Radiation therapy
tumor
PRIMARY TUMOR, TUMOR
Planning CT (axial images at 2–3 mm intervals from the inferior part of the kidney to the femoral shaft) was performed. Patients underwent scanning in the supine position under custom immobilization. Adjusting the bladder volume, such as pooling urine by drinking water, was preferable for reducing the dose to the intestine and fulfilling the bladder dose constraint.The gross tumor volume (GTV) was contoured using digital rectal examination, imaging and endoscopy and included the primary tumor and metastatic lymph nodes. The clinical target volume (CTV) for the primary tumor was defined as 1.0–2.0 cm expanding to the GTV. No margin for potential microscopic invasion to the metastatic lymph node regions was added to the GTV. The subclinical CTV included the mesorectum, presacrum, bilateral internal and external iliac and bilateral inguinal lymph node regions. The planning target volume (PTV) was set by adding a 5–10-mm margin to the CTV.A total of 59.4 Gy was delivered with photons (≥6 MV) in 33 fractions for 6.6 weeks (1.8 Gy/day) using 3-dimensional conformal radiation therapy (3D-CRT) or intensity-modulated radiation therapy (IMRT). IMRT with two-step or simultaneous integrated boost (SIB) techniques was acceptable. For patients treated with 3D-CRT or IMRT with the two-step technique, a prescription dose (1.8 Gy/fraction) was administered to the reference point placed at the center of the PTV. Pelvic irradiation was initially administered at 36.0 Gy in 20 fractions, and a further 23.4 Gy was irradiated to the PTV of the primary tumor and metastatic lymph nodes in 13 fractions. For patients treated with IMRT using the two-step technique, 1.8 Gy/fraction was prescribed to D95% for the PTV. If IMRT using the SIB technique was selected, 1.8 Gy/fraction was prescribed to D95% for the PTV for the primary tumor and metastatic lymph nodes and 1.5 Gy/fraction was prescribed for the subclinical PTV minus the primary tumor and metastatic lymph node regions. Dose constraints for the organs at risk