Thyroid exposure to scattered radiation and associated second cancer risk from paediatric radiotherapy for extracranial tumours.

This study was conducted to estimate the scattered thyroid dose and relevant second cancer risk from radiotherapy for extracranial tumours during childhood.  Anteroposeterior and posteronaterior field irradiations employed during the treatment of Hodgkin's disease, neuroblastoma and Wilms' tumour were simulated on two humanoid phantoms representing 5- and 10-y-old patients. Measurements were performed using thermoluminescent dosemeters. Practical thyroid lead shields with thicknesses of 2-10 mm were placed in the phantoms' neck region. The lifetime risk for cancer induction was assessed using sex- and age-specific risk factors. Thyroid dose per monitor unit varied from 28.1 to 492.4 µGy by the primary irradiation site and patient's age. The 10-mm-thick lead shield led to a dose reduction up to 28.9 %. For typical prescribed tumour doses, the total risks for thyroid cancer development after radiotherapy of 5- and 10-y-old male patients were 0.05-0.99  and 0.03-0.48 %, respectively. The corresponding risks for females increased to 0.29-5.51 and 0.17-2.94 %.

Peripheral dose measurements for 6 and 18 MV photon beams on a linear accelerator with multileaf collimator.

Peripheral dose (PD) to critical structures outside treatment volume is of clinical importance. The aim of the current study was to estimate PD on a linear accelerator equipped with multileaf collimator (MLC). Dose measurements were carried out using an ionization chamber embedded in a water phantom for 6 and 18 MV photon beams. PD values were acquired for field sizes from 5 x 5 to 20 x 20 cm2 in increments of 5 cm at distances up to 24 cm from the field edge. Dose data were obtained at two collimator orientations where the measurement points are shielded by MLC and jaws. The variation of PD with the source to skin distance (SSD), depth, and lateral displacement of the measurement point was evaluated. To examine the dependence of PD upon the tissue thickness at the entrance point of the beam, scattered dose was measured using thermoluminescent dosemeters placed on three anthropomorphic phantoms simulating 5- and 10-year-old children and an average adult patient. PD from 6 MV photons varied from 0.13% to 6.75% of the central-axis maximum dose depending upon the collimator orientation, extent of irradiated area, and distance from the treatment field. The corresponding dose range from 18 MV x rays was 0.09% to 5.61%. The variation of PD with depth and with lateral displacements up to 80% of the field dimension was very small. The scattered dose from both photon beams increased with the increase of SSD or tissue thickness along beam axis. The presented dosimetric data set allows the estimation of scattered dose outside the primary beam.

Data required for testicular dose calculation during radiotherapy of seminoma.

The purpose of this study was to provide the required data for the direct calculation of testicular dose resulting from radiotherapy in patients with seminoma. Paraortic (PA) treatment fields and dog-leg (DL) portals including paraortic and ipsilateral pelvic nodes were simulated on a male anthropomorphic phantom equipped with an artificial testicle. Anterior and posterior irradiations were performed for five different PA and DL field dimensions. Dose measurements were carried out using a calibrated ionization chamber. The dependence of testicular dose upon the distance separating the testicle from the treatment volume and upon the tissue thickness at the entrance point of the beam was investigated. A clamshell lead shield was used to reduce testicular dose. The scattered dose to testicle was measured in nine patients using thermoluminescent dosimeters. Phantom and patient exposures were generated with a 6 MV x-ray beam. Linear and nonlinear regression analysis was employed to obtain formulas describing the relation between the radiation dose to an unshielded and/or shielded testicle with the field size and the distance from the inferior field edge. Correction factors showing the variation of testicular dose with the patient thickness along beam axis were found. Bland-Altman statistical analysis showed that testicular dose obtained by the proposed calculation method may differ from the measured dose value by less than 25%. The current study presents a method providing reasonable estimations of testicular dose for individual patients undergoing PA or DL radiotherapy.

Phase I/II trial of external irradiation plus medium-dose brachytherapy given concurrently to liposomal doxorubicin and cisplatin for advanced uterine cervix carcinoma.

BACKGROUND AND PURPOSE: Although the standard of care for patients with locally advanced uterine cervix carcinoma is cisplatin-(CDDP-)based chemotherapy and irradiation (RT), the optimal regimen remains to be elucidated. A phase I/II study was conducted to evaluate the dose limiting toxicity (DLT) and the maximum tolerated dose (MTD) of liposomal doxorubicin (Caelyx) combined with CDDP and RT for cervical cancer. PATIENTS AND METHODS: 24 patients with stage IIB-IVA were enrolled (Table 1). They all received external RT (up to 50.4 Gy) and two medium-dose rate (MDR) brachytherapy implants (20 Gy each at point A). The Caelyx starting dose of 7 mg/m2/week was increased in 5-mg/m2 increments to two levels. The standard dose of CDDP was 20-25 mg/m2/week. RESULTS: Concurrent chemoradiation (CCRT) sequelae and the DLTs (grade 3 myelotoxicity and grade 3 proctitis in five patients treated at the 17 mg/m2/week Caelyx dose level) are shown in Tables 2, 3, 4, and 5. After a median follow-up time of 17.2 months (range 4-36 months), four patients had died, 15 showed no evidence of progressive disease, and five (20.8%, 95% confidence interval [CI]: 12.5-29.1%) were alive with relapse (Figure 1). There were seven complete (29.1%, 95% CI: 19.8-38.4%) and 17 partial clinical responses (95% CI: 61.1-80.1%). The median progression-free survival was 10.4 months. Causes of death were local regional failure with or without paraaortic node relapse combined with distant metastases (Table 6). CONCLUSION: The MTD of Caelyx given concurrently with CDDP and RT was determined at the 12 mg/m2/week dose level. The above CCRT schema is a well-tolerated regimen, easy to administer in ambulatory patients, and results appear promising.

Influence of initial electron beam parameters on Monte Carlo calculated absorbed dose distributions for radiotherapy photon beams.

Our aim in the present study was to investigate the effects of initial electron beam characteristics on Monte Carlo calculated absorbed dose distribution for a linac 6 MV photon beam. Moreover, the range of values of these parameters was derived, so that the resulted differences between measured and calculated doses were less than 1%. Mean energy, radial intensity distribution and energy spread of the initial electron beam, were studied. The method is based on absorbed dose comparisons of measured and calculated depth-dose and dose-profile curves. All comparisons were performed at 10.0 cm depth, in the umbral region for dose-profile and for depths past maximum for depth-dose curves. Depth-dose and dose-profile curves were considerably affected by the mean energy of electron beam, with dose profiles to be more sensitive on that parameter. The depth-dose curves were unaffected by the radial intensity of electron beam. In contrast, dose-profile curves were affected by the radial intensity of initial electron beam for a large field size. No influence was observed in dose-profile or depth-dose curves with respect to energy spread variations of electron beam. Conclusively, simulating the radiation source of a photon beam, two of the examined parameters (mean energy and radial intensity) of the electron beam should be tuned accurately, so that the resulting absorbed doses are within acceptable precision. The suggested method of evaluating these crucial but often poorly specified parameters may be of value in the Monte Carlo simulation of linear accelerator photon beams.

Conceptus radiation dose and risk from chest screen-film radiography.

The objectives of the present study were to (a) estimate the conceptus radiation dose and risks for pregnant women undergoing posteroanterior and anteroposterior (AP) chest radiographs, (b) study the conceptus dose as a function of chest thickness of the patient undergoing chest radiograph, and (c) investigate the possibility of a conceptus to receive a dose of more than 10 mGy, the level above which specific measurements of conceptus doses may be necessary. Thermoluminescent dosimeters were used for dose measurements in anthropomorphic phantoms simulating pregnancy at the three trimesters of gestation. The effect of chest thickness on conceptus dose and risk was studied by adding slabs of lucite on the anterior and posterior surface of the phantom chest. The conceptus risk for radiation-induced childhood fatal cancer and hereditary effects was calculated based on appropriate risk factors. The average AP chest dimension (d(a)) was estimated for 51 women of childbearing age from chest CT examinations. The value of d(a) was estimated to be 22.3 cm (17.4-27.2 cm). The calculated maximum conceptus dose was 107 x 10(-3) mGy for AP chest radiographs performed during the third trimester of pregnancy with maternal chest thickness of 27.2 cm. This calculation was based on dose data obtained from measurements in the phantoms and d(a) estimated from the patient group. The corresponding average excess of childhood cancer was 10.7 per million patients. The risk for hereditary effects was 1.1 per million births. Radiation dose for a conceptus increases exponentially as chest thickness increases. The conceptus dose at the third trimester is higher than that of the second and first trimesters. The results of the current study suggest that chest radiographs carried out in women at any time during gestation will result in a negligible increase in risk of radiation-induced harmful effects to the unborn child. After a properly performed maternal chest X-ray, there is no need for individual conceptus dose estimations.

Assessment of patient effective radiation dose and associated radiogenic risk from extracorporeal shock-wave lithotripsy.

The aim of the present study was to calculate patient effective dose and associated radiogenic risk from fluoroscopy guided extracorporeal shock-wave lithotripsy procedures. Fluoroscopy required during extracorporeal shock-wave lithotripsy was classified in two types identified by beam orientation: antero-posterior and 30 degrees anterior-oblique projected exposures. Duration of each exposure was monitored in 124 patients undergoing extracorporeal shock-wave lithotripsy treatment for ureteral stones. The dose from a kidney-ureter-bladder radiograph and the dose per min of fluoroscopy along antero-posterior and anterior-oblique projections were measured at 13 organs/tissues using an anthropomorphic phantom and thermoluminescence dosimetry. A radio-opaque object was placed in the phantom to simulate an ureteral stone at the proximal and distal ureter. The total effective dose in male and female patients with proximal ureteral stones was 1.71 mSv and 1.82 mSv, respectively. The corresponding values for male and female patients with distal ureteral stones was 0.76 mSv and 1.62 mSv, respectively. In the United States, the theoretical sex-averaged radiogenic excess of fatal cancers was estimated to be 140 per million and 85 per million of patients treated for proximal and distal ureteral stone, respectively. The average radiogenic risk for genetic defect associated to treatments of proximal and distal ureteral stones was found to be 2.5 and 24.4 per million of births, respectively. The radiation risk from a typical fluoroscopy guided extracorporeal shock-wave lithotripsy treatment of ureteral stones is low. Presented data may be used to determine patient effective dose from extracorporeal shock-wave lithotripsy procedures performed in any laboratory.

Comparison of four methods for assessing patient effective dose from radiological examinations.

Three methods of indirect effective dose estimation were reviewed and compared to a direct effective dose determination method. An anthropomorphic phantom and thermoluminescence dosimetry were used to obtain dosimetric data associated with anterior-posterior (AP) abdominal radiography, posterior-anterior (PA) chest radiography, PA head radiography, and AP heart fluoroscopy. Effective dose was determined using: (i) organ specific dose values directly determined by thermoluminescence dosimeters, (ii) data published by National Radiological Protection Board (NRPB) and entrance surface dose (ESD), (iii) NRPB data and dose area product (DAP), (iv) energy imparted derived from DAP. The effective dose values estimated from the Rando phantom measurements were 161, 32.3, and 8.4 microSv/projection for the abdomen, chest, and head radiographs, respectively. Cardiac fluoroscopy yielded an effective dose value of 111 microSv/min. The effective dose values obtained indirectly using NRPB data and DAP were in good agreement with directly assessed values in all simulated exposures (difference <8%). The effective doses using NRPB data and ESD values differed from directly assessed values by less than 15% for the radiographic exposures and 60% for heart fluoroscopy. The energy imparted method yielded 136, 31, and 6.6 microSv/projection for the abdomen, chest, and head radiographs, respectively, and 111 microSv/min for heart fluoroscopy. Indirect patient effective dose determination using the NRPB dosimetric data and the measured value of incident radiation allows for reliable patient effective dose estimates. The use of DAP rather than ESD is recommended because it yields accurate results even for complex radiologic exposures involving fluoroscopy. The value of energy imparted may be used for the accurate determination of patient effective dose, especially when specific organ dose values are not of interest. The calculation of energy imparted with the use of EAP provides a reliable starting point for estimation of effective dose from radiologic examinations for which dosimetric data are not provided by NRPB.