Radiotherapy adapted to spatial and temporal variability in tumor hypoxia.
OBJECTIVE
To explore the feasibility and clinical potential of adapting radiotherapy to temporal and spatial variations in tumor oxygenation.


METHODS
Repeated dynamic contrast enhanced magnetic resonance (DCEMR) images were taken of a canine sarcoma during the course of fractionated radiation therapy. The tumor contrast enhancement was assumed to represent the oxygen distribution. The IMRT plans were retrospectively adapted to the DCEMR images by employing tumor dose redistribution. Optimized nonuniform tumor dose distributions were calculated and compared with a uniform dose distribution delivering the same integral dose to the tumor. Clinical outcome was estimated from tumor control probability (TCP) and normal tissue complication probability (NTCP) modeling.


RESULTS
The biologically adapted treatment was found to give a substantial increase in TCP compared with conventional radiotherapy, even when only pretreatment images were used as basis for the treatment planning. The TCP was further increased by repeated replanning during the course of treatment, and replanning twice a week was found to give near optimal TCP. Random errors in patient positioning were found to give a small decrease in TCP, whereas systematic errors were found to reduce TCP substantially. NTCP for the adapted treatment was similar to or lower than for the conventional treatment, both for parallel and serial normal tissue structures.


CONCLUSIONS
Biologically adapted radiotherapy is estimated to improve treatment outcome of tumors having spatial and temporal variations in radiosensitivity.
Søvik
Aste
A
Department of Medical Physics, The Norwegian Radium Hospital, Oslo, Norway.
Malinen
Eirik
E
Skogmo
Hege K
HK
Bentzen
Søren M
SM
Bruland
Oyvind S
OS
Olsen
Dag Rune
DR
D000818:Animals; D015687:Cell Hypoxia / Q000502:physiology*; D004285:Dogs; D004307:Dose-Response Relationship, Radiation; D005240:Feasibility Studies; D008279:Magnetic Resonance Imaging / Q000379:methods; D011336:Probability; D011836:Radiation Tolerance; D050397:Radiotherapy, Intensity-Modulated; D012189:Retrospective Studies; D012509:Sarcoma / Q000532:radiotherapy*