Dosimetry for tangential chest wall irradiation.

The skin-sparing effect of megavoltage photons is lost to a varying extent when tangential beams are used to irradiate the chest wall. The skin dose for this technique, with and without a bolus, was investigated for 4- and 6-MV photons using film, thermoluminescent dosimeters, and an ionization chamber. Metal/tissue interface effects were observed when a flexible brass fabric material was used as a bolus.     

Dosimetry concepts and measurements in food irradiation processing

The associations between the dosimetry concepts, Minimum absorbed dose (D_min), maximum absorbed dose (D_max), and average dose and median dose are investigated for the case of a large cobalt-60 plaque source irradiating homogeneous bulk product in a two-pass, two-sided irradiation. It is assumed that to a first approximation the intensity of radiation decreases exponentially with the depth, t, in the product. A series of mathematical relationships is derived for the average dose, the maximum and minimum dose, the median dose [defined as (D_max + D_min)/2], and the uniformity ratio (defined as U.R. = (D_max/D_min). The relationships are derived in terms of a constant D₀ (the dose on the surface of the product in the pass close to the source) and the relaxation length (μt) of the radiation in the product. Since the uniformity ratio and other dose parameters can be calculated for certain chosen values of μt, the individual values of μ (the energy absorption coefficient) and t do not need to be known. By dividing the dose range from D_min to D_max into 10 equal fractions, the amount of product irradiated to each of the fractions is calculated, and it is shown that, independent of the value of U.R., about a third of the product receives a dose in the first fraction above D_min. It is also shown that for a given median dose, the average dose decreases as U.R. increases. The calculated dose relationships are confirmed by measurements in homogeneous dummy product, using the lyoluminescence of glutamine to measure dose. The implications of these results for the regulation of the food irradiation process and for the design of irradiation facilities are discussed.     

Dosimetry with phantom for total body irradiation(TBI)

Total body irradiation(TBI) is being used as a method of preparation for bone marrow transplantation(BMT). In TBI, the dose calculation is based on dosimetry using a phantom. We measured the basic dose with a phantom using a 10 MV X-rays. We confirmed the accuracy of the dose calculation performed in our facilities and investigated a method of more accurate dosimetry. We measured the variation in dose according to the size of the phantom and the depth using a tough water phantom, and examined the difference in TMR according to SCD, field size, and size of the phantom. Consequently, the dose has been changed regardless of the size of the phantom at larger than 80 x 30 x 30 cm(3), and it is about 1% larger than 30 x 30 x 30 cm(3). Also TMR has changed according to various conditions, including the size of the phantom, field size, and SCD. Therefore, it was found that dosimetry using the 30 x 30 x 30 cm(3) phantom leads to underestimation in dose calculation, and there is no difference in dose between the field size of 151.5 x 160 cm(2) and 151.5 x 80 cm(2). It is also necessary to consider the effect of the vertical size of the phantom.     

Dosimetry of blood irradiation using an alanine/ESR dosimeter.

A batch of 80 DL-alanine dosimeters was supplied to Hemocentro of the Hospital and Clinics of Faculdade de Medicina de Ribeir?o Preto (HC-FM RP) SP, Brazil for the purpose of quality control of the radiation dose delivered to blood bags. The irradiation was made using two (40 x 40) cm2 parallel opposed radiation fields each with 80 cm of source to surface distance in the Radiotherapy Section of HC-FMRP with the 60Co teletherapy unit. The calculated radiation absorbed dose at the center of the box was 20 Gy. The dosimeter readings were performed using a Varian E-4 ESR Spectrometer operating in X-band. For the 80 dosimeters and over the irradiation volume throughout a blood bag, the minimum and maximum doses were 14 and 23 Gy, respectively. The mean dose was (18 +/- 2) Gy (1sigma), and the coefficient of variability was 11.1%. Alanine dosimeters demonstrated easy handling, good precision and adequate sensitivity for this application.     

Dosimetry problems in irradiation of mediastinal tumours (author's transl)]

Various physical parameters are described for evaluation of the quality of the irradiation plane. Of these, the integral dose and the dose gradient index are regarded as particularly significant and their calculation is included in a computerised dosimetry programme. Examples are drawn from the comparison of various mediastinum irradiation techniques: 60Co, high energy X-rays, fast electrons.     

Dose estimation in postoperative keloid irradiation with special consideration of ovarian dose

For a long time now, surgery followed by irradiation has been the preferred therapy in the treatment of keloids. Radiation can be administered by means of X-rays (energy level less than or equal to 100 KV), electrons (energy level less than or equal to 5 MeV) or 192Ir wires. The choice of one of these methods depends on the availability of suitable facilities within a short period of time (less than 24 hours postoperatively), and the possibility of adapting the irradiation field quickly and easily to the scar. A further criterion is the dose received by underlying organs possibly, especially the ovaries of women of child-bearing age. It consists of primary and secondary (scattered) parts of radiation and was measured in two standard field sizes for the various types of radiation so as to allow a rapid evaluation. Apart from the types of radiation mentioned above, such measurements were also carried out for 125I seeds. With a field size of 20 x 1.5 cm2 and a surface dose of 10 Gy, ovaries at a depth of 10 cm in the central beam will receive a dose of between less than 1 m Gy in electron therapy to around 1 Gy in X-ray therapy (100 KV).     

外照射事故人体辐射损伤的剂量表达和测量

在事故受照射人员的医学处理中, 为了估计损伤程度, 要求提供受照者的剂量学参数, 这些参数应能较好的反映人体损伤效应。目前, 文献上使用的剂量表达方法是多种多样的, 我国的剂量学工作者对干细胞活存计权方法做了研究。研究结果表明, 对于骨髓型放射病剂量范围内的照射, 干细胞剂量可以表达全身造血组织的损伤程度。当然, 对于高度不均匀的外照射, 全身辐射损伤除了用干细胞剂量参数表达外, 还应给出受高剂量照射部证或某些关键器官的剂量。此外, 还对事故物理剂量测量方法做了实验研究。结果表明, 中国生产的4种手表红宝石具有良好的剂量学特性, 是一种比较实用的个人事故剂量计。     

宫颈癌复发放疗中不同照射方式的剂量学研究

目的针对宫颈癌复发病例,比较逆向调强(IMRT)、三维适形(3D-CRT)及超级伽玛刀弧形适形(SGS-CRT)三种照射方式的剂量学特点。方法对15例宫颈癌复发患者进行IMRT、3D-CRT及SGS-CRT计划设计,以包绕计划靶区(PTV)体积95%的等剂量线为处方剂量线,分别给予50Gy的处方剂量,分次方案均为2Gy×25次,根据剂量-体积直方图(DVH)评价三种照射方式中靶区和危及器官的剂量学特点。结果 3D-CRT的95%处方剂量包括靶区体积(99.9%±0.2%)高于IMRT(99.5%±0.5%)及SGS-CRT(99.3%±0.8%,P<0.05);SGS-CRT的靶区剂量梯度(85%±20%)明显高于IMRT(10%±7%)及3D-CRT(8%±5%,P<0.05);IMRT的适形指数(0.9±0.3)优于SGS-CRT(0.8±0.2,P<0.05),且SGS-CRT优于3D-CRT(0.7±0.5,P<0.05)。DVH显示,在10~30Gy之间,SGS-CRT膀胱平均受照体积(27.8%)明显低于IMRT(40.1%)和3D-CRT(57.4%,P<0.05);在5~45Gy之间,直肠平均受照射体积SGS-CRT(25.4%)明显低于IMRT(48.9%)和3D-CRT(73.2%,P<0.05);在小肠剂量分布上,三种照射方式无显著差异。结论在宫颈癌复发放疗中,SGS-CRT具有一定剂量学优势,值得在临床应用中进一步探讨。     

Dosimetry of combined intracavitary and external irradiation of carcinoma of the uterine cervix.

Dose distribution around intracavitary applicators (Stockholm technique) has been investigated. The gradient of dose around the combination of intrauterine and vaginal applicators used is steep. The position of the uterus with and without the radium applicators inserted varies. Together with the steep dose gradient this implies that external irradiation following intracavitary treatment involves a risk for overdosage to tissues in the vicinity of the uterus and underdosage to the parametrium.     

Dosimetry comparison between interstitial and intracavitary irradiation in the treatment of uterine cervix cancer

Locally advanced carcinoma of the uterine cervix, and carcinoma of the cervical stump are managed primarily by endocurietherapy [ECT] combined with external-beam pelvic irradiation. Two afterloading techniques of endocurietherapy are used, first, the intracavitary technique with 137Cesium, and second, the interstitial technique with 192Iridium. Because of displacement of the bladder and rectum away from the applicator in intracavitary ECT, compared to interstitial ECT where vaginal packing cannot be used, the rectal and bladder reference point doses are much lower. The use of the interstitial endocurietherapy technique should be limited to specific presentations where the distorted anatomy does not permit good intracavitary dosimetry in cases of locally advanced cervical and cervical stump cancers. A higher risk of major bowel and bladder complications must be accepted in order to achieve local tumor control if the Transperineal Template 192Iridium Endocurietherapy is required and used.     

Dosimetry of lower segment irradiation in Hodgkin disease. II. Radiation burden of risk organs

The radiation exposure of the risk organs kidneys, spinal marrow, gonads, liver, and pancreas was determined for three different photon energies (Co-60, continuous radiation with 6 MV and 10 MV) at the inverted Y field, as it is applied generally for the infradiaphragmatic segment irradiation of malignant lymphomas. For this purpose, the authors made use of the thermoluminescence dosimetry and film dosimetry in the Alderson phantom. The most important results are: More than half of the left kidney receives more than 50% of the applied focal dose, about 20% receive more than 90% of the focal dose. The participation of the right kidney is minimal. If the dose exceeds 20 Gy, the lumbar spinal marrow is sufficiently protected by a satellite in the dv field. A displacement of the ovaries in caudomedial direction behind the vesical absorber does not protect the ovarian function in a satisfactory manner; the ovaries should be displaced in craniolateral direction on the alae ossis ilii. We recommend the use of a testicular lead protection even if the inguinal lymph nodes are only irradiated with the vd field.