Effect of the modification of CT scanner calibration curves on dose using density correction methods for chest cancer

PurposeThis work sought to establish whether the choice of CT scanner calibration curve has a significant effect on dose computation using density correction methods for chest cancer.Material and methodsCIRS^®062 phantom was used to calculate the Hounsfield Unit using 80, 120 and 140 kV. Four CT calibration curves were implanted in the Eclipse^® TPS. Forty-two irradiation fields for 4 patients with lung cancer were included and analysed. The patients were treated with 3-dimensional radiation therapy. For each patient, 3 treatment plans were generated using exactly the same beam configuration. In plan 1, the dose was calculated using the Modified Batho (MB) method. In plan 2, the dose was calculated using the Batho power law (BPL) method. In plan 3, the dose was calculated using the Equivalent Tissue Air Ratio (ETAR) method. To evaluate the treatment plans computed by the three methods, the monitor units, dose volume histograms, conformity index, homogeneity index, planning target volumes conformity index, geometrical index and 2D gamma index were compared. The statistical analysis was carried out using Wilcoxon signed rank test.ResultsThe three density correction methods in plans 1, 2 and 3 using tested curves produced a difference less than 1% for MUs and DVH. Wilcoxon test showed a statically significant difference for MUs using ETAR method with calibration curves based on 80 and 120 kV. There was no significant difference for the quality indices between plan 1, 2 and 3, (P > 0.05), but a significant difference for the planning target volumes conformity index between plans 1, 2 and 3 (P < 0.05) was observed. The 2D gamma analysis showed that 100% of pixels had gamma ≤ 1.ConclusionThe impact of the modification of CT calibration curves on dose is negligible for chest cancer using density correction methods. One calibration curve can be used to take into account the density correction for lung.     

Monte Carlo study on the secondary cancer risk estimations for patients undergoing prostate radiotherapy: A humanoid phantom study

AimThe aim of this study was to estimate the secondary malignancy risk from the radiation in FFB prostate linac-based radiotherapy for different organs of the patient.BackgroundRadiation therapy is one of the main procedures of cancer treatment. However, the application the radiation may impose dose to organs of the patient which can be the cause of some malignancies.Materials and methodsMonte Carlo (MC) simulation was used to calculate radiation doses to patient organs in 18 MV linear accelerator (linac) based radiotherapy. A humanoid MC phantom was used to calculate the equivalent dose s for different organs and probability of secondary cancer, fatal and nonfatal risk, and other risks and parameters related to megavoltage radiation therapy. In out-of-field radiation calculation, it could be seen that neutrons imparted a higher dose to distant organs, and the dose to surrounding organs was mainly due to absorbed scattered photons and electron contamination.ResultsOur results showed that the bladder and skin with 54.89 × 10⁻³ mSv/Gy and 46.09 × 10⁻³ mSv/Gy, respectively, absorbed the highest equivalent dose s from photoneutrons, while a lower dose was absorbed by the lung at 3.42 × 10⁻³ mSv/Gy. The large intestine and bladder absorbed 55.00 × 10⁻³ mSv/Gy and 49.08 × 10⁻³, respectively, which were the highest equivalent dose s due to photons. The brain absorbed the lowest out-of-field dose, at 1.87 × 10⁻³ mSv/Gy.ConclusionsWe concluded that secondary neutron portion was higher than other radiation. Then, we recommended more attention to neutrons in the radiation protection in linac based high energy radiotherapy.     

The evaluation of the feasibility of carotid sparing intensity modulated radiation therapy technique for comprehensive breast irradiation

PurposeTo investigate the feasibility of carotid sparing intensity modulated radiation therapy (CS-IMRT) to minimize the radiation dose to carotid arteries for comprehensive irradiation of breast cancer patients who have risk factors for atherosclerosis. The dose distribution of CS-IMRT technique and the conventional irradiation technique were also compared.Patients and methodsTen patients who were previously treated with comprehensive three-dimensional conformal radiation therapy (3DCRT) were selected. DICOM data were used to contour the carotid artery and to create the virtual CS-IMRT plans for each patient. 3DCRT and CS-IMRT plans were compared in terms of conformity index, homogeneity index, and the doses to organ at risk and carotid arteries.ResultsThe homogeneity and conformity indices were better with CS-IMRT plans compared to 3DCRT plan. The homogeneity index was 1.13 vs 1.11 (p = 0.007) for 3DCRT and CS-IMRT and the conformity index was 0.96 vs 0.97 (p = 0.006) for 3DCRT and CS-IMRT. The radiation dose to the carotid arteries were reduced by applying CS-IMRT without compromising the target volume coverage. When the carotid artery was considered as organ at risk for CS-IMRT planning, the median of V50 was decreased to 0% from 12.5% compared to 3DCRT plans (p = 0.017). The median of the maximum dose to the carotid artery was decreased under 50 Gy with CS-IMRT.ConclusionsCS-IMRT can significantly reduce the unnecessary radiation dose to the carotid arteries compared with conventional 3DCRT technique while maintaining target volume coverage. CS-IMRT technique can be considered for breast cancer patient with high risk of atherosclerosis.     

Bladder dose–surface maps and urinary toxicity: Robustness with respect to motion in assessing local dose effects

The purpose of this study was to quantify the impact of inter-fraction modifications of bladder during RT of prostate cancer on bladder dose surface maps (DSM).Eighteen patients treated with daily image-guided Tomotherapy and moderate hypofractionation (70–72.8 Gy at 2.5–2.6 Gy/fr in 28 fractions and full bladder) were considered. Bladder contours were delineated on co-registered daily Megavoltage CT (MVCT) by a single observer and copied on the planning CT to generate dose–volume/surface histograms (DVH/DSH) and bladder DSMs. Discrepancies between planned and daily absorbed doses were analyzed through the average of individual systematic errors, the population systematic errors and the population random errors for the DVH/DSHs and DSMs.In total, 477 DVH/DSH and 472 DSM were available. DSH and DVH showed small population systematic errors of absolute surfaces (<3.4 cm²) and volumes (<8.4 cm³) at the highest doses.The dose to the posterior bladder base assessed on DSMs showed a mean systematic error below 1 Gy, with population systematic and random errors within 4 and 3 Gy, respectively. The region surrounding this area shows higher mean systematic errors (1–3 Gy), population systematic (8–11 Gy) and random (5–7 Gy) errors.In conclusion, DVH/DSH and DSMs are quite stable with respect to inter-fraction variations in the high-dose region, within about 2 cm from bladder base. Larger systematic variations occur in the anterior portion and cranially 2.5–3.5 cm from the base.Results suggest that dose predictors related to the high dose area (including the trigone dose) are likely to be sufficiently reliable with respect to the expected variations due to variable bladder filling.     

Incorrect dosimetric leaf separation in IMRT and VMAT treatment planning: Clinical impact and correlation with pretreatment quality assurance

PurposeDynamic treatment planning algorithms use a dosimetric leaf separation (DLS) parameter to model the multi-leaf collimator (MLC) characteristics. Here, we quantify the dosimetric impact of an incorrect DLS parameter and investigate whether common pretreatment quality assurance (QA) methods can detect this effect.Methods16 treatment plans with intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) technique for multiple treatment sites were calculated with a correct and incorrect setting of the DLS, corresponding to a MLC gap difference of 0.5 mm. Pretreatment verification QA was performed with a bi-planar diode array phantom and the electronic portal imaging device (EPID). Measurements were compared to the correct and incorrect planned doses using gamma evaluation with both global (G) and local (L) normalization. Correlation, specificity and sensitivity between the dose volume histogram (DVH) points for the planning target volume (PTV) and the gamma passing rates were calculated.ResultsThe change in PTV and organs at risk DVH parameters were 0.4–4.1%. Good correlation (>0.83) between the PTV_mean dose deviation and measured gamma passing rates was observed. Optimal gamma settings with 3%L/3 mm (per beam and composite plan) and 3%G/2 mm (composite plan) for the diode array phantom and 2%G/2 mm (composite plan) for the EPID system were found. Global normalization and per beam ROC analysis of the diode array phantom showed an area under the curve <0.6.ConclusionsA DLS error can worsen pretreatment QA using gamma analysis with reasonable credibility for the composite plan. A low detectability was demonstrated for a 3%G/3 mm per beam gamma setting.     

Influence of voxel S factors on three-dimensional internal dosimetry calculations

Internal dosimetry is a fundamental instrument for the personalization of nuclear medicine therapies, to maximize the therapeutic effect while minimizing the radiation burden to other organs. Three-dimensional (3D) dosimetry can quantify the impact of heterogeneous radiopharmaceutical distributions in organs, lesions and tissues.We analysed the influence of radionuclide voxel S factors in 3D dosimetry of ¹¹¹In, ¹⁷⁷Lu and ⁹⁰Y, the most used radionuclides in Peptide Receptor Radionuclide Therapy (PRRT). Calculations were carried out for kidneys on a workstation equipped with a software for 3D dosimetry (Imalytics STRATOS, Philips AG), adopting a computational anthropomorphic phantom and, retrospectively, the SPECT-CT image series of a clinical case of PRRT.Two sets of voxel S factors were adopted: the pre-loaded Philips kernels, calculated by direct Monte Carlo simulation, and the ones calculated through a previously proposed analytical approach. Philips ¹¹¹In kernel did not account for mono-energetic Auger or Conversion electrons.Results indicate a difference of about −32% in voxel S factors for ¹¹¹In in 4.42 mm voxel size and around −35% in 4.80 mm voxel size, particularly self-dose values; this lead to significant shift in dose histograms and average doses. For ¹⁷⁷Lu and ⁹⁰Y, differences are about 2% and 12% for 4.42 mm voxels and about −8% and 9% for 4.80 mm voxels, respectively, attributable to the different calculation methods of the voxel S factors; this does not lead to significant discrepancies between the two dose histograms. Consequently, voxel S factors must account accurately for all radiations emitted by the nuclide.     

Protection effect of cerium oxide nanoparticles against radiation-induced acute lung injuries in rats

IntroductionRadiation therapy is one of the most common tools for treating cancer. The aim is to deliver adequate doses of radiation to kill cancer cells and the most challenging part during this procedure is to protect normal cells from radiation. One strategy is to use a radioprotector to spare normal tissues from ionizing radiation effects. Researchers have pursued cerium oxide nanoparticles as a therapeutic agent, due to its diverse characteristics, which include antioxidant properties, making it a potential radioprotector.Materials and methodsOne hundred rats were divided into five groups of A) control group, intraperitoneal (IP) saline injection was done twice a week; B) bi-weekly IP injection of 14.5 nM (0.00001 mg/kg) CNP for two weeks; C) a single whole thorax radiation dose of 18 Gy; D) a single whole thorax radiation dose of 18 Gy + bi-weekly injection of 14.5 nM CNP for two weeks after radiation; E) bi-weekly IP injection of 14.5 nM CNP for two weeks prior to radiation + a single whole thorax radiation dose of 18 Gy. Thirty days after irradiation, 7 rats from each group were anesthetized and their lungs extracted for histopathological examination.ResultsStatistical analyses revealed that CNP significantly decreased the incidence of tissue collapse and neutrophile aggregation in rats receiving CNP before radiation in comparison with the radiation group.ConclusionThe results suggested the possibility of using CNP as a future radioprotector due to its ability to protect normal cells against radiation-induced damage.     

NTCP modeling analysis of acute hematologic toxicity in whole pelvic radiation therapy for gynecologic malignancies – A dosimetric comparison of IMRT and spot-scanning proton therapy (SSPT)

PurposeThis treatment planning study was conducted to determine whether spot scanning proton beam therapy (SSPT) reduces the risk of grade ⩾3 hematologic toxicity (HT3+) compared with intensity modulated radiation therapy (IMRT) for postoperative whole pelvic radiation therapy (WPRT).Methods and materialsThe normal tissue complication probability (NTCP) of the risk of HT3+ was used as an in silico surrogate marker in this analysis. IMRT and SSPT plans were created for 13 gynecologic malignancy patients who had received hysterectomies. The IMRT plans were generated using the 7-fields step and shoot technique. The SSPT plans were generated using anterior-posterior field with single field optimization. Using the relative biological effectives (RBE) value of 1.0 for IMRT and 1.1 for SSPT, the prescribed dose was 45 Gy(RBE) in 1.8 Gy(RBE) per fractions for 95% of the planning target volume (PTV). The homogeneity index (HI) and the conformity index (CI) of the PTV were also compared.ResultsThe bone marrow (BM) and femoral head doses using SSPT were significantly lower than with IMRT. The NTCP modeling analysis showed that the risk of HT3+ using SSPT was significantly lower than with IMRT (NTCP = 0.04 ± 0.01 and 0.19 ± 0.03, p = 0.0002, respectively). There were no significant differences in the CI and HI of the PTV between IMRT and SSPT (CI = 0.97 ± 0.01 and 0.96 ± 0.02, p = 0.3177, and HI = 1.24 ± 0.11 and 1.27 ± 0.05, p = 0.8473, respectively).ConclusionThe SSPT achieves significant reductions in the dose to BM without compromising target coverage, compared with IMRT. The NTCP value for HT3+ in SSPT was significantly lower than in IMRT.     

Gated carbon-ion scanning treatment for pancreatic tumour with field specific target volume and organs at risk

ObjectiveTo assess the feasibility of treatment planning for pancreatic tumours subject to respiratory motion using field-specific target volumes (FTV) and field-specific organs at risk (FOAR) using four-dimensional computed tomography (4DCT).MethodsFourteen pancreatic cancer patients underwent 4DCT. Radiation oncologists contoured the gross tumour volume (GTV), clinical target volume (CTV), spinal cord, duodenum, kidneys, and stomach. The gating duty cycle was set to 30 % around exhalation. FTV and FOAR were calculated using the 4DCT dataset. Planning target volumes (PTV) and planning organs at risk volumes (PRV) were defined as equal to FTV and FOAR, respectively. A dose of 55.2 Gy relative biological effectiveness (RBE) was planned to target the PTV from four beam angles. A single field uniform dose (SFUD) plan was selected. The dose distribution, including intrafractional motion changes, was generated.ResultsThe mean volume of target receiving 95 % of the planned doses was 96.4 ± 4.1 % to the GTV and 94.7 ± 0.9 % to the CTV. The highest dose to 2 cc of duodenal volume was 27.5 Gy (RBE). The volume of the stomach receiving ⩾30 Gy (RBE) was <7.0 cc in all patients. All metrics for OARs satisfied dose constraints.ConclusionDose to the CTV was covered sufficiently by the 4DCT-generated FTV, and dose to OARs was reduced by 4DCT-generated FOAR. This methodology may prevent adverse reactions while preserving local tumour control.     

Utilization of cone-beam CT for offline evaluation of target volume coverage during prostate image-guided radiotherapy based on bony anatomy alignment

AimTo assess target volume coverage during prostate image-guided radiotherapy based on bony anatomy alignment and to assess possibility of safety margin reduction.BackgroundImplementation of IGRT should influence safety margins. Utilization of cone-beam CT provides current 3D anatomic information directly in irradiation position. Such information enables reconstruction of the actual dose distribution.Materials and methodsSeventeen prostate patients were treated with daily bony anatomy image-guidance. Cone-beam CT (CBCT) scans were acquired once a week immediately after bony anatomy alignment. After the prostate, seminal vesicles, rectum and bladder were contoured, the delivered dose distribution was reconstructed. Target dose coverage was evaluated by the proportion of the CTV encompassed by the 95% isodose. Original plans employed a 1 cm safety margin. Alternative plans assuming a smaller 7 mm margin between CTV and PTV were evaluated in the same way. Rectal and bladder volumes were compared with the initial ones. Rectal and bladder volumes irradiated with doses higher than 75 Gy, 70 Gy, 60 Gy, 50 Gy and 40 Gy were analyzed.ResultsIn 12% of reconstructed plans the prostate coverage was not sufficient. The prostate underdosage was observed in 5 patients. Coverage of seminal vesicles was not satisfactory in 3% of plans. Most of the target underdosage corresponded to excessive rectal or bladder filling. Evaluation of alternative plans assuming a smaller 7 mm margin revealed 22% and 11% of plans where prostate and seminal vesicles coverage, respectively, was compromised. These were distributed over 8 and 7 patients, respectively.ConclusionSufficient dose coverage of target volumes was not achieved for all patients. Reducing of safety margin is not acceptable. Initial rectal and bladder volumes cannot be considered representative for subsequent treatment.     

Concomitant chemo-radiotherapy for unresectable oesophageal cancer: A mono-institutional study on 40 patients

Background/AimTo analyse clinical response, overall (OS) and disease free survival (DFS) and toxicity in patients with unresectable oesophageal cancer treated by concomitant chemo-radiotherapy (CRT).Materials and methodsForty patients with stage IIa–IVa biopsy proven oesophageal carcinoma were treated with CRT. All patients were studied with endoscopy and CT and judged unresectable after multidisciplinary discussion. CRT consisted of 3 cycles of cisplatin 100 mg/m² or carboplatin 300 mg/m² on day 1 and 5-fluorouracil 1000 mg/m² as a continuous infusion of 96 h associated with concurrent 3D-conformal RT. By using 15 MeV X-rays, a total dose of 60–66 Gy was delivered with daily fractions of 1.8–2.0 Gy.ResultsComplete response (CR), partial response (PR) and no response (NR) were observed in 50%, 20% and 20% of cases, respectively. Of the 20 patients with CR, 15 developed loco-regional recurrent disease. OS and DFS rates at 3 and 5 years were 38%, 8%, 49% and 10%, respectively. Total radiation dose ≥60 Gy improved loco-regional control and complete response (CR vs. PR + NR; p = 0.004) influenced both DFS and loco-regional control. Grade 3 gastrointestinal and haematological acute toxicity occurred in 3/40 patients (7.5%). One patient developed grade 4 renal failure. Late toxicity was reported in 2/40 patients (5.0%), consisting of grade 3 radiation pneumonitis.ConclusionsConcomitant CRT for unresectable oesophageal cancer can result in an acceptable loco-regional control with limited toxicity. Response after treatment and total radiation dose influenced the outcome.     

Patient radiation biological risk in computed tomography angiography procedure

Computed tomography angiography (CTA) has become the most valuable imaging modality for the diagnosis of blood vessel diseases; however, patients are exposed to high radiation doses and the probability of cancer and other biological effects is increased. The objectives of this study were to measure the patient radiation dose during a CTA procedure and to estimate the radiation dose and biological effects.The study was conducted in two radiology departments equipped with 64-slice CT machines (Aquilion) calibrated according to international protocols. A total of 152 patients underwent brain, lower limb, chest, abdomen, and pelvis examinations. The effective radiation dose was estimated using ImPACT scan software. Cancer and biological risks were estimated using the International Commission on Radiological Protection (ICRP) conversion factors.The mean patient dose value per procedure (dose length product [DLP], mGy·cm) for all examinations was 437.8 ± 166, 568.8 ± 194, 516.0 ± 228, 581.8 ± 175, and 1082.9 ± 290 for the lower limbs, pelvis, abdomen, chest, and cerebral, respectively. The lens of the eye, uterus, and ovaries received high radiation doses compared to thyroid and testis. The overall patient risk per CTA procedure ranged between 15 and 36 cancer risks per 1 million procedures. Patient risk from CTA procedures is high during neck and abdomen procedures. Special concern should be provided to the lens of the eye and thyroid during brain CTA procedures. Patient dose reduction is an important consideration; thus, staff should optimize the radiation dose during CTA procedures.     

Effect of diagnostic cone-beam computed tomography protocols on image quality,patient dose,and lesion detection

ObjectiveTo evaluate the effect of cone-beam computed tomography (CBCT) image acquisition protocols on image quality, lesion detection, delineation, and patient dose.Methods100-patients and a CTDI phantom combined with an electron density phantom were examined using four different CBCT-image acquisition protocols during image-guided transarterial chemoembolization (TACE). Protocol-1 (time: 6 s, tube rotation: 360°), protocol-2 (5 s, 300°), protocol-3 (4 s, 240°) and protocol-4 (3 s, 180°) were used. The protocols were first investigated using a phantom. The protocols that were found to be clinically appropriate in terms of image quality and radiation dose were then assessed on patients. A higher radiation dose and/or a poor image quality were inappropriate for the patient imaging. Patient dose (patient-entrance dose and dose-area product), image quality (Hounsfield Unit, noise, signal-to-noise ratio and contrast-to-noise ratio), and lesion delineation (tumor-liver contrast) were assessed and compared using appropriate statistical tests. Lesion detectability, sensitivity, and predictive values were estimated for CBCT-image data using pre-treatment patient magnetic resonance imaging.ResultsThe estimated patient dose showed no statistical significance (p > 0.05) between protocols-2 and -3; the assessed image quality between these protocols manifested insignificant difference (p > 0.05). Two other phantom protocols were not considered for patient imaging due to significantly higher dose (protocols-1) and poor image quality (protocol-4). Lesion delineation and detection were insignificant (p > 0.05) between protocols-2 and -3. Lesion sensitivities generated were 81–89% (protocol-2) and 81–85% (protocol-3) for different lesion types.ConclusionData acquisition using protocols-2 and -3 provided good image quality, lesion detection and delineation with acceptable patient dose during CBCT-imaging mainly due to similar frame numbers acquired.     

On-site audits to investigate the quality of radiation physics of radiation therapy institutions in the Republic of Korea

PurposeTo investigate and improve the domestic standard of radiation therapy in the Republic of Korea.MethodsOn-site audits were performed for 13 institutions in the Republic of Korea. Six items were investigated by on-site visits of each radiation therapy institution, including collimator, gantry, and couch rotation isocenter check; coincidence between light and radiation fields; photon beam flatness and symmetry; electron beam flatness and symmetry; physical wedge transmission factors; and photon beam and electron beam outputs.ResultsThe average deviations of mechanical collimator, gantry, and couch rotation isocenter were less than 1 mm. Those of radiation isocenter were also less than 1 mm. The average difference between light and radiation fields was 0.9 ± 0.6 mm for the field size of 20 cm × 20 cm. The average values of flatness and symmetry of the photon beams were 2.9% ± 0.6% and 1.1% ± 0.7%, respectively. Those of electron beams were 2.5% ± 0.7% and 0.6% ± 1.0%, respectively. Every institutions showed wedge transmission factor deviations less than 2% except one institution. The output deviations of both photon and electron beams were less than ±3% for every institution.ConclusionsThrough the on-site audit program, we could effectively detect an inappropriately operating linacs and provide some recommendations. The standard of radiation therapy in Korea is expected to improve through such on-site audits.     

Evaluating the predictive value of quantec rectum tolerance dose suggestions on acute rectal toxicity in prostate carcinoma patients treated with IMRT

AimTo investigate the predictive value of convenience of rectum dosimetry with Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) dose limits, maximum rectum dose (Dmax), total rectal volume (TVrectum), rectal volume included in PTV (VrectumPTV) on Grade 2–3 acute rectal toxicity for utilization in clinical practice.BackgroundNumerous previous data have reported frequent acute proctitis after external-beam RT of prostate cancer. Predicting toxicity limited with dose information is inadequate in clinical practice due to comorbidities and medications used.Materials and MethodSixty-four non-metastatic prostate cancer patients treated with IMRT were enrolled. Patients were treated to a total dose of 70–76 Gy. Rectal dose volume histograms (DVH) of all patients were evaluated retrospectively, and a QUANTEC Score between 0 and 5 was calculated for each patient. The correlation between the rectal DVH data, QUANTEC score, TVrectum, VrectumPTV, rectum Dmax and Grade 2–3 rectal toxicity was investigated.ResultsIn the whole group grade 1, 2 and 3 acute rectal toxicities were 25%, 18.8% and 3.1%, respectively. In the DVH data, rectum doses of all patients were under RTOG dose limits. Statistically significant correlation was found between grade 2–3 rectal toxicity and TVrectum (p = 0,043); however. It was not correlated with QUANTEC score, VrectumPTV and Dmax.ConclusionOur results were not able to show any significant correlation between increasing convenience with QUANTEC limits and lower rectal toxicity. Conclusively, new dosimetric definitions are warranted to predict acute rectal toxicity more accurately in prostate cancer patients during IMRT treatment.     

Optimal planning parameters for simultaneous boost IMRT treatment of prostate cancer using a Beam Modulator™

ObjectiveTo determine the optimum energy and beam arrangement for prostate intensity-modulated radiation therapy (IMRT) delivery using an Elekta Beam Modulator? linear accelerator, in order to inform decisions when commissioning IMRT for prostate cancer.MethodsCMS XiO was used to create IMRT plans for a prostate patient. Arrangements with 3, 5, 7, 9 and 11 equally spaced fields, containing both a direct anterior and a direct posterior beam were used, with both 6 MV and 10 MV photons. The effects of varying the maximum number of iterations, leaf increment, number of intensity levels and minimum segment size were investigated. Treatment plans were compared using isodose distributions, conformity indices for targets and critical structures, target dose homogeneity, body dose and plan complexity.ResultsTarget dose conformity and homogeneity and sparing of critical structures improved with an increasing number of beams, although any improvements were small for plans containing more than five fields. Set-ups containing a direct posterior field provided superior conformality around the rectum to anterior beam arrangements. Mean non-target dose and total number of monitor units were higher with 6 MV for all beam arrangements. The dose distribution resulting from seven 6 MV beams was considered clinically equivalent to that with five 10 MV beams.ConclusionMethods have been developed to plan IMRT treatments using XiO for delivery with a Beam Modulator? that fulfil demanding dose criteria, using many different set-ups. This study suggests that 6 MV photons can produce prostate IMRT plans that are comparable to those using 10 MV. Work is ongoing to develop a complete class solution.     

In vivo skin dose measurement using MOSkin detectors in tangential breast radiotherapy

The purpose of this study is to measure patient skin dose in tangential breast radiotherapy. Treatment planning dose calculation algorithm such as Pencil Beam Convolution (PBC) and in vivo dosimetry techniques such as radiochromic film can be used to accurately monitor radiation doses at tissue depths, but they are inaccurate for skin dose measurement. A MOSFET-based (MOSkin) detector was used to measure skin dose in this study. Tangential breast radiotherapies (“bolus” and “no bolus”) were simulated on an anthropomorphic phantom and the skin doses were measured. Skin doses were also measured in 13 patients undergoing each of the techniques. In the patient study, the EBT2 measurements and PBC calculation tended to over-estimate the skin dose compared with the MOSkin detector (p < 0.05) in the “no bolus radiotherapy”. No significant differences were observed in the “bolus radiotherapy” (p > 0.05). The results from patients were similar to that of the phantom study. This shows that the EBT2 measurement and PBC calculation, while able to predict accurate doses at tissue depths, are inaccurate in predicting doses at build-up regions. The clinical application of the MOSkin detectors showed that the average total skin doses received by patients were 1662 ± 129 cGy (medial) and 1893 ± 199 cGy (lateral) during “no bolus radiotherapy”. The average total skin doses were 4030 ± 72 cGy (medial) and 4004 ± 91 cGy (lateral) for “bolus radiotherapy”. In some cases, patient skin doses were shown to exceed the dose toxicity level for skin erythema. Hence, a suitable device for in vivo dosimetry is necessary to accurately determine skin dose.     

Oral administration of melatonin modulates the expression of tumor necrosis factor-α (TNF-α) gene in irradiated rat cervical spinal cord

AimWe aimed to determine the changes in TNF-α expression and Malondialdehyde (MDA) level in a short time after irradiation. Furthermore, we evaluated the effect of melatonin on the modulation of TNF-α gene expression.BackgroundThe radio-sensitivity of the cervical spinal cord limits the dose of radiation which can be delivered to tumors in the neck region. There is increasing evidence that TNF-α has a role in the development of the acute phase of spinal cord injury.Materials/MethodsFour groups of rats were investigated. Group 1 (vehicle treatment) served as the control. Group 2 (radiation) was treated with the vehicle, and 30 min later, the rats were exposed to radiation. Group 3 (radiation + melatonin) was given an oral administration of melatonin (100 mg/kg body weight) and 30 min later exposed to radiation in the same manner as in group 2. Group 4 (melatonin-only) was also given an oral administration of melatonin (100 mg/kg body weight). 5 mg/kg of melatonin was administered daily to rats in groups 3 and 4, and the vehicle was administered daily to rats in groups 1 and 2.ResultsThree weeks after irradiation, TNF-α gene up-regulated almost 5 fold in the irradiated group compared to the normal group. TNF-α gene expression in the melatonin pretreatment group, compared to the radiation group, was significantly down-regulated 3 weeks after irradiation (p < 0.05). MDA levels increased after irradiation and then significantly decreased under melatonin treatment.ConclusionWe suggest that inhibition of TNF-α expression by oral administration of melatonin may be a therapeutic option for preventing radiation-induced spinal cord injury.