Dose Accumulation for Pelvic Stereotactic Ablative Radiotherapy Reirradiation

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Normal tissue dose constraints for reirradiation are not well-established.
• Accurate cumulative dose evaluation is challenging due to anatomical changes and fraction size.

Purpose of the Study:

• To retrospectively evaluate cumulative normal tissue doses in pelvic stereotactic ablative radiotherapy (SABR) reirradiation.
• To assess the feasibility of advanced dose evaluation methods and gather preliminary data on safe cumulative doses.

Main Methods:

• Retrospective analysis of 56 patients undergoing pelvic SABR reirradiation.
• Deformable image registration (DIR) to transfer original dose distributions to reirradiation CT scans.
• Calculation of cumulative doses in equivalent dose in 2-Gy fractions (EQD2) and summed maximum doses (D0.5 cc).

Main Results:

• Cumulative doses up to 82.8 Gy (rectum), 110.2 Gy (bladder), 69.8 Gy (colon), 101.4 Gy (sacral plexus), and 108.1 Gy (vessels) were observed.
• Small bowel received cumulative doses up to 111.9 Gy (D0.5 cc).
• No severe toxicity events were attributed to reirradiation or cumulative doses.

Conclusions:

• Demonstrated feasibility of 3D evaluation of cumulative normal tissue doses in pelvic SABR reirradiation.
• Preliminary data suggest no observed toxicity related to delivered cumulative or reirradiation doses.