conclusion: ClearCheck is a convenient tool in the evaluation of hypofractionated plans and the conversion to conventional 2Gy-fraction constraints. Along with the user’s ability to modify the α/β ratio, there is an instantaneous assessment of EQD2. With control in the manner reported, a planner is also able to ensure critical structure constraints are expressed in terms of maximum dose, mean dose, or dose for a specified volume, all essential for the conversion of EQD2 doses. While the EQD2 values are accurately calculated within the software, opportunity for erroneously reported values does, however, exist. In these instances, such as with normal tissues objectives receiving less than 2Gy/fraction, a warning should be provided, alerting the user of the priority in verifying the validity of results.

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Keywords

Not Applicable / None Entered.

Taxonomy

TH- External Beam- Photons: General (most aspects)

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