Abstract

Purpose: To compare the plan quality, normal brain dosimetry and temporal lobe dosimetry of three different radiotherapy techniques- 3field 3DCRT (3F), IMRT and 4- field non-coplanar technique (4FNC) for large irregular non functioning pituitary adenoma (NFPA).

Materials and Methods: CT data sets of 28 patients previously treated for NFPA by either a 3F or IMRT (14 patients each) radiotherapy of physicians’ choice were utilized to prepare 4FNC to obtain 95% isodose coverage of planning target volume (PTV). GTV previously contoured by CT-MRI fusion was unchanged. The PTV was created by a uniform 3-D expansion of GTV by 5mm margin. Bilateral Temporal lobes were contoured if not done previously. Plan quality was compared by Target coverage, New Conformity Index (NCI) and Homogeneity index (HI).  Normal tissue sparing was compared by volume of normal Brain beyond the PTV receiving 80%, 60% and the mean dose, and volume of bilateral temporal lobes receiving the target dose. NCI was calculated using the formula D max /Dp & HI was calculated as D2-D98/Dp x 100.

Results: Mean age of the cohort was 36 years with 21 male and 7 female patients. All patients had undergone immobilisation with thermoplast mask with neck flexion or neutral position (16: 12). Twelve patients had undergone 3DCRT with 3F beam arrangement (1: 2-field, 11: 3 field) and 14 had undergone IMRT, non-coplanar beam arrangement being utilized in 14 patients (more commonly with 3DCRT compared to IMRT- 10:4). Two patients had undergone radiotherapy with the 4-field non- coplanar technique. Median volume of PTV was 50cc (range=10 to 185cc). Dose prescription ranged from 45Gy/25 fractions to 54Gy/30 fractions. Mean 95% coverage of PTV by 3F: 4FNC: IMRT was 94%, 95% and 95% respectively. Comparison of mean NCI between 3F, IMRT and 4FNC was 1.08, 1.02 and 1.06 respectively and mean HI between 3F, IMRT and 4FNC was 10.7, 8.84 and 8.9 respectively. Volume of the normal brain beyond the PTV receiving 80%, 60% and 50% of the prescription dose between the 3F, IMRT and 4FNC was D80- 7.88: 4.2: 5.8, D60- 14.5: 7.9: 9 and  D50- 18.7: 13: 11. Dose to 13% of right temporal (RT) and left temporal (LT) lobes by 3F, IMRT and 4FNC was RT- 87.8%: 84%: 79% and LT- 89%: 82%: 79%. While it was seen that the target coverage, NCI and HI was superior with IMRT, 4FNC technique while performed in neck flexion position was superior in terms of lesser mean dose to normal brain and dose to bilateral temporal lobes especially in patients with larger PTV’s.

Conclusion: The four field non coplanar technique provides superior target and normal tissue dosimetry in patients with large PTV non-functioning pituitary adenomas.

Optimization of radiation therapy in non-functioning pituitary adenoma based on temporal lobe dosimetry.