Objective:To evaluate the effect of setup errors from daily cone-beam computed tomography (CBCT) on the accumulated dose under different image-guidance (IG) strategies, aiming to investigate the appropriate IG strategies during radiotherapy for the spine metastases.Methods:A total of 720 CBCT scans of 36 vertebral lesions were obtained. All 36 lesions were divided into the simultaneous boosting (PTV 40 Gy/20f, GTV 60 Gy/20f, n=20) and conventional radiotherapy groups (PTV 40 Gy/20f, n=16). The actual fractionated plan was recalculated simulatively after transferring the isocenter of the initial plan according to the interfraction setup error. Under no daily image-guidance (no-DIG) strategies including twice imaging guidance weekly (TIG), initial 5 days then weekly imaging guidance (5D+ WIG), WIG and no imaging guidance (NIG), the dose deviation was calculated between the delivered dose accumulated by each actual fractionated plan and the dose distribution under DIG. The tolerance of dose deviation for the target was within ±5% and the D max of the spinal cord was limited below 45 Gy. Results:Under different image-guidance strategies of TIG, 5D+ WIG, WIG and NIG, the median dose deviation was approximately ±1% for the CTV D 95% and D max of spinal cord. However, the median dose deviation was beyond -5% for the PTV D 95% when conventional radiotherapy was given. The median dose deviation was approximately 10% for the D max of spinal cord and the proportion of cases whose maximum irradiated dose of spinal cord was more than 4500 cGy was ≥70%. Also, the median dose deviation was beyond -5% for the GTV D 95% and PTV D 95% when simultaneous boosting was delivered. Conclusions:Because the dose deviation of CTV and spinal cord is within the tolerance limit, the image-guidance strategies could be chosen according to the clinical practice when conventional radiotherapy is delivered. However, the dose deviation of spinal cord, GTV and PTV exceeds the tolerance limit under no-DIG strategies when simultaneous boosting is delivered. Hence, it is necessary to perform daily IGRT for the spine metastases.

Objective:To investigate the advantage of three dimensional(3D)-printed tissue compensators in radiotherapy for superficial tumors at irregular sites.Methods:A subcutaneous xenograft model of prostate cancer in nude mice was established. Mice were randomly divided into no tissue compensator group( n=6), common tissue compensator group( n=6), and 3D-printed tissue compensator group( n=6). Computed tomography (CT) images of nude mice in the 3D-printed tissue compensator group were acquired. Compensator models were made using polylactic acid, and material properties were evaluated by measuring electron density. CT positioning images of the three groups after covering the corresponding tissue compensators were acquired to delineate the gross tumor volume (GTV). Nude mice in the three groups were irradiated with 6 MV X-rays at the prescribed dose. The prescribed dose for the three groups was 1 500 cGy. The dose distribution in the GTV of the three groups was calculated and compared using the analytical anisotropic algorithm in the Eclipse 13.5 treatment planning system. The metal-oxide-semiconductor field-effect transistor was used to verify the actual dose received on the skin surface of nude mice. Results:The air gap in the 3D-printed tissue compensator group and the common tissue compensator group was 0.20±0.07 and 0.37±0.07 cm 3, respectively ( t=4.02, P<0.01). For the no tissue compensator group, common tissue compensator group, and 3D-printed tissue compensator group, the D95% in the target volume was (1 188.58±92.21), (1 369.90±146.23), and (1 440.29±45.78) cGy, respectively ( F=9.49, P<0.01). D98% was (1 080.13±88.30), (1 302.76±158.43), and (1 360.23±48.71) cGy, respectively ( F=11.17, P<0.01). Dmean was (1 549.08±44.22), (1 593.05±65.40), and (1 638.87±40.83) cGy, respectively ( F=4.59, P<0.05). The measured superficial dose was (626.03±26.75), (1 259.83±71.94), and (1 435.30±67.22) cGy, respectively ( F=263.20, P<0.001). The percentage variation in tumor volume growth after radiation was not significantly different between the common tissue compensator group and the 3D-printed tissue compensator group ( P>0.05). Conclusions:3D-printed tissue compensators fit well to the body surface, which reduces air gaps, effectively increases the dose on the body surface near the target volume, and provides ideas for radiotherapy for superficial tumors at some irregular sites.