BIOSUITE, NEW SOFTWARE FOR RADIOBIOLOGICAL CUSTOMISATION OF DOSE AND FRACTON SIZE IN EBRT

Abstract

Purpose: BioSuite is a program developed to help clinicians to identify cases eligible for escalation and/or altered fractionation and to quantify this potential using biological models of normal tissue and tumour response to EBRT. Materials: BioSuite consists in a single executable file developed in C++. The input data are DVHs from a TPS (Philips Pinnacle) as well as a more general DVH format. Plans are defined by parameters such as the number of fractions or a default prescription dose. These DVHs are in turn associated with an endpoint defined by a biological model and a set of parameters. From these models (LKB, Relative Seriality and enhanced LQ Poisson TCP), evaluation of NTCP or TCP can be performed forwardly or inversely. The forward evaluation is made in real-time as the operator modifies plan or endpoint parameters. The inverse evaluation (or optimisation) finds the dose multiplication factor (DMP) rescaling the DVH or number of fractions of a given size which take the complication risk to a prior set level. An isotoxic can also be done, which consists of computing for a fraction-number range the highest DMP (and thus TCP) for a constant NTCP. An upper TCP limit can be set (e.g. 99%) to avoid excessive doses in particular cases. The operator can finally generate dose-response curves to visually assess plan quality. Isotoxic optimisation was applied to 33 plans from our institution whose DVHs were exported to BIOSUITE. Results: For most of these plans, scope for escalation and/or altered fractionation was found, suggesting these patients were undertreated. In cases with a very small tumour and consequently small volume of irradiated normal tissue, the models implemented in BioSuite suggested treatments very similar to those currently done in SBRT i.e. TCP close to 100% for as low as 3 fractions. Serial organ DVHs in the plan can drastically affect the BIOSUITE fractionation strategy, making hypofractionation no longer viable.