Significant Differences In Dose Distributions Research Articles

Impact of log file source and data frequency on accuracy of log file-based patient specific quality assurance

Performing phantom measurements for patient-specific quality assurance (PSQA) adds a significant amount of time to the adaptive radiotherapy procedure. Log file based PSQA can be used to increase the efficiency of this process. This study compared the dosimetric accuracy of high-frequency linear accelerator (Linac) log files and low-frequency log data stored in the oncology information system (OIS). Thirty patients were included, that were recently treated in the head and neck (HN), brain, and prostate region with volumetric modulated arc therapy (VMAT) and an additional ten patients treated using stereotactic body radiation therapy (SBRT) with 3D-conformal radiotherapy (3D-CRT) technique. Log data containing a single fraction were used to calculate the dose distributions. The dosimetric differences between Linac log files and OIS logs were evaluated with a gamma analysis with 2%/2 mm criterion and dose threshold of 30%. The original treatment plan was used as a reference. Moreover, DVH parameters of D98%, D50%, and D2% of the planning-target volume (PTV) and dose to several organs at risk (OARs) were reported. Significant differences in dose distributions between the two log types and the original dose were observed for PTV D98% and D2% (r < 0.001) for HN cases, PTV D98% (r = 0.005) for brain cases, and PTV D50% (r = 0.015) for prostate cases. No significant differences were found between the two log types with respect to D50%. The root mean square (RMS) error of the leaf positions of the OIS log was approximately twice the RMS error of the Linac log file for VMAT plans, but identical for 3D-CRT plans. The relationship between the gamma pass rate and the RMS error showed a moderate correlation for the Linac log files (r = −0.58, p < 0.001) and strong correlation for OIS logs (r = −0.71, p < 0.001). Furthermore, all doses calculated using Linac log files and OIS log data had a GPR >90% for an RMS error < 3.3 mm. Based on these findings, a tolerance limit of RMS error of 3.3 mm for considering OIS log based PSQA was established. Nevertheless, the OIS log data quality should be improved to achieve adequate PSQA.

Interobserver Variations in Target Delineation in Intensity-Modulated Radiation Therapy for Nasopharyngeal Carcinoma and its Impact on Target Dose Coverage.

To investigate the differences between physicians in target delineation in intensity-modulated radiation therapy for nasopharyngeal carcinoma as well as their impact on target dose coverage. Ninety-nine in-hospital patients were randomly selected for retrospective analysis, and the target volumes were delineated by 2 physicians. The target volumes were integrated with the original plans, and the differential parameters, including the Dice similarity coefficient (DSC), Hausdorff distance (HD), and Jaccard similarity coefficient (JSC) were recorded. The dose-volume parameters to evaluate target dose coverage were analyzed by superimposing the same original plan to the 2 sets of images on which the target volumes were contoured by the 2 physicians. The significance of differences in target volumes and dose coverage were evaluated using statistical analysis. The target dose coverage for different sets of target volumes showed statistically significant differences, while the similarity metrics to evaluate geometric target volume differences did not. More specifically, for PGTVnx, the median DSC, JSC, and HD were 0.85, 0.74, and 11.73, respectively; for PCTV1, the median values were 0.87, 0.77, and 11.78, respectively; for PCTV2, the median values were 0.90, 0.82, and 16.12, respectively. For patients in stages T3-4, DSC, and JSC were reduced but HD was increased compared to those in stages T1-2. Dosimetric analysis indicated that, for the target volumes, significant differences between the 2 physicians were found in D95, D99, and V100 for all the target volumes (ie, PGTVnx, PCTV1, and PCTV2) across the whole group of patients, as well as in patients with disease stages T3-4 and T1-2. The target volumes delineated by the 2 physicians had a high similarity, but the maximal distances between the outer contours of the 2 sets were significantly different. In patients with advanced T stages, significant differences in dose distributions were found, stemming from the deviations of target delineation.

Cochlea sparing with a stratified scheme of dose limitation employed in intensity-modulated radiotherapy for nasopharyngeal carcinoma: A dosimetry study

Hearing loss is 1 of the major complications after radiotherapy in nasopharyngeal carcinoma (NPC) patients, how to minimize dose to cochlea in order to reduce the incidence of sensorineural hearing loss is a critical task. This study is to investigate a stratified scheme of cochlea sparing based on T stage in intensity-modulated radiotherapy. We designed a comparison between 2 plans of cochlea sparing plan (C-Plan) and regular noncochlea sparing plan (R-Plan) from 19 NPC patients with 2, 3, 8, and 6 cases of T1, T2, T3, and T4 stage, respectively. The outcomes showed that target coverage parameters and dose-volume histogram features were of no significant difference, with a significant difference in dose distribution between C-Plan and R-Plan in cochlea and eustachian, e.g., ipsilateral cochlea Dmean 4619.75 ± 1134.09 cGy in C-Plan and 5061.03 ± 1121.09 cGy in R-Plan (p = 0.000), contralateral cochlea Dmean 4386.73 ± 945.14 cGy in C-Plan and 4991.38 ± 961.21 cGy in R-Plan (p = 0.000). Meanwhile, there was no significant difference in dose distribution in spinal cord, brainstem, and other OARs. Our dosimetry study showed cochlea sparing in intensity-modulated radiotherapy for NPC reduced cochlea dose to different extent, so we suggested a stratified scheme of cochlea sparing based on T stage could be a useful and practical tool for both physicists and radiation doctors.

Simulation study of dosimetric effect in proton beam therapy using concomitant boost technique for unresectable pancreatic cancers.

The purpose of this study is to investigate the dose distribution of proton beam therapy (PBT) using a concomitant boost technique for unresectable pancreatic cancers. This simulation study involved 36 patients with unresectable pancreatic cancer. The irradiation dose was set as 67.5 gray equivalent (GyE) with 25 fractions using concomitant boost technique. The irradiation dose was set as 50 GyE to cover the whole target and another posterior beam of 17.5 GyE was added to ensure that 10% isodose line was not delivered to the gastrointestinal (GI) tract. Dose distribution of the gross tumor volume and GI tract was examined. V55GyE, 60GyE, 65GyE were 80.8, 66.5, and 42.4%, respectively, and mean dose was 64.1 GyE in all patients. The distance from the GI tract showed significant difference in dose distribution (P = 0.002 in V55GyE, 0.0009 in V60GyE, 0.003 in V65GyE, and 0.02 in mean dose, respectively). Location, tumor diameter, or lymph nodes metastasis did not show any difference. We found that irradiated dose is closely related to the distance from the GI tract. Clinically, this protocol is expected to have outstanding effects on local control of tumors compared to conventional PBT.

Experimental verification of a methodology for Monte Carlo modeling of multileaf collimators using the code Geant4

Among the many algorithms developed for evaluation of dose distributions in radiotherapy, the Monte Carlo methods provide more realistic results. In intensity modulated radiation therapy, significant differences in dose distributions within the fields defined by the multileaf collimator (MLC) could have significant radiobiology effects. Thus, it is important to model thoroughly the MLC to allow more accurate radiotherapy delivery. The objective of this work is to describe and to validate a methodology for modeling of MLCs using code Geant4. The Varian Millennium 120-leaf MLC was modeled using this methodology and it was experimentally verified. The leaves of the MLC were built using three types of solid (G4Box, G4Tubs and G4ExtrudeSolid) and the Boolean operation of subtraction (G4SubtractionSolid). Based on this methodology, it is possible to simulate other Varian MLC models using Geant4 or other MC code.

Resection Cavity Contraction Effects in the Use of Radioactive Sources (1-25 versus Cs-131) for Intra-Operative Brain Implants&#x0D;

Background and ObjectivesIntra-parenchymal brain surgical resection cavities usually contract in volume following low dose rate (LDR) brachytherapy implants. In this study, we systematically modeled and assessed dose variability resulting from such changes for I-125 versus Cs-131 radioactive sources.MethodsResection cavity contraction was modeled based on 95 consecutive patient cases, using surveillance magnetic resonance (MR) images. The model was derived for single point source geometry and then fully simulated in 3D where I-125 or Cs-131 seeds were placed on the surface of an ellipsoidal resection cavity. Dose distribution estimated via TG-43 calculations and biological effective dose (BED) calculations were compared for both I-125 and Cs-131, accounting for resection cavity contractions.ResultsResection cavity volumes were found to contract with an effective half-life of approximately 3.4 months (time to reach 50% of maximum volume contraction). As a result, significant differences in dose distributions were noted between I-125 and Cs-131 radioactive sources. For example, when comparing with static volume, assuming no contraction effect, I-125 exhibited a 31.8% and 30.5% increase in D90 and D10 values (i.e., the minimal dose to 90% and 10% of the volume respectively) in the peripheral target areas over the follow-up period of 20.5 months. In contrast, Cs-131 seeds only exhibited a 1.44% and 0.64% increase in D90 and D10 values respectively. Such discrepancy is likewise similar for BED calculations.ConclusionResection cavity contractions affects Cs-131 dose distribution significantly less than that of I-125 for permanent brain implants. Care must be taken to account for cavity contractions when prescribing accumulative doses of a radioactive source in performing the brain implant procedures.

전립선암의 방사선치료에서 토모테라피와 VMAT의 치료계획에 따른 유용성 평가

전립선암의 방사선치료에서 토모테라피와 용적변조회전치료(volumetric modulated arc therapy, VMAT)의 치료계획에 따른 유용성 평가를 위해 흡수선량, 선량체적곡선(dose volume histogram, DVH), 치료효율성, MapCHECK2를 이용한 선량 검증 정확도 결과를 각각 비교 분석하였다. 대상으로는 2014년 7월부터 12월까지 H 대학병원 방사선종양학과에서 토모테라피 치료를 받은 전립선암 환자 중 12명을 무작위로 선택하였다. 흡수선량과 DVH를 분석한 결과 종양조직과 방광에서 두 방사선 치료계획이 근소한 차이를 나타냈지만 처방선량의 오차범위인 -5%에서+3%안에 포함됐고 정상조직 부작용 확률 권고치인 견딤선량 범위를 넘지 않았다. 치료시간은 2.5배 짧고 MU(monitor unit)도 10.3배 작아 VMAT가 치료효율성이 높았다. 선량정확도는 모두 95% 이상의 통과기준에 포함 되었으며 VMAT가 2.3% 더 높게 나타났다. 토모테라피와 VMAT 모두 종양조직에 적합한 선량이 흡수되었으며 정상조직의 견딤선량 범위를 넘지 않아 선량분포특성에서 큰 차이는 없었다. 하지만 치료시간이 짧고, total MU가 낮아 치료효율성이 좋고 선량 검증의 정확도 또한 우수한 VMAT를 선택하는 것이 치료에 더 유용할 것으로 사료된다. In this study, to evaluate the usefulness of the treatment plan of tomotherapy and volumetric modulated arc therapy (VMAT) in the radiotherapy for prostate cancer, the absorbed dose, dose volume histogram (DVH), treatment efficiency, and the results of dose verification accuracy using MapCHECK2 were compared and analyzed. Of the prostate cancer patients who underwent tomotherapy treatment in the Radiologic Oncology of H University Hospital between July 2014 and December 2014, 12 patients were randomly selected. As a result of analyzing the absorbed dose and DVH, both radiologic treatment plans showed slight differences in the treatment of the cancer tissues and the bladder, but the difference was in the error range of -5% to +3%, and did not exceed the side effect guideline or the tolerance dose limit. VMAT showed higher treatment efficiency than tomotherapy with a 2.5 times shorter treatment time and a 10.3 times less monitor unit (MU). Both showed 95% or higher dose accuracy satisfying the standard. VMAT showed 2.3% higher efficiency than tomotherapy. In both tomotherapy and VMAT, appropriate doses were absorbed for cancer tissues, and did not exceed the tolerance dose for normal tissues showing no significant difference in dose distribution. However, considering the shorter treatment time, lower total MU, and better treatment efficiency and dose verification accuracy, VMAT may be more useful than tomotherapy in cancer treatments.

Comparison of trigeminal neuralgia radiosurgery plans using two film detectors for the commissioning of small photon beams

Trigeminal neuralgia (TN) is a chronic, episodic facial pain syndrome that can be extremely intense, and it occurs within the regions of the face that are innervated by the three branches of the trigeminal nerve. Stereotactic radiosurgery (SRS) is the least invasive procedure to treat TN. SRS uses narrow photon beams that require high spatial resolution techniques for their measurement. The use of radiographic or radiochromic films for small‐field dosimetry is advantageous because high spatial resolution and two‐dimensional dose measurements can be performed. Because these films have different properties, it is expected that the calculated dose distributions for TN patients will behave differently, depending on the detector used for the commissioning of the small photon beams. This work is based on two sets of commissioned data: one commissioned with X‐OMAT V2 film and one commissioned with EBT2 film. The calculated dose distributions for 23 TN patients were compared between the commissioning datasets. The variables observed were the differences in the half widths of the 35 and 40 Gy isodose lines (related to the entrance distance to the brainstem) and the volume of the brainstem that received a dose of 12 Gy or more (V12). The results of this comparison showed that there were statistically significant differences between the two calculated dose distributions. The magnitudes of these differences were up to 0.33 mm and 0.38 mm for the 35 and 40 Gy isodose lines. The corresponding difference for the V12 was up to 2.1 cc. It is clear that these differences may impact the treatment of TN patients, and then it must be important to perform this type of analysis when observing complication rates. Clinical reports on irradiation techniques for trigeminal neuralgia should consider that different detectors used for commissioning treatment planning systems might result in small but significant differences in dose distributions.PACS number: 87.55.km

Clinical impact of using the deterministic patient dose calculation algorithm Acuros XB for lung stereotactic body radiation therapy

Purpose. To evaluate the clinical impact of using the deterministic dose calculation algorithm, Acuros XB, for early stage lung cancer patients undergoing stereotactic body radiotherapy (SBRT). Material and methods. Seventy-seven stage I non-small cell lung cancer patients who underwent lung SBRT from 2008 to 2012 at our center were included in this study. All treatment plans originally calculated by the anisotropic analytical algorithm (AAA) were recalculated using the AAA and Acuros XB algorithms with identical monitor units and beam arrangements. The dose, dose distribution, conformality number (CN) and heterogeneity index (HI) of the target were determined for each plan. A paired matched t-test was used to evaluate the difference between the mean dose, the dose distribution, and the CN and HI for the target. The importance of tumor (volume, location), patient (pulmonary functional, body mass index) and treatment (number of SBRT beams) on the dose distributions obtained from the two algorithms was statistically determined using linear regression analyses. Results. The mean target dose was same for both algorithms. Compared to AAA, a small and significant difference in dose distribution in the target was found for the Acuros XB algorithm, resulting in lower conformity (−2.1%, p < 0.0001) and higher heterogeneity (p < 0.0001) of dose. Single logistic regression identified pulmonary function, number of beams and target location as being correlated with the difference of CN between the two calculations. Multivariate analysis indicated that the patient's pulmonary function (p = 0.0296) was the only predictor for the difference in conformality between the two dose calculation algorithms. Conclusions. In lung SBRT, the patient's pulmonary function is responsible for the difference in target dose distribution between the Acuros XB and AAA algorithms. The Acuros XB algorithm could be used to advantage in patients with compromised pulmonary function based on its accurate modeling of lung tissue in comparison to AAA.

SU-E-J-98: Evaluating Commercial Orthopedic Metal Artifact Reduction Tool (OMAR) for CT Simulation in Radiotherapy for Head-And-Neck Cases

Purpose: Many head-and-neck (H&N) patients have dental implants which can induce severe metal artifacts in CT images. This study assessed the performance and the effectiveness of the commercial orthopedic metal artifact reduction function (O-MAR) for radiotherapy of H&N patients. Methods: 20 H&N images scanned by Philips Brilliance Big Bore CT were used for the assessment. After O-MAR correction, the CT Hounsfield number and noise were measured and compared between the original and OMAR corrected images. Structures were contoured by a radiation oncologist on each of the two image sets. These contoured structure volumes on the original CT image were compared with those on O-MAR corrected CT image by radiation therapy planning system. After volumetric-modulated arc therapy (VMAT) planning was performed on the original CT image, this plan was translated and calculated on O-MAR corrected images. Each DVH was compared and the gamma passing rate was calculated for comparing dose distributions. Results: CT Hounsfield numbers became closer to the reference values after O-MAR correction. The standard deviations of the selected ROIs were reduced from 323.9 HU to 195.6 HU in air and from 43.5 HU to 24.7 HU in tissue. The volumes of contoured structure showed minute change. The difference between two DVH was less than 0.5%. The gamma pass rates of dose distributions calculated on the original and OMAR corrected images were higher than 99.9% in the case of closed-mouth-images but were about 80% in the case of opened-mouth-images when using 1mm and 1% distance-to-agreement criterion. Conclusion: The O-MAR algorithm is suitable for the entire radiation treatment planning process by increasing the accuracy of CT Hounsfield numbers and reducing noises. Although there was no significant difference in dose distribution for most cases, the O-MAR correction was shown to have an impact on opened-mouth-images.

SU-E-T-517: Ray Tracing and Mote Carlo Based Dose Computation for Chest Wall and Ribs for Lung Cancer Patients Treated with Cyberknife

Purpose: Chest wall and ribs are considered organs at risk while treating lung tumors adjacent to chest wall. This study was to evaluate the dosimetric differences in chest wall and ribs irradiation for Cyberknife stereotactic body radiation therapy (SBRT) when treatment plans were computed using Ray Tracking Algorithm (RTA) and Monte Carlo Algorithm (MCA). Methods: Twenty eight lung cancer patients who had tumors abutting the chest wall were selected for this study. A uniform 2cm thickness of chest wall and appropriate portions of rib were contoured for evaluating dose distribution using RTA and MCA of Cyberknife MultiPlan software (version‐3.5.2). Treatment plans were first computed using RTA and then were recomputed using MCA without changing the total monitor unit (MU). Range of prescription dose was 50Gy‐60Gy (mean=54.6Gy). Studied dosimetric parameters were maximum point dose and doses to 1cc, 5cc, 10cc, 30cc, 50cc, 70cc, and 100cc of chest wall. Maximum point dose and doses to 1cc, 2cc, 5cc, and 10cc of ribs were also studied. These parameters were considered as clinically more relevant. Results: Dosimetric computation results revealed that RTA overestimated dose to both the chest wall and the ribs for all the studied parameters. Increase of average dose was in the range of 7.5–12.1% (p‐value 0.05), and 10.3–13.4% (p‐value <0.05) for chest wall and ribs, respectively. The lower the volume of interest, the larger was the difference in dose for the two algorithms. Average difference in maximum point dose for chest wall was 11.2% (p‐value <0.001) and that was 13.4% for ribs (p‐value <0.002). Conclusion: As compared to Monte Carlo algorithm, Ray Tracing algorithm significantly overestimates dose to chest wall and ribs. Although treatment planning with Monte Carlo is more involved, it should be used because of accuracy and significant difference in dose distribution in chest wall and ribs.

Dosimetric evaluations of the interplay effect in respiratory‐gated intensity‐modulated radiation therapy

The interplay between a mobile target and a dynamic multileaf collimator can compromise the accuracy of intensity-modulated radiation therapy (IMRT). Our goal in this study is to investigate the dosimetric effects caused by the respiratory motion during IMRT. A moving phantom was built to simulate the typical breathing motion. Different sizes of the gating windows were selected for gated deliveries. The residual motions during the beam-on period ranged from 0.5 to 3 cm. An IMRT plan with five treatment fields from different gantry angles were delivered to the moving phantom for three irradiation conditions: Stationary condition, moving with the use of gating system, and moving without the use of gating system. When the residual motion was 3 cm, the results showed significant differences in dose distributions between the stationary condition and the moving phantom without gating beam control. The overdosed or underdosed areas enclosed about 33% of the treatment area. In contrast, the dose distribution on the moving phantom with gating window set to 0.5 cm showed no significant differences from the stationary phantom. With the appropriate setting of the gating window, the deviation of dose from the respiratory motion can be minimized. It appeals that limiting the residual motion to less than 0.5 cm is critical for the treatments of mobile structures.