Enhanced Renal Toxicity of Total Body Irradiation Combined with Radioimmunotherapy

PURPOSE: Total body irradiation (TBI) with and without additional radioimmunotherapy (RIT) was examined for renal toxicity after stem cell transplantation. PATIENTS AND METHODS: Serum creatinine levels of 35 patients (15 female, 20 male, median age 40.5 years, range 17-60 years) after TBI alone and of 23 patients (eight female, 15 male, median age 47, range 16-58 years) after TBI with additional RIT were determined between 10/1997 and 11/1999. TBI was performed by external-beam radiotherapy in six fractions over 3 days with renal doses of 12 Gy in the TBI-alone group and 6 Gy in the group with additional RIT. The mean kidney dose due to the (188)Re-radiolabeled antibody was estimated to be 8.3 Gy (2.3-11.6 Gy). RESULTS: Within 12 months after treatment, creatinine levels increased from 77 mmol/l (SD +/- 11) to 89 mmol/l (SD +/- 20) for TBI alone and from 78 mmol/l (SD +/- 13) to 144 mmol/l (SD +/- 52) for combined TBI and RIT. CONCLUSION: Despite a 50% reduction of the external-beam contribution to the kidney dose, the application of approximately 10 GBq (188)Re-labeled anti-CD66 monoclonal antibody with a calculated renal dose of 8.3 Gy (range 2.3-11.5 Gy) led to renal toxicity, as reported previously. In the absence of a positive dose-response relationship for the (188)Re-labeled antibody, the observation may be explained by an underestimation of the biologically effective dose and the inaccuracy of the dose determination at the glomerular level.     

20 Years of Experience in Static Intensity-Modulated Total-Body Irradiation and Lung Toxicity

PURPOSE: To analyze lung complications after allogeneic or autologous transplantation following total-body irradiation (TBI) with compensators, so-called sIMRT (static intensity-modulated radiotherapy). PATIENTS AND METHODS: Between 1983 and 1998, 257 patients with different hematologic malignancies underwent TBI in six fractions to a total dose of 12 Gy within 3 consecutive days (212 with 11 Gy lung dose) prior to allogeneic (n=174) or autologous (n=83) transplantation. 40 patients were <16 years of age. Minimum follow-up time was 5 years. Median follow-up period was 110 months (13-231 months). RESULTS: 5-year survival rate was 47.9%, 5-year tumor-related mortality 23%, 5-year treatment-related mortality 29.2% (12 Gy lung dose: 53.3%+/-14.6%, 11 Gy: 24.1%+/-5.7%). Interstitial pneumonitis (IP) developed in 28 of 257 patients (10.9% +/- 3.8%). IP incidences in the allogeneic and autologous groups were 14.4% (+/-5.6%) and 3.6% (0-7.6%), respectively. IP incidences with 12/11 Gy lung dose were 22% (+/-12%)/8.5% (+/-3.7%). IP mortality was 9.3% (+/-3.6%). 13 of 28 patients with IP had a cytomegalovirus infection, five an acute graft-versus-host disease grade IV of the lungs. IP incidences with 12/11 Gy lung dose were 25% (9-50%)/4.2% (0.2-19.1%) in patients <16 years, and 20.7% (9.4-37.4%) and 13.3% (+/-6.5%) in older patients after allogeneic transplantation. CONCLUSION: Compensator-generated static intensity-modulated TBI with a total dose of 12 Gy and a lung dose of 11 Gy is a modern and comfortable treatment with moderate lung toxicity, small dose inhomogeneities and little setup failure before transplantation. Especially patients <16 years of age benefit from lung dose reduction.     

Clinical application of GAFCHROMIC EBT film for in vivo dose measurements of total body irradiation radiotherapy.

The GAFCHROMIC EBT film model is a fairly new film product designed for absorbed dose measurements of high-energy photon beams. In vivo dosimetry for total body irradiation (TBI) remains a challenging task due to the extended source-to-surface distance (SSD), low dose rates, and the use of beam spoilers. EBT film samples were used for dose measurements on an anthropomorphic phantom using a TBI setup. Additionally, in vivo measurements were obtained for two TBI patients. Phantom results verified the suitability of the EBT film for TBI treatment in terms of accuracy, reproducibility, and dose linearity. Doses measured were compared to conventional dosimeter measurements using thermoluminescent dosimeters (TLDs), resulting in an agreement of 4.1% and 6.7% for the phantom and patient measurements, respectively. Results obtained from the phantom and patients confirm that GAFCHROMIC EBT films are a suitable alternative to TLDs as an in vivo dosimeter in TBI radiotherapy.     

Basic and clinical studies of total body irradiation for bone marrow transplantation

Basic and clinical studies of total body irradiation (TBI) with respect to the dose distribution are described. TBI was performed with 10 MV X-rays at the Department of Radiology of Hyogo College of Medicine Hospital. Two opposed bilateral fields were used, the source-axis distance was 400 cm, and the dose rate was 10 cGy/min. At 55 cm from the rear concrete wall, the back-scattered radiation from the wall was 0.91% of the radiation dose. The beam flatness was +/- 2.9% within 130 cm of the diagonal by using a beam flattening filter improved. The surface dose was 93.5% of the peak dose by the acrylic bolus (1.5 cm thickness) placed on the source side 45 cm from the center of the body axis. We devised compensating filters using lead plates to improve dose distribution of the head, neck and thorax. The effectiveness of the compensating filters in producing a homogeneous dose distribution was checked by the thermoluminescent dosimeters (TLDs) in a Rando phantom. The average dose distribution to each site when the compensators used was 94% for the head, 104% for the neck, and 99% for the thorax when the scheduled dose was taken as 100%. TBI was performed 4 to 1 days before bone marrow transplantation, and 10 Gy was given in equal daily fractions of 2.5 Gy over 4 days. During TBI, the patients were placed in the supine position with the knees bent. The body surface dose was measured with pairs of TLDs at the head, neck, thorax, and pelvis in 32 patients. At the pelvis, the dose was measured simultaneously with an ionization chamber. The average doses were 91% for the head, 95% for the neck, 93% for the thorax, and 106% for the pelvis.     

Evaluation of the accuracy of a compensating filter based on compact NC-Mill for radiation therapy

The present report describes the fabrication technique and dosimetry aspects of a desktop numerically controlled milling machine (NC-Mill) based a compensator system that uses lead clay (Shield cray, Reactor Experiments, Inc., U.S.A.). Effective path lengths of patients were determined for CT image sets using the ray-tracing technique and converted to compensator thickness with the equivalent TMR method. Rigid urethane foam was processed with the NC-Mill to produce a mold for filters, and the lead clay was adopted as the compensating material. The dose distribution was measured on the compensating plane of an anthropomorphic phantom and a stair-step PMMA phantom. It was found that the radiation field with inhomogeneous dose was as high as 30%+/-3% with the compensating filters. In addition, when the absorbed dose at the central axis of 52 compensating filters that were used clinically was measured, 75.0% showed an error of less than +/-3%, and 3.8% showed the maximum dose error: >+/-5%. Overall, the present system was capable of producing dose uniformity to within +/-5% for a stair-step phantom, an anthropomorphic phantom, and clinical situations.     

Total body irradiation using a modified standing technique: a single institution 7 year experience.

We describe a simple standing technique for delivering total body irradiation (TBI) using large horizontal fields, made possible by the off-centre installation of a non-dedicated treatment unit in a pre-existing bunker. Patients are treated using anterior and posterior fields with customized lung compensators. This technique enables the dose to the lung to be accurately calculated and modified to avoid overdose and to minimize the risk of pneumonitis. From February 1991 to December 1997, 94 patients with a variety of haematological malignancies were given fractionated TBI using this technique prior to allogenic or autologous bone marrow transplantation. Patients received a total dose of 14.4 Gy given in eight fractions over 4 days, with at least 6 h between fractions. The prescribed dose to the lungs was reduced to 12 Gy in eight fractions. The technique was well tolerated, took less than 10 min to set up and did not disrupt the daily routine use of the machine. Doses to all measured points on the trunk and head were within +/-6% of the prescribed dose. Doses to the lungs were within +/-5% of the prescribed dose. There were no early respiratory deaths in the 37 autologous transplant patients. There were 10 (17%) respiratory deaths in the 57 allogeneic transplant patients, 3 of confirmed infectious aetiology.     

In vivo ESR dosimetry in total body irradiation

Total body irradiation (TBI) using high doses (about 10 Gy) with photons in the range between 1 and 10 MV combined with intensive chemotherapy has been used successfully in treatment of acute and chronic leukemia before bone marrow transplantation. One of the principal international guidelines in TBI is to use in vivo dosimetry in order to compare the prescribed dose with that absorbed. The use of in vivo dosimetry is also useful as a retrospective evaluation of any deviation from the prescribed dose greater than +/- 5% for relevant parts of the body, especially in the lung and in other organs at risk. In this paper, Electron Spin Resonance (ESR), using alanine dosimeters, is demonstrated to be a powerful tool for absorbed dose evaluation in TBI by detection of free radicals produced in alanine by ionizing radiation. In this study, we present the results obtained using ESR dosimetry in eleven patients undergoing TBI. The major advantages appear to be: 1. the ESR signal in alanine dosimetry is stable for years without fading: 2. the detection of the ESR signal does not destroy the information and so enables a retrospective judgment of the TBI plan adopted.     

电离室灵敏体积对调强放射治疗剂量学验证准确性的影响

目的研究电离室灵敏体积对调强放射治疗绝对剂量验证的影响。方法将调强治疗计划移植到重建的数字化体模上计算吸收剂量，对单个照射野和整个计划，分别在等中心点、最大剂量点以及剂量梯度大和剂量分布均匀的区域选取一些有代表意义的剂量点，用0．6、0．125和0．015cc电离室在固体水体模中分别测量各点的吸收剂量，并与TPS计算值进行比较。结果等中心和剂量分布均匀区域，各电离室测量值与计算值的相对误差均在5％范围内；最大剂量点和剂量梯度较大区域，0．6cc电离室误差达到8％和12％，小体积电离室误差较小。结论0．6和0．125cc电离室可用于剂量梯度较小处的绝对剂量验证，在最大剂量点和剂量梯度大的区域，误差较大，0．015cc电离室较适用于调强放射治疗剂量验证。     

Long-term effects of total-body irradiation on the kidney of Rhesus monkeys

PURPOSE: To investigate the long-term effects of total-body irradiation (TBI) on kidneys in non-human primates. METHODS AND MATERIALS: The kidneys of Rhesus monkeys were histologically examined at 6-8 years after TBI with low single doses of 4.5-8.5Gy or two fractions of 5.4Gy. The kidneys of age-matched non-irradiated monkeys served as controls. Irradiation was performed on adult monkeys aged about 3 years; 6-8 years later animals were sacrificed and the kidneys removed and processed for histology. A semi-quantitative scoring system was used to evaluate overall histological damage. Glomerular changes were also morphometrically analysed according to previously published criteria. In selected dose groups (pro)thrombotic and inflammatory changes were investigated by immunostaining cryosections with antibodies against von Willebrand factor (vWF), leukocytes and macrophages. RESULTS: Histological changes were generally mild and only seen in kidneys irradiated with doses higher than 7 Gy. Glomerular changes were characterized by increased mesangial matrix and capillary dilatation. Tubulo-interstitial changes included hypercellularity, fibrosis and mild tubular atrophy. The mean glomerular area expressing vWF protein in the irradiated kidneys was not different from that in the age-matched controls. Numbers of infiltrating leukocytes were not significantly different between irradiated kidneys and controls. However, slightly increased numbers of macrophages were present in the renal cortex after irradiation. CONCLUSIONS: Renal damage after TBI of Rhesus monkeys with single doses of 4.5-8.5 Gy or two fractions of 5.4 Gy was mild, even after follow-up times of 6-8 years.     

Relation between chromosomal aberrations and radiation dose during the process of TBI

PURPOSE: The purposes of this study were (1) to consider the dose-response relationship in-vivo at high dose range by using the Colcemid method, which begins with predicting the risk of future late complication caused by a fixed dose of chromosomal aberration of peripheral lymphocytes after radiation emission and (2) to compare in-vivo and in-vitro dose-responses for chromosomal aberrations in lymphocytes of cancer patients undergoing total body irradiation (TBI). METHODS: Eight patients diagnosed with hematological malignancies entered this study. TBI planning with a 6 MV linear accelerator consisted of 4 Gy/2 fractions/day, and the total treatment dose was 12 Gy. RESULTS: At the observable dose range of up to 10 Gy, the unstable chromosomal aberrations of both dicentrics and fragments increased with the increment of irradiated dose, regardless of in-vivo or in-vitro irradiated samples. However, the average number of dicentrics and fragments obtained from in-vitro samples was found to be higher than that for in-vivo samples. CONCLUSION: This result strongly suggests that in-vivo dose-response curves are necessary to estimate the absorbed dose in-vivo. In-vivo dose-response curves obtained from cancer patients would be very important for standard curves for biodosimetry.     

Biodistribution and internal dosimetry of the 188Re-labelled humanized monoclonal antibody anti-epidemal growth factor receptor, nimotuzumab, in the locoregional treatment of malignant gliomas

OBJECTIVE: To evaluate the biodistribution, internal radiation dosimetry and safety of the 188Re-labelled humanized monoclonal antibody nimotuzumab in the locoregional treatment of malignant gliomas. METHODS: Single doses of 370 or 555 MBq of 188Re-labelled nimotuzumab were locoregionally administered to nine patients with recurrent high-grade gliomas, according to an approved dose-escalation study. SPECT, planar scintigraphy and magnetic resonance images were combined for dosimetric and pharmacokinetic studies. Blood and urine samples were collected to evaluate clinical laboratory parameters and for absorbed doses calculations. Biodistribution, internal dosimetry, human anti-mouse antibody response and toxicity were evaluated and reported. RESULTS: The 188Re-nimotuzumab showed a high retention in the surgically created resection cavity with a mean value of 85.5+/-10.3%ID 1 h post-injection. It produced mean absorbed doses in the tumour region of approximately 24.1+/-2.9 Gy in group I (patients receiving 370 MBq) and 31.1+/-6.4 Gy in group II (patients receiving 555 MBq); the normal organs receiving the highest absorbed doses were the kidneys, liver and urinary bladder. About 6.2+/-0.8%ID was excreted by the urinary pathway. The maximum tolerated dose was 370 MBq because two patients showed severe adverse effects after they received 555 MBq of 188Re-nimotuzumab. No patient developed human anti-mouse antibody response. CONCLUSIONS: A locoregional single dose of 188Re-labelled nimotuzumab of approximately 370 MBq could be used safely in the routine treatment of patients suffering with high-grade gliomas. The efficacy of this therapy needs to be evaluated in a phase II clinical trial.     

Fractionated and hyperfractionated total body irradiation in the conditioning of allogenic bone marrow transplant in acute lymphatic leukemia. Results

Two different Total Body Irradiation (TBI) regimens were employed (1981 to July 1983) in Genoa in the conditioning program for the allogeneic Bone Marrow Transplantation (BMT) of 22 patients suffering from Acute Lymphoblastic Leukemia (ALL) in remission (7 patients in 1st remission, and 15 in 2nd remission). All patients were treated with Cyclophosphamide -60 mg/kg administered for two consecutive days (day -7 and -6)--and subsequently underwent fractionated TBI (days -3, -2, -1), that is, our conventional TBI regimen: 3.3 Gy/day per 3 days (total dose: 9.9 Gy). From August 1983 through 1988, 33 patients (14 in 1st remission and 19 in 2nd remission) were given 2 Gy twice a day, 6 hours apart, for 3 consecutive days (total dose: 12 Gy). Cyclosporine A was used for GvHD prophylaxis. At 58 months, out of the total figure of ALL patients in 2nd remission, 19% of those treated with 9.9 Gy/3 fr/3 days (fractionated TBI) is likely to be in remission, versus 65% of the cases treated with 12 Gy/6 fr/3 days (p less than 0.01) (hyperfractionated TBI); the actuarial overall survival is 23% after fractionated vs 60% after hyperfractionated TBI (p = 0.05). The incidence of idiopathic interstitial pneumonitis was very low (3.6%). Thus, we conclude that, in ALL patients in second remission, hyperfractionated TBI (12 Gy/6 fr/3 days) yields better results than fractionated TBI (9.9 Gy/3 fr/3 days), with lower relapse rate (33% vs 83%) and higher survival.     

Radiation injury of boron neutron capture therapy using mixed epithermal- and thermal neutron beams in patients with malignant glioma.

The purpose of this study was to clarify the radiation injury in acute or delayed stage after boron neutron capture therapy (BNCT) using mixed epithermal- and thermal neutron beams in patients with malignant glioma. Eighteen patients with malignant glioma underwent mixed epithermal- and thermal neutron beam and sodium borocaptate between 1998 and 2004. The radiation dose (i.e. physical dose of boron n-alpha reaction) in the protocol used between 1998 and 2000 (Protocol A, n = 8) prescribed a maximum tumor volume dose of 15 Gy. In 2001, a new dose-escalated protocol was introduced (Protocol B, n = 4); it prescribes a minimum tumor volume dose of 18 Gy or, alternatively, a minimum target volume dose of 15 Gy. Since 2002, the radiation dose was reduced to 80-90% dose of Protocol B because of acute radiation injury. A new Protocol was applied to 6 glioblastoma patients (Protocol C, n = 6). The average values of the maximum vascular dose of brain surface in Protocol A, B and C were 11.4+/-4.2 Gy, 15.7+/-1.2 and 13.9+/-3.6 Gy, respectively. Acute radiation injury such as a generalized convulsion within 1 week after BNCT was recognized in three patients of Protocol B. Delayed radiation injury such as a neurological deterioration appeared 3-6 months after BNCT, and it was recognized in 1 patient in Protocol A, 5 patients in Protocol B. According to acute radiation injury, the maximum vascular dose was 15.8+/-1.3 Gy in positive and was 12.6+/-4.3 Gy in negative. There was no significant difference between them. According to the delayed radiation injury, the maximum vascular dose was 13.8+/-3.8 Gy in positive and was 13.6+/-4.9 Gy in negative. There was no significant difference between them. The dose escalation is limited because most patients in Protocol B suffered from acute radiation injury. We conclude that the maximum vascular dose does not exceed over 12 Gy to avoid the delayed radiation injury, especially, it should be limited under 10 Gy in the case that tumor exists in speech center.     

Myelotoxicity and RBE of 211At-conjugated monoclonal antibodies compared with 99mTc-conjugated monoclonal antibodies and 60Co irradiation in nude mice.

The rationale of this study was to determine the myelotoxicity in nude mice of the alpha-emitter 211At conjugated to monoclonal antibodies (mAbs) and to compare the effect with an electron emitter, (99m)Tc, and external irradiation from a 60Co source, for estimation of the relative biological effectiveness (RBE). METHODS: 211At and (99m)Tc were conjugated to the IgG1 mAbs MX35 and 88BV59. Nude female BALB/c mice, 8- to 12-wk old, were injected intraperitoneally or intravenously. The biodistribution was determined 3, 6, and 18 h after injection. The bone-to-blood and bone marrow-to-blood activity concentration ratios (BBLR and BMBLR, respectively) were determined for simultaneously injected 211At- and (99m)Tc-mAbs. Bone marrow samples were taken from the femur. For each mouse, the whole-body retention was measured as well as the blood activity by repeated blood samples from the tail vein (0), 1, 3, 6, 12, and 18 h after injection. External-beam irradiation from a 60Co source was also performed at 3 different dose levels. White blood cell (WBC) counts, red blood cell counts, platelet counts, and hemoglobin were determined for each mouse initially and on days 1, 4, 5, 7, 15, 22, and 27 after injection. The calculations of the absorbed dose to the bone marrow were based on the BBLR, BMBLR, the cumulated activities, and the absorbed fractions. The absorbed fractions, phi, for alpha-particles and electrons in the bone marrow were calculated using Monte Carlo simulations based on a bone marrow dosimetry model. RESULTS: The BMBLR was 0.58 +/- 0.06 and 0.56 +/- 0.06 for the 211At- and (99m)Tc-mAbs, respectively. No significant variation in BMBLR with time was found. The absorbed fractions for alpha-particles and electrons in the bone marrow were 0.88 and 0.75, respectively. The mean absorbed fractions of the photons from (99m)Tc were 0.033 and 0.52 for 140 and 18.3 keV, respectively. When different amounts of 211At- and (99m)Tc-mAbs (0.09-1.3 and 250-1,300 MBq, respectively) were administered intraperitoneally or intravenously, corresponding to absorbed doses to the bone marrow of 0.01-0.60 and 0.39-1.92 Gy, respectively, the WBC counts was suppressed by 1%-90% and 23%-89%, respectively. When external-beam irradiation with a 60Co source was performed to absorbed doses of 1.4, 1.9, and 2.4 Gy, the WBC counts was suppressed by 47%-90%. These results indicate a myelotoxic in vivo RBE of 3.4 +/- 0.6 for alpha-particles compared with (99m)Tc and 5.0 +/- 0.9 compared with 60Co irradiation. CONCLUSION: The effect on the WBC counts from bone marrow irradiation with 211At-mAbs indicates an in vivo RBE of 3.4 +/- 0.6 in comparison with (99m)Tc-mAbs. The RBE value compared with external irradiation is 5.0 +/- 0.9.     

Dosimetric analysis of radioimmunotherapy with 186Re-labeled bivatuzumab in patients with head and neck cancer.

From December 1999 until July 2001, a phase I dose escalation study was performed with (186)Re-labeled bivatuzumab, a humanized monoclonal antibody against CD44v6, on patients with inoperable recurrent or metastatic head and neck cancer. The aim of the trial was to assess the safety and tolerability of intravenously administered (186)Re-bivatuzumab and to determine the maximum tolerated dose (MTD) of (186)Re-bivatuzumab. The data were also used for dosimetric analysis of the treated patients. Dosimetry is used to estimate the absorbed doses by nontarget organs, as well as by tumors. It can also help to explain toxicity that is observed and to predict organs at risk because of the therapy given. METHODS: Whole-body scintigraphy was used to draw regions around sites or organs of interest. Residence times in these organs and sites were calculated and entered into the MIRDOSE3 program, to obtain absorbed doses in all target organs except for red marrow. The red marrow dose was calculated using a blood-derived method. Twenty-one studies on 18 patients, 5 female and 16 male, were used for dosimetry. RESULTS: The mean red marrow doses were 0.49 +/- 0.03 mGy/MBq for men and 0.64 +/- 0.03 mGy/MBq for women. The normal organ with the highest absorbed dose appeared to be the kidney (mean dose, 1.61 +/- 0.75 mGy/MBq in men and 2.15 +/- 0.95 mGy/MBq in women; maximum kidney dose in all patients, 11 Gy), but the doses absorbed are not expected to lead to renal toxicity. Other organs with doses exceeding 0.5 mGy/MBq were the lungs, the spleen, the heart, the liver, the bones, and the testes. The doses delivered to the tumor, recalculated to the MTD level of 1.85 GBq/m(2), ranged from 3.8 to 76.4 Gy, with a median of 12.4 Gy. A good correlation was found between platelet and white blood cell counts and the administered amount of activity per kilogram of body weight (r = -0.79). CONCLUSION: Dosimetric analysis of the data revealed that the range of doses to normal organs seems to be well within acceptable and safe limits. Tumor doses ranged from 4 to 76 Gy. Given the acceptable tumor doses, (186)Re-labeled bivatuzumab could be a good candidate for future adjuvant radioimmunotherapy in patients with minimal residual disease.     

Concepts for critical organ dosimetry in three-dimensional image-based breast brachytherapy

PURPOSE: To investigate dose-volume histogram (DVH) parameters for organs at risk (OARs) in sectional three-dimensional image-based accelerated partial breast irradiation. METHODS AND MATERIALS: Skin, lung, and ribs were defined as OARs and the heart was discussed. Two different skin-contouring methods were tested on phantom before applying to the patient cohort. First, an inside skin wall contour was delineated with three different wall thicknesses to demonstrate the influence of contouring on DVH parameter. Second a structure was defined, delineated outside of the phantom surface, such that a three-dimensional skin volume was extended like a virtual bolus contour. Point dose values and DVH parameters were reported for 25 patient cases. RESULTS: The DVH parameters D0.1 cc = 65+/-21, D1 cc = 45+/-8, and D10 cc = 30+/-4 cGy/pulse for the outside skin structure around the breast corresponded to skin surface areas of 1+/-1, 6+/-3, and 6+/-11cm2. Lung volume receiving 20 Gyalphabeta3 was 8.3+/-11cm3. D0.1 cc and D2 cc in the most exposed rib were 0.7+/-0.3 and 0.4+/-0.2 Gy/pulse, respectively. CONCLUSION: In accelerated partial breast irradiation treatment planning, dose to OAR can be reported in a more sophisticated way with DVH parameters than using points only. The suggested method of skin delineation using the defined outside structure allows calculating reliable and reproducible DVH parameters.     

The dose response of normoxic polymer gel dosimeters measured using X-ray CT

X-ray CT was used to determine the dose response of normoxic polymer gel dosimeters. Normoxic polymer gel dosimeters were manufactured and irradiated up to 150 Gy. Up to 50 CT images were acquired on a Toshiba Aquilion Multislice CT scanner using protocols for 80 kV and 135 kV to determine dose response. HU-dose sensitivity, the linear regression of data for the HU versus dose for the linear part of the curve up to 60 Gy was 0.38+/-0.07 HU Gy(-1) for 135 kV and 0.37+/-0.01 HU Gy(-1) for 80 kV. Dose resolution was found to be < 1.3 Gy for an absorbed dose range up to 70 Gy for 135 kV, similar to that measured previously for polyacrylamide gel (PAG). Although the HU-dose sensitivity was lower than that previously measured for PAG gel dosimeters it had a greater range of absorbed dose indicating that normoxic polymer gel dosimeters have potential in CT gel dosimetry.     

Dose response characteristics and basic dose distribution data for a polymerization-based dosemeter gel evaluated using MR

A safe and reproducible mixing procedure for the manufacture of a polymerization-based dosemeter gel evaluated using MRI (PoMRI) is presented. The dose response, obtained by irradiating gel-filled vials with absorbed doses in the interval 0-20 Gy and evaluated with respect to 1/T2, was found to be linear in the interval 0-8 Gy, with a sensitivity of 0.211 s-1Gy-1 (r2 = 0.998) at 1.5 T. Evaluation of the same set of vials with respect to 1/T1 gave a sensitivity of 0.018 s-1Gy-1 (r2 = 0.960). PoMRI and diode data were compared for standard photon and electron treatment beams. A deviation of less than 3% was found between the two methods for central depth dose curves as well as dose profiles (2 mm for electrons in the steep dose gradient regions). The importance of the method used for background correction for the reliability of the results was also evaluated. Barex (with a wall thickness of 1.5 mm) was investigated for use as phantom material and found to be favourable compared with glass. The results obtained in this study show that PoMRI has excellent potential as a 3D detector.