Organ Equivalent Dose Research Articles

EP-1615: Second cancer risk after radiation of localized prostate cancer with and without flattening filter

Purpose: Radiotherapy is a standard treatment modality with curative intent for localized prostate cancer. Prostate cancer is a disease of elderly men. Nevertheless these patients have a remaining life span of ten years or more. Radiotherapy compared to surgery may increase the risk for second cancer. Minimizing this risk can be one criterion in deciding for a specific technique. Therefore we compared the organ equivalent dose (OED) and excess absolute risk (EAR) for second cancer for different treatment techniques. Material and methods: For ten patients four different plans were calculated, using a seven field intensity modulated radiotherapy (IMRT) and a single arc volumetric modulated arc therapy (VMAT) with and without flattening filter. The optimization was performed as simultaneous integrated boost in 33 fractions, aiming for 59.4 Gy minimum dose to the PTV and 71.0 Gy minimum dose and 74.2 Gy maximum dose to the CTV. The OED was computed for the urinary bladder and the rectum from dose volume histograms for the linear-exponential and the plateau dose-response model. The EAR can be derived from the OED, taking age modifying parameters into account. The statistical analysis was performed using the Wilcoxon test in IBM® SPSS® Statistics 23 (IBM Corporation). Results: Within one technique (IMRT or VMAT) the average value of the OED is lower for the flattening filter free (FFF) mode compared to flat beams (FB) in both organs and for both dose-response models with one exception: In the urinary bladder it is the other way round for IMRT and the linear-exponential model. These results are statistically significant (level of significance 5%). The results for VMAT are statistically significant for the rectum only in both models. Comparing IMRT and VMAT the results are ambiguous: For the linear-exponential model the OED is lower with IMRT for both FB and FFF, for the plateau model lower OEDs are achieved with VMAT. All results are significant, except of one (lin-exp. model, FFF, urinary bladder, p = 7.4%). Conclusion: Some statistically significant differences have been found for the different treatment techniques and modes. However, they depend on the dose-response model. For the plateau model the lowest EAR is found for VMAT FFF in both organs at risk, for the linear-exponential model IMRT FB shows the minimum values. Plan quality and efficiency should additionally be regarded before the decision for a specific technique and mode.

Predicted Rate of Secondary Malignancies Following Adjuvant Proton Versus Photon Radiation Therapy for Thymoma

Thymic malignancies are the most common tumors of the anterior mediastinum. The benefit of adjuvant radiation therapy for stage II disease remains controversial, and patients treated with adjuvant radiation therapy are at risk of late complications, including radiation-induced secondary malignant neoplasms (SMNs), that may reduce the overall benefit of treatment. We assess the risk of predicted SMNs following adjuvant proton radiation therapy compared with photon radiation therapy after resection of stage II thymic malignancies to determine whether proton therapy improves the risk-benefit ratio. Ten consecutive patients treated with double-scattered proton beam radiation therapy (DS-PBT) were prospectively enrolled in an institutional review board-approved proton registry study. All patients were treated with DS-PBT. Intensity modulated radiation therapy (IMRT) plans for comparison were generated. SMN risk was calculated based on organ equivalent dose. Patients had a median age of 65years (range, 25-77years), and 60% were men. All patients had stage II disease, and many had close or positive margins (60%). The median dose was 50.4Gy (range, 50.4-54.0Gy) in 1.8-Gy relative biological effectiveness daily fractions.No differences in target coverage were seen with DS-PBT compared with IMRT plans. Significant reductions were seen in mean and volumetric lung, heart, and esophageal doses with DS-PBT compared with IMRT plans (all P≤.01). Significant reductions in SMNs in the lung, breast, esophagus, skin, and stomach were seen with DS-PBT compared with IMRT. For patients with thymoma diagnosed at the median national age, 5 excess secondary malignancies per 100 patients would be avoided by treating them with protons instead of photons. Treatment with proton therapy can achieve comparable target coverage but significantly reduced doses to critical normal structures, which can lead to fewer predicted SMNs compared with IMRT. By decreasing expected late complications, proton therapy may improve the therapeutic ratio of adjuvant radiation therapy for patients with stage II thymic malignancies.

Calculation of conversion coefficients using Chinese adult reference phantoms for air submersion and ground contamination

The effective and organ equivalent dose coefficients have been widely used to provide assessment of doses received by adult members of the public and by workers exposed to environmental radiation from nuclear facilities under normal or accidental situations. Advancements in phantom types, weighting factors, decay data, etc, have led to the publication of newer results in this regard. This paper presents a new set of conversion coefficients for air submersion and ground contamination (with the use of Geant4) for photons from 15 keV to 10 MeV using the Chinese and International Commission on Radiological Protection (ICRP) adult reference male and female phantoms. The radiation fields, except for energy spectrum at low energies, were validated by the data obtained from the Monte Carlo code YURI. The effective dose coefficients of monoenergetic photons, obtained for the ICRP adult reference phantoms, agree well with recently published data for air submersion and ground contamination with a plane source at a depth of 0.5 g cm−2 in soil, but an average difference of 36.5% is observed for ground surface contamination with the abovementioned radiation field. The average differences in organ equivalent dose coefficients between the Chinese and the ICRP adult reference phantoms are within 6% for most organs, but noticeable differences of up to 70% or even higher are found at photon energies below 30 keV under air submersion. The effective dose coefficients obtained with the Chinese adult reference phantoms are greater than those of the ICRP adult reference phantoms above 30 keV and 0.5 MeV for ground contamination and air submersion, respectively; the average differences from the Chinese adult reference phantoms are about 3.6% and 0.4% in the whole energy range with maximum differences of 31.8% and 27.6% at 15 keV for air submersion and ground contamination respectively. These differences are attributed to anatomical discrepancies in overlying tissue mass of an individual organ and the body mass between the Chinese and the ICRP adult reference phantoms. These monoenergetic photon conversion coefficients are subsequently used to evaluate radionuclides with decay data from ICRP publication 107.

Internal dosimetry for radioembolization therapy with Yttrium-90 microspheres.

The absorbed doses in the liver and adjacent viscera in Yttrium‐90 radioembolization therapy for metastatic liver lesions are not well‐documented. We sought for a clinically practical way to determine the dosimetry of this advent treatment. Six different female XCAT BMIs and seven different male XCAT BMIs were generated. Using Monte Carlo GATE code simulation, the total of 100MBq 90Y was deposited uniformly in the source organ, liver. Self‐irradiation and absorbed doses in lung, kidney and bone marrow were calculated. The mean energy of Yittrium‐90 (i.e., 0.937 MeV) was used. The S‐values and equivalent doses in target organs were estimated. The dose absorbed in the liver was between 84 and 53 Gy and below the target of 80 to 150 Gy. The absorbed dose in the bone marrow, lungs, and kidneys are very low and below 0.1 , 0.4, and 0.5 Gy respectively. Our study indicates that larger activities than the conventional dose of 3 GBq may be both required and safe. Further confirmations in clinical settings are needed.

Organ and Effective Dose Coefficients for Cranial and Caudal Irradiation Geometries: Neutrons

With the introduction of new recommendations by ICRP Publication 103, the methodology for determining the protection quantity, effective dose, has been modified. The modifications include changes to the defined organs and tissues, the associated tissue weighting factors, radiation weighting factors, and the introduction of reference sex-specific computational phantoms (ICRP Publication 110). Computations of equivalent doses in organs and tissues are now performed in both the male and female phantoms and the sex-averaged values used to determine the effective dose. Dose coefficients based on the ICRP 103 recommendations were reported in ICRP Publication 116, the revision of ICRP Publication 74 and ICRU Publication 57. The coefficients were determined for the following irradiation geometries: anterior-posterior (AP), posterior-anterior (PA), right and left lateral (RLAT and LLAT), rotational (ROT), and isotropic (ISO). In this work, the methodology of ICRP Publication 116 was used to compute dose coefficients for neutron irradiation of the body with parallel beams directed upward from below the feet (caudal) and directed downward from above the head (cranial). These geometries may be encountered in the workplace from personnel standing on contaminated surfaces or volumes and from overhead sources. Calculations of organ and tissue absorbed doses for caudal and cranial exposures to neutrons ranging in energy from 10-9 MeV to 10 GeV have been performed using the MCNP6 radiation transport code and the adult reference voxel phantoms of ICRP Publication 110. At lower energies the effective dose per particle fluence for cranial and caudal exposures is less than AP orientations while above about 30 MeV the cranial and caudal values are greater.

Radiation-Induced Second Cancer Risk from External Beam Photon Radiotherapy for Head and Neck Cancer: Impact on in-Field and Out-of-Field Organs

The purpose of this paper is to provide data on development of second primary cancers within or adjacent to tissue irradiated in the treatment of primary head and neck cancers using different techniques and modalities.Materials and methods:We selected five patients with HandN tumors located in base of the tongue for risk assessment. In order to examine the impact of choices of various planning techniques, numbers of beams and beam energy used in treatment plans - 7 and 9 field Intensity modulated radiotherapy (IMRT) plans using 6MV and 10 MV beam energies and a 6MV Volumetric modulated arc therapy (VMAT) plans were planned. Out-of-field measurements for secondary photon doses for the treatment plans were measured using diode-dosimeters and solid water slabs. Differential dose-volume histograms (DVH) for all 5 patients and 5 techniques, were exported and used to calculate organ equivalent dose (OAR), excess absolute risk (EAR), and life-time attributable risk (LAR) for in-field organs.Results:For all treatment plans, the DVH showed clinically acceptable values; adequate clinical target coverage and dose constraints were met for all organs at risk. There was a clear advantage for the VMAT plan; it provided superior organ at risk (OAR) sparing and adequate target coverage. VMAT has relatively low monitor units at 0.93±0.034 times 7F6. The average percentage scattered to prescription doses for the five patients at 15, 30, 45, 60 and 75 cm from the isocenter were 0.9212 ± 0.115, 0.2621 ± 0.080, 0.1617 ± 0.057, 0.0936 ± 0.026, 0.0296 ± 0.014, for VMAT.Conclusion:Organ-specific LAR was higher with VMAT compared to 7F6 for skin. 6-MV VMAT is an acceptable alternative to IMRT for HandN cancer and offers advantages in terms of sparing adjacent OAR.

Our Experience with Subcutaneously Anchored Sutureless Devices in Pediatric Patients

The aim of this study is to develop the assessment technique of the effective dose by calculating the organ equivalent dose with a Monte Carlo (MC) simulation and a computational human phantom for the naturally occurring radioactive material (NORM) added consumer products. In this study, we suggests the method determining the MC source term based on the skin-point source enabling the convenient and conservative modeling of the various type of the products. To validate the skin-point source method, the organ equivalent doses were compared with that by the product modeling source of the realistic shape for the pillow, waist supporter, sleeping mattress etc. Our results show that according to the source location, the organ equivalent doses were observed as the similar tendency for both source determining methods, however, it was observed that the annual effective dose with the skin-point source was conservative than that with the modeling source with the maximum 3.3 times higher dose. With the assumption of the gamma energy of 1 MeV and product activity of 1 Bq g−1, the annual effective doses of the pillow, waist supporter and sleeping mattress with skin-point source was 3.09E-16 Sv Bq−1 year−1, 1.45E-15 Sv Bq−1 year−1, and 2,82E-16 Sv Bq−1 year−1, respectively, while the product modeling source showed 9.22E-17 Sv Bq−1 year−1, 9.29E-16 Sv Bq−1 year−1, and 8.83E-17 Sv Bq−1 year−1, respectively. In conclusion, it was demonstrated in this study that the skin-point source method could be employed to efficiently evaluate the annual effective dose due to the usage of the NORM added consumer products.

Comparison of treatment planning techniques in treatment of carcinoma of left breast: Second cancer perspective

AimTo compare the secondary cancer risk (SCR) between different planning techniques for treatment of Ca. Left-Breast patient. Materials and methodsFive treatment plans; 3DCRT tangential fields with physical wedge (PW), enhanced dynamic wedges (EDW), electronic compensator (EC), IMRT tangential fields (ITF) and Volumetric modulated arc (VMAT) plan (partial arcs) with 6MV photon beams were generated for a carcinoma of Left breast patient of age 40 to a prescription dose of 50Gy in 25 fractions. The SCR was estimated using the organ equivalent dose (OED) concept with a linear-exponential, a plateau, and a linear dose-response model for OARs. Also, the low dose-bath volume (5Gy) was calculated for all the plans. ResultsFor contra lateral breast the SCR relative to PW were (linear, plateau, linear-exponential) (−26.0%, −35.0%, −39.0%) for VMAT, (−50.0%,−50.0%,−51.0%) for ITF, (−48.0%, −49.0%,−49.0%) for EC and (−33.0%, −24% , −25.0%) for EDW respectively. The relative SCR (plateau) for heart and left lung were (−66.0% & −73.0%) for VMAT, (−20.0% & −6.0%) for ITF, (−24.0% & −18.0%) for EC and ( −17.0% & −14.0%)for EDW. In contrast, for skin the relative SCR (linear - exponential) were 78.0%, −8.0%, −13.0% and −10.0% for VMAT, ITF, EC and EDW respectively. The 5Gy low dose volume relative to PW for VMAT was 201.45%, whereas the same for ITF, EC and EDW were 17.0%, −7.33% and −4.3%. ConclusionCompared to all plans, VMAT plan showed high conformity for CTV and superior heart and left lung sparing. But SCR for skin and the low dose bath volume were significantly high in VMAT. ITF plan showed relatively better sparing for contra lateral breast and heart. EC plan shows moderately good sparing for OARs while scoring least SCR value for skin next to EDW. EDW and PW plans were similar but later had high SCR for contra lateral-breast. Planning techniques like ITF and VMAT can be strongly considered for left breast, provided better skin sparing techniques and less dose spillage can be achieved.

Estimation of radiation cancer risk in CT-KUB

The increased demand for computed tomography (CT) in radiological scanning examinations raises the question of a potential health impact from the associated radiation exposures. Focusing on CT kidney-ureter-bladder (CT-KUB) procedures, this work was aimed at determining organ equivalent dose using a commercial CT dose calculator and providing an estimate of cancer risks. The study, which included 64 patients (32 males and 32 females, mean age 55.5 years and age range 30–80 years), involved use of a calibrated CT scanner (Siemens-Somatom Emotion 16-slice). The CT exposures parameter including tube potential, pitch factor, tube current, volume CT dose index (CTDIvol) and dose-length product (DLP) were recorded and analyzed using CT-EXPO (Version 2.3.1, Germany). Patient organ doses, including for stomach, liver, colon, bladder, red bone marrow, prostate and ovaries were calculated and converted into cancer risks using age- and sex-specific data published in the Biological Effects of Ionizing Radiation (BEIR) VII report. With a median value scan range of 36.1cm, the CTDIvol, DLP, and effective dose were found to be 10.7mGy, 390.3mGycm and 6.2mSv, respectively. The mean cancer risks for males and females were estimated to be respectively 25 and 46 out of 100,000 procedures with effective doses between 4.2mSv and 10.1mSv. Given the increased cancer risks from current CT-KUB procedures compared to conventional examinations, we propose that the low dose protocols for unenhanced CT procedures be taken into consideration before establishing imaging protocols for CT-KUB.

ICRP Publication 133: The ICRP computational framework for internal dose assessment for reference adults: specific absorbed fractions.

Dose coefficients for assessment of internal exposures to radionuclides are radiological protection quantities giving either the organ equivalent dose or effective dose per intake of radionuclide following ingestion or inhalation. In the International Commission on Radiological Protection’s (ICRP) Occupational Intakes of Radionuclides (OIR) publication series, new biokinetic models for distribution of internalised radionuclides in the human body are presented as needed for establishing time-integrated activity within organs of deposition (source regions). This series of publications replaces Publications 30 and 68 (ICRP, 1979, 1980, 1981, 1988, 1994b). In addition, other fundamental data needed for computation of the dose coefficients are radionuclide decay data (energies and yields of emitted radiations), which are given in Publication 107 (ICRP, 2008), and specific absorbed fraction (SAF) values – defined as the fraction of the particle energy emitted in a source tissue region that is deposited in a target tissue region per mass of target tissue. This publication provides the technical basis for SAFs relevant to internalised radionuclide activity in the organs of Reference Adult Male and Reference Adult Female as defined in Publications 89 and 110 (ICRP, 2002, 2009). SAFs are given for uniform distributions of mono-energetic photons, electrons, alpha particles, and fission-spectrum neutrons over a range of relevant energies. Electron SAFs include both collision and radiative components of energy deposition. SAF data are matched to source and target organs of the biokinetic models of the OIR publication series, as well as the Publication 100 (ICRP, 2006) Human Alimentary Tract Model and the Publication 66 (ICRP, 1994a) Human Respiratory Tract Model, the latter as revised within Publication 130 (ICRP, 2015). This publication further outlines the computational methodology and nomenclature for assessment of internal dose in a manner consistent with that used for nuclear medicine applications. Numerical data for particle-specific and energy-dependent SAFs are given in electronic format for numerical coupling to the respiratory tract, alimentary tract, and systemic biokinetic models of the OIR publication series.

A treatment planning study of proton arc therapy for para-aortic lymph node tumors: dosimetric evaluation of conventional proton therapy, proton arc therapy, and intensity modulated radiotherapy.

BackgroundThe purpose of this study is to evaluate the dosimetric benefits of a proton arc technique for treating tumors of the para-aortic lymph nodes (PALN).MethodIn nine patients, a proton arc therapy (PAT) technique was compared with intensity modulated radiation therapy (IMRT) and proton beam therapy (PBT) techniques with respect to the planning target volume (PTV) and organs at risk (OAR). PTV coverage, conformity index (CI), homogeneity index (HI) and OAR doses were compared. Organ-specific radiation induced cancer risks were estimated by applying organ equivalent dose (OED) and normal tissue complication probability (NTCP).ResultsThe PAT techniques showed better PTV coverage than IMRT and PBT plans. The CI obtained with PAT was 1.19 ± 0.02, which was significantly better than that for the IMRT techniques. The HI was lowest for the PAT plan and highest for IMRT. The dose to the OARs was always below the acceptable limits and comparable for all three techniques. OED results calculated based on a plateau dose–response model showed that the risk of secondary cancers in organs was much higher when IMRT or PBT were employed than when PAT was used. NTCPs of PAT to the stomach (0.29 %), small bowel (0.69 %) and liver (0.38 %) were substantially lower than those of IMRT and PBT.ConclusionThis study demonstrates that there is a potential role for PAT as a commercialized instrument in the future to proton therapy.

Estimation of radiation-induced secondary cancer risks for early-stage non–small cell lung cancer patients after stereotactic body radiation therapy

PurposeIn this study, we evaluated radiation-induced secondary lung cancer risks for the lung and the breast from stereotactic body radiation therapy treatment of early-stage non–small cell lung cancer with different radiation therapy treatment modalities. Methods and materialsTen patients (5 men and 5 women) with early-stage non–small cell lung cancer who received definitive stereotactic body radiation therapy treatments were retrospectively selected. For each patient, two 3-dimensional conformal radiation therapy (3D-CRT) plans using 6- and 10-MV photons, respectively; a helical tomotherapy (HT) plan; and 2 volumetric modulated arc therapy (VMAT) plans using 1 and 2 arcs, respectively, were generated. The excess absolute risk (EAR) for secondary cancer occurrence was calculated using 3 organ equivalent dose models: the linear-exponential model, the plateau model, and the linear model for prescription dose range of 30 to 70 Gy. ResultsThe 3D-CRT plans showed significantly lower monitor units compared with the rotational intensity modulate radiation therapy plans. Based on each of the 3 organ equivalent dose models, HT and VMAT plans showed comparable average EARs to both the lung and the breast compared with the 3D-CRT plans in the prescription dose range of 30 to 70 Gy. At a prescription dose of 50 Gy and using the linear-exponential model, the average lung EAR estimation ranged from 15.7 ± 5.3 to 16.0 ± 6.5 per 10,000 patients per year with the 5 delivery techniques, and the average EAR estimation for the breast ranged from 18.0 ± 14.0 to 21.0 ± 15.0 per 10,000 patients per year. The secondary cancer risk increased approximately linearly with mean organ dose. The 3D-CRT plans showed significantly higher secondary cancer risk for the ipsilateral lung and lower risk for the contralateral lung compared with the HT and VMAT plans. ConclusionsRotational intensity modulate radiation therapy techniques including helical tomotherapy and VMAT do not increase secondary cancer risks for the lung or the breast compared with 3D-CRT techniques, despite higher monitor units used.

Biodistribution and Radiation Dosimetry of 11C-Nicotine from Whole-Body PET Imaging in Humans.

This study assessed the in vivo distribution of 11C-nicotine and the absorbed radiation dose from whole-body 11C-nicotine PET imaging of 11 healthy (5 male and 6 female) subjects. Methods: After an initial CT attenuation scan, 11C-nicotine was administered via intravenous injection. A dynamic PET scan was acquired for 90 s with the brain in the field of view, followed by a series of 13 whole-body PET scans acquired over a 90-min period. Regions of interest were drawn over organs visible in the reconstructed PET images. Time-activity curves were generated, and the residence times were calculated. The absorbed radiation dose for the whole body was calculated by entering the residence time in OLINDA/EXM 1.0 software to model the equivalent organ dose and the effective dose for a 70-kg man. Results: The mean residence times for 11C-nicotine in the liver, red marrow, brain, and lungs were 0.048 ± 0.010, 0.031 ± 0.005, 0.021 ± 0.004, and 0.020 ± 0.005 h, respectively. The mean effective dose for 11C-nicotine was 5.44 ± 0.67 μSv/MBq. The organs receiving the highest absorbed dose from the 11C-nicotine injection were the urinary bladder wall (14.68 ± 8.70 μSv/MBq), kidneys (9.56 ± 2.46 μSv/MBq), liver (8.94 ± 1.67 μSv/MBq), and spleen (9.49 ± 3.89 μSv/MBq). The renal and hepatobiliary systems were the major clearance and excretion routes for radioactivity. Conclusion: The estimated radiation dose from 11C-nicotine administration is relatively modest and would allow for multiple PET examinations on the same subject.

Individualized assessment of the probability for developing in-field solid tumors from radiation therapy for testicular cancer

Introduction Testicular cancer is a highly treatable malignancy which is usually presented in young adults. Purpose The purpose of this study was to combine individualized dosimetric data with an advanced non-linear risk model for the patient-specific assessment of the probability for solid cancer induction after three-dimensional conformal radiotherapy for testicular cancer. Materials and methods Ten patients with early stage seminomatous testicular cancer were subjected to a planning computed tomography scan. Treatment plans were generated with an 18 MV photon beam delivering 20 Gy in 10 fractions to para-aortic lymph node region. Differential dose-volume histograms were defined with a bin width of 0.01 Gy for radiosensitive organs exposed to primary radiation. For each study participant, the organ equivalent dose (OED) of colon, stomach and liver and the associated lifetime risk for carcinogenesis were estimated with a mechanistic model. This model accounts for the effects of cell repopulation and target dose fractionation. Results The range of the calculated OEDs of the colon, stomach and liver was found to be 251.3–500.4 cGy, 37.3–79.8 cGy and 43.0–70.3 cGy, respectively. The patient-specific lifetime probability for the appearance of colon malignancies varied from 0.74% to 1.94% by the patient’s age at the time of irradiation and the organ radiation exposure. The corresponding lifetime risk ranges for stomach and liver cancer induction were equal to 0.42–0.81% and 0.14–0.22%, respectively. Conclusion The knowledge of the patient-specific probability for developing solid tumors prior to radiotherapy for testicular cancer may facilitate treatment decisions and improve risk management. Disclosure There is not any relationship that may bias our presentation.

An effective dose assessment technique with NORM added consumer products using skin-point source on computational human phantom

The aim of this study is to develop the assessment technique of the effective dose by calculating the organ equivalent dose with a Monte Carlo (MC) simulation and a computational human phantom for the naturally occurring radioactive material (NORM) added consumer products. In this study, we suggests the method determining the MC source term based on the skin-point source enabling the convenient and conservative modeling of the various type of the products. To validate the skin-point source method, the organ equivalent doses were compared with that by the product modeling source of the realistic shape for the pillow, waist supporter, sleeping mattress etc. Our results show that according to the source location, the organ equivalent doses were observed as the similar tendency for both source determining methods, however, it was observed that the annual effective dose with the skin-point source was conservative than that with the modeling source with the maximum 3.3 times higher dose. With the assumption of the gamma energy of 1MeV and product activity of 1Bqg−1, the annual effective doses of the pillow, waist supporter and sleeping mattress with skin-point source was 3.09E-16SvBq−1year−1, 1.45E-15SvBq−1year−1, and 2,82E-16SvBq−1year−1, respectively, while the product modeling source showed 9.22E-17SvBq−1year−1, 9.29E-16SvBq−1year−1, and 8.83E-17SvBq−1year−1, respectively. In conclusion, it was demonstrated in this study that the skin-point source method could be employed to efficiently evaluate the annual effective dose due to the usage of the NORM added consumer products.

Organ-specific radiation-induced cancer risk estimates due to radiotherapy for benign pigmented villonodular synovitis

Pigmented villonodular synovitis (PVNS) is a benign disease affecting synovial membranes of young and middle-aged adults. The aggressive treatment of this disorder often involves external-beam irradiation. This study was motivated by the lack of data relating to the radiation exposure of healthy tissues and radiotherapy-induced cancer risk. Monte Carlo methodology was employed to simulate a patient’s irradiation for PVNS in the knee and hip joints with a 6 MV photon beam. The average radiation dose received by twenty-two out-of-field critical organs of the human body was calculated. These calculations were combined with the appropriate organ-, age- and gender-specific risk coefficients of the BEIR-VII model to estimate the lifetime probability of cancer development. The risk for carcinogenesis to colon, which was partly included in the treatment fields used for hip irradiation, was determined with a non-linear mechanistic model and differential dose-volume histograms obtained by CT-based 3D radiotherapy planning. Risk assessments were compared with the nominal lifetime intrinsic risk (LIR) values. Knee irradiation to 36 Gy resulted in out-of-field organ doses of 0.2–24.6 mGy. The corresponding range from hip radiotherapy was 1.2–455.1 mGy whereas the organ equivalent dose for the colon was up to 654.9 mGy. The organ-specific cancer risks from knee irradiation for PVNS were found to be inconsequential since they were at least 161.5 times lower than the LIRs irrespective of the patient’s age and gender. The bladder and colon cancer risk from radiotherapy in the hip joint was up to 3.2 and 6.6 times smaller than the LIR, respectively. These cancer risks may slightly elevate the nominal incidence rates and they should not be ignored during the patient’s treatment planning and follow-up. The probabilities for developing any other solid tumor were more than 20 times lower than the LIRs and, therefore, they may be considered as small.

Modelling second malignancy risks from low dose rate and high dose rate brachytherapy as monotherapy for localised prostate cancer

Background and purposeTo estimate the risks of radiation-induced rectal and bladder cancers following low dose rate (LDR) and high dose rate (HDR) brachytherapy as monotherapy for localised prostate cancer and compare to external beam radiotherapy techniques. Materials and methodsLDR and HDR brachytherapy monotherapy plans were generated for three prostate CT datasets. Second cancer risks were assessed using Schneider’s concept of organ equivalent dose. LDR risks were assessed according to a mechanistic model and a bell-shaped model. HDR risks were assessed according to a bell-shaped model. Relative risks and excess absolute risks were estimated and compared to external beam techniques. ResultsExcess absolute risks of second rectal or bladder cancer were low for both LDR (irrespective of the model used for calculation) and HDR techniques. Average excess absolute risks of rectal cancer for LDR brachytherapy according to the mechanistic model were 0.71 per 10,000 person-years (PY) and 0.84 per 10,000 PY respectively, and according to the bell-shaped model, were 0.47 and 0.78 per 10,000 PY respectively. For HDR, the average excess absolute risks for second rectal and bladder cancers were 0.74 and 1.62 per 10,000 PY respectively. The absolute differences between techniques were very low and clinically irrelevant. Compared to external beam prostate radiotherapy techniques, LDR and HDR brachytherapy resulted in the lowest risks of second rectal and bladder cancer. ConclusionsThis study shows both LDR and HDR brachytherapy monotherapy result in low estimated risks of radiation-induced rectal and bladder cancer. LDR resulted in lower bladder cancer risks than HDR, and lower or similar risks of rectal cancer. In absolute terms these differences between techniques were very small. Compared to external beam techniques, second rectal and bladder cancer risks were lowest for brachytherapy.

Radiation dosimetry of 18F-FDG PET/CT: incorporating exam-specific parameters in dose estimates.

BackgroundWhole body fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) is the standard of care in oncologic diagnosis and staging, and patient radiation dose must be well understood to balance exam benefits with the risk from radiation exposure. Although reference PET/CT patient doses are available, the potential for widely varying total dose prompts evaluation of clinic-specific patient dose. The aims of this study were to use exam-specific information to characterize the radiation dosimetry of PET/CT exams that used two different CT techniques for adult oncology patients and evaluate the practicality of employing an exam-specific approach to dose estimation.MethodsWhole body PET/CT scans from two sets of consecutive adult patients were retrospectively reviewed. One set received a PET scan with a standard registration CT and the other a PET scan with a diagnostic quality CT. PET dose was calculated by modifying the standard reference phantoms in OLINDA/EXM 1.1 with patient-specific organ mass. CT dose was calculated using patient-specific data in ImPACT. International Commission on Radiological Protection publication 103 tissue weighting coefficients were used for effective dose.ResultsOne hundred eighty three adult scans were evaluated (95 men, 88 women). The mean patient-specific effective dose from a mean injected 18F-FDG activity of 450 ± 32 MBq was 9.0 ± 1.6 mSv. For all standard PET/CT patients, mean effective mAs was 39 ± 11 mAs, mean CT effective dose was 5.0 ± 1.0 mSv and mean total effective dose was 14 ± 1.3 mSv. For all diagnostic PET/CT patients, mean effective mAs was 120 ± 51 mAs, mean CT effective dose was 15.4 ± 5.0 mSv and mean total effective dose was 24.4 ± 4.3 mSv. The five organs receiving the highest organ equivalent doses in all exams were bladder, heart, brain, liver and lungs.ConclusionsPatient-specific parameters optimize the patient dosimetry utilized in the medical justification of whole body PET/CT referrals and optimization of PET and CT acquisition parameters. Incorporating patient-specific data into dose estimates is a worthwhile effort for characterizing patient dose, and the specific dosimetric information assists in the justification of risk and optimization of PET/CT.

ASSESSMENT OF DIAGNOSTIC MULTILEAF COLLIMATOR FOR CEPHALOMETRIC EXPOSURE REDUCTION USING OPTICALLY STIMULATED LUMINESCENT DOSEMETERS.

A diagnostic multileaf collimator (MLC) was developed for diagnostic radiography dose reduction. Optically stimulated luminescent dosemeters (OSLDs) were used to evaluate the efficacy of this device for dental radiography cephalometric exposure reduction. The OSLD dosimetric characteristics for 80 kVp cephalometric exposure were first obtained. The batch homogeneity and reproducibility were 1.67 % and 0.18-1.58, respectively. Good linearity was obtained between the OSLD dose and response, and the angular dependence was within ±4 %. The equivalent organ doses for the left eye, right eye and thyroid were 41.20±6.58, 178.86±1.71 and 171.12±8.78 μSv and 36.80±0.33, 156.63±0.22 and 22.04±0.13 μSv for the open and MLC fields, respectively. The MLC-induced dose reductions for the left and right eyes of in field were 10.67±16.78 and 12.42±8.84 %, respectively, and that of the thyroid gland of out of field was 87±8.82 %, considering combined uncertainty. Therefore, use of diagnostic MLC for dose reduction during dental radiography cephalometric exposure is both feasible and effective.

ICRP dose coefficients: computational development and current status.

Major current efforts within Committee 2 of the International Commission on Radiological Protection (ICRP) involve the development of dose coefficients for inhalation and ingestion of radionuclides, and those for exposure to environmental radiation fields. These efforts build upon changes in radiation and tissue weighting factors (Publication 103), radionuclide decay schemes (Publication 107), computational phantoms of the adult reference male and female (Publication 110), external dose coefficients for adult reference workers for idealised radiation fields (Publication 116), models of radionuclide intake (Publications 66, 100 and 130), and models of radionuclide systemic biokinetics (Publication 130). This paper will review the overall computational framework for both internal and external dose coefficients. For internal exposures, the work entails assessment of organ self-dose and cross-dose from monoenergetic particle emissions (specific absorbed fraction), absorbed dose per nuclear transformation (S value), time-integrated activity of the radionuclide in source tissues (inhalation, ingestion, and systemic biokinetic models), and their numerical combination to yield the organ equivalent dose or effective dose per activity inhaled or ingested. Various challenges are reviewed that were not included in the development of Publication 30 dose coefficients, which were based upon much more simplified biokinetic models and computational phantoms. For external exposures, the computations entail the characterisation of environmental radionuclide distributions, the transport of radiation particles through that environment, and the tracking of energy deposition to the organs of the exposed individual. Progress towards the development of dose coefficients to members of the general public (adolescents, children, infants and fetuses) are also reviewed.