Angle of concavity in planning target volume can be adopted as selection criteria for intensity-modulated radiation therapy or three-dimensional conformal radiotherapy technique in brain tumors.

INTRODUCTION: With innovation of medical imaging, radiotherapy attempts to conform the high dose region to the planning target volume (PTV). The present work aimed to assess the angle of concavity in PTV can be adopted as selection criteria for intensity-modulated radiation therapy (IMRT) or three-dimensional conformal radiotherapy (3DCRT) technique in Brain tumors.

MATERIALS AND METHODS: Thirty previously irradiated patients with brain tumors were replanned with both 3DCRT and IMRT technique. Angle of concavity (dip) in the PTV near the organs at risk was measured in the contoured structure set images of each patient. These cases were divided into three groups where angles were 0°, >120° and <120°. Dose of 60 Gy/30# was fixed.

RESULTS: In Group 1, the IMRT plan had better TV95% as compared to 3DCRT respectively with significant P value (P = 0.002). Mean of conformity index (CI) and Homogeneity Index (HI) were comparable. For Group 2 (angle >120°), the IMRT plan had better TV95% as compared to 3DCRT respectively with a significant P value (P = 0.021). HI and CI were not significant. For Group 3 (<120°), IMRT plan had better TV95% as compared to 3DCRT respectively with a significant P value (P = 0.001). HI and CI were better in IMRT arm with significant P value.

CONCLUSION: The results from this study showed that the angle of concavity can be considered as an additional objective tool for selection criteria whether tumor can be treated with IMRT or 3DCRT. Tumors where angle of concavity was <120°, HI and CI provided more uniformity and conformity of dose distribution inside PTV with significant P values.