Summary of meeting on “Radiobiological modelling in treatment planning” at the BIR on 12 December 2006

Abstract

The subject was covered more widely than the terse title suggests. One might say that radiobiological treatment planning involves most of radiobiology and all of radiation pathology. There was much of interest from seven excellent speakers. Modelling is now entirely respectable scientifically, being used in economic and weather forecasting, climate, voting predictions and cosmology. For radiotherapy, modelling is highly practical and is necessary in optimization of treatment plans and in any new modality being developed. The first speaker, Prof. Bleddyn Jones (Birmingham), spoke on ‘‘The clinical aspects, what should modelling provide?’’ The answer was greater confidence in clinical decision making, especially now, when new treatments are breaching standard methods. Intensity-modulated radiation therapy (IMRT ) involves essentially ‘‘simultaneous boost in a field’’ and so depends on non-standard dose per fraction for selected subvolumes. We need to know how much improvement in tumour control probability (TCP) might be expected, and how much increase or decrease in normal tissue complication probability (NTCP). Although absolute values of these in percentage points cannot be predicted accurately, their ranking order can be helpful in optimization of treatment planning already. He pointed out that tumour cure statistics have provided much of the data for modelling, but that tumour regrowth delay data can be useful too. His list of practical current uses for modelling with BED (biologically effective dose) included the following ‘‘bullets’’: treatment gap compensation; correction of treatment dose delivery errors; choice of dose per fraction in altered radiotolerance; comparative assessments of dose–time fractionation schedules; assessment of new techniques; analysis of optimum dose per fraction; dose rate compensations; and high linear energy transfer (LET) compensations. All these are now being aided by active modelling. Dr Danielle Powers (Hammersmith Hospital) gave a beautifully illustrated presentation on ‘‘The clinical perspective of radiobiological modelling’’. She described the recent technological developments in radiotherapy (imaging, positioning devices, forward and inverse planning programmes, tumour tracking and real-time dose recording) and listed seven ‘‘bullets’’ of modern treatment delivery: 3D conformal RT; intensity-modulated RT; brachytherapy at HDR (high dose rate); respiratory gating; stereotactic bodyframe RT; proton beam (and heavy-ion) RT; and 4D RT (tumour size tracking). She emphasized the potential advantages but the present uncertainties of predicting individual patient’s radiosensitivities. Her final emphasis was on the necessity for further accurate data collection. An interinstitutional data bank of treatment protocols and outcomes was needed, for which the Academic Clinical Oncology and Radiobiology Research Network (ACORRN) could be helpful. Prof. John Hopewell (Oxford) showed that revisiting old (30 years) radiobiological experimental animal data (from the acknowledged peacefulness of partial retirement) could lead to fresh insights. His special contribution had been to show that repair of radiobiological damage after irradiation is not monoexponential but consists of two (or more) rates of repair, most simply one of 5–15 min and a slow one of 3–5 h. It was not allowing for these which has led to much confusion about repair. Prof. Alan Nahum (Clatterbridge) described assumptions involved in calculating TCP and NTCP for various radiotherapy situations. He mentioned the BIOPLAN programme (published by himself and Beatriz SanchezNieta), which they generously offer from alan.nahum@ccotrust.nhs.uk and which the present reporter has used successfully for clinical cases. He mentioned that hypofractionation (fewer and larger fractions) is appropriate in certain limited circumstances and can save resources. Address correspondence to: Jack F Fowler, University of Wisconsin Medical School, Madison, USA. E-mail: jackfowler@btinternet.com The British Journal of Radiology, 81 (2008), 89–90