Haris Varveris

Radiation dose to conceptus resulting from tangential breast irradiation

PURPOSE To estimate the radiation dose to the conceptus resulting from tangential breast irradiation. METHODS AND MATERIALS Conceptus radiation doses were measured in anthropomorphic phantoms simulating the geometry of a pregnant woman at the first, second, and third trimesters of gestation. Medial and lateral field irradiations were generated using a 6-MV X-ray beam. Dose measurements were performed with thermoluminescent dosimeters. RESULTS For a treatment course delivering 50 Gy to the tumor, conceptus dose at the first trimester of gestation was found to be 2.1-7.6 cGy, depending on the field size used and the distance between conceptus and primary irradiation field. The corresponding dose ranges to the conceptus during the second and third trimesters of gestation were 2.2-24.6 cGy and 2.2-58.6 cGy, respectively. Dose data and formulas are presented to estimate conceptus dose for individual patients undergoing breast radiotherapy during the entire pregnancy. CONCLUSIONS This study may be of value in the management of pregnant women needing tangential breast irradiation, because it provides the required information to estimate conceptus dose.

Radiotherapy of Hodgkin's disease in early pregnancy: embryo dose measurements

BACKGROUND AND PURPOSE Limited information exists on the possibility of pregnant women undergoing radiotherapy for Hodgkins disease in early pregnancy. The purpose of this study was to measure embryo dose resulting from treatment of supra-diaphragmatic Hodgkins disease at the first trimester of gestation. MATERIALS AND METHODS A humanoid phantom was used to simulate pregnancy at the first trimester of gestation. Embryo dose, was measured using three different field sizes that may be applied for local field irradiation in each of the regions of neck, axilla, neck-mediastinum and for mantle treatment. A shielding device consisting of 5 cm of lead was used to reduce the embryo dose. Dose measurements were carried out using thermoluminescent dosimeters. Phantom exposures were made with a 6 MV photon beam. RESULTS Local field irradiation in the regions of neck or axilla always resulted in embryo doses below 10 cGy. For local field irradiation in the region of neck-mediastinum and for mantle treatment, the radiation dose to a shielded embryo was 2.8-18.6 and 4.2-24.5 cGy depending upon the distance from the field isocenter and the field size used, respectively. The corresponding dose for an unshielded embryo exceeded 10 cGy. All the above embryo doses were obtained for a tumor dose of 40 Gy. CONCLUSIONS Local field irradiation in the regions of neck or axilla may be safely performed even without uterus shielding. For local field irradiation in the region of neck-mediastinum and for mantle radiotherapy, the extent of the irradiated area, the distance separating the embryo from the field isocenter and the tumor dose are the factors, determining whether the radiation dose to a shielded embryo may possibly be reduced below 10 cGy.

Embryo/Fetus Radiation Dose and Risk from Dual X-ray Absorptiometry Examinations

Abstract: The aim of the current study was to estimate the embryo/fetus radiation doses and risks associated with spinal and hip dual X-ray absorptiometry (DXA) scans performed on the pregnant mother. The results were compared with the embryo/fetus dose from a thoracolumbar radiograph and pelvic radiograph. Posteroanterior (PA) lumbar spine and proximal femur scans during the first, second and third trimesters were performed on a phantom simulating pregnancy at the three trimesters of gestation. All scans were carried out using a Hologic 1000/W pencil beam DXA unit. Moreover, embryo/fetus doses from a (a) thoracolumbar radiograph and (b) pelvic radiograph were estimated for all periods of gestation using the same phantom. Radiation doses were measured using thermoluminescent dosimeters. The dose reduction achievable by shielding the embryo/fetus with a protective apron during DXA scans was studied for all trimesters of gestation. The embryo/fetus doses during the first trimester were measured to be 1.7 mGy and 2.7 mGy for the PA spine and femur DXA scan, respectively, for an embryo/fetus located 8.5 cm from the anterior maternal surface. The risk of excess fatal cancer was 0.2 per million unborn children irradiated in utero for measurements of the spine and 0.3 per million unborn children for measurements of the femur. The embryo/fetus doses during the second and third trimesters were 2.7 mGy and 4.9 mGy respectively for the scans of the lumbar spine. The risk of childhood fatal cancer was 0.3 per million for the second trimester and 0.5 per million for the third trimester. The embryo/fetus radiation doses during the second and third trimesters were estimated as 1.4 mGy and 1.0 mGy respectively for the examinations of the proximal femur. The risk of childhood fatal cancer was 0.1 per million for both trimesters. The use of the apron resulted in a very small change in the dose absorbed by the embryo/fetus. The embryo/fetus dose associated with both DXA modes investigated in the current study is at least 700 times lower in comparison with embryo/fetus dose from a thoracolumbar or pelvic radiograph in all periods of gestation. In conclusion, the embryo/fetus dose in bone density measurements of spine and femur using pencil beam DXA is lower than the average daily natural background in the United States of 8 mGy. The health provider can decide whether a DXA scanning is beneficial to a pregnant woman, taking into account the potential radiation risks to the embryo/fetus presented in the current study.

A METHOD OF ESTIMATING FETAL DOSE DURING BRAIN RADIATION THERAPY

PURPOSE To develop a simple method of estimating fetal dose during brain radiation therapy. METHODS AND MATERIALS An anthropomorphic phantom was modified to simulate pregnancy at 12 and 24 weeks of gestation. Fetal dose measurements were carried out using thermoluminescent dosimeters. Brain radiation therapy was performed with two lateral and opposed fields using 6 MV photons. Three sheets of lead, 5.1-cm-thick, were positioned over the phantoms abdomen to reduce fetal exposure. Linear and nonlinear regression analysis was used to investigate the dependence of radiation dose to an unshielded and/or shielded fetus upon field size and distance from field isocenter. RESULTS Formulas describing the exponential decrease of radiation dose to an unshielded and/or shielded fetus with distance from the field isocenter are presented. All fitted parameters of the above formulas can be easily derived using a set of graphs showing their correlation with field size. CONCLUSION This study describes a method of estimating fetal dose during brain radiotherapy, accounting for the effects of gestational age, field size and distance from field isocenter. Accurate knowledge of absorbed dose to the fetus before treatment course allows for the selection of the proper irradiation technique in order to achieve the maximum patient benefit with the least risk to the fetus.

Scattered dose to thyroid from prophylactic cranial irradiation during childhood: a Monte Carlo study

The purpose of this study was to estimate the scattered dose to thyroid from prophylactic cranial irradiation during childhood. The MCNP transport code and mathematical phantoms representing the average individual at ages 3, 5, 10, 15 and 18 years old were employed to simulate cranial radiotherapy using two lateral opposed fields. The mean radiation dose received by the thyroid gland was calculated. A 10 cm thick lead block placed on the patients couch to shield the thyroid was simulated by MCNP code. The Monte Carlo model was validated by measuring the scattered dose to the unshielded and shielded thyroid using three different humanoid phantoms and thermoluminescense dosimetry. For a cranial dose of 18 Gy, the thyroid dose obtained by Monte Carlo calculations varied from 47 to 79 cGy depending upon the age of the child. Appropriate placement of the couch block resulted in a thyroid dose reduction by 39 to 54%. Thyroid dose values at all possible positions of the radiosensitive gland with respect to the inferior field edge at five different patient ages were found. The mean difference between Monte Carlo results and thyroid dose measurements was 9.6%.

Radiation dose to laterally transposed ovaries during external beam radiotherapy for cervical cancer

The purpose of this study was to estimate the radiation dose to laterally transposed ovaries from external beam radiotherapy for cervical cancer. Dose measurements were performed in a modified humanoid phantom using a 6 MV photon beam. The dependence of the ovarian dose upon the field size, the distance from the primary irradiation field and the presence of wedges or gonadal shielding was determined. For a tumor dose of 45 Gy, ovarian dose was 0.88–8.51 Gy depending on the field size employed and the location of the transposed ovary in respect to the treatment field. Positioning of 7 cm thick shielding reduced the dose to ovary by less than 19%. The use of wedges increased the ovarian dose by a factor up to 1.5. Accurate radiographic localization of the ovaries allows the use of the presented dosimetric results to obtain a reasonable prediction of the ovarian dose.

Testicular dose and associated risk from inverted-Y field irradiation in patients with Hodgkin's disease

This study aims to estimate testicular dose and the associated risks for infertility and hereditary effects from inverted-Y field irradiation Radiotherapy was simulated on a humanoid phantom using a 6 MV photon beam. Testicular dose was measured for various field sizes and tissue thicknesses along beam axis using an ionization chamber. Gonadal dose was reduced by placing lead cups around the testes supplemented by a field edge block. For a tumor dose of 40 Gy, testicular dose was 0.56-6.52 Gy depending upon the field size and the distance from the inferior field edge. The corresponding dose to shielded testes was 0.12-1.96 Gy. The increase of tissue thickness in reased the testicular dose up to 40%. An excess risk of hereditary disorders of (7-391) per 10000 births was calculated. The treatment parameters, the presence of gonad shield and the somatometric characteristics determine whether testicular dose can exceed 1 Gy which allows a complete recovery of spermatogenesis.