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On cold spots in tumor subvolumes
Wolfgang A Tomé1, Jack F Fowler
1Department of Human Oncology, University of Wisconsin Medical School, CSC, Madison 53792, USA. tome@mail.humonc.wisc.edu
Medical Physics
|August 1, 2002
Summary
Even small cold spots (1% of tumor volume) receiving significantly lower doses can drastically reduce tumor control probability (TCP). Careful attention to these cold regions is crucial in radiotherapy planning to maintain treatment efficacy.
Area of Science:
- Radiation oncology
- Medical physics
Background:
- Intensity-modulated radiotherapy (IMRT) can create cold spots in target volumes, particularly near critical structures.
- These cold spots, even if small, can compromise tumor control probability (TCP).
Purpose of the Study:
- To quantify the impact of cold spots (varying in size and dose deficit) on TCP and effective uniform dose (EUD).
- To determine critical thresholds for dose deficits in small target volumes.
Main Methods:
- Utilized the Niemierko-Goitein linear-quadratic model with a gamma50 slope of 1-3.
- Employed two-bin and four-bin differential dose-volume histogram (DVH) models to simulate cold spots.
- Varied cold spot dose deficits from 1% to 50% and fractional volumes from 1% to 90%.
Main Results:
- TCP decreased rapidly with increasing dose deficit, even for cold spots as small as 1% of the tumor volume.
- In a four-subvolume model (80% target at 10% boost), a 1% cold volume deficit >20% significantly reduced TCP and EUD.
- Moderate loss in TCP and EUD occurred for a 1% subvolume deficit <20%.
Conclusions:
- Small-volume cold regions with significant dose deficits pose a substantial risk to tumor control.
- Radiotherapy planning must carefully address and minimize dose deficits in small target volumes.
- Constraining the target's effective uniform dose (EUD) to be at least the prescription dose can mitigate the negative effects of cold spots.