6～21MeV高能电子束深度剂量曲线测定方法的研究

目的：探讨电子束深度剂量曲线的测定方法，为临床选择电子束治疗方案提供物理基础。方法：在电子直线加速器上分别测量６、９、１２、１５、１８、２１ＭｅＶ六档标称能量，经φ３、φ４、φ５圆形及固定１０×１０ｃｍ限光筒后输出的电子束深度电离曲线。采用Ｅ０＝２．３３Ｒ５０，ｉ及Ｅ０＝０．８１８＋１．９３５Ｒ５０，ｉ＋０．０４０（Ｒ５０，ｉ）２分别计算平均入射能量Ｅ０，并推导出利用Ｓｗ，ａ、Ｐｕ或ＣＥ从百分深度电离量直接计算百分深度剂量的公式。结果：所引用二种Ｅ０计算公式的差异在２．１％之内，该差异对参考点剂量及深度剂量曲线几乎没有影响。通过对所获得深度剂量曲线与深度电离曲线的比较看到：其８５％峰值深度Ｒ８５，ｄ及半峰值深度Ｒ５０，ｄ均大于深度电离曲线上的对应值，且该差别随平均入射能量的增加而加大。结论：深度剂量曲线应在测得深度电离曲线后，经计算平均入射能量Ｅ０，查出对应深度的Ｓｗ，ａ、Ｐｕ或ＣＥ，进而由百分深度电离量求得。

放射疗法

0239624 镓全身SPECT(单光子发射计算机X线断层扫描术)[日]/油井信春∥日放技会志.-2001,57(10).-1179～1181冀医情

Dosimetric study comparing photon and electron beams for boosting the tumor bed in early-stage breast cancer

Objective： The aim of our study was to assess and compare the potential dosimetric advantages and drawbacks of photon beams and electron beams as a boost for the tumor bed in superficial and deep seated early-stage breast cancer. Methods： We planned CTs of 10 women with early breast cancer underwent breast conservative surgery were selected. Tumor bed was defined as superficial and deep with a cut of point 4 cm, those with less than 4 cm were defined as superficial tumors representing 4 patients and those with depth of 4 cm or more were classified as deep tumors representing 6 patients. The clinical target volume （C＇I＇V） was defined as the area of architectural .distortion surrounded by surgical clips. The plan- ning target volume （PTV） was the C＇I＇V plus margin 1 cm. A dose of 10 Gy.in 2 Gy fractions was given concurrently at the last week of treatment. Organs at risk （OARs） were heart, lungs, contra-lateral breast and a 5 mm thick skin segment of the breast surface. Dose volume histograms were defined to quantify the quality of concurrent treatment plans assessing target coverage and sparing OARs. The following treatment techniques were assessed： photon beam with 3D-conformal technique and a single electron beam. Results： For superficial tumors better coverage for CTV and P＇I＇V with good homogeneity with better CI was found for the 3D conformal radiotherapy （3DCRT） but with no significant planning objectives over electron beam. For deep tumors, the 3DCRT met the planning objectives for C＇I＇V, PTV with better coverage and fewer hot spots with better homogeneity and CI. For superficial tumors, OARs were spared by both techniques with better sparing for the electron beam where as for deep tumors also OARs were well spared by both techniques. Conclusion： Boosting the tumor bed in early- stage breast cancer with optimized photon may be preferred to electron beam for both superficial and deep tumors. The OARs dose sparing effect may allow for a potential long-term toxicity risk reduction and better cosmesis.

Dosimetric evaluation using the diode measurements for total skin electron therapy technique

Objective： The purpose of this study was to present the dosimetric study and evaluation the dose delivered to the skin tumor by using diode detector with total skin electron therapy （TSET）. Methods： The total skin electron irradiation （TSEI） technique was used to treat ten patients with histological confirmed mycosis fungoides according to the Stanford staging system at the Radiotherapy Department, National Cancer Institute, Cairo University, Egypt. High dose rate electron beams with low electron energy 5 MeV from a Siemens linear accelerator were used for treatment. Diodes were calibrated at TSET distance 300 cm and field size （35 × 35） cm^2. Results： The result of diodes measurements showed the dose to flat surface of the body was within ：1：10 % from the prescribed dose. Special areas of the body such as the perineum ＆ eyelid showed large deviation up to 30% variation from the prescription dose. Conclusion： The diode results of this study will be used as a quality assurance check for all new patients treated with TSET and to compare it to the prescribed dose delivered to the patients. It is recommends to evaluate the diodes measurements for all patients throughout the full treatment cycle and to identify individually the boost dose areas.