Young Kyung Lim

Single-Dose Versus Fractionated Stereotactic Radiotherapy for Brain Metastases

PURPOSE To evaluate the efficacy of stereotactic radiotherapy in patients with brain metastases by comparing two different treatment regimens, single-dose radiosurgery (SRS) and fractionated stereotactic radiotherapy (FSRT). METHODS AND MATERIALS Between November 2003 and December 2008, 98 patients with brain metastases were included. Fifty-eight patients were treated with SRS, and forty were treated with FSRT. Fractionated stereotactic radiotherapy was used for large lesions or lesions located near critical structures. The median doses were 20 Gy for the SRS group and 36 Gy in 6 fractions for the FSRT group. RESULTS With a median follow-up period of 7 months, the median survival was 7 months for all patients, with a median of 6 months for the SRS group and 8 months for the FSRT group (p = 0.89). Local progression-free survival (LPFS) rates at 6 months and 1 year were 81% and 71%, respectively, for the SRS group and 97% and 69%, respectively, for the FSRT group (p = 0.31). Despite the fact that FSRT was used for large lesions and lesions in adverse locations, LPFS was not inferior to SRS. Toxicity was more frequently observed in the SRS group than in the FSRT group (17% vs. 5%, p = 0.05). CONCLUSIONS Because patients treated with FSRT exhibited similar survival times and LPFS rates with a lower risk of toxicity in comparison to those treated with SRS, despite the fact that FSRT was used for large lesions and lesions in adverse locations, we find that FSRT can particularly be beneficial for patients with large lesions or lesions located near critical structures. Further investigation is warranted to determine the optimal dose/fractionation.

MICROSCOPIC GOLD PARTICLE-BASED FIDUCIAL MARKERS FOR PROTON THERAPY OF PROSTATE CANCER

PURPOSE We examined the feasibility of using fiducial markers composed of microscopic gold particles and human-compatible polymers as a means to overcome current problems with conventional macroscopic gold fiducial markers, such as dose reduction and artifact generation, in proton therapy for prostate cancer. METHODS AND MATERIALS We examined two types of gold particle fiducial marker interactions: that with diagnostic X-rays and with a therapeutic proton beam. That is, we qualitatively and quantitatively compared the radiographic visibility of conventional gold and gold particle fiducial markers and the CT artifacts and dose reduction associated with their use. RESULTS The gold particle fiducials could be easily distinguished from high-density structures, such as the pelvic bone, in diagnostic X-rays but were nearly transparent to a proton beam. The proton dose distribution was distorted <5% by the gold particle fiducials with a 4.9% normalized gold density; this was the case even in the worst configuration (i.e., parallel alignment with a single-direction proton beam). In addition, CT artifacts were dramatically reduced for the gold particle mixture. CONCLUSION Mixtures of microscopic gold particles and human-compatible polymers have excellent potential as fiducial markers for proton therapy for prostate cancer. These include good radiographic visibility, low distortion of the depth-dose distribution, and few CT artifacts.

Risk of second cancer from scattered radiation of intensity-modulated radiotherapies with lung cancer

PurposeTo compare the risk of secondary cancer from scattered and leakage doses following intensity-modulated radiotherapy (IMRT), volumetric arc therapy (VMAT) and tomotherapy (TOMO) in patients with lung cancer.MethodsIMRT, VMAT and TOMO were planned for five lung cancer patients. Organ equivalent doses (OEDs) are estimated from the measured corresponding secondary doses during irradiation at various points 20 to 80 cm from the iso-center by using radio-photoluminescence glass dosimeter (RPLGD).ResultsThe secondary dose per Gy from IMRT, VMAT and TOMO for lung cancer, measured 20 to 80 cm from the iso-center, are 0.02~2.03, 0.03~1.35 and 0.04~0.46 cGy, respectively. The mean values of relative OED of secondary dose of VMAT and TOMO, which is normalized by IMRT, ranged between 88.63% and 41.59% revealing 88.63% and 41.59% for thyroid, 82.33% and 41.85% for pancreas, 77.97% and 49.41% for bowel, 73.42% and 72.55% for rectum, 74.16% and 81.51% for prostate. The secondary dose and OED from TOMO became similar to those from IMRT and VMAT as the distance from the field edge increased.ConclusionsOED based estimation suggests that the secondary cancer risk from TOMO is less than or comparable to the risks from conventional IMRT and VMAT.

A comparison of the quality assurance of four dosimetric tools for intensity modulated radiation therapy

Abstract Background. This study was designed to compare the quality assurance (QA) results of four dosimetric tools used for intensity modulated radiation therapy (IMRT) and to suggest universal criteria for the passing rate in QA, irrespective of the dosimetric tool used. Materials and methods. Thirty fields of IMRT plans from five patients were selected, followed by irradiation onto radiochromic film, a diode array (Mapcheck), an ion chamber array (MatriXX) and an electronic portal imaging device (EPID) for patient-specific QA. The measured doses from the four dosimetric tools were compared with the dose calculated by the treatment planning system. The passing rates of the four dosimetric tools were calculated using the gamma index method, using as criteria a dose difference of 3% and a distance-to-agreement of 3 mm. Results. The QA results based on Mapcheck, MatriXX and EPID showed good agreement, with average passing rates of 99.61%, 99.04% and 99.29%, respectively. However, the average passing rate based on film measurement was significantly lower, 95.88%. The average uncertainty (1 standard deviation) of passing rates for 6 intensity modulated fields was around 0.31 for film measurement, larger than those of the other three dosimetric tools. Conclusions. QA results and consistencies depend on the choice of dosimetric tool. Universal passing rates should depend on the normalization or inter-comparisons of dosimetric tools if more than one dosimetric tool is used for patient specific QA.

Normal liver sparing by proton beam therapy for hepatocellular carcinoma: Comparison with helical intensity modulated radiotherapy and volumetric modulated arc therapy

To the Editor, Technical advances in radiotherapy (RT) planning systems using computed tomography (CT), such as three-dimensional conformal RT (3D-CRT), along with greater understanding of partial liver tolerance have increased the use of RT in the non-surgical management of patients with hepatocellular carcinoma (HCC) [1]. Radiation-induced liver disease (RILD) is one of the most common dose limiting toxicities in patients receiving RT for HCC. While most cases of RILD are self-limiting and manageable with supportive care, this complication may result in the deterioration of hepatic reserve, with severe injury resulting in liver failure and death. Therefore, when treating HCC patients with RT, it is important not only to maximize the effective dose delivered to the tumor but to minimize the dose delivered to the surrounding normal liver. Intensity-modulated radiotherapy (IMRT), using intensity-modulated beams to deliver a high dose to the tumor while reducing the dose to the surrounding normal tissues, and image-guided RT (IGRT) have been available. Recently, the more sophisticated RT techniques, such as helical-IMRT (H-IMRT), a type of fusion technology that combines IMRT and IGRT, and volumetric modulated arc therapy (VMAT), which uses modulated treatment apertures [defi ned by dynamic multi-leaf collimator (MLC)] and dose rate, have been shown to provide equal or better tumor coverage and better sparing of normal tissues than 3D-CRT and/or IMRT in patients with HCC [2 – 7]. Proton beam therapy (PBT) is another promising treatment option that can deliver a high radiation dose to the tumor while minimizing the radiation dose delivered to the remaining normal liver due to the unique characteristics of proton beams, the Bragg peak, allowing deposition of high doses of radiation within the target, with much lower doses outside the target. However, despite the conceptual benefi ts and promising clinical outcomes of PBT [8 – 13], it is remained unclear whether PBT is benefi cial in reducing the irradiated liver volume comparing with aforementioned more sophisticated RT techniques or not. Therefore, this study was designed to compare the effects of PBT, H-IMRT, and VMAT on irradiated liver volume in patients with HCC.

Secondary neutron dose measurement for proton eye treatment using an eye snout with a borated neutron absorber

BackgroundWe measured and assessed ways to reduce the secondary neutron dose from a system for proton eye treatment.MethodsProton beams of 60.30 MeV were delivered through an eye-treatment snout in passive scattering mode. Allyl diglycol carbonate (CR-39) etch detectors were used to measure the neutron dose in the external field at 0.00, 1.64, and 6.00 cm depths in a water phantom. Secondary neutron doses were measured and compared between those with and without a high-hydrogen–boron-containing block. In addition, the neutron energy and vertices distribution were obtained by using a Geant4 Monte Carlo simulation.ResultsThe ratio of the maximum neutron dose equivalent to the proton absorbed dose (H(10)/D) at 2.00 cm from the beam field edge was 8.79 ± 1.28 mSv/Gy. The ratio of the neutron dose equivalent to the proton absorbed dose with and without a high hydrogen-boron containing block was 0.63 ± 0.06 to 1.15 ± 0.13 mSv/Gy at 2.00 cm from the edge of the field at depths of 0.00, 1.64, and 6.00 cm.ConclusionsWe found that the out-of-field secondary neutron dose in proton eye treatment with an eye snout is relatively small, and it can be further reduced by installing a borated neutron absorbing material.

Prediction of Output Factor, Range, and Spread-Out Bragg Peak for Proton Therapy

In proton therapy, patient quality assurance (QA) requires measuring the beam range, spread-out Bragg peak (SOBP), and output factor. If these values can be predicted by using sampling measurements or previous QA data to find the correlation between beam setup parameters and measured data, efforts expended on patient QA can be reduced. Using sampling data, we predicted the range, SOBP, and output factor of the proton beam. To obtain sampling data, we measured the range, SOBP, and output factor for 14 data points at each of 24-beam range options, from 4-28 cm. Prediction conformity was evaluated by the difference between predicted and measured patient QA data. Results indicated that for 60% of patients, the values could be predicted within 3% of dose uncertainty.

The effect of a contrast agent on proton beam range in radiotherapy planning using computed tomography for patients with locoregionally advanced lung cancer.

PURPOSE We evaluated the effect of a contrast agent (CA) on proton beam range in a treatment planning system (TPS) for patients with locoregionally advanced lung cancer. METHODS AND MATERIALS Two sets of computed tomography (CT) images (with and without CA) were obtained from 20 patients with lung cancer. Because the increase in Hounsfield unit (∆HU) value of the heart and great vessels due to the effect of CA is most prominent among thoracic structures, to evaluate the effect of CA on proton beam range in the TPS, we compared the calculated distal ranges in the plan with CA-enhanced CT with those with corrected CT, in which the HU values of the heart and great vessels in the CA-enhanced CT were replaced by average HU values obtained from the unenhanced CT. RESULTS The mean ∆HU value and the longest length of the heart and great vessels within the proton beam path in the field that passed through these structures were 189 ± 29 HU (range, 110-250 HU) and 7.1 ± 1.1 cm (range, 2.6-11.2 cm), respectively. The mean distal range error in the TPS because of the presence of CA was 1.0 ± 0.7 cm (range, 0.2-2.6 cm). CONCLUSION If CA-enhanced CT images are used for radiotherapy planning using a proton beam for the treatment of lung cancer, our results suggest that the HU values of the heart and great vessels should be replaced by the average HU values of soft tissue to avoid discrepancies between planned and delivered doses.

CHARACTERISTICS OF MOVEMENT-INDUCED DOSE REDUCTION IN TARGET VOLUME: A COMPARISON BETWEEN PHOTON AND PROTON BEAM TREATMENT

We compared the main characteristics of movement-induced dose reduction during photon and proton beam treatment, based on an analysis of dose-volume histograms. To simulate target movement, a target contour was delineated in a scanned phantom and displaced by 3 to 20 mm. Although the dose reductions to the target in the 2 treatment systems were similar for transverse (perpendicular to beam direction) target motion, they were completely different for longitudinal (parallel to beam direction) target motion. While both modalities showed a relationship between the degree of target shift and the reduction in dose coverage, dose reduction showed a strong directional dependence in proton beam treatment. Clinical simulation of target movement for a prostate cancer patient showed that, although coverage and conformity indices for a 6-mm lateral movement of the prostate were reduced by 9% and 16%, respectively, for proton beam treatment, they were reduced by only 1% and 7%, respectively, for photon treatment. This difference was greater for a 15-mm target movement in the lateral direction, which lowered the coverage and conformity indices by 34% and 54%, respectively, for proton beam treatment, but changed little during photon treatment. In addition, we found that the equivalent uniform dose (EUD) and homogeneity index show similar characteristics during target movement. These results suggest that movement-induced dose reduction differs significantly between photon and proton beam treatment. Attention should be paid to the target margin in proton beam treatment due to the distinct characteristics of heavy ion beams.

Combination effects of tissue heterogeneity and geometric targeting error in stereotactic body radiotherapy for lung cancer using CyberKnife

We have investigated the combined effect of tissue heterogeneity and its variation associated with geometric error in stereotactic body radiotherapy (SBRT) for lung cancer. The treatment plans for eight lung cancer patients were calculated using effective path length (EPL) correction and Monte Carlo (MC) algorithms, with both having the same beam configuration for each patient. These two kinds of plans for individual patients were then subsequently recalculated with adding systematic and random geometric errors. In the ordinary treatment plans calculated with no geometric offset, the EPL calculations, compared with the MC calculations, largely overestimated the doses to PTV by ∼21%, whereas the overestimation were markedly lower in GTV by ∼12% due to relatively higher density of GTV than of PTV. When recalculating the plans for individual patients with assigning the systematic and random geometric errors, no significant changes in the relative dose distribution, except for overall shift, were observed in the EPL calculations, whereas largely altered in the MC calculations with a consistent increase in dose to GTV. Considering the better accuracy of MC than EPL algorithms, the present results demonstrated the strong coupling of tissue heterogeneity and geometric error, thereby emphasizing the essential need for simultaneous correction for tissue heterogeneity and geometric targeting error in SBRT of lung cancer. PACS numbers: 87.55.D, 87.55.kh, 87.53.Ly, 87.55.‐xWe have investigated the combined effect of tissue heterogeneity and its variation associated with geometric error in stereotactic body radiotherapy (SBRT) for lung cancer. The treatment plans for eight lung cancer patients were calculated using effective path length (EPL) correction and Monte Carlo (MC) algorithms, with both having the same beam configuration for each patient. These two kinds of plans for individual patients were then subsequently recalculated with adding systematic and random geometric errors. In the ordinary treatment plans calculated with no geometric offset, the EPL calculations, compared with the MC calculations, largely overestimated the doses to PTV by ∼21%, whereas the overestimation were markedly lower in GTV by ∼12% due to relatively higher density of GTV than of PTV. When recalculating the plans for individual patients with assigning the systematic and random geometric errors, no significant changes in the relative dose distribution, except for overall shift, were observed in the EPL calculations, whereas largely altered in the MC calculations with a consistent increase in dose to GTV. Considering the better accuracy of MC than EPL algorithms, the present results demonstrated the strong coupling of tissue heterogeneity and geometric error, thereby emphasizing the essential need for simultaneous correction for tissue heterogeneity and geometric targeting error in SBRT of lung cancer. PACS numbers: 87.55.D, 87.55.kh, 87.53.Ly, 87.55.-x.