See the following..... I believe proton therapy is preferred only when the cancer is very localized and difficult to target...

Proton therapy may be advised for anal cancer in specific situations where its unique properties can provide an advantage over traditional radiation therapy (like X-ray-based treatments such as IMRT). Proton therapy delivers radiation with high precision, targeting tumors while minimizing damage to surrounding healthy tissues due to its ability to deposit most of its energy at a specific depth (the Bragg peak) and then stop, reducing "exit dose" radiation.
For anal cancer, proton therapy might be considered in the following scenarios:
Preserving Nearby Organs: Anal cancer is typically treated with chemoradiation (chemotherapy combined with radiation). The anus, rectum, bladder, reproductive organs, and pelvic bones are close to the treatment area. Proton therapy can reduce radiation exposure to these structures, potentially lowering the risk of side effects like bowel or bladder dysfunction, sexual dysfunction, or pelvic bone damage.

Recurrent Disease: In cases where anal cancer recurs after prior radiation, proton therapy might be used to target the tumor while sparing previously irradiated tissues, reducing the risk of cumulative toxicity.

Complex Tumor Location: If the tumor is in a challenging location (e.g., near the sacral nerves or involving lymph nodes in the pelvis), proton therapy’s precision might help avoid nerve damage or other complications.

Reducing Long-Term Side Effects: For younger patients or those with a good prognosis (e.g., early-stage squamous cell carcinoma of the anus), proton therapy might be considered to minimize long-term risks like secondary cancers or chronic gastrointestinal issues.

Patient-Specific Factors: It may be recommended for patients with specific comorbidities (e.g., inflammatory bowel disease) where minimizing radiation to healthy tissue is critical, or in cases where standard radiation doses might exceed safe limits for nearby organs.

When It’s Typically Not Advised
Standard Cases: For most patients with anal cancer (especially early-stage disease), conventional radiation therapy (like intensity-modulated radiation therapy, IMRT) combined with chemotherapy (e.g., 5-FU and mitomycin-C) is highly effective, with cure rates exceeding 80% for localized disease. Proton therapy’s added cost and limited availability often make it unnecessary unless there’s a clear benefit.

Lack of Evidence: While proton therapy shows promise, large-scale clinical trials directly comparing it to IMRT for anal cancer are limited. It’s not yet a standard recommendation in guidelines like those from the National Comprehensive Cancer Network (NCCN) unless specific circumstances apply.

Expert Consensus
Doctors typically weigh factors like tumor stage (e.g., T1-T4), lymph node involvement, patient health, and prior treatments.