Application of biological effective dose (BED) to estimate the duration of symptomatic relief and repopulation dose equivalent in palliative radiotherapy and chemotherapy.
OBJECTIVE
To investigate the potential for mathematic modeling in the assessment of symptom relief in palliative radiotherapy and cytotoxic chemotherapy.


METHODS
The linear quadratic model of radiation effect with the overall treatment time and the daily dose equivalent of repopulation is modified to include the regrowth time after completion of therapy.


RESULTS
The predicted times to restore the original tumor volumes after treatment are dependent on the biological effective dose (BED) delivered and the repopulation parameter (K); it is also possible to estimate K values from analysis of palliative treatment response durations. Hypofractionated radiotherapy given at a low total dose may produce long symptom relief in slow-growing tumors because of their low alpha/beta ratios (which confer high fraction sensitivity) and their slow regrowth rates. Cancers that have high alpha/beta ratios (which confer low fraction sensitivity), and that are expected to repopulate rapidly during therapy, are predicted to have short durations of symptom control. The BED concept can be used to estimate the equivalent dose of radiotherapy that will achieve the same duration of symptom relief as palliative chemotherapy.


CONCLUSIONS
Relatively simple radiobiologic modeling can be used to guide decision-making regarding the choice of the most appropriate palliative schedules and has important implications in the design of radiotherapy or chemotherapy clinical trials. The methods described provide a rationalization for treatment selection in a wide variety of tumors.
Jones
Bleddyn
B
Department of Clinical Oncology, Imperial College School of Medicine, Hammersmith Hospital, London, UK.
Cominos
Matilda
M
Dale
Roger G
RG
D002277:Carcinoma / Q000188:drug therapy* / Q000532:radiotherapy*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000532:radiotherapy; D002295:Carcinoma, Transitional Cell / Q000188:drug therapy / Q000532:radiotherapy; D016014:Linear Models; D009369:Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D010166:Palliative Care / Q000706:statistics & numerical data*; D011853:Radiobiology; D012062:Relative Biological Effectiveness