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. 2023 Jun 9;8(6):101281.
doi: 10.1016/j.adro.2023.101281. eCollection 2023 Nov-Dec.

Plan Assessment Metrics for Dose Painting in Stereotactic Radiosurgery

Benjamin Z Tham  1 , Dionne Aleman  1 , Håkan Nordström  2 , Nelly Nygren  2 , Catherine Coolens  3
Affiliations

Plan Assessment Metrics for Dose Painting in Stereotactic Radiosurgery

Benjamin Z Tham et al. Adv Radiat Oncol. .

Abstract

Purpose: As radiation therapy treatment precision increases with advancements in imaging and radiation delivery, dose painting treatment becomes increasingly feasible, where targets receive a nonuniform radiation dose. The high precision of stereotactic radiosurgery (SRS) makes it a good candidate for dose painting treatments, but no suitable metrics to assess dose painting SRS plans exist. Existing dose painting assessment metrics weigh target overdose and underdose equally but are unsuited for SRS plans, which typically avoid target underdose more. Current SRS metrics also prioritize reducing healthy tissue dose through selectivity and dose fall-off, and these metrics assume single prescriptions. We propose a set of metrics for dose painting SRS that would meet clinical needs and are calculated with nonuniform dose painting prescriptions.

Methods and materials: Sample dose painting SRS prescriptions are first created from Gamma Knife SRS cases, apparent diffusion coefficient magnetic resonance images, and various image-to-prescription functions. Treatment plans are found through semi-infinite linear programming optimization and using clinically determined isocenters, then assessed with existing and proposed metrics. Modified versions of SRS metrics are proposed, including coverage, selectivity, conformity, efficiency, and gradient indices. Quality factor, a current dose painting metric, is applied both without changes and with modifications. A new metric, integral dose ratio, is proposed as a measure of target overdose.

Results: The merits of existing and modified metrics are demonstrated and discussed. A modified conformity index using mean or minimum prescription dose would be suitable for dose painting SRS with integral or maximum boost methods, respectively. Either modified efficiency index is a suitable replacement for the existing gradient index.

Conclusions: The proposed modified SRS metrics are appropriate measures of plan quality for dose painting SRS plans and have the advantage of giving equal values as the original SRS metrics when applied to single-prescription plans.

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Conflict of interest statement

Håkan Nordström and Nelly Nygren are employees of Elekta Instrument AB.

Figures

Figure 1
Figure 1
Example isodose lines to illustrate the differences in calculating using minimum or mean. (A) A clinical plan with a single prescription of 21 Gy. (B) A dose painting plan with minimum and mean prescriptions of 21 and 24.15 Gy, respectively. The voxel color indicates the prescribed dose, and isodose lines are based on the treatment plan dose.
Figure 2
Figure 2
Example histograms to illustrate the differences in assessments for clinical single-dose prescriptions and for dose painting by numbers prescriptions. The quality volume histograms and dose volume histograms are for the target and planning target volume surrounding the target.
Figure 3
Figure 3
Correlation matrix for applicable assessment metrics.
Figure 4
Figure 4
Comparison between mean- and minimum-oriented metrics for (A) Paddick conformity index, (B) gradient index, and (C) efficiency index calculated for dose painting plans, with clinical plans marked in △. The data set is separated by dose painting dose boost level and by case to illustrate the effect on each metric.
Figure 5
Figure 5
Comparison between quality factor (QF)hot and QFhot,150%, with clinical plans marked in △.
See this image and copyright information in PMC

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