Michael Mazonakis

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.

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.

Comparison of two volumetric techniques for estimating liver volume using magnetic resonance imaging

To compare the conventional technique of manual planimetry with the point counting technique for estimating liver volume from magnetic resonance imaging (MRI) data.

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.

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.

Radiation dose and cancer risk to children undergoing skull radiography

Background: Limited data exist in the literature concerning the patient-effective dose from paediatric skull radiography. No information has been provided regarding organ doses, patient dose during PA skull projection, risk of cancer induction and dose to comforters, i.e. individuals supporting children during exposure. Objective: To estimate patient-effective dose, organ doses, lifetime cancer mortality risk to children and radiation dose to comforters associated with skull radiography. Materials and methods: Data were collected from 136 paediatric examinations, including AP, PA and lateral skull radiographs. Entrance-surface dose (ESD) and dose to comforters were measured using thermoluminescent dosimeters. Patients were divided into the following age groups: 0.5–2, 3–7, 8–12 and 13–18 years. The patient-effective dose and corresponding organ doses were calculated using data from the NRPB and Monte Carlo techniques. The risk for fatal cancer induction was assessed using appropriate risk coefficients. Results: For AP, PA and lateral skull radiography, effective dose ranges were 8.8–25.4, 8.2–27.3 and 8.4–22.7 μSv respectively, depending upon the age of the child. For each skull projection, the organs receiving doses above 10 μGy are presented. The number of fatal cancers was found to be less than or equal to 2 per 1 million children undergoing a skull radiograph. The mean radiation dose absorbed by the hands of comforters was 13.4 μGy. Conclusions: The current study provides detailed tabular and graphical data on ESD, effective dose, organ doses and lifetime cancer mortality risk to children associated with AP, PA and lateral skull projections at all patient ages.

Calculation of organ doses from breast cancer radiotherapy: a Monte Carlo study

The current study aimed to: a) utilize Monte Carlo simulation methods for the assessment of radiation doses imparted to all organs at risk to develop secondary radiation induced cancer, for patients undergoing radiotherapy for breast cancer; and b) evaluate the effect of breast size on dose to organs outside the irradiation field. A simulated linear accelerator model was generated. The in‐field accuracy of the simulated photon beam properties was verified against percentage depth dose (PDD) and dose profile measurements on an actual water phantom. Off‐axis dose calculations were verified with thermoluminescent dosimetry (TLD) measurements on a humanoid physical phantom. An anthropomorphic mathematical phantom was used to simulate breast cancer radiotherapy with medial and lateral fields. The effect of breast size on the calculated organ dose was investigated. Local differences between measured and calculated PDDs and dose profiles did not exceed 2% for the points at depths beyond the depth of maximum dose and the plateau region of the profile, respectively. For the penumbral regions of the dose profiles, the distance to agreement (DTA) did not exceed 2 mm. The mean difference between calculated out‐of‐field doses and TLD measurements was 11.4%±5.9%. The calculated doses to peripheral organs ranged from 2.32 cGy up to 161.41 cGy depending on breast size and thus the field dimensions applied, as well as the proximity of the organs to the primary beam. An increase to the therapeutic field area by 50% to account for the large breast led to a mean organ dose elevation by up to 85.2% for lateral exposure. The contralateral breast dose ranged between 1.4% and 1.6% of the prescribed dose to the tumor. Breast size affects dose deposition substantially. PACS numbers: 87.10.rt, 87.56.bd, 87.53.Bn, 87.55.K‐, 87.55.ne, 87.56.jf, 87.56.J‐

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: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.Hintergrund und Ziel:Im Stadium IIB–IVA des Zervixkarzinoms stehen die simultane Strahlentherapie und Chemotherapie eindeutig im Vordergrund. Ihre Rolle bei der Behandlung gynäkologischer Malignome ist noch zu klären. Daher sollten bei Patientinnen mit Karzinomen der Cervix uteri, Stadium IIB–IVA, die sich einer kombinierten Behandlung mit Caelyx, CDDP und Radiotherapie (RT) unterzogen, die maximal tolerierte Dosis (MTD) und die dosislimitierende Toxizit.t (DLT) bestimmt werden.Patienten und Methodik:24 Patientinnen wurden in die Studie eingeschlossen (Tabelle 1). Alle erhielten eine externe Bestrahlung (bis 50,4 Gy) und zusätzlich zwei MDR-(Medium-Dose-Rate-)RT-Implantationen (je 20 Gy in Punkt A). Die Caelyx-Anfangsdosis von 7 mg/m2/Woche wurde in Schritten von 5 mg/m2 erhöht. Die Standarddosis von CDDP betrug 20–25 mg/m2/Woche. Caelyx (20 mg) und CDDP (50 mg) wurden während der ersten und zweiten intrauterinen Implantation infundiert.Ergebnisse:DLTs wurden bei fünf mit 17 mg/m2/Woche behandelten Patientinnen beobachtet. Dies hatte bei vier von sechs Patientinnen eine Verzögerung der Behandlung um 1 Woche zur Folge (Tabellen 2, 3, 4 und 5). Nach einer medianen Beobachtungszeit von 17,2 Monaten waren vier Patientinnen gestorben, 15 zeigten keine Progression, und fünf (20,8%, 95%-Konfidenzintervall [CI]: 12,5–29,1%) überlebten mit Rezidiven (Abbildung 1). Klinisch wurde bei sieben Patientinnen eine komplette (29,1%, 95%-CI: 19,8–38,4%) und bei 17 eine partielle Remission (95%-CI: 61,1–80,1%) festgestellt. Die mediane progressionsfreie Überlebenszeit betrug 10,4 Monate. Todesursachen waren lokoregionale Ausbreitung mit oder ohne Rezidiv in den paraaortalen Lymphknoten in Kombination mit Fernmetastasen (Tabelle 6).Schlussfolgerung:Die MTD von Caelyx bei gleichzeitiger Verabreichung mit CDDP und RT lag bei 12 mg/m2/Woche. Diese Dosis wurde gut vertragen. Sie wird für Phase-II/III-Studien empfohlen und scheint vielversprechende Ergebnisse zu zeitigen.

Bladder and rectum volume estimations using CT and stereology

Twelve prostate cancer patients underwent a treatment planning CT prior to radiotherapy. Stereologic method based on Cavalieri principle was applied to CT images. Systematic and random sampling of CT slices were performed with alternative ways for assessing the volumes of bladder and rectum. The contribution of point counting to the precision of the obtained volume estimations was analysed. It was found that 100-150 test points counted on only 5-7 systematically sampled slices through bladder or rectum suffice for reliable volume estimations of the above organs. Also, the superiority of systematic vs random sampling was confirmed. The suggested volumetric method gives the possibility of generating unbiased and efficient bladder and rectum volume assessments directly from CT data with great saving in labour.

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.