Shyh-An Yeh

Cognitive function before and after intensity-modulated radiation therapy in patients with nasopharyngeal carcinoma: a prospective study.

PURPOSEnTo evaluate the effects of radiation therapy (RT) on neurocognitive function in patients with nasopharyngeal carcinoma (NPC).nnnMETHODS AND MATERIALSnThirty patients with NPC treated with intensity-modulated RT were included. Dose-volume histograms of the temporal lobes were obtained in every patient. Neurocognitive tests were administered individually to each patient 1 day before initiation of RT and at least 12 months after completion of RT. Cognitive functioning status was evaluated as change in scores over time.nnnRESULTSnAmong the total of 30 patients, 23 patients (76.7%) had significantly lower post-RT cognitive functioning scores compared with their pre-RT scores (p = 0.033). The cognitive functioning scores had significantly declined in the domains of short-term memory, language abilities, and list-generating fluency (p = 0.020, 0.023, and 0.001, respectively). Compared with patients with a mean dose to the temporal lobes of 36 Gy or less, patients with a mean dose of greater than 36 Gy had a significantly greater reduction in cognitive functioning scores (p = 0.017). Patients in whom V60 of the temporal lobes (i.e., the percentage of the temporal lobe volume that had received >60 Gy) was greater than 10% also had a greater reduction in cognitive functioning scores than those in whom V60 was 10% or less (p = 0.039).nnnCONCLUSIONSnThe results of our study indicated that RT could have deleterious effects on cognitive function in patients with NPC. Efforts should be made to reduce the radiation dose and irradiated volume of temporal lobes without compromising the coverage of target volume.

Normal tissue complication probability modeling for cochlea constraints to avoid causing tinnitus after head-and-neck intensity-modulated radiation therapy

BackgroundRadiation-induced tinnitus is a side effect of radiotherapy in the inner ear for cancers of the head and neck. Effective dose constraints for protecting the cochlea are under-reported. The aim of this study is to determine the cochlea dose limitation to avoid causing tinnitus after head-and-neck cancer (HNC) intensity-modulated radiation therapy (IMRT).MethodsIn total 211 patients with HNC were included; the side effects of radiotherapy were investigated for 422 inner ears in the cohort. Forty-nine of the four hundred and twenty-two samples (11.6xa0%) developed grade 2+ tinnitus symptoms after IMRT, as diagnosed by a clinician. The Late Effects of Normal Tissues–Subjective, Objective, Management, Analytic (LENT-SOMA) criteria were used for tinnitus evaluation. The logistic and Lyman-Kutcher-Burman (LKB) normal tissue complication probability (NTCP) models were used for the analyses.ResultsThe NTCP-fitted parameters were TD50u2009=u200946.31xa0Gy (95xa0% CI, 41.46–52.50), γ50u2009=u20091.27 (95xa0% CI, 1.02–1.55), and TD50u2009=u200946.52xa0Gy (95xa0% CI, 41.91–53.43), mu2009=u20090.35 (95xa0% CI, 0.30–0.42) for the logistic and LKB models, respectively. The suggested guideline TD20 for the tolerance dose to produce a 20xa0% complication rate within a specific period of time was TD20u2009=u200933.62xa0Gy (95xa0% CI, 30.15–38.27) (logistic) and TD20u2009=u200932.82xa0Gy (95xa0% CI, 29.58–37.69) (LKB).ConclusionsTo maintain the incidence of grade 2+ tinnitus toxicity <20xa0% in IMRT, we suggest that the mean dose to the cochlea should be <32xa0Gy. However, models should not be extrapolated to other patient populations without further verification and should first be confirmed before clinical implementation.

Calibration of EBT2 film using a red‐channel PDD method in combination with a modified three‐channel technique

PURPOSEnAshland Inc. EBT2 and EBT3 films are widely used in quality assurance for radiation therapy; however, there remains a relatively high degree of uncertainty [B. Hartmann, M. Martisikova, and O. Jakel, Homogeneity of Gafchromic EBT2 film, Med. Phys. 37, 1753-1756 (2010)]. Micke et al. (2011) recently improved the spatial homogeneity using all color channels of a flatbed scanner; however, van Hoof et al. (2012) pointed out that the corrected nonuniformity still requires further investigation for larger fields. To reduce the calibration errors and the uncertainty, the authors propose a new red-channel percentage-depth-dose method in combination with a modified three-channel technique.nnnMETHODSnFor the ease of comparison, the EBT2 film image used in the authors previous study (2012) was reanalyzed using different approaches. Photon beams of 6-MV were delivered to two different films at two different beam on times, resulting in the absorption doses of ranging from approximately 30 to 300 cGy at the vertical midline of the film, which was set to be coincident with the central axis of the beam. The film was tightly sandwiched in a 30(3)-cm(3) polystyrene phantom, and the pixel values for red, green, and blue channels were extracted from 234 points on the central axis of the beam and compared with the corresponding depth doses. The film was first calibrated using the multichannel method proposed by Micke et al. (2010), accounting for nonuniformities in the scanner. After eliminating the scanner and dose-independent nonuniformities, the film was recalibrated via the dose-dependent optical density of the red channel and fitted to a power function. This calibration was verified via comparisons of the dose profiles extracted from the films, where three were exposed to a 60° physical wedge field and three were exposed to composite fields, and all of which were measured in a water phantom. A correction for optical attenuation was implemented, and treatment plans of intensity modulated radiation therapy and volumetric modulated arc therapy were evaluated.nnnRESULTSnThe method described here demonstrated improved accuracy with reduced uncertainty. The relative error compared with the measurements of a water phantom was less than 1%, and the overall calibration uncertainty was less than 2%. Verification tests revealed that the results were close to those of the authors previous study, and all differences were within 3%, except those with a high-dose gradient. The gamma pass rates (2%/2 mm) of the treatment plan evaluated using the method described here were greater than 99%, and no obvious stripe patterns were observed in the dose-difference maps.nnnCONCLUSIONSnSpatial homogeneity was significantly improved via the calibration method described here. This technique is both convenient and time-efficient because it does not require cutting the film, and only two exposures are necessary.

An intelligence system approach using artificial neural networks to evaluate the quality of treatment planning for nasopharyngeal carcinoma

The quality of the nasopharyngeal carcinoma (NPC) treatment plans evaluation using three types of artificial neural networks (ANNs) are instructed by three different training algorithms.xa0Three ANNsxa0including Elman (ANN-E), feed-forward (ANN-FF), and pattern recognition (ANN-PR)xa0were trained by using three different models, that is,xa0leave-one-out (Train-loo), random selection (Train-random), and user defined (Train-user) method. One hundred sets of NPC treatment plans were collected as the input data of the neural networks. The conformal index (CI) and homogeneity index (HI) were used as the characteristic values and also to train the neurons.xa0Four grades (A, B, C, and D) were classified in degrading order.xa0The over-training issue is considered between the train data and the number of neurons. The receiver operating characteristic (ROC) curves were obtained to evaluate the performed accuracies. The optimal numbers of neurons for ANN-E, ANN-FF, and ANN-PR, in the loo method are 6, 24, and 9; in the random-selection method, they are 26, 22, and 4; and in the user-defined method they are 12, 8, and 11 neurons, respectively. The optimal size of train data is 92% of total inputs in the cases of ANN-Exa0and ANN-FFxa0and 76% in the case of ANN-PR. The networks with higher accuracy are ANN-PR-looxa0(93.65 ± 3.60%), ANN-FF-looxa0(88.05 ± 5.84%), and ANN-E-looxa0(87.55 ± 5.86%), respectively. The networks with shorter training time are ANN-PR-randomxa0(0.55 ± 0.11xa0s), ANN-PR-userxa0(0.59 ± 0.08xa0s), and ANN-PR-userxa0(1.07 ± 0.16xa0s), respectively. The ROC curves show that the ANN-PR-looxa0approach has the highest sensitivity, which is 99%. ANN-PR-looxa0reduces the amount of trail-and-error during the iterative process of generating inverse treatment plans. It is concluded that the ANN-PR-looxa0is an excellent model among the three for classifying the quality of treatment plans for NPC. n n xa0 n n Key words:xa0Artificial neural networks (ANNs), dose-volume histogram (DVH), intelligence system, nasopharyngealxa0carcinomaxa0(NPC).

A Light-Field-Based Method to Adjust On-Axis Rounded Leaf End MLC Position to Predict Off-Axis MLC Penumbra Region Dosimetric Performance in a Radiation Therapy Planning System

Purpose. An analytical and experimental study of split shape dose calculation correction by adjusting the position of the on-axis round leaf end position is presented. We use on-axis corrected results to predict off-axis penumbra region dosimetric performance in an intensity-modulated radiation therapy treatment planning system. Materials and Methods. The precise light-field edge position (X tang.p) was derived from the on-axis 50% dose position created by using the nominal light field for geometric and mathematical manipulation. Leaf position (X mlc.p) could be derived from X tang.p by defining in the treatment planning system for monitor unit calculation. On-axis offset (correction) could be obtained from the position corresponding to 50% of the central axis dose minus the Xmlc.p position. The off-axis 50% dose position can then be derived from the on-axis 50% dose position. Results. The monitor unit calculation of the split shape using the on-axis rounded leaf end MLC penumbra region could provide an under-or overdose of 7.5% per millimeter without an offset correction. When using the on-axis rounded leaf end offset correction to predict the off-axis dose, the difference between the off- and on-axis 50% dose position is within ±1.5u2009mm. Conclusions. It is possible to achieve a dose calculation within 0.5% error for an adjusted MLC leaf edge location in the treatment planning system with careful measurement and an accurate on-axis offset correction. Dose calculations located at an off-axis spilt shape region should be used carefully due to noncorrectable errors which were found to be up to 10%.

A light field-based method to adjust rounded leaf end MLC position for split shape dose calculation correction in a radiation therapy treatment planning system

We present an analytical and experimental study of split shape dose calculation correction by adjusting the position of the round leaf end position in an intensity‐modulated radiation therapy treatment planning system. The precise light field edge position (Xtang.p) was derived from 50% of the central axis dose created by nominal light field using geometry and mathematical methods. Leaf position (Xmlc.p), defined in the treatment planning system for monitor unit calculation, could be derived from Xtang.p. Offset (correction) could be obtained by the position corresponding to 50% of the central axis dose minus the Xmlc.p position. For SSD from 90 cm to 120 cm at 6 MV and 10 MV, the 50% dose position was located outside of Xmlc,p in the MLC leaf position range of +8u2009cm to ‐8u2009cm, where the offset correction positively increased, whereas the offset correction negatively increased when the MLC leaf position was in the range of ‐12u2009cm to ‐8u2009cm and +20u2009cm to +8u2009cm when the 50% position was located inside Xmlc,p. The monitor unit calculation could provide underdosage or overdosage of 7.5% per mm without offset correction. Calibration could be performed at a certain SSD to fit all SSD offset corrections. With careful measurement and an accurate offset correction, it is possible to achieve the dose calculation with 0.5% error for the adjusted MLC leaf edge location in the treatment planning system. PACS number: 87.53.Tf, 87.55.x, 87.55.D, 87.55.dk

A conceptual design of rotating board technique for delivering total skin electron therapy

PURPOSEnThis study presents a novel technique in which a uniform radiation dose to the whole body, soles, and scalp vertex can be achieved in one electron beam treatment fraction.nnnMETHODSnThe patient was treated at a machine with a home-made rotating board. The patients were treated in two groups in the prone and supine positions by leaning onto an inner rotational board in the prone and supine positions. Each group can further be separated into two subgroups using tilting and rotational positions for treatment.nnnRESULTSnOne of the beams was directed 15.5 degrees upward and 15.5 degrees downward from the horizontal axis to provide a field size of as large as 200 cm in height and 140 cm in width. An incline angle of 31.5 degrees anteriorly (forward) or posteriorly (backward) of the outer frame at an angle rotated 60 degrees clockwise or counterclockwise to the inner frame was found to be most appropriate. The output for the rotating board total skin electron therapy (RB-TSET) was 0.046 cGy/MU at ISD of 350 cm. The beam characteristics of the RB-TSET depth dose curves were R50 = 2.48 cm, dmax = 0.7 cm, E0 = 5.78 MeV, and Rp = 3.4 cm.nnnCONCLUSIONSnThe RB-TSET technique presented in this study is able to deliver a uniform radiation dose to the patients skin surface, the scalp vertex, and soles of the feet all at one time, eliminating the trouble of having to further irradiate these two regions separately when using the Stanford six field technique.

Geometric error of cervical point A calculated through traditional reconstruction procedures for brachytherapy treatment.

Brachytherapy used in local cervical cancer is still widely based on 2D standard dose planning with the prescription to point A, which is invisible on imaging and located at a high-dose gradient. In this study, the geometric location error of point A was investigated. It is traditionally reconstructed in the treatment planning system after carefully digitizing the point marks that were previously drawn on the orthogonal radiographs into the system. Two Cartesian coordinates of point A were established and compared. One was built up based on the geometric definition of point A and would be taken as the true coordinate, while the other was built up through traditional clinical treatment procedures and named as the practical coordinate. The orthogonal film reconstruction technique was used and the location error between the practical and the true coordinate introduced from the variations of, first, the angle between the tandem and the simulator gantry rotation axis, and second, the interval between the tandem flange and the simulator isocenter, was analyzed. The location error of point A was higher if the tandem was rotated away from the gantry rotation axis or if the location of the tandem flange was set away from the isocenter. If a tandem with a 30° curvature was rotated away from the gantry rotation axis 10° in the anterior-posterior (AP) view, and there was an 8.7 cm interval between the flange and the isocenter, the location error of point A would be 3 mm without including other errors from simulator calibration, data input, patient setup, and movements. To reduce the location error of point A calculated for traditional reconstruction procedures, it is suggested to move the couch or patient to make the mid-point of two points A near the isocenter and the tandem in the AP view parallel to the gantry rotation axis as much as possible. PACS number: 87.55.km.Brachytherapy used in local cervical cancer is still widely based on 2D standard dose planning with the prescription to point A, which is invisible on imaging and located at a high‐dose gradient. In this study, the geometric location error of point A was investigated. It is traditionally reconstructed in the treatment planning system after carefully digitizing the point marks that were previously drawn on the orthogonal radiographs into the system. Two Cartesian coordinates of point A were established and compared. One was built up based on the geometric definition of point A and would be taken as the true coordinate, while the other was built up through traditional clinical treatment procedures and named as the practical coordinate. The orthogonal film reconstruction technique was used and the location error between the practical and the true coordinate introduced from the variations of, first, the angle between the tandem and the simulator gantry rotation axis, and second, the interval between the tandem flange and the simulator isocenter, was analyzed. The location error of point A was higher if the tandem was rotated away from the gantry rotation axis or if the location of the tandem flange was set away from the isocenter. If a tandem with a 30° curvature was rotated away from the gantry rotation axis 10° in the anterior–posterior (AP) view, and there was an 8.7 cm interval between the flange and the isocenter, the location error of point A would be 3 mm without including other errors from simulator calibration, data input, patient setup, and movements. To reduce the location error of point A calculated for traditional reconstruction procedures, it is suggested to move the couch or patient to make the mid‐point of two points A near the isocenter and the tandem in the AP view parallel to the gantry rotation axis as much as possible. PACS number: 87.55.km

Use dose bricks concept to implement nasopharyngeal carcinoma treatment planning.

Purpose. A “dose bricks” concept has been used to implement nasopharyngeal carcinoma treatment plan; this method specializes particularly in the case with bell shape nasopharyngeal carcinoma case. Materials and Methods. Five noncoplanar fields were used to accomplish the dose bricks technique treatment plan. These five fields include (a) right superior anterior oblique (RSAO), (b) left superior anterior oblique (LSAO), (c) right anterior oblique (RAO), (d) left anterior oblique (LAO), and (e) superior inferior vertex (SIV). Nondivergence collimator central axis planes were used to create different abutting field edge while normal organs were blocked by multileaf collimators in this technique. Results. The resulting 92% isodose curves encompassed the CTV, while maximum dose was about 115%. Approximately 50% volume of parotid glands obtained 10–15% of total dose and 50% volume of brain obtained less than 20% of total dose. Spinal cord receives only 5% from the scatter dose. Conclusions. Compared with IMRT, the expenditure of planning time and costing, “dose bricks” may after all be accepted as an optional implementation in nasopharyngeal carcinoma conformal treatment plan; furthermore, this method also fits the need of other nonhead and neck lesions if organ sparing and noncoplanar technique can be executed.

An innovative method to acquire the location of point A for cervical cancer treatment by HDR brachytherapy

Brachytherapy of local cervical cancer is generally accomplished through film‐based treatment planning with the prescription directed to point A, which is invisible on images and is located at a high‐dose gradient area. Through a standard reconstruction method by digitizing film points, the location error for point A would be 3 mm with a condition of 30° curvature tandem, which is 10° away from the gantry rotation axis of a simulator, and has an 8.7 cm interval between the flange and the isocenter. To reduce the location error of the reconstructed point A, this paper proposes a method and demonstrates its accuracy. The Cartesian coordinates of point A were derived by acquiring the locations of the cervical os (tandem flange) and a dummy seed located in the tandem above the flange. To verify this analytical method, ball marks in a commercial “Isocentric Beam Checker” were selected to simulate the two points A, the os, and the dummies. The Checker was placed on the simulator couch with its center ball coincident with the simulator isocenter and its rotation axis perpendicular to the gantry rotation axis. With different combinations of the Checker and couch rotation angles, the orthogonal films were shot and all coordinates of the selected points were reconstructed through the treatment planning system and compared with that calculated through the analytical method. The position uncertainty and the deviation prediction of point A were also evaluated. With a good choice of the reference dummy point, the position deviations of point A obtained through this analytical method were found to be generally within 1 mm, with the standard uncertainty less than 0.5 mm. In summary, this new method is a practical and accurate tool for clinical usage to acquire the accurate location of point A for the treatment of cervical cancer patient. PACS number(s): 87.55.kmBrachytherapy of local cervical cancer is generally accomplished through film-based treatment planning with the prescription directed to point A, which is invisible on images and is located at a high-dose gradient area. Through a standard reconstruction method by digitizing film points, the location error for point A would be 3 mm with a condition of 30° curvature tandem, which is 10° away from the gantry rotation axis of a simulator, and has an 8.7 cm interval between the flange and the isocenter. To reduce the location error of the reconstructed point A, this paper proposes a method and demonstrates its accuracy. The Cartesian coordinates of point A were derived by acquiring the locations of the cervical os (tandem flange) and a dummy seed located in the tandem above the flange. To verify this analytical method, ball marks in a commercial Isocentric Beam Checker were selected to simulate the two points A, the os, and the dummies. The Checker was placed on the simulator couch with its center ball coincident with the simulator isocenter and its rotation axis perpendicular to the gantry rotation axis. With different combinations of the Checker and couch rotation angles, the orthogonal films were shot and all coordinates of the selected points were reconstructed through the treatment planning system and compared with that calculated through the analytical method. The position uncertainty and the deviation prediction of point A were also evaluated. With a good choice of the reference dummy point, the position deviations of point A obtained through this analytical method were found to be generally within 1 mm, with the standard uncertainty less than 0.5 mm. In summary, this new method is a practical and accurate tool for clinical usage to acquire the accurate location of point A for the treatment of cervical cancer patient. PACS number(s): 87.55.km.