乳腺癌术后放疗时靶外组织剂量的研究

STUDY ON THE DOSE TO TISSUES OUTSIDE THE RADIATION FIELD DURING POST OPERATIVE RADIOTHERAPY IN PATIENTS WITH BREAST CANCER

本文借助非均匀组织等效拟人体模型（ｐｈａｎｔｏｍ ），模拟成年女性左侧乳腺癌术后放疗，研究了医用电子直线加速器产生的９ ＭｅＶ电子束和６ ＭＶ Ｘ射线对乳腺癌放疗时靶外组织的受照剂量。结果表明，单次照射剂量２０ Ｇｙ 时，在胸壁照射区域，电子束照射时体表的受照剂量较高，位于野内左后壁的剂量明显低于野外右乳腺的剂量，野外组织受照剂量波动较大，Ｘ 射线照射时野外组织受照剂量波动较小，受照剂量最高的是具有一定深度的纵膈；在淋巴引流区域，Ｘ射线照射时邻近靶区的组织受照剂量较高。阴影屏蔽可使电子束所致的靶外组织剂量下降９４％ ～５３７％ ，使Ｘ射线所致的靶外组织剂量下降１９７％ ～５３６％ ；接触屏蔽可使Ｘ射线所致的靶外组织剂量下降４４２％ ～６５６％ 。

In this paper, the dose to tissues outside the radiation field was studied during the post operative radiotherapy of breast cancer with a 9 MeV electron beam from a medical linear accelerator or with 6 MV X rays, using a non uniform tissue equivalent phantom and stimulating the radiotherapy for a adult female patient with cancer in her left breast. The results show that when the fractional dose was 2.0 Gy, dose to body surface within the exposed region of chest wall was higher for electron beam and dose to the left posterior chest wall in radiation field was obviously lower than that to the right outside the field and there was a large fluctuation in doses to tissues outside the field, but there was a small one for X rays. For X rays, the maximum dose was in mediastinum with a certain deepness. In the region of lymph nodes, doses to tissues adjacent to the target were high. With using shadow shields, doses to tissues outside the target were descended 9.4%~53.7% for electron beam and 19.7%~53.6% for X rays, but with using contact shields, they were decreased 44.2%~65.6% for X rays. (