Hypoxia dose painting by numbers: a planning study

Abstract

Purpose: To investigate the feasibility of different hypoxia dose painting strategies in head-and-neck radiotherapy; the potential benefit was limited by the stipulation of isotoxicity with respect to the conventional intensity-modulated radiotherapy (IMRT) treatment.

Methods and materials: Thirteen head-and-neck cancer patients were included into the planning study. For each patient, three different treatment plans were created: a conventional IMRT plan, an additional uniform dose escalation (uniDE) of 10% to the fluorodeoxyglucose (FDG)-positive volume, and a plan in which dose painting by numbers (DPBN) was implemented. Dose painting by numbers was realized according to a map of dose-escalation factors calculated from dynamic [(18)F]-fluoromisonidazole (FMISO) positron emission tomography data.

Results: Both dose-escalation approaches were shown to be feasible under the constraint of limiting normal tissue doses to the level of conventional IMRT. For DPBN, the prescriptions could be fulfilled in larger regions of the target than for uniDE. Fluorodeoxyglucose-positive volumes had sizes up to 94 cm(3). In contrast, regions receiving comparable dose levels with DPBN presented volumes in the range of 0-2.7 cm(3). Overtreatment of the target was observed with uniDE in most of the cases, whereas some regions did not receive the required dose to overcome hypoxia-induced radiation insensitivity. Tumor control probability increased from 55.9% with conventional IMRT to 57.7% for the uniDE method in the patient group. For DPBN, a potential increase in tumor control probability from 55.9% to 70.2% was determined. Therefore, DPBN seems to result in higher benefits for the patients.

Conclusion: Dose painting by numbers delivers the dose more effectively than an additional uniform boost to the FDG-positive area. If hypoxia could be adequately quantified with a simple imaging technique like FMISO positron emission tomography, DPBN in head-and-neck cancer could substantially increase tumor control.