Radiotherapy (RT) with concurrent 5-fluorouracil and mitomycin-C (5FU/MMC) combination is the treatment of choice for non-metastatic locally advanced anal squamous cell carcinoma (ASCC). While, locally advanced AC treatment involves elective inguinal lymph node irradiation along with concurrent chemotherapy with significant improvement of locoregional control and colostomy free survival, many oncologists believe that routine, elective irradiation of bilateral inguinal areas of patients with limited disease (T1-T3) without lymph node involvement may be overtreatment and the larger radiation target that includes entire pelvis and bilateral inguinal region causes significant acute and late toxicities.~SLNB is the standard procedure currently used for breast cancer staging. The most significant observation was that when the SLN is negative, no further ALND or adjuvant axillary radiation is need for those patients. The SLNB had shown a better diagnostic accuracy (31% vs.25%) and higher sensitivity (85% vs.75%) than FDG-PET imaging to detect inguinal lymph node metastasis. Given better diagnostic accuracy and high sensitivity of SLNB, this technique could be used precisely to define target population who could be spared of prophylactic inguinal irradiation.~The investigators hypothesize that patients with early clinical stage node negative anal cancer (T1-T3N0) have low risk of subclinical inguinal lymph node involvement that can be detected by a combination of PET imaging and SLNB. Hence, any early stage AC patients with node negative disease confirmed by PET imaging and SLNB have relatively low risk of nodal failure and so inguinal radiation could be avoided. This approach would limit over treatment of early stage patients, reduce acute and late toxicities. This will be tested in a phase II study with close follow up of study patients so that inguinal relapse if any occur will be salvaged successfully. If this treatment approach is successful, it could be practice changing with improvement of H-QOL of patient.
The purpose of this study is to see whether avoiding preventative radiation to the groin in patients with normal sentinel node biopsy and PET-CT, is at least as effective treating cancer as giving preventative radiation to the groin for patients with anal canal cancer.~The investigators also want to know if avoiding radiation to the groin will cause fewer side effects and better quality of life