Treatment guidelines for non-Hodgkin's lymphoma, like treatment guidelines for all cancers, are intended to give doctors (or whoever is reading them) a set of evidence-based recommendations for the best known standards of cancer care according to the latest findings and studies.
They generally will include other information along with treatment guidelines, such as incidence, diagnostic criteria, clinical staging requirements, and risk assessments, among other things.
However, the main purpose of treatment guidelines for non-Hodgkin's lymphoma is to provide physicians and other health care professionals with a road map to follow in prescribing the appropriate cancer treatment to their patients.
Arguably the most influential set of treatment guidelines for all cancers are published by the National Comprehensive Cancer Network (NCCN), which is under the wing of the US National Cancer Institute. The NCCN is a network of over 20 member hospitals including the most prestigious in the country, such as MD Anderson, Duke, Stanford and others. When one is admitted to one of these hospitals, one can expect to receive treatment for their non-Hodgkin's lymphoma according to the published guidelines.
That said, all published guidelines are meant as a framework for treatment only, and patients are always to be regarded individually against the guidelines, not as a one-guideline-treats-all kind of approach.
Other influentual treatment guidelines include those published by the American Society of Clinical Oncology as well as those published by the European Society of Clinical Oncology.
Meanwhile, individual health networks will often use their own evidence-based oncology treatment guidelines. This is true for United States-based health networks such as Kaiser Permanente as well as the Cancer Treatment Centers of America, and for networks abroad as well. Examples include the German Hodgkin's Study Group, which publishes a set of treatment guidelines for Hodgkin's and non-Hodgkin's lymphoma, and the London Health Sciences Centre's London Regional Cancer Program.
When treated for non-Hodgkin's lymphoma or any cancer at a private practice medical facility that is not under the umbrella of any National agency, treatment guidelines will inevitably vary from practice to practice. Some states have established oncology quality consortiums to try and ensure that all patients, regardless of where they seek treatment, get the best possible treatment, but this isn't the case nationwide.
It would not be out of line to ask your doctor what set of treatment guidelines he or she intends to use if you are their patient. In fact many people find the ability to follow the decision-making process as it is laid out in clinical practice guidelines as taking some of the mystery and the fear out of the treatment process.