Radiation treatment planning in brain tumours Potential impact of 3-O-methyl-6-[¹⁸F]fluoro-L-DOPA and PET

Aim:

Amino acid PET has become an important diagnostic tool for brain tumour imaging. In this data analysis, the potential impact of amino acid PET with 3-O-methyl-6-[¹⁸F]fluoro-L-DOPA ([¹⁸F]OMFD) on radiation treatment planning is addressed by the following questions: 1. Was tumour tissue identified with OMFD-PET which was not covered by the conventionally derived planning target volume (PTV)? 2. Would the PTV have been changed incorporating OMFD-PET?

Patients, methods:

OMFD-PET of 25 patients after subtotal resection of malignant glioma was evaluated. The region of elevated tracer uptake of PET and of contrast enhancing masses on MRI were outlined as separate gross tumour volumes (GTV_MRI and GTV_OMFD) and reconstructed in the planning CT for comparison with the conventionally drawn GTV_conv. A PTV_new based on GTV_conv+MRI was calculated. Pairwise differential volumes were calculated to estimate overlap and differential volumes delineation by each image modality and the PTV_conv and PTV_new respectively.

Results:

Differential volume analysis showed > 10 cm3 of GTV_OMFD outside GTV_conv and GTV_MRI in 5/25 patients respectively. From GTV_MRI >10 cm3 were found outside GTV_OMFD in 8/25 patients. Although all tumour areas indicated by
[¹⁸F]OMFD were covered by the conventionally derived PTV, based on a GTV_OMFD+MRI, the PTV_new would have been enlarged >20% in seven patients. In seven patients the PTV_new would have been reduced.

Conclusion:

OMFD-PET indicated tumour tissue outside the tumour region identified with MRI, adding valuable information for the delineation of the GTV in radiation treatment planning. OMFD-PET contains the potential to tailor the high dose radiation to the appropriate tumour volume, especially if dose escalation is desired.