A New Approach to Highly Conformal Hippocampal-sparing Whole-brain Radiotherapy: A Feasibility Study.

BACKGROUND/AIM: Hippocampal-sparing whole-brain radiotherapy (HS-WBRT) is increasingly used for multiple brain metastases. However, most studies have not reported dose conformity indices (CI). In the only study indicating the CI, conformity was low (CI=0.7). We developed a new technique to achieve a significantly higher CI and better dose coverage.

PATIENTS AND

METHODS

Ten patients received 30 Gy of HS-WBRT for brain metastases. Three variants of treatment plans (VAR1, VAR2, VAR3) were investigated. Volumetric modulated arc therapy plans with two (2ROT) or three rotations (3ROT) were created for each variant. Plans were compared for compliance with hippocampal sparing criteria, CI (where a higher value indicates better conformity), and homogeneity index (HI, where a lower value indicates better homogeneity).

RESULTS

Best results (highest CI, lowest HI) were achieved with the VAR3-3ROT technique (a new method), which yielded a CI=0.92-0.95 and a HI=0.05-0.09. VAR3-2ROT led to a CI=0.90-0.95 and a HI=0.06-0.11. With the other techniques, CI and HI ranged between 0.77-0.87 and 0.15-0.32, respectively.

CONCLUSION

Our new technique achieved both appropriate hippocampal sparing and very high dose conformity of ≥0.9. Significant underdosage outside the hippocampal-sparing area was avoided.