调强适形放疗对深部肿瘤皮肤剂量的影响(英文)

Objective: The purpose of this study was to investigate the impact of intensity modulated radiotherapy (IMRT) on surface doses for brain, abdomen and pelvis deep located tumors treated with 6 MV photon and to evaluate the skin dose calculation accuracy of the XIO 4.04 treatment planning system. Methods: More investigations for the influences of IMRT on skin doses would increase its applications for many treatment sites. Measuring skin doses in real treatment situations would reduce the uncertainty of skin dose prediction. In this work a pediatric human phantom was covered by a layer of 1 mm bolus at three treatment sites and thermoluminescent dosimeter (TLD) chips were inserted into the bolus at each treatment site before CT scan. Two different treatment plans [three-dimensional conformal radiation therapy (3DCRT) and IMRT] for each treatment sites were performed on XIO 4.04 treatment planning system using superposition algorism. Results: The results showed that the surface doses for 3DCRT were higher than the surface doses in IMRT by 1.6%, 2.5% and 3.2% for brain, abdomen and pelvis sites respectively. There was good agreement between measured and calculated surface doses, where the calculated surface dose was 15.5% for brain tumor calculated with 3DCRT whereas the measured surface dose was 12.1%. For abdomen site the calculated surface dose for IMRT treatment plan was 16.5% whereas the measured surface dose was 12.6%. Conclusion: The skin dose in IMRT for deep seated tumors is lower than that in 3DCRT which is another advantage for the IMRT. The TLD readings showed that the difference between the calculated and measured point dose is negligible. The superposition calculation algorism of the XIO 4.04 treatment planning system modeled the superficial dose well.     

乳腺癌保乳术后常规、三维适形及两种调强放疗技术剂量学评估(英文)

Objective: The purpose of this study was to compare the dose distribution and dose volume histogram (DVH) of the planning target volume (PTV) and organs at risk (OARs) among conventional radiation therapy (CR), three-dimensional conformal radiation therapy (3DCRT), two-step intensity-modulated radiation therapy (TS-IMRT) and direct machine parameter optimization intensity-modulated radiation therapy (DMPO-IMRT) after breast-conserving surgery. Methods: For each of 20 randomly chosen patients, 4 plans were designed using 4 irradiation techniques. The prescribed dose was 50 Gy/2 Gy/25 f, 95% of the planning target volume received this dose. The cumulated DVHs and 3D dose distributions of CR, 3DCRT, TS-IMRT and DMPO-IMRT plans were compared. Results: For the homogeneity indices, no statistically significant difference was observed among CR, 3DCRT, TS-IMRT and DMPO-IMRT while the difference of the conformality indices were statistically significant. With regard to the organs at risk, IMRT and 3DCRT showed a significantly fewer exposure dose to the ipsilateral lung than CR in the high-dose area while in the low-dose area, IMRT demonstrated a significant increase of exposure dose to ipsilateral lung, heart and contralateral breast compared with 3DCRT and CR. In addition, the monitor units (MUs) for DMPO-IMRT were approximately 26% more than those of TS-IMRT and the segments of the former were approximately 24% less than those of the latter. Conclusion: Compared with CR, 3DCRT and IMRT improved the homogeneity and conformity of PTV, reduced the irradiated volume of OARs in high dose area but IMRT increased the irradiated volume of OARs in low dose area. DMPO-IMRT plan has fewer delivery time but more MUs than TS-IMRT.     

放射治疗电子射野影像系统的系统摆位误差的评估(英文)

Objective:The aim of this work was to quantify the extent of set-up errors to conduct a quality assurance(QA)aspect of treatment delivery,verification of the treatment field’s position on different days using electronic portal.Methods:This study was carried out on 12 patients,treated for pelvis tumor;and total of 240 images obtained by electronic portal image device(EPID)were analyzed.The EPIs acquire using EPID attached to the Siemens linear accelerator.The anatomy matching software(Theraview)was used and displacement in two dimensions were noted for each treatment field to study patient setup errors.Results:The percentages of mean deviations less than 5 mm in X direction were 65%&92%,from 5–10 mm were 31%&19%and more than 10 mm were 11%&9%for A/P and lateral direction respectively.The percentages of mean deviations less than 5 mm in Y direction were 65%&63%,from 5–10 mm were 33%&28%and more than 10 mm were 22%&29%.The mean deviations in 2D-vector errors were≤5 mm in 47%and 46%,5–10 mm in 36%and 37%and>10 mm in37%and 37%of images in the A/P and lateral direction respectively.Conclusion:The results revealed that the ranges of set up errors are immobilization method to improve reproducibility.The observed variations were not within the limits..     

不能手术的Ⅲ期非小细胞肺癌患者每周紫杉醇和卡铂并同步放疗的诱导化疗:一个Ⅱ期研究结果(英文)

Objective: several trials have suggested the superiority of concurrent chemoradiotherapy. It has been hypothesized that the addition of systemic dose sequential chemotherapy to concurrent chemoradiotherapy, as induction or as consolidation, might further improve survival rates. So we sought to evaluate the safety and efficacy of induction paclitaxel and carboplatin followed by weekly paclitaxel and carboplatin with concurrent radiotherapy in inoperable stage Ⅲ non-small cell lung cancer (NSCLC). Methods: Fifty-six patients with stage Ⅲ inoperable NSCLC received induction chemotherapy with 2 cycles of paclitaxel 200 mg/m2 and carboplatin AUC-6 every 3 weeks then patients were assigned to concurrent chemoradiotherapy with paclitaxel 45 mg/m2 and carboplatin AUC-2 weekly along with concurrent radiotherapy at dose of 60 Gy (1.8 Gy/d x 5 d/week). Results: Median age of the 56 eligible patients was 61 years, most of them were males (87.5%). Squamous cell carcinoma was the most common pathological type (55.4%) and 85.7% had a performance status of 1. The majority of patients were presented with stage ⅢB (62.5%). Neutropenia was the most common toxicity during induction therapy (12.5% expressed grade 3) whereas esophagitis was the most common non hematologic adverse reaction during concurrent chemoradiotherapy (14.3% of grade 3). The overall response rate was 71.6% with complete response in 19.6%. After median follow up of 20 months, the median survival time was 13 months (95% CI: 10.917-15.083) and 1 year overall survival rate was 53.6%. Conclusion: This regimen has demonstrated an acceptable toxicity profile and encouraging response to treatment. Evaluation of this regimen in larger number and a phase Ⅲ trial are recommended.     

两种调强治疗计划系统的Axesse加速器光子束模型验收测试

目的 研究Monaco、Oncentra TPS的Axesse加速器光子束模型的验收测试,以期确定两者同时验收的完整方法。方法 验收前考虑两TPS相矛盾的参数,将加速器对应参数调至两TPS的交集部分;验收分为点、面、MLC特性模拟测试,MLC特性测试包括凹凸槽、穿射、“offset”、“Gain”值等。     

超声引导下两种乳腺肿物活检方式对导管内原位癌误诊率的比较:空芯针穿刺与微创旋切系统两种不同活检方式对比研究(英文)

Objective:The objective of this study was to compare the underestimation rate of invasive carcinoma cases with ductal carcinoma in situ (DCIS) at percutaneous ultrasound-guided core biopsies of breast lesions between 14-gauge automated core needle biopsy (ACNB) and 11-gauge vacuum-assisted biopsy (VAB), and analyze the diagnostic advantages and insufficiencies in DCIS between this two methods, and to determine the relationship between the lesion type (masses or microcalcifications on radiological findings ) and DCIS underestimation rate. Methods:We collected 152 breast lesions which were diagnosed as DCIS by retrospectively reviewing data about ultrasound-guided biopsies of breast lesions (from February 2003 to July 2010). There were 98 lesions in 95 patients by 14-gauge ACNB, and 54 lesions in 52 patients by 11-gauge VAB (The system used in this study called Mammatome, MMT). The clinical and radiological findings were reviewed; meanwhile all the selected patients had histological results of the biopsies and follow-up surgeries which also achieved the reliable pathological results to compare with the biopsy results. The differences between two correlated histological results defined as underestimation, and the histological DCIS underestimation rates were compared between the two groups. According to the radiological characteristics, each group was classified into two subgroups (masses or microcalcifications group), and the differences between subgroups were also analyzed. Results:The DCIS underestimation rate was 45.9% (45/98) for 14-gauge ACNB and 16.6% (9/54) for MMT. According to the lesion type on ultrasonography, DCIS underestimation was 31.0% (26/84) in masses (43.1% using ACNB and 12.1% using MMT; P = 0.003) and 42.6% (29/68) in microcalcifications (48.9% using ACNB and 23.8% using MMT; P = 0.036). Conclusion:The underestimation rate of invasive carcinoma in cases with DCIS at ultrasound-guided core biopsies is significantly higher for ACNB than for MMT. Furthermore, this difference does not alter among the two lesion types presented on ultrasonography. So ultrasound-guided VAB (MMT system) could be an effective and useful method for the diagnosis of DCIS lesions no matter what the lesion type is.     

体内放射治疗肿瘤患者剂量学验证系统在准确性和效率方面的评估(英文)

Objective: This study aimed to evaluate of the accuracy and efficiency of the in-vivo dosimetry systems for routine cancer patient dose verification. Methods: In vivo dosimetry, using diodes and thermoluminescent dosimeters (TLD) is performed in many radiotherapy departments to verify the dose delivered during treatment. A total of 40 TLD divided into two batches (one of 20 and other of 20 TLD) were used. Different doses of Co 60 beam were delivered to the TLD chips at different depths. Diodes were irradiated at different depths in a (30 × 30 × 30) cm3 water slab phantom with various conditions of Field sizes, monitor units and SSDs. Results: The limitation of the in-vivo dosimetry technique is that dose can only be in system readout difficulty and type of readout (TLD system and diode) as the patient dose is directly measured. Several authors have investigated the measurements was 1.3%, with a standard deviation of 2.6%. Results were normally distributed around a mean as -0.39 and 0.34 respectively. After the evaluation of in vivo dosimetry brain case as an example, the mean doses for both eyes were 1.8%, with a standard deviation of 2.7%. These results are similar to studies conducted with diodes and TLD’s. Conclusion: The diode is superior to TLD, since the diode measurements can be obtained on line and allows an immediate check. Other advantages of diodes include high sensitivity, good spatial resolution, and small size, simplicity of used.     

甲状腺肿瘤患者血清中MBL和MASP-2的表达水平及其意义(英文)

Objective:The aim of the study was to detect the levels of mannose-binding lectin(MBL),MBL-associated serine protease 2(MASP-2) and explore the clinical significances of them in patients with primary thyroid neoplasms.Methods:By using ELISA method,we detected the serum levels of MBL and MASP-2 in 26 patients with papillary thyroid carcinoma(PTC),30 patients with thyroid adenoma(TA) and 26 healthy people,respectively.Results:Serum MBL level was(565.23 ± 76.70) μg/L in PTCs higher than(324.267 ± 24.74) μg/L in TAs,and(152.69 ± 16.95) μg/L in healthy of controlling group.There was statistical significance between PTC and TA(P < 0.05),however there was no difference between TA and healthy(P > 0.05).Serum MASP-2 level was(726.153 ± 78.88) μg/L in PTCs higher than(379.266 ± 30.26) μg/L in TAs,and(203.846 ± 29.09) μg/L in healthy.Serum MASP-2 level was higher in PTCs than TAs,and the difference had statistical significance(P < 0.01).But no difference was observed between in TAs and healthy.Conclusion:These findings might reflect inflammatory processes induced by defense mechanisms,in response to the development of the tumour.MBL may also be involved in the elimination of possible tumourigenic pathogens.     

奥沙利铂联合替吉奥胶囊治疗晚期胃癌患者62例的临床观察(英文)

Objective:The aim of this study was to evaluate the efficacy and safety profile of DeFazio(S-1)combined with oxaliplatin against unresectable advanced or metastatic gastric cancer.Methods:Oxaliplatin was given intravenously at 130mg/m2for 2 h on d1 and S-1 was administered bid.at 80 mg/m2/day on d1–14 followed by a 7-day rest during the 3-week schedule.Results:All 62 patients were assessed for efficacy and adverse events.The response and disease control rates were 47.3%and 80.8%,respectively.The median time to progression was 7.8 months,and the median overall survival was11.6 months.The grade 3/4 adverse events were hematological toxicities,including neutropenia(11.3%),thrombocytopenia(9.7%)and gastrointestinal reactions(6.5%).Conclusion:The SOX regimen(oxaliplatin,130 mg/m2d1;S-1,80 mg/m2/day,bid.d1-14,q3w)provide a favorable efficacy and safety profile in patients with advanced gastric cancer.     

Simultaneous integrated boost for breast cancer using IMRT: a radiobiological and treatment planning study

PURPOSE: The purpose of this work is to explore the possibility of using intensity-modulated radiation therapy (IMRT) to deliver the boost dose to the tumor bed simultaneously with the whole-breast IMRT to reduce the radiation treatment time by 1-2 weeks. METHODS AND MATERIALS: The biologically effective dose (BED) for different treatments was calculated using the linear-quadratic (LQ) model with parameters previously derived for breast cancer from clinical data (alpha/beta = 10Gy, alpha = 0.3Gy(-1)). A potential doubling time of 15 days (from in vitro measurements) for breast cancer and a generic alpha/beta ratio of 3 Gy for normal tissues were used. A series of regimens that use IMRT as initial treatment and an IMRT simultaneous integrated boost (SIB) were derived using biologic equivalence to conventional schedules. Possible treatment plans with IMRT SIB to the tumor bed were generated for 2 selected breast patients, 1 with a shallow tumor and 1 with a deep-seated tumor. Plans with a simultaneous integrated electron boost were also generated for comparison. Dosimetric merits of these plans were evaluated based on dose volume histograms. RESULTS: A commonly used conventional treatment of 45 Gy (1.8 Gy x 25) to the whole breast and then a boost of 20 Gy (2 Gy x 10) is biologically equivalent to an alternative plan of 1.8 Gy x 25 to the whole breast with a 2.4 Gy x 25 SIB to the tumor bed. The new regime reduces treatment time from 7 to 5 weeks. For the patient with a deep-seated tumor, the IMRT plans reduce the volume of the breast that receives high doses (compared with the conventional photon boost plan) and provides good coverage of the target volumes. CONCLUSION: It is biologically and dosimetrically feasible to reduce the overall treatment time for breast radiotherapy by using an IMRT simultaneous integrated boost. For selected patient groups, IMRT plans with a new regimen can be equal to or better than conventional plans.     

Steep dose gradients for simultaneous integrated boost IMRT

Steep dose gradients between two planning target volumes (PTVs) as may be required for simultaneous integrated boosts (SIB) should be an option provided by IMRT algorithms. The aim was to analyse the geometry of the SIB problem and to implement the results in an algorithm for IMRT segment generation denoted two-step intensity modulated radiotherapy (2-Step IMRT). It was hypothesized that a gap between segments directed to the inner and the outer PTV would steepen the dose gradient. The mathematical relationships were derived from the individual dose levels and the geometry (diameters) of the PTVs. The results generated by means of 2-Step IMRT segments were equivalent or better than the segment generation using a commercial IMRT planning system. The dose to both the inner and the outer PTV was clearly more homogeneous and the composite objective value was the lowest. The segment numbers were lower or equal – with better sparing of the surrounding tissue. In summary, it was demonstrated that 2-Step IMRT was able to achieve steep dose gradients for SIB constellations.     

Dosimetric advantages of IMRT simultaneous integrated boost for high-risk prostate cancer

PURPOSE: A sequential two-phase process, initial and boost irradiation, is the common practice for the radiotherapy management of high-risk prostate cancer. In this work, we explore the feasibility of using intensity modulated radiation therapy (IMRT) simultaneous integrated boost (SIB), a single-phase process, to simultaneously deliver high dose to the prostate and lower dose to the pelvic nodes. In addition, we introduce the concept of voxel-equivalent dose for the comparison of treatment plans. METHODS AND MATERIALS: The SIB is designed to deliver the same dose (e.g., 45 Gy, 25 x 1.8 Gy) as the conventional method to the pelvic nodes and to deliver higher doses to prostate in the same 25 fractions (i.e., hypofractionation). The equivalent uniform dose (EUD) was used to determine suitable SIB fractionations that deliver the biologically equivalent doses to prostate. For tumor, the EUD was estimated based on the linear quadratic (LQ) model. The most recent LQ parameters derived from clinical data for prostate cancer were used. The sensitivity of LQ parameters was evaluated. The EUD for normal tissue was computed based on the widely used Lyman model. To be able to consider biologic effectiveness spatially (e.g., voxel by voxel), we propose a new concept, termed the voxel-equivalent dose (VED). The calculation of VED was similar to that for EUD, except that it was done within a voxel. To demonstrate dosimetric feasibility and advantages of the proposed IMRT SIB, we have performed a retrospective planning study on selected patient cases using commercial IMRT and three-dimensional (3D) planning systems. Four treatment scenarios were considered: (1) the conventional 3D plan for initial whole-pelvic irradiation and subsequent conventional 3D boost plan for prostate gland, (2) the conventional 3D plan for initial whole-pelvic irradiation and subsequent IMRT boost plan for prostate, (3) IMRT plan for initial whole-pelvic irradiation and subsequent IMRT boost plan for prostate, and (4) IMRT SIB. EUDs and VED-based dose-volume histograms for prostate, pelvic nodes, small bowel, rectum, bladder, and other tissue for all 4 scenarios were compared. RESULTS: A series of equivalent hypofractionation regimens suitable for the IMRT SIB were obtained for high-risk prostate cancer. For example, the conventional treatment regimen of 42 x 1.8 Gy (EUD = 75.4 Gy) would be equivalent to a SIB regimen of 25 x 2.54 Gy. From the comparison of 3D VED dose distributions and dose-volume histograms between the SIB and the conventional two-phase irradiation, we found that the SIB offers better or equivalent dose conformity to prostate and pelvic nodes and better sparing to the critical structures. For example, for the 4 treatment scenarios with a prostate EUD of 75.4 Gy, the corresponding rectal EUDs are 67.1 (3D + 3D), 65.6 Gy (3D + IMRT), 63.7 Gy (IMRT + IMRT), and 62.0 Gy (SIB). CONCLUSIONS: A new IMRT simultaneous integrated boost strategy that irradiates prostate via hypofractionation while irradiating pelvic nodes with the conventional fractionation is proposed for high-risk prostate cancer. Compared to the conventional two-phase treatment, the proposed SIB technique offers potential advantages, including better sparing of critical structures, more efficient delivery, shorter treatment duration, and better biologic effectiveness.     

Hypofractionated high-dose irradiation for the treatment of malignant astrocytomas using simultaneous integrated boost technique by IMRT

PURPOSE: We evaluated the clinical significance of hypofractionated high-dose irradiation using simultaneous integrated boost technique with intensity-modulated radiation therapy (IMRT) for the treatment of malignant astrocytomas (MAs). METHODS AND MATERIALS: Twenty-five patients with MAs were treated by IMRT. Three layered planning target volumes (PTVs) were contoured. PTV-1 was the area of enhanced lesion with 5-mm margin; PTV-2 was the area with 15-mm margin surrounding the PTV-1; PTV-3 was the area of perifocal edema. Irradiation was performed in 8 fractions, and only the dose for PTV-1 was escalated from 48 Gy to 68 Gy while maintaining the dose for PTV-2 (40 Gy) and PTV-3 (32 Gy). The clinical outcome of IMRT was compared with 60 MA patients treated by conventional external beam irradiation (EBI). RESULTS: The progression-free survival of patients in the IMRT group was significantly longer than that in the EBI group (p < 0.0001). No distant failure was observed in both groups. In the IMRT group, dissemination was the most frequent cause of death (70%). The overall survival of patients in the IMRT group was better than that in the EBI group (p = 0.043). CONCLUSIONS: Our regimen of IMRT contributed to the control of both the regional and infiltrating tumors, resulting in better survival of patients.     

Effect of patient setup errors on simultaneously integrated boost head and neck IMRT treatment plans

PURPOSE: The purpose of this study is to determine dose delivery errors that could result from random and systematic setup errors for head-and-neck patients treated using the simultaneous integrated boost (SIB)-intensity-modulated radiation therapy (IMRT) technique. METHODS AND MATERIALS: Twenty-four patients who participated in an intramural Phase I/II parotid-sparing IMRT dose-escalation protocol using the SIB treatment technique had their dose distributions reevaluated to assess the impact of random and systematic setup errors. The dosimetric effect of random setup error was simulated by convolving the two-dimensional fluence distribution of each beam with the random setup error probability density distribution. Random setup errors of sigma = 1, 3, and 5 mm were simulated. Systematic setup errors were simulated by randomly shifting the patient isocenter along each of the three Cartesian axes, with each shift selected from a normal distribution. Systematic setup error distributions with Sigma = 1.5 and 3.0 mm along each axis were simulated. Combined systematic and random setup errors were simulated for sigma = Sigma = 1.5 and 3.0 mm along each axis. For each dose calculation, the gross tumor volume (GTV) received by 98% of the volume (D(98)), clinical target volume (CTV) D(90), nodes D(90), cord D(2), and parotid D(50) and parotid mean dose were evaluated with respect to the plan used for treatment for the structure dose and for an effective planning target volume (PTV) with a 3-mm margin. RESULTS: Simultaneous integrated boost-IMRT head-and-neck treatment plans were found to be less sensitive to random setup errors than to systematic setup errors. For random-only errors, errors exceeded 3% only when the random setup error sigma exceeded 3 mm. Simulated systematic setup errors with Sigma = 1.5 mm resulted in approximately 10% of plan having more than a 3% dose error, whereas a Sigma = 3.0 mm resulted in half of the plans having more than a 3% dose error and 28% with a 5% dose error. Combined random and systematic dose errors with sigma = Sigma = 3.0 mm resulted in more than 50% of plans having at least a 3% dose error and 38% of the plans having at least a 5% dose error. Evaluation with respect to a 3-mm expanded PTV reduced the observed dose deviations greater than 5% for the sigma = Sigma = 3.0 mm simulations to 5.4% of the plans simulated. CONCLUSIONS: Head-and-neck SIB-IMRT dosimetric accuracy would benefit from methods to reduce patient systematic setup errors. When GTV, CTV, or nodal volumes are used for dose evaluation, plans simulated including the effects of random and systematic errors deviate substantially from the nominal plan. The use of PTVs for dose evaluation in the nominal plan improves agreement with evaluated GTV, CTV, and nodal dose values under simulated setup errors. PTV concepts should be used for SIB-IMRT head-and-neck squamous cell carcinoma patients, although the size of the margins may be less than those used with three-dimensional conformal radiation therapy.     

On the performances of different IMRT treatment planning systems for selected paediatric cases

Background

To evaluate the performance of seven different TPS (Treatment Planning Systems: Corvus, Eclipse, Hyperion, KonRad, Oncentra Masterplan, Pinnacle and PrecisePLAN) when intensity modulated (IMRT) plans are designed for paediatric tumours.

Methods

Datasets (CT images and volumes of interest) of four patients were used to design IMRT plans. The tumour types were: one extraosseous, intrathoracic Ewing Sarcoma; one mediastinal Rhabdomyosarcoma; one metastatic Rhabdomyosarcoma of the anus; one Wilm's tumour of the left kidney with multiple liver metastases. Prescribed doses ranged from 18 to 54.4 Gy. To minimise variability, the same beam geometry and clinical goals were imposed on all systems for every patient. Results were analysed in terms of dose distributions and dose volume histograms.

Results

For all patients, IMRT plans lead to acceptable treatments in terms of conformal avoidance since most of the dose objectives for Organs At Risk (OARs) were met, and the Conformity Index (averaged over all TPS and patients) ranged from 1.14 to 1.58 on primary target volumes and from 1.07 to 1.37 on boost volumes. The healthy tissue involvement was measured in terms of several parameters, and the average mean dose ranged from 4.6 to 13.7 Gy. A global scoring method was developed to evaluate plans according to their degree of success in meeting dose objectives (lower scores are better than higher ones). For OARs the range of scores was between 0.75 ± 0.15 (Eclipse) to 0.92 ± 0.18 (Pinnacle³ with physical optimisation). For target volumes, the score ranged from 0.05 ± 0.05 (Pinnacle³ with physical optimisation) to 0.16 ± 0.07 (Corvus).

Conclusion

A set of complex paediatric cases presented a variety of individual treatment planning challenges. Despite the large spread of results, inverse planning systems offer promising results for IMRT delivery, hence widening the treatment strategies for this very sensitive class of patients.     

An approach for practical multiobjective IMRT treatment planning

PURPOSE: To introduce and demonstrate a practical multiobjective treatment planning procedure for intensity-modulated radiation therapy (IMRT) planning. METHODS AND MATERIALS: The creation of a database of Pareto optimal treatment plans proceeds in two steps. The first step solves an optimization problem that finds a single treatment plan which is close to a set of clinical aspirations. This plan provides an example of what is feasible, and is then used to determine mutually satisfiable hard constraints for the subsequent generation of the plan database. All optimizations are done using linear programming. RESULTS: The two-step procedure is applied to a brain, a prostate, and a lung case. The plan databases created allow for the selection of a final treatment plan based on the observed tradeoffs between the various organs involved. CONCLUSIONS: The proposed method reduces the human iteration time common in IMRT treatment planning. Additionally, the database of plans, when properly viewed, allows the decision maker to make an informed final plan selection.     

MRI-based treatment planning for radiotherapy: dosimetric verification for prostate IMRT

PURPOSE: Magnetic resonance (MR) and computed tomography (CT) image fusion with CT-based dose calculation is the gold standard for prostate treatment planning. MR and CT fusion with CT-based dose calculation has become a routine procedure for intensity-modulated radiation therapy (IMRT) treatment planning at Fox Chase Cancer Center. The use of MRI alone for treatment planning (or MRI simulation) will remove any errors associated with image fusion. Furthermore, it will reduce treatment cost by avoiding redundant CT scans and save patient, staff, and machine time. The purpose of this study is to investigate the dosimetric accuracy of MRI-based treatment planning for prostate IMRT. METHODS AND MATERIALS: A total of 30 IMRT plans for 15 patients were generated using both MRI and CT data. The MRI distortion was corrected using gradient distortion correction (GDC) software provided by the vendor (Philips Medical System, Cleveland, OH). The same internal contours were used for the paired plans. The external contours were drawn separately between CT-based and MR imaging-based plans to evaluate the effect of any residual distortions on dosimetric accuracy. The same energy, beam angles, dose constrains, and optimization parameters were used for dose calculations for each paired plans using a treatment optimization system. The resulting plans were compared in terms of isodose distributions and dose-volume histograms (DVHs). Hybrid phantom plans were generated for both the CT-based plans and the MR-based plans using the same leaf sequences and associated monitor units (MU). The physical phantom was then irradiated using the same leaf sequences to verify the dosimetry accuracy of the treatment plans. RESULTS: Our results show that dose distributions between CT-based and MRI-based plans were equally acceptable based on our clinical criteria. The absolute dose agreement for the planning target volume was within 2% between CT-based and MR-based plans and 3% between measured dose and dose predicted by the planning system in the physical phantom. CONCLUSIONS: Magnetic resonance imaging is a useful tool for radiotherapy simulation. Compared with CT-based treatment planning, MR imaging-based treatment planning meets the accuracy for dose calculation and provides consistent treatment plans for prostate IMRT. Because MR imaging-based digitally reconstructed radiographs do not provide adequate bony structure information, a technique is suggested for producing a wire-frame image that is intended to replace the traditional digitally reconstructed radiographs that are made from CT information.