Abstract:
Objective To compare the doses distribution among 3DCRT, IMRT, and VMAT for multiple primary cancers of the esophagus.
Methods Seven patients with multiple primary cancers of the esophagus were selected. The patients underwent a CT simulator scan, and the targets were contoured. The clinical target volume (CTV) included the entire esophagus and lymph node areas in the mediastinum. The planning target volume included the CTV plus a 5 mm margin. Three radiotherapy plans were designed for each patient, namely, 3DCRT, seven-field IMRT, and one-arch VMAT. The dose distribution in the target volumes and critical organs were compared among the three plans.
Results D99 of the target volume of the IMRT or VMAT plan was significantly higher than that of the 3DCRT plan (49.4±0.8, 49.2± 0.7, and 43.9 ±2.8 Gy, respectively; P < 0.001) Compared with the 3DCRT plans, we found that V30 was lower but V5 of the lungs was significantly increased in IMRT or VMAT (IMRT vs. VMAT vs. 3DCRT, V30:11.8 % ± 2.5 %, 10.5 %±2.1%, and 13.2 % ± 2.1%, P= 0.096; V5:92.5 % ± 3.2 %, 93.6 %±5.6 %, and 68.5 % ± 2.1%, P < 0.001). V30 in the heart and D1 in the spinal cord were also significantly lower in IMRT and VMAT. The VAMT plan had no significant difference in the dose omogeneity of the target volume and DVH of critical organs, but had less treatment time (VMAT vs. IMRT, 3.0 ±0.6 min, 6.2± 0.2 min, P < 0.001) compared with the IMRT plan.
Conclusion IMRT or VMAT radiotherapy plan improves the target volume by over 95 % of the isocenter dose line. These radiotherapy plans decrease V30 in the heart and D1 in the spinal cord, but significantly increase V5 in the lungs. Given that V5 in the lungs is much higher than the current recommended lung dose limitation, the use of IMRT or VMAT in treating the entire esophagus or mediastinum should be performed carefully. The dose distribution of the single-arc VMAT plan has no significant difference with that of the IMRT plan, but the treatment time is shortened by 52 %.