A TCP‐NTCP estimation module using DVHs and known radiobiological models and parameter sets

Abstract

Radiotherapy treatment plan evaluation relies on an implicit estimation of the tumor control probability (TCP) and normal tissue complication probability (NTCP) arising from a given dose distribution. A potential application of radiobiological modeling to radiotherapy is the ranking of treatment plans via a more explicit determination of TCP and NTCP values. Although the limited predictive capabilities of current radiobiological models prevent their use as a primary evaluative tool, radiobiological modeling predictions may still be a valuable complement to clinical experience. A convenient computational module has been developed for estimating the TCP and the NTCP arising from a dose distribution calculated by a treatment planning system, and characterized by differential (frequency) dose‐volume histograms (DDVHs). The radiobiological models included in the module are sigmoidal dose response and Critical Volume NTCP models, a Poisson TCP model, and a TCP model incorporating radiobiological parameters describing linear‐quadratic cell kill and repopulation. A number of sets of parameter values for the different models have been gathered in databases. The estimated parameters characterize the radiation response of several different normal tissues and tumor types. The system also allows input and storage of parameters by the user, which is particularly useful because of the rapidly increasing number of parameter estimates available in the literature. Potential applications of the system include the following: comparing radiobiological predictions of outcome for different treatment plans or types of treatment; comparing the number of observed outcomes for a cohort of patient DVHs to the predicted number of outcomes based on different models/parameter sets; and testing of the sensitivity of model predictions to uncertainties in the parameter values. The module thus helps to amalgamate and make more accessible current radiobiological modeling knowledge, and may serve as a useful aid in the prospective and retrospective analysis of radiotherapy treatment plans.PACS number: 87.53.Tf

The photon dose calculation algorithm used in breast radiotherapy has significant impact on the parameters of radiobiological models

“…First, each homogeneous dose level of the dDVH was converted to a total dose delivered in 2 Gy fractions with the biological effective dose (BED) method, (22) with $\alpha /\beta =4.6\hspace{0.17em}\text{Gy}$ (23) . Next, the TCP was calculated using the Poisson model for an inhomogeneous dose distribution (24) using Eq. (1): $\text{TCP}=false(1/2false){\sum }_{\mathrm{normali}}{\mathrm{normalv}}_{\mathrm{normali}}\exp (2{\gamma }_{50}(1-{\mathrm{normalD}}_{\mathrm{normali}}/{\mathrm{normalD}}_{50})/\ln 2)$with ${\mathrm{v}}_{\mathrm{i}}$ the volume irradiated to a homogeneous dose ${\mathrm{D}}_{\mathrm{i}}$, ${\mathrm{D}}_{50}$ the dose that locally controls 50% of the tumors, and ${\gamma }_{50}$ the expected change in TCP if the dose changes by 1% around ${\mathrm{normalD}}_{50}$.…”

“…During the clinical follow‐up study, only the prescribed dose was known. Hence, the TCP of the homogeneous delivery of the prescription dose, (24) (i.e., 93.4%) was the reference TCP for further investigation, starting with its comparison to the mean ${\text{TCP}}_{\text{PBC}-\text{Hom}}$, using the Student's t ‐test.…”

Dosimetric performance of the new high‐definition multileaf collimator for intracranial stereotactic radiosurgery

“…DVHs may be a preliminary step in evaluating statistics such as tumor control and normal tissue complication probabilities. ( 5 , 6 ) However, when comparing a large number of plans, DVHs contain large amounts of data and make the comparison difficult and cumbersome.…”

A new plan quality index for dose painting radiotherapy

“…Biologically related models, such as tumor control probability (TCP) and normal tissue complication probability (NTCP), have been widely used for evaluating the quality of RT plans 20 , 21 , 22 . In particular, several studies addressed TCP models for an inhomogeneously irradiated tumor 23 , 24 .…”