Dose-volume and complication in interstitial implants for breast carcinoma

Area of Science:

• Radiation Oncology
• Medical Physics
• Breast Cancer Treatment

Background:

• External beam radiation combined with interstitial iridium-192 boosts is common for breast cancer.
• Smaller tumors (T1-T2) have low complication rates with this technique.
• Advanced stages require larger volumes and higher doses, increasing complication incidence.

Purpose of the Study:

• To investigate dose-volume relationships in interstitial breast radiotherapy.
• To correlate these relationships with soft tissue radiation injury risk.
• To offer a method for clinical evaluation of interstitial implants.

Main Methods:

• Retrospective analysis of 111 breast cancer patients (5 with complications, 51 without).
• Calculation of tissue volumes enclosed by isodose surfaces (10-50 Gy).
• Development of a complication probability curve using a linear logistic model based on the 20 Gy isodose surface.

Main Results:

• Mean tissue volume at specified dose levels was significantly higher (p<0.05) in patients with complications.
• A complication probability versus dose-volume curve, using the 20 Gy isodose surface, closely fitted the data (p<0.006).
• Calculated treatment volume effectively separates patients by complication probability.

Conclusions:

• Dose-volume analysis is a viable method for assessing soft tissue complication risk in interstitial breast radiotherapy.
• This method can be used for clinical risk assessment and inter-institutional comparisons.
• Treatment volume within the 20 Gy isodose surface predicts complication probability.