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Determining Planning Priorities for SABR for Oligometastatic Disease: A Secondary Analysis of the SABR-COMET Phase II
Matthew Van Oirschot1, Alanah Bergman2, Wilko F A R Verbakel3
1London Health Sciences Centre, London, Ontario, Canada.
Purpose:
SABR may improve survival in patients with oligometastases, but for some lesions, safe delivery of SABR may require a reduction in delivered dose or target coverage. This study assessed the association between target coverage compromise and oncologic and survival outcomes.
Methods And Materials:
Patients with a controlled primary malignancy and 1 to 5 oligometastases were randomized (1:2) between standard of care (SOC) treatment and SOC plus SABR. In patients receiving SABR, the target dose coverage was reduced to meet organ at risk (OAR) constraints, if necessary. The D99 value (minimum dose received by the hottest 99% of the planning target volume [PTV]) was used as a measure of PTV coverage for each treatment plan, and the relationship between the coverage compromise index (CCI, defined as D99/prescription dose) and patient outcomes was assessed.
Results:
Sixty-two patients in the SABR arm had dosimetric information available and a total of 109 lesions were evaluated. The mean CCI per lesion was 0.96 (95% CI, 0.56-1.61). Of the 109 lesions evaluated, 29.4% (n = 32) required coverage compromise (CCI <0.9). Adrenal metastases required coverage compromise in 100% of analyzed lesions (n = 7). CCI was not significantly associated with lesional control, adverse events, overall survival (OS), or progression-free survival (PFS).
Conclusions:
Target compromise was required in a substantial minority of cases, but PTV coverage was not associated with OS, progression-free survival, or lesional control. This suggests that OAR constraints used for SABR treatments in the oligometastatic setting should continue to be prioritized during planning.
Insights
Stereotactic ablative radiotherapy (SABR) dose reduction for oligometastases did not impact survival outcomes. Prioritizing organ at risk constraints during planning is recommended, even if it compromises target coverage.
Area of Science:
- Radiation Oncology
- Medical Physics
Background:
- Stereotactic ablative radiotherapy (SABR) offers survival benefits for oligometastases.
- Dose or target coverage reduction may be necessary for safe SABR delivery in certain lesions.
- Assessing the impact of compromised target coverage on outcomes is crucial.
Purpose of the Study:
- To evaluate the association between target coverage compromise and oncologic and survival outcomes in patients receiving SABR for oligometastases.
Main Methods:
- Randomized trial comparing standard of care (SOC) with SOC plus SABR for 1-5 oligometastases.
- Dose reduction implemented to meet organ at risk (OAR) constraints.
- Coverage Compromise Index (CCI), defined as D99/prescription dose, used to measure planning target volume (PTV) coverage.
Main Results:
- 29.4% of lesions required coverage compromise (CCI <0.9).
- Adrenal metastases universally required coverage compromise (100%).
- No significant association found between CCI and lesional control, adverse events, overall survival (OS), or progression-free survival (PFS).
Conclusions:
- Target coverage compromise in SABR for oligometastases did not negatively affect OS, PFS, or lesional control.
- Prioritizing OAR constraints during treatment planning is supported.
- Current OAR constraints for SABR in oligometastatic disease should be maintained.
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