Spatial aspects of combined modality radiotherapy.
OBJECTIVE
A combined modality radiotherapy (CMRT) incorporates both external beam radiotherapy (EBT) and targeted radionuclide therapy (TRT) components. The spatial aspects of this combination were explored by utilising intensity modulated radiotherapy (IMRT) to provide a non-uniform EBT dose distribution.


METHODS
Three methods of prescribing the required non-uniform distribution of EBT dose are described, based on both physical and biological criteria according to the distribution of TRT uptake. The results and consequences of these prescriptions are explored by application to three examples of patient data.


RESULTS
The planning procedure adopted allowed IMRT plans to be produced that met the prescription requirements. However, when the treatment was planned as a CMRT, compared with the use of EBT alone, more satisfactory target doses could be achieved with lower doses to normal tissues. The effects of errors in EBT delivery and in the functional data were found to cause a non-uniform prescription to tend towards the uniform case.


CONCLUSIONS
The methods and results are relevant for more general biological treatment planning, in which IMRT may be used to produce dose distributions prescribed according to tumour function. The effects of delivery and dose calculation errors can have a significant impact on how such treatments should be planned.
Bodey
Rachel K
RK
Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Surrey, UK.
Evans
Phil M
PM
Flux
Glenn D
GD
D001918:Brachytherapy; D019583:Dose Fractionation, Radiation; D006801:Humans; D009447:Neuroblastoma / Q000532:radiotherapy; D010235:Paraganglioma / Q000532:radiotherapy; D010347:Patient Care Planning; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013964:Thyroid Neoplasms / Q000532:radiotherapy; D016896:Treatment Outcome