J Cammin¹*, T Bouton², E Chacko³, E Paranada⁴, B Zhang⁵, S Chen⁶, J Molitoris⁷, B Yi⁸, (1) University of Maryland, Baltimore, MD, (2) Maryland Proton Treatment Center, ,,(3) Maryland Proton Treatment Center, ,,(4) University of Maryland Medical Center, ,,(5) University of Maryland School of Medicine, Baltimore, MD, (6) University of Maryland School of Medicine, Baltimore, MD, (7) University of Maryland School of Medicine, Baltimore, ,(8) University of Maryland School of Medicine, Baltimore, MD

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  J Cammin

TU-I345-IePD-F4-2 (Tuesday, 7/12/2022) 3:45 PM - 4:15 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 4

Purpose: To evaluate different planning strategies for head-and-neck radiation with volumetric-modulated arc therapy for robustness against dosimetric uncertainties from inter-fractional variations in shoulder positioning.

Methods: Clinical plans from 10 patients were replanned in the RayStation v10A treatment planning system (TPS) using the clinical ‘base’ plan (no shoulder-avoidance), and two shoulder-sparing approaches: (a) ‘shoulder-PRV’: adding a shoulder-block structure to the optimizer, and (b) ‘shoulder-protect’: using a feature in the TPS that closes the MLC’s over the protected structure to avoid entrance dose. Inter-fractional shoulder motion was estimated from setup CBCT acquired just before the patients’ treatments. Dosimetric robustness of the three planning approaches was assessed by recalculating dose on the setup CBCT’s and comparing target coverage and OAR doses between the first fraction and subsequent treatment fractions.

Results: The clinical base plans exhibited considerable variations in the target DVH’s from fraction to fraction, including outliers when shoulder position varied strongly from the initial position. For example, in one patient the dose D2% to the target was 115% of the prescription dose for the fraction with largest shoulder motion but was reduced to a maximum of 112% (shoulder-PRV) and 110% (shoulder-protect), respectively. Both shoulder-sparing techniques reduced variability in target coverage and OAR doses. On average, the standard deviations were reduced by 20% (PTV D95%), 29% (PTV mean dose), and 13% (D0.03cc to spinal cord) relative to the standard deviations of the base plan without shoulder-avoidance. Mean dose to the shoulders was reduced by 37% on average with the shoulder-sparing planning approaches.

Conclusion: Shoulder-sparing planning techniques should be applied in treatment planning for head-and-neck radiation with volumetric-modulated arc-therapy to achieve dosimetric robustness against inter-fractional shoulder displacement.

Keywords

Treatment Planning, Intensity Modulation, Setup Errors

Taxonomy

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

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