Volume and time factors in interstitial gamma-ray therapy.

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Established principles in interstitial gamma-ray implantation dictate relationships between time-dose and volume.
• Two classical assumptions guide treatment planning: dose reduction at high dose rates and dose decrease with increased volume.

Purpose of the Study:

• To critically examine the validity of two long-standing assumptions in interstitial gamma-ray therapy based on recent publications.
• To evaluate the necessity of total dose reduction at high dose rates and dose adjustment for varying lesion volumes.

Main Methods:

• Review and analysis of recent clinical publications and experiences in interstitial gamma-ray therapy.
• Comparison of current clinical findings with traditional time-dose and volume-dose principles.

Main Results:

• The assumption that total dose must be reduced when dose rate exceeds 6,000-7,000 rads/seven days is not clinically substantiated.
• Total dose appears to be the primary determinant of treatment efficacy; dose rates can be increased significantly without altering total dose.
• The principle of decreasing dose with increasing volume is not rigidly applicable to interstitial gamma-ray therapy; larger lesions may necessitate higher doses.

Conclusions:

• Total dose is the critical parameter in interstitial gamma-ray therapy, not the dose rate.
• Dose compensation for volume is not always necessary; larger lesions may require higher doses for effective treatment.
• Adherence to these revised principles can lead to a higher percentage of controlled lesions.