기존의 쐐기(wedge) 필터를 사용하는 접선조사(tangential irradiation) 방식의 일반적인 유방암 방사선치료와 동일한 접선 조사야(filed)를 사용하면서 쐐기 필터를 삽입하는 대신 다엽콜리메터의 움직임을 통해 치료부위의 선량분포를 균일하게 형성토록 하는 접선 세기조절 방사선치료(tangential breast Intensity modulated radiotherapy, T-B IMRT)가 유방암치료에 적용되고 있다. 본 연구에서는 T-B IMRT치료계획에서 계산된 선량분포를 기존의 쐐기 필터를 사용한 일반적인 접선조사 방식의 치료계획과 비교하여 치료표적 및 중요장기에서의 선량분포 측면에서 T-B IMRT의 타당성을 살펴보고, 실제 T-B IMRT치료 빔 조사 시 선량 측정 및 치료계획 결과와의 오차 분석을 통해 선량 분포의 정확도를 확인하고자 하였다. 기존의 쐐기필터를 이용한 접선조사 방식으로 치료한 유방암 환자 15명을 대상으로 T-B IMRT치료계획을 세운 후, 계산된 선량분포를 비교, 분석하였다. T-B IMRT치료계획에서 치료표적 부피 내 선량분포의 균일도가 기존의 쐐기를 사용한 접선조사 방식보다 향상된 결과를 보였으며, 주변의 정상조직과 중요장기의 선량을 상대적으로 줄일 수 있음을 확인할 수 있었다. T-B IMRT의 실제 치료조사 시 선량정확도를 분석하기 위해 적합한 팬텀을 사용하여 품질보증(QA) 치료계획을 수립하였다. 원기둥 형태의 아크릴에 이온전리함을 삽입한 형태의 팬텀을 사용하여 치료계획과 실제 치료 빔 조사를 통해 측정된 절대선량 값을 비교하였으며, 평균 오차는 $0.7{\pm}1.4%$로 분석되었다. 이차원 다이오드 검출기 배열장치를 이용한 선량분포의 정확도 분석에서는 치료계획 시 계산된 선량분포와 실제 측정된 선량분포의 gammaevaluation (3%, 3 mm 기준)를 통해 평균 $97.3{\pm}2.9%$의 합격률(passrate)로 타당성 있는 정확도를 보여주었다. 본 연구를 통해 선량분포 측면에서 기존 쐐기필터를 이용한 접선 조사방식의 방사선치료 대비 T-B IMRT의 장점을 확인할 수 있었고, T-B IMRT에 적합하게 수립된 품질보증 과정을 통해 실제 조사되는 선량의 정확도를 확인할 수 있었다.
기존의 쐐기(wedge) 필터를 사용하는 접선조사(tangential irradiation) 방식의 일반적인 유방암 방사선치료와 동일한 접선 조사야(filed)를 사용하면서 쐐기 필터를 삽입하는 대신 다엽콜리메터의 움직임을 통해 치료부위의 선량분포를 균일하게 형성토록 하는 접선 세기조절 방사선치료(tangential breast Intensity modulated radiotherapy, T-B IMRT)가 유방암치료에 적용되고 있다. 본 연구에서는 T-B IMRT치료계획에서 계산된 선량분포를 기존의 쐐기 필터를 사용한 일반적인 접선조사 방식의 치료계획과 비교하여 치료표적 및 중요장기에서의 선량분포 측면에서 T-B IMRT의 타당성을 살펴보고, 실제 T-B IMRT치료 빔 조사 시 선량 측정 및 치료계획 결과와의 오차 분석을 통해 선량 분포의 정확도를 확인하고자 하였다. 기존의 쐐기필터를 이용한 접선조사 방식으로 치료한 유방암 환자 15명을 대상으로 T-B IMRT치료계획을 세운 후, 계산된 선량분포를 비교, 분석하였다. T-B IMRT치료계획에서 치료표적 부피 내 선량분포의 균일도가 기존의 쐐기를 사용한 접선조사 방식보다 향상된 결과를 보였으며, 주변의 정상조직과 중요장기의 선량을 상대적으로 줄일 수 있음을 확인할 수 있었다. T-B IMRT의 실제 치료조사 시 선량정확도를 분석하기 위해 적합한 팬텀을 사용하여 품질보증(QA) 치료계획을 수립하였다. 원기둥 형태의 아크릴에 이온전리함을 삽입한 형태의 팬텀을 사용하여 치료계획과 실제 치료 빔 조사를 통해 측정된 절대선량 값을 비교하였으며, 평균 오차는 $0.7{\pm}1.4%$로 분석되었다. 이차원 다이오드 검출기 배열장치를 이용한 선량분포의 정확도 분석에서는 치료계획 시 계산된 선량분포와 실제 측정된 선량분포의 gamma evaluation (3%, 3 mm 기준)를 통해 평균 $97.3{\pm}2.9%$의 합격률(pass rate)로 타당성 있는 정확도를 보여주었다. 본 연구를 통해 선량분포 측면에서 기존 쐐기필터를 이용한 접선 조사방식의 방사선치료 대비 T-B IMRT의 장점을 확인할 수 있었고, T-B IMRT에 적합하게 수립된 품질보증 과정을 통해 실제 조사되는 선량의 정확도를 확인할 수 있었다.
The tangential breast intensity modulated radiotherapy (T-B IMRT) technique, which uses the same tangential fields as conventional 3-dimensional conformal radiotherapy (3D-CRT) plans with physical wedges, was analyzed in terms of the calculated dose distribution feature and dosimetric accuracy of be...
The tangential breast intensity modulated radiotherapy (T-B IMRT) technique, which uses the same tangential fields as conventional 3-dimensional conformal radiotherapy (3D-CRT) plans with physical wedges, was analyzed in terms of the calculated dose distribution feature and dosimetric accuracy of beam delivery during treatment. T-B IMRT plans were prepared for 15 patients with breast cancer who were already treated with conventional 3D-CRT. The homogeneity of the dose distribution to the target volume was improved, and the dose delivered to the normal tissues and critical organs was reduced compared with that in 3D-CRT plans. Quality assurance (QA) plans with the appropriate phantoms were used to analyze the dosimetric accuracy of T-B IMRT. An ionization chamber placed at the hole of an acrylic cylindrical phantom was used for the point dose measurement, and the mean error from the calculated dose was $0.7{\pm}1.4%$. The accuracy of the dose distribution was verified with a 2D diode detector array, and the mean pass rate calculated from the gamma evaluation was $97.3{\pm}2.9%$. We confirmed the advantages of a T-B IMRT in the dose distribution and verified the dosimetric accuracy from the QA performance which should still be regarded as an important process even in the simple technique as T-B IMRT in order to maintain a good quality.
The tangential breast intensity modulated radiotherapy (T-B IMRT) technique, which uses the same tangential fields as conventional 3-dimensional conformal radiotherapy (3D-CRT) plans with physical wedges, was analyzed in terms of the calculated dose distribution feature and dosimetric accuracy of beam delivery during treatment. T-B IMRT plans were prepared for 15 patients with breast cancer who were already treated with conventional 3D-CRT. The homogeneity of the dose distribution to the target volume was improved, and the dose delivered to the normal tissues and critical organs was reduced compared with that in 3D-CRT plans. Quality assurance (QA) plans with the appropriate phantoms were used to analyze the dosimetric accuracy of T-B IMRT. An ionization chamber placed at the hole of an acrylic cylindrical phantom was used for the point dose measurement, and the mean error from the calculated dose was $0.7{\pm}1.4%$. The accuracy of the dose distribution was verified with a 2D diode detector array, and the mean pass rate calculated from the gamma evaluation was $97.3{\pm}2.9%$. We confirmed the advantages of a T-B IMRT in the dose distribution and verified the dosimetric accuracy from the QA performance which should still be regarded as an important process even in the simple technique as T-B IMRT in order to maintain a good quality.
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제안 방법
This was done to verify that a physical wedge and T-B IMRT could provide a solution to the heterogeneous dose distribution of the open-field plan. All the plans were created in the Panther system, and the ARTISTE LINAC was used for beam delivery.
1a. Conventional 2-tangential fields were set up, and 3 plans were generated, which differed in the application of the beam intensity modulation device to the tangential fields: an open field plan, one that used a physical wedge in the lateral field, and a T-B IMRT plan. The calculated dose distribution in each plan was compared with the dose measurement obtained using Gafchromic EBT2 film (International Specialty Products, Wayne, NJ, USA) inserted between the 2 cylindrical phantoms as shown in Fig.
11. Film analysis results for the verification of the T-B IMRT function to make correction of the inhomogeneous dose distribution. (a) dose distribution applying the open fields.
In the present study, QA was performed using 2 methods. First, a point dose was measured using an ionization chamber and the cylindrical acrylic phantom, which enabled the simulation of the geometry of the breast. In the second process, the dose distribution was analyzed using the 2D diode detector array, MapCHECK.
In addition, the dose accuracy of T-B IMRT was examined by measuring dose distribution. T-B IMRT plans were generated using the computed tomography (CT) data of patients who had been treated with conventional 3D-CRT using the wedge technique, and the feasibility of these plans was analyzed by comparing the calculated dose value and the dose volume histogram (DVH) of the target and the OAR. The absolute dose and dose distribution were measured using T-B IMRT quality assurance (QA) plans generated with the specialized phantoms and compared with calculated data to verify the dosimetric accuracy during the process of beam delivery.
Although the dose distribution is usually assessed using film measurements, 2D diode detector array was used to minimize expenses and because the MapCHECK is an effective method for the analysis of the pass rate values from the gamma evaluation process. The MapCHECK was placed in the sagittal direction of detector arrays in this study because it enabled the analysis of the wider dose distributions caused by the tangential fields of T-B IMRT.
T-B IMRT plans were generated using the computed tomography (CT) data of patients who had been treated with conventional 3D-CRT using the wedge technique, and the feasibility of these plans was analyzed by comparing the calculated dose value and the dose volume histogram (DVH) of the target and the OAR. The absolute dose and dose distribution were measured using T-B IMRT quality assurance (QA) plans generated with the specialized phantoms and compared with calculated data to verify the dosimetric accuracy during the process of beam delivery.
The accuracy of dose distribution was analyzed with MapCHECK (SunNuclear, Melbourne, FL, USA), a 2D diode detector array that was inserted into the MapPHAN (SunNu- clear, Melbourne, FL, USA), a water equivalent solid phantom, and the CT images were acquired with the placement of diode array's plane in the sagittal direction.
The calculated dose data of T-B IMRT were compared with those of 3D-CRT, and each plan was normalized with the constraint that 90% of the isodose surface should cover 90% of the CTV to enable the objective analysis of the dose data in the 2 plans. The mean dose, maximum dose and homogeneity index (HI)14) of the CTV were compared to analyze the appropriateness and homogeneity of the dose distribution in the CTV.
3. The coincidences in dose distribution were analyzed with the gamma evaluation method, and the selected tolerance parameters for the gamma index were 3% dose difference and 3 mm distance to agreement between the calculated dose and the dose measured with the MapCHECK.
The dose distributions obtained by the irradiating films inserted between the cylindrical phantoms suggest that higher doses were delivered to the anterior part of the phantom, which is characterized by reduced thickness in the direction of the beam angle when only open fields were applied. The problem of inhomogeneous dose distributions could be solved by applying the physical wedge and the T-B IMRT method, as demonstrated by the results of dose calculation in RTP and film measurements.
The respiratory target motional effect can introduce some error in the real breast treatment, which should be considered in the future study with the analysis of dosimetric errors in T-B-IMRT compared with the conventional 3D-CRT under the respiratory motional conditions.
The dosimetric accuracy of T-B IMRT was analyzed using QA plans that were created with the appropriate phantoms. Two QA plans were created for each T-B IMRT patient to verify the absolute point dose and the dose distribution, resulting in the generation and implementation of 30 QA plans for 15 patients for dose measurement.
대상 데이터
The A1SL ion chamber (Standard Imaging, Middleton, WI, USA) was used, and the CT images were acquired and applied for the creation of QA plans with the Panther RTP system. An A1SL ion chamber with 0.057 cm3 of air volume and a DOSE1 (IBA Dosimetry, Schwarzenbruck, Germany) electrometer were used for the measurement of point dose. The relative calibration process for the measurement of a point dose was performed in the conditions of 10×10 cm2 field size, 100 cm SAD (source to axis distance) and 5 cm depth.
2. The A1SL ion chamber (Standard Imaging, Middleton, WI, USA) was used, and the CT images were acquired and applied for the creation of QA plans with the Panther RTP system. An A1SL ion chamber with 0.
이론/모형
The 3D-CRT plans were created in the Eclipse system (Varian, PaloAlto, CA, USA) and the pencil beam convolution algorithm was used for dose calculation. The energy of photon was 6 MV and the applied fields were tangential fields with the insertion of physical wedge.
The T-B IMRT plans were prepared with the direct aperture optimization algorithm11-13) in the Panther (Prowess, Concord, CA, USA) radiation treatment planning (RTP) system, and the dedicated linear accelerator (LINAC) for the plan was ARTISTE (Siemens, Erlangen, Germany). The CT and structure data for target and OARs were transferred using the DICOM RT format, and the same gantry angles were maintained for the tangential fields.
The present study analyzed the suitability and effectiveness of T-B IMRT by comparison with the calculated dose data for 3D-CRT using the wedge technique. In addition, the dose accuracy of T-B IMRT was examined by measuring dose distribution.
성능/효과
The average of irradiated MUs for each treatment was 320.5 for 3D-CRT and 257.9 for T-B IMRT, as shown in Fig. 9, which indicates that T-B IMRT was more effective with regard to the time and work requirements during the treatment. The effect of T-B IMRT on the correction of the heterogeneous dose distribution and the role of a physical wedge in 3D-CRT were shown in Fig.
The mean pass rate in the gamma evaluation between the measured dose distribution and the dose calculated with the 15 QA plans for T-B IMRT was 97.3±2.9%, as shown in Fig. 14, which confirmed the accuracy of the T-B IMRT dose distributions.
The measured point doses and the dose distribution data for the 15 T-B IMRT patients obtained using the QA showed good agreement with the calculated data in the RTP system, which verified the accuracy of the Panther RTP and ARTISTE LINAC systems for T-B IMRT delivery.
The optimization constraints for CTV were that 95% isodose (prescription) surface had to cover 95% of the CTV and no portion of the CTV could receive more than 110% of the pre scription dose, which was aimed at improving the dose homogeneity of the CTV. The optimization constraints for OARs were not applied owing to the limited number of fields in a T-B IMRT and to simplify the optimizing process.
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