环形与椭圆形施源器的剂量学比较。

Dosimetric comparison of ring and ovoid applicators.

作者信息

Tuncell N, Toy A, Demiral A N, Cetingoz R, Garipagaoglu M

机构信息

Department of Radiation Oncology, Akdeniz University Medical School, Antalya, Turkey.

出版信息

J BUON. 2009 Jul-Sep;14(3):451-5.

PMID:19810138

Abstract

PURPOSE

To compare the dosimetry of different vaginal applicators used in the postoperative vaginal cuff irradiation.

MATERIALS AND METHODS

In this model dosimetric study, standard ovoid applicator sets with 3 cap sizes (small/15 mm, medium/20 mm, and large/25 mm), and ring applicator sets with 3 diameter sizes (small/26 mm, medium/30 mm, large/34 mm) each with 3 different angles (30, 45, and 60 degrees) were used. Calculations were performed in Plato TPS (Treatment Planning System) as dwell positions of 2.5 mm step and equal dwell time for the sources. For ovoid applicators, the source positions 1-5 were loaded as active on each catheter, and in ring applicators the source positions 1-12, and 18-29; 1-14, and 19-32; 1-17, and 22-37 were loaded for small, medium and large ones, respectively. In addition to ICRU rectum reference point (R(1)), 4 different rectum reference points (RP(s)) (R(2)-R(5)) were defined 1 cm apart. The vaginal cuff RP (V(c)) was defined at 5 mm depth from the vaginal surface. The reference volume dose distribution was obtained according to the V(c) (100%) reference point. The width (w), max-min length (h, h'), and max-min thickness (t, t') of the reference isodoses were measured and max-min reference volume (v, v') was calculated.

RESULTS

R(1) dose was higher for ovoids (43.1%) than ring (28.6%), in all applicators. The increase of R(1) dose was parallel to the increase of ovoid/ring size (70-89%). As the applicator (ovoid-ring) size increased, max thickness of the reference isodose also increased (19-50%). For the largest size, the max increase was 62% (74.1-119.88 cm(3)) and 93% (59.15-114.24 cm(3)) for v and v', respectively. However, the magnitude of the reference volume was independent of the ring angle.

CONCLUSION

In the present study it was found that when ring applicators were used according to recommended dwell positions, max rectum reference dose decreased in comparison to ovoid applicators; on the other hand, it should be noted that the size of the reference volume also decreased significantly.

摘要

目的

比较术后阴道残端照射中使用的不同阴道施源器的剂量学。

材料与方法

在本模型剂量学研究中，使用了标准卵形施源器套装，有3种帽尺寸（小/15毫米、中/20毫米、大/25毫米），以及环形施源器套装，有3种直径尺寸（小/26毫米、中/30毫米、大/34毫米），每种套装有3种不同角度（30度、45度和60度）。在Plato治疗计划系统（TPS）中进行计算，源的驻留位置步长为2.5毫米，驻留时间相等。对于卵形施源器，源位置1至5在每个导管上设为激活状态，对于环形施源器，源位置1至12以及18至29；1至14以及19至32；1至17以及22至37分别用于小、中、大尺寸的施源器。除国际辐射单位与测量委员会（ICRU）直肠参考点（R(1)）外，还定义了4个不同的直肠参考点（RP(s)）（R(2) - R(5)），彼此相距1厘米。阴道残端参考点（V(c)）定义在距阴道表面5毫米深处。根据V(c)（100%）参考点获得参考体积剂量分布。测量参考等剂量线的宽度（w）、最大 - 最小长度（h，h'）和最大 - 最小厚度（t，t'），并计算最大 - 最小参考体积（v，v'）。

结果

在所有施源器中，卵形施源器的R(1)剂量（43.1%）高于环形施源器（28.6%）。R(1)剂量的增加与卵形/环形施源器尺寸的增加平行（70 - 89%）。随着施源器（卵形 - 环形）尺寸增加，参考等剂量线的最大厚度也增加（19 - 50%）。对于最大尺寸，v和v'的最大增加分别为62%（74.1 - 119.88立方厘米）和93%（59.15 - 114.24立方厘米）。然而，参考体积的大小与环形施源器的角度无关。