In this study the treatment process will be closely monitored using a novel imaging technology, a PET/CT scanner. PET stands for Positron Emission Tomography and in this case it will be combined with a conventional x-ray Computerized Tomography (CT) scan. This is not a study of any particular form of treatment. The treatment you receive will be the most appropriate standard treatment whether you are in the study or not.

The goal of radiation therapy is to deliver a given amount of radiation dose to the area where there is a lymphoma tumour. We are doing this study to see which part of the tumour reacts to the radiation treatment, and which part does not react, by monitoring the progress of your treatment with a combined PET/CT scan. In particular, changes of the size and shape of the tumour that occur during the treatment can be detected and will be visible on the images. These images will be thoroughly analysed. The ability of the PET/CT scanner to detect these changes during a course of radiation treatment will be the subject of this study. We will also be able to see if this information will eventually relate to or predict whether lymphoma tumours will be completely eradicated by the treatment.

Inclusion Criteria:

• Histologic diagnosis of NHL:Any histology
• Stage I-IV
• Measurable disease by CT scan (gross disease measuring at least 2 cm in any one dimension)
• Planned radiation dose prescription >=30 gy, >=20 fractions, >=3weeks duration
• Informed consent
• Previous chemotherapy is allowed, provided the above eligibility criteria are me

Exclusion Criteria:

• To minimize effect from breathing motion, patients presenting with parenchymal lung tumours and tumours involving liver and stomach will be excluded
• Concurrent systemic chemotherapy (glucocorticoids when used alone is allowed)