Objective To analyze the volumetric and dosimetric variations in radiation treatment planning(RTP) using CT images based on normal and extended reconstructed field-of-view(FOV). Methods Original data of CT scans from 16 cases of nasopharyngeal carcinomas were reconstructed to form 2 sets of CT images with Dermal(45 cm)and EFOV(65 cm),which were then exposed to RTP. Contouring of targets/OAR including GTV(gross tumor volume),CTV(clinical target volume,CTV),brain stem, lens, parotids and cord was made on normsl FOV CT set.A 7-field equi-angular IMRT (intensity modulated radiation Therapy)plan was generated with prescribed GTV dose of 70 Gy.Two sets 0f CT images were fused in DICOM coordinate system and targets/OARs on normal FOV CT were copied to EFOV CT.IMRT plans were then transplanted from normal FOV to EFOV CT,with the same isocenter on DICOM coordinates.Volumetric and dosimetrie variations including GTV,CTV brain stem,lens, parotids and cord were calculated on dose-volume-histogram(DVH).For dosimetric verification,IMRT plans were input into fluence maps of Mapcheck 1175 phantom based on normal FOV and EFOV, and DTA(distance to agreement)was used to analyze the passing rate of calculated/measured absolute doses at 5 cm depth.Paired-t test was used to compare the passing rate of field 1-7 of IMRT plans based on 2 CT sets.Results Volumes of targets and OARs on 2 CT sets of different FOVs were statistically different.with larger calculated volume on norlual FOV in all cases.There was no statistic difference in the maximal(Dmax) doses received by all targets and OARs except the small-volume lens, in which the dose was higher on normal CT than that on EFOV CT(t=-3.14,P<0.007).The mean doses(Dmean)to the CTV(clinical target volume)and GTV(gross tumor volume)were higher on EFOV than normal FOV CT(t=-6.45,-5.65,P<0.001).There was no statistic difference in Dmean received by OARs and the minimal dose (Dmin)by all targets and OARs(P>0.05).There was also no statistic difference in the passing rate of field 1-7 of IMRT plans based on 2 CT sets.Conclusions There were volumetric and dosimetric variations as evaluated on DVH using different reconstructed FOV during CT simulation,though the difference between the passing rates as verified in 2 dimensional fluence map was not significant.

Objective To investigate the dosimetric differences among three types of breath hold mode ( free breath:FB, thoracic deep inspiration breath hold: T-DIBH, abdomen deep inspiration breath hold:A-DIBH) and to explore the optimal breath hold method in the postoperative radiotherapy of left-side breast cancer patients with minimum dose to normal tissues and organs at risk. Methods A total of eighteen patients with left-side breast cancer patients who underwent postoperative radiotherapy were enrolled in this study. Three CT simulation scans with three different breath hold method ( FB, T-DIBH, and A-DIBH ) were performed for each patient. Dosimetric differences were compared among plans generated on these three different CT image sets. Results There was no significant difference in the volume, mean dose, and homogeneity of planning target volume ( PTV) among plans generated from three different image sets (P>0. 05). The mean heart dose, mean LAD dose and mean ipsilateral lung dose in plans generated from CT image sets with FB, T-DIBH and A-DIBH were (3. 21 ± 1. 02), (1. 74 ± 0. 51), (1. 31 ±0. 41) Gy (W =171, P <0. 05), (34. 61 ± 13. 51), (14. 38 ±10. 20), (9. 21 ± 6. 53) Gy (W=171, P<0. 05), and (8. 31 ±2. 75), (7. 46 ±1. 96), (6. 89 ±1. 79) Gy (W=171, P<0. 05), respectively. Conclusions Compared with plans with FB, plans with DIBH ( T-DIBH and A-DIBH ) achieved lower cardiac, LAD and pulmonary doses. A-DIBH achieved a better normal dose reduction than T-DIBH.