Risk-adaptive optimization: Selective boosting of high-risk tumor subvolumes

Abstract

Background and purpose-A tumor subvolume-based, risk-adaptive optimization strategy is presented.Methods and materials-Risk-adaptive optimization employs a biological objective function instead of an objective function based on physical dose constraints. Using this biological objective function, TCP is maximized for different tumor risk regions while at the same time minimizing NTCP for organs at risk (OAR). The feasibility of risk-adaptive optimization was investigated for a variety of tumor subvolume geometries, risk-levels, and slopes of the TCP curve. Furthermore, the impact of a correlation parameter, δ, between TCP and NTCP on risk-adaptive optimization was investigated.Results-Employing risk-adaptive optimization, it is possible in a prostate cancer model to increase EUD by up to 35.4 Gy in tumor subvolumes having the highest risk classification without increasing predicted normal tissue complications in organs at risk. For all tumor subvolume geometries investigated, we found that the EUD to high-risk tumor subvolumes could be increased significantly without increasing normal tissue complications above those expected from a treatment plan aiming for uniform dose coverage of the PTV. We furthermore found that the tumor subvolume with the highest risk classification had the largest influence on the design of the risk-adaptive dose distribution. The parameter δ had little effect on risk-adaptive optimization. However, the clinical parameters D 50 and γ 50 that represent the risk classification of subtumor volumes had the largest impact on risk-adaptive optimization.Conclusions-On the whole, risk-adaptive optimization yields heterogeneous dose distributions that match the risk level distribution of different subvolumes within the tumor volume.

On the impact of functional imaging accuracy on selective boosting IMRT

“…Ref. 5 for the details), utilize a prescription of 39 fx / 2 Gy to 98% PTV, which is based on the IMRT dose prescription used in Ref. [21].…”

“…Currently, the integration of biological information into radiotherapy (RT) treatment planning with the aim of boosting high-risk tumor subvolumes is of great interest [1][2][3][4][5][6][7][8] -this concept has been termed either 'selective boosting' [4][5][6] or 'dose painting' [7][8]. To achieve selective boosting IMRT based on patient-specific biological information, the following techniques and methods have to be available: a highly conformal RT delivery technique, a method to decide on the boosting level, and a functional or molecular imaging modality having high imaging accuracy.…”

“…The boosting level for high-risk tumor subvolumes can be determined in one of three ways: 1) based on radiobiological optimal trade-off between tumor control probability (TCP) and normal tissue complication probability (NTCP) by using clinical parameters [5,[11][12][13][14][15], 2) based on functional imaging intensity for high risk tumor subvolumes (i.e. a prescription function is deduced from functional imaging intensities) [8], and 3) based on clinical experience (i.e.…”

Volumetric-modulated arc therapy (RapidArc) vs. conventional fixed-field intensity-modulated radiotherapy for 18F-FDG-PET-guided dose escalation in oropharyngeal cancer: A planning study

“…6 The anticipated toxicity would be reduced because the volumes receiving very high radiation doses would be significantly smaller. 7 The success of a focal dose escalation strategy would depend on the accurate detection of these biologically radioresistant regions. This could be achieved with functional imaging techniques, such as fluorine-18-fluorodeoxyglucose-positron emission tomography ( 18 F-FDG-PET).…”

Comprehensive Approach to Coregistration of Autoradiography and Microscopy Images Acquired from a Set of Sequential Tissue Sections

“…Specific biomarker probes can be administered and visualized in vivo with the aid of functional imaging modalities such as PET. In addition, it has been suggested that the efficacy of radiation treatment may be increased considerably by creating and delivering heterogeneous dose distributions based on PET data (1)(2)(3). However, until now, only phase I dose escalation trials based on 18 F-FDG imaging have been conducted (4,5).…”