The purpose of this study is to validate the dosimetric parameters that correlate with acute hematologic toxicity (HT) in patients with rectal cancer treated with neoadjuvant chemoradiotherapy.

The investigators' ongoing retrospective study investigated the clinical and dosimetric parameter (dosimetry of pelvic bone marrow) which relate with acute hematologic toxicity in patient with rectal cancer treated with neoadjuvant chemoradiotherapy. In order to validate the dosimetric limitation of pelvic bone marrow in decreasing the intensity of HT, the investigators want to conduct a study to observe the acute HT without assigning any specific interventions to the subjects of the study, who will receive the standard treatment according to the multidisciplinary team's (MDT) decision and patient choice. Therefore, this study's type is observational.

Inclusion Criteria:

• rectal cancer
• receive neoadjuvant chemoradiotherapy

Exclusion Criteria:

• hematological system disorders

Both gender is OK and there is no limitation for age.