AIM:To study the leakage-penumbra(LP)effect with a proposed correction method for the step-and-shoot intensity modulated radiation therapy(IMRT).METHODS:Leakage-penumbra dose profiles from 10 randomly selected prostat...AIM:To study the leakage-penumbra(LP)effect with a proposed correction method for the step-and-shoot intensity modulated radiation therapy(IMRT).METHODS:Leakage-penumbra dose profiles from 10 randomly selected prostate IMRT plans were studied.The IMRT plans were delivered by a Varian 21 EX linear accelerator equipped with a 120-leaf multileaf collimator(MLC).For each treatment plan created by the Pinnacle3 treatment planning system,a 3-dimensional LP dose distribution generated by 5 coplanar photon beams,starting from 0o with equal separation of 72 o,was investigated.For each photon beam used in the stepand-shoot IMRT plans,the first beam segment was set to have the largest area in the MLC leaf-sequencing,and was equal to the planning target volume(PTV).The overshoot effect(OSE)and the segment positional errors were measured using a solid water phantom with Kodak(TL and X-OMAT V)radiographic films.Film dosimetric analysis and calibration were carried out using a film scanner(Vidar VXR-16).The LP dose profiles were determined by eliminating the OSE and segment positional errors with specific individual irradiations.RESULTS:A non-uniformly distributed leaf LP dose ranging from 3%to 5%of the beam dose was measured in clinical IMRT beams.An overdose at the gap between neighboring segments,represented as dose peaks of up to 10%of the total BP,was measured.The LP effect increased the dose to the PTV and surrounding critical tissues.In addition,the effectdepends on the number of beams and segments for each beam.Segment positional error was less than the maximum tolerance of 1 mm under a dose rate of 600 monitor units per minute in the treatment plans.The OSE varying with the dose rate was observed in all photon beams,and the effect increased from 1 to 1.3 Gy per treatment of the rectal intersection.As the dosimetric impacts from the LP effect and OSE may increase the rectal post-radiation effects,a correction of LP was proposed and demonstrated for the central beam profile for one of the planned beams.CONCLUSION:We concluded that the measured dosimetric impact of the LP dose inaccuracy from photon beam segment in step-and-shoot IMRT can be corrected.展开更多
AIMTo investigated the dose enhancement due to the incorporation of nanoparticles in skin therapy using the kilovoltage (kV) photon and megavoltage (MV) electron beams. Monte Carlo simulations were used to predict the...AIMTo investigated the dose enhancement due to the incorporation of nanoparticles in skin therapy using the kilovoltage (kV) photon and megavoltage (MV) electron beams. Monte Carlo simulations were used to predict the dose enhancement when different types and concentrations of nanoparticles were added to skin target layers of varying thickness.METHODSClinical kV photon beams (105 and 220 kVp) and MV electron beams (4 and 6 MeV), produced by a Gulmay D3225 orthovoltage unit and a Varian 21 EX linear accelerator, were simulated using the EGSnrc Monte Carlo code. Doses at skin target layers with thicknesses ranging from 0.5 to 5 mm for the photon beams and 0.5 to 10 mm for the electron beams were determined. The skin target layer was added with the Au, Pt, I, Ag and Fe<sub>2</sub>O<sub>3</sub> nanoparticles with concentrations ranging from 3 to 40 mg/mL. The dose enhancement ratio (DER), defined as the dose at the target layer with nanoparticle addition divided by the dose at the layer without nanoparticle addition, was calculated for each nanoparticle type, nanoparticle concentration and target layer thickness.RESULTSIt was found that among all nanoparticles, Au had the highest DER (5.2-6.3) when irradiated with kV photon beams. Dependence of the DER on the target layer thickness was not significant for the 220 kVp photon beam but it was for 105 kVp beam for Au nanoparticle concentrations higher than 18 mg/mL. For other nanoparticles, the DER was dependent on the atomic number of the nanoparticle and energy spectrum of the photon beams. All nanoparticles showed an increase of DER with nanoparticle concentration during the photon beam irradiations regardless of thickness. For electron beams, the Au nanoparticles were found to have the highest DER (1.01-1.08) when the beam energy was equal to 4 MeV, but this was drastically lower than the DER values found using photon beams. The DER was also found affected by the depth of maximum dose of the electron beam and target thickness. For other nanoparticles with lower atomic number, DERs in the range of 0.99-1.02 were found using the 4 and 6 MeV electron beams.CONCLUSIONIn nanoparticle-enhanced skin therapy, Au nanoparticle addition can achieve the highest dose enhancement with 105 kVp photon beams. Electron beams, while popular for skin therapy, did not produce as high dose enhancements as kV photon beams. Additionally, the DER is dependent on nanoparticle type, nanoparticle concentration, skin target thickness and energies of the photon and electron beams.展开更多
Liver metastases occur commonly in many solid malignancies.With advances in systemic therapies and increased life expectancy,the role of using local therapies in oligo-metastases is rapidly increasing.Stereotactic bod...Liver metastases occur commonly in many solid malignancies.With advances in systemic therapies and increased life expectancy,the role of using local therapies in oligo-metastases is rapidly increasing.Stereotactic body ra-diotherapy(SBRT)is an emerging precision therapy that is being used more frequently in the treatment for un-resectable liver metastases.This review focuses on the role of SBRT for liver metastases,principles of treatment,clinical outcomes,toxicity,and optimal patient selection.展开更多
Hepatocellular carcinoma(HCC)is a common malignancy with high mortality rates.While surgery can be curative in early-stage disease,80% of patients cannot undergo surgical resection.Stereotactic body radiotherapy(SBRT)...Hepatocellular carcinoma(HCC)is a common malignancy with high mortality rates.While surgery can be curative in early-stage disease,80% of patients cannot undergo surgical resection.Stereotactic body radiotherapy(SBRT),an emerging,non-invasive,precision treatment,has shown promising results across various stages of HCC and has thus been adopted in practice to varying degrees around the world.This article aims to review current guideline recommendations on SBRT,clinical evidence,and outcome comparisons with other local treatment modalities.Attempts are also made to compare the differences in clinical trials between Asian and Western countries.展开更多
Radiological imaging has a critical role in the diagnosis of sarcomas and in evaluating therapy response assessment.The current gold standard for response assessment in solid tumors is the Response Evaluation Criteria...Radiological imaging has a critical role in the diagnosis of sarcomas and in evaluating therapy response assessment.The current gold standard for response assessment in solid tumors is the Response Evaluation Criteria in Solid Tumors,which evaluates changes in tumor size as a surrogate endpoint for therapeutic efficacy.However,tumors may undergo necrosis,changes in vascularization or become cystic in response to therapy,with no significant volume changes;thus,size assessments alone may not be adequate.Such morphological changes may give rise to radiographic phenotypes that are not easily detected by human operators.Fortunately,recent advances in high-performance computing and machine learning algorithms have enabled deep analysis of radiological images to extract features that can provide richer information about intensity,shape,size or volume,and texture of tumor phenotypes.There is growing evidence to suggest that these image-derived or“radiomic features”are sensitive to biological processes such as necrosis and glucose metabolism.Thus,radiomics could prove to be a critical tool for assessing treatment response and may present an integral complement to existing response criteria,opening new avenues for patient assessment in sarcoma trials.展开更多
文摘AIM:To study the leakage-penumbra(LP)effect with a proposed correction method for the step-and-shoot intensity modulated radiation therapy(IMRT).METHODS:Leakage-penumbra dose profiles from 10 randomly selected prostate IMRT plans were studied.The IMRT plans were delivered by a Varian 21 EX linear accelerator equipped with a 120-leaf multileaf collimator(MLC).For each treatment plan created by the Pinnacle3 treatment planning system,a 3-dimensional LP dose distribution generated by 5 coplanar photon beams,starting from 0o with equal separation of 72 o,was investigated.For each photon beam used in the stepand-shoot IMRT plans,the first beam segment was set to have the largest area in the MLC leaf-sequencing,and was equal to the planning target volume(PTV).The overshoot effect(OSE)and the segment positional errors were measured using a solid water phantom with Kodak(TL and X-OMAT V)radiographic films.Film dosimetric analysis and calibration were carried out using a film scanner(Vidar VXR-16).The LP dose profiles were determined by eliminating the OSE and segment positional errors with specific individual irradiations.RESULTS:A non-uniformly distributed leaf LP dose ranging from 3%to 5%of the beam dose was measured in clinical IMRT beams.An overdose at the gap between neighboring segments,represented as dose peaks of up to 10%of the total BP,was measured.The LP effect increased the dose to the PTV and surrounding critical tissues.In addition,the effectdepends on the number of beams and segments for each beam.Segment positional error was less than the maximum tolerance of 1 mm under a dose rate of 600 monitor units per minute in the treatment plans.The OSE varying with the dose rate was observed in all photon beams,and the effect increased from 1 to 1.3 Gy per treatment of the rectal intersection.As the dosimetric impacts from the LP effect and OSE may increase the rectal post-radiation effects,a correction of LP was proposed and demonstrated for the central beam profile for one of the planned beams.CONCLUSION:We concluded that the measured dosimetric impact of the LP dose inaccuracy from photon beam segment in step-and-shoot IMRT can be corrected.
文摘AIMTo investigated the dose enhancement due to the incorporation of nanoparticles in skin therapy using the kilovoltage (kV) photon and megavoltage (MV) electron beams. Monte Carlo simulations were used to predict the dose enhancement when different types and concentrations of nanoparticles were added to skin target layers of varying thickness.METHODSClinical kV photon beams (105 and 220 kVp) and MV electron beams (4 and 6 MeV), produced by a Gulmay D3225 orthovoltage unit and a Varian 21 EX linear accelerator, were simulated using the EGSnrc Monte Carlo code. Doses at skin target layers with thicknesses ranging from 0.5 to 5 mm for the photon beams and 0.5 to 10 mm for the electron beams were determined. The skin target layer was added with the Au, Pt, I, Ag and Fe<sub>2</sub>O<sub>3</sub> nanoparticles with concentrations ranging from 3 to 40 mg/mL. The dose enhancement ratio (DER), defined as the dose at the target layer with nanoparticle addition divided by the dose at the layer without nanoparticle addition, was calculated for each nanoparticle type, nanoparticle concentration and target layer thickness.RESULTSIt was found that among all nanoparticles, Au had the highest DER (5.2-6.3) when irradiated with kV photon beams. Dependence of the DER on the target layer thickness was not significant for the 220 kVp photon beam but it was for 105 kVp beam for Au nanoparticle concentrations higher than 18 mg/mL. For other nanoparticles, the DER was dependent on the atomic number of the nanoparticle and energy spectrum of the photon beams. All nanoparticles showed an increase of DER with nanoparticle concentration during the photon beam irradiations regardless of thickness. For electron beams, the Au nanoparticles were found to have the highest DER (1.01-1.08) when the beam energy was equal to 4 MeV, but this was drastically lower than the DER values found using photon beams. The DER was also found affected by the depth of maximum dose of the electron beam and target thickness. For other nanoparticles with lower atomic number, DERs in the range of 0.99-1.02 were found using the 4 and 6 MeV electron beams.CONCLUSIONIn nanoparticle-enhanced skin therapy, Au nanoparticle addition can achieve the highest dose enhancement with 105 kVp photon beams. Electron beams, while popular for skin therapy, did not produce as high dose enhancements as kV photon beams. Additionally, the DER is dependent on nanoparticle type, nanoparticle concentration, skin target thickness and energies of the photon and electron beams.
文摘Liver metastases occur commonly in many solid malignancies.With advances in systemic therapies and increased life expectancy,the role of using local therapies in oligo-metastases is rapidly increasing.Stereotactic body ra-diotherapy(SBRT)is an emerging precision therapy that is being used more frequently in the treatment for un-resectable liver metastases.This review focuses on the role of SBRT for liver metastases,principles of treatment,clinical outcomes,toxicity,and optimal patient selection.
基金supported in part by Shenzhen Science and Technol-ogy Program(grant number KQTD20180411185028798)a Varian Medical Systems Research Grant.
文摘Hepatocellular carcinoma(HCC)is a common malignancy with high mortality rates.While surgery can be curative in early-stage disease,80% of patients cannot undergo surgical resection.Stereotactic body radiotherapy(SBRT),an emerging,non-invasive,precision treatment,has shown promising results across various stages of HCC and has thus been adopted in practice to varying degrees around the world.This article aims to review current guideline recommendations on SBRT,clinical evidence,and outcome comparisons with other local treatment modalities.Attempts are also made to compare the differences in clinical trials between Asian and Western countries.
基金This research was supported by the Sarcoma Alliance for Research through Collaboration LMSARC research fundthe philanthropic LMS360 research fund from the University of Michigan LMS360.
文摘Radiological imaging has a critical role in the diagnosis of sarcomas and in evaluating therapy response assessment.The current gold standard for response assessment in solid tumors is the Response Evaluation Criteria in Solid Tumors,which evaluates changes in tumor size as a surrogate endpoint for therapeutic efficacy.However,tumors may undergo necrosis,changes in vascularization or become cystic in response to therapy,with no significant volume changes;thus,size assessments alone may not be adequate.Such morphological changes may give rise to radiographic phenotypes that are not easily detected by human operators.Fortunately,recent advances in high-performance computing and machine learning algorithms have enabled deep analysis of radiological images to extract features that can provide richer information about intensity,shape,size or volume,and texture of tumor phenotypes.There is growing evidence to suggest that these image-derived or“radiomic features”are sensitive to biological processes such as necrosis and glucose metabolism.Thus,radiomics could prove to be a critical tool for assessing treatment response and may present an integral complement to existing response criteria,opening new avenues for patient assessment in sarcoma trials.
