| Object：Utilizing the unique property of CyberKnife, we compared the stereotacticbody radiotherapy (SBRT) of massive liver cancer tumor, the size of which is largerthan10cm, with a single target and double targets. Then we discussed about the tumorcoverage and dose to sensitive organs.Method：We selected14cases of primitive massive liver cancer which was largerthan10cm.9of the cases had the tumor in the right liver lobe,5cases in the left lobe.We designed two treatment plans for each case: designed a single PTV for the lesion;divided the whole target area into two sub targets (PTV1and PTV3) along the directionof S/I and another sub-target with overlapping dose (PTV2). The physicist can giveproper adjustment based on the shape of tumor and its relation with organs at risksurrounded. Took the same prescription dose50Gy/5F. The dose threshold of organs atrisk referred to AAPM TG101Report. The Multiplan4.0system used adversealgorithm and gave the results with the dose threshold of each organ at risk[4]. Then weevaluated the tumor coverage, stomach and duodenum D10cc, jejunum D5cc, kidney D200cc, liver D700cc, spinal cord D10%and skin D10cc.Compare the outcomes of these twoplans and evaluate the difference of tumor coverage and dose threshold of organs at riskusing the two strategies.Result：With the same prescription dose of50Gy/5F and the same dose thresholdof sensitive organs, the tumor coverage with the double-target treatment plan increased20.5%-35.6%, and mis-irradiated volume decreased70.86cc-227.37cc compared withthe single target plan. The BEDs of organs at risk were similar with the sameprescription dose.Conclusion：In contrast with the single target treatment plan, the double-targettreatment plan greatly improved the tumor coverage, significantly decreased themis-irradiated volume, but increased the treating time for patients. At the same time, it also increased the low dose extra radiation of KV level from the image system duringthe CybeKnife treatment. |
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