Dosimetric comparison of postoperative intensity-modulated radiotherapy for stage II - III rectal cancer

Objective To explore the optimal method of protecting bone marrow in postoperative concurrent chemoradiotherapy of stage Ⅱ - Ⅲ rectal cancer by comparing two techniques of intensitymodulated radiotherapy (IMRT). Methods Fifteen patients with stage Ⅱ - Ⅲ rectal cancer after surgery had CT simulation. Clinical target volume, small bowel, bladder and bone marrow were contoured. Two IMRT treatment plannings with and without bone marrow-sparing (BMS-IMRT and IMRT) were separately designed. The dose distribution was compared based on that 95％ of the planning target volume received the prescribed dose. Results BMS-IMRT had an advantage over IMRT in terms of conformity indices ( 1. 06∶1. 04, t =- 2. 61, P =0. 023 ), but inferior to I M RT for homogeneity indices ( 0. 81 : 0. 75, t =- 2. 34, P =0.037)). Compared with IMRT, BMS-IMRT reduced the V5, V10, V20, V30, V40 of bone marrow (97.09％∶98.72％, t=-2.34, P=0.037;92.38％∶96.46％, t=-2.41, P=0.033;83.36％∶91.70％, t=-3. 18, P=0.008;51.47％∶69.65％, t=-4.92, P=0.000;36.34％∶49.57％, t=-2.66, P =0. 021 ). The doses received by small bowel and bladder were similar between BMS-IMRT and IMRT, except that the V20 of bladder was lower in BMS-IMRT (77. 32％∶92. 39％, t =-3.52, P=0. 004). Conclusions BMS-IMRT reduces low dose volume of bone marrow without increasing dose to other risk organs. BMS-IMRT might reduce acute hematologic toxicity and increase the feasibility of postoperative concurrent chemoradiotherapy in stage Ⅱ -Ⅲ rectal cancer. Key words: Rectal neoplasms/radiotherapy;  Radiotherapy, postoperative;  Radiotherapy, intensity-modulated;  Dosimetry