二维电离室矩阵在调强适形放疗剂量学验证中的应用

剂量学验证是放射治疗中质量保证的重要一环,也是调强适形放射治疗(IMRT)应用于临床时必不可少的一个步骤,随着放射物理技术的发展,新设备和新方法在不断应用,为临床放射治疗提供了更好、更便捷的质量保证与控制手段.二维电离室矩阵(MatriXX)是一种快速的剂量测量系统,是目前较先进的调强治疗实时二维验证系统之一,它可以测量照射野的剂量分布和强度分布,在剂量学验证中,可以极大地简化验证工作量,提高验证效率.     

Prolonged hormonal therapy and external beam radiation independently increase the risk of Persistent Hypogonadism in men treated with prostate brachytherapy

PurposeTo identify variables that predict persistent hypogonadism and castration in patients with prostate cancer (PCa) treated with brachytherapy (BT).Materials and MethodsA retrospective analysis was performed on 1,053 patients receiving BT ± external beam radiation therapy (EBRT) ± hormone therapy (HT) for NCCN low, intermediate, or high-risk PCa between 1990 and 2011. Patients were categorized as not receiving HT (n = 438, 41.6%), ≤6 months (n = 317, 31.1%) or > 6 months (n = 298, 28.3%) of HT. 572 (54.3%) received BT alone, and 481 had combination therapy. The five- and 10-year freedom from persistent hypogonadism (T < 280 ng/dL) and castration (T < 50 ng/dL) for each group was evaluated with Kaplan-Meier estimates. Multivariable cox proportional hazards models were used to compare the risk of persistent hypogonadism and castration at a median followup of 6.5 years (posttreatment to final T) (IQR: 4.3–9.1 years; range: 1.0–19.2 years).ResultsThe 5-year freedom from hypogonadism rates were 92.4%, 88.9%, and 87.0% for patients with no HT, ≤ 6 months and >6 months of HT, respectively (10-year rates: 66.7%, 55.3%, 40.5%); p < 0.01. The 5-year freedom from castration rates were 99.2%, 98.0%, and 98.4%, respectively (10-year rates: 97.9%, 95.5%, 90.9%); p = 0.078. Number of months of HT (HR = 1.04, p = 0.030) and BT with EBRT vs. BT alone (HR = 1.56, p = 0.010) significantly increased the risk of persistent hypogonadism. Number of months of HT was the only variable which increased the risk of persistent castration (HR = 1.09, p = 0.014).ConclusionsThe addition of EBRT to BT is an independent risk factor for persistent hypogonadism. Prolonged HT additionally increases the risk of persistent hypogonadism and castration.     

External beam planning module of Eclipse for external beam radiation therapy

Eclipse is a 3-dimensional (3D) treatment planning system for radiation therapy offered by Varian Medical Systems, Inc. The system has the network connectivity for the electronic transfer of image datasets and digital data communication among different equipment. The scope of this project for this special issue of Medical Dosimetry on 3D treatment planning systems is the assessment of planning tools in the external beam planning module of Eclipse to generate optimized treatment plans for patients undergoing external beam radiation therapy. This treatment planning system is relatively mature to be able to generate (1) simple treatment plans, (2) conformal radiation therapy plans, (3) static intensity-modulated radiation therapy (IMRT) plans, (4) volumetric-modulated arc therapy (VMAT) plans, and (5) treatment plans for electron beam therapy. The treatment planning tools are relatively plentiful to assist in the radiation therapy treatment planning. Some new features have been incorporated in the latest version and are helpful for making high-quality treatment plans. However, the location of the tools is not intuitive, and hence, familiarity with the user interface is essential to the efficient use of the treatment planning system. In addition, there are a number of dose algorithms available for the computation of dose distributions. The understanding of each dose computation algorithm is essential for the optimal use of this treatment planning system.     

The use of diode dosimetry in quality improvement of patient care in radiation therapy

The purpose of this work is to improve the quality of patient care in radiation therapy by implementing a comprehensive quality assurance (QA) program aiming to enhance patient in vivo dosimetry on a routine basis. The characteristics of two commercially available semi-conductor diode dosimetry systems were evaluated. The diodes were calibrated relative to an ionization chamber-electrometer system with calibrations traceable to the National Institute of Standards and Technology (NIST). Correction factors of clinical relevance were quantified to convert the diode readings into patient dose. The results of dose measurements on 6 patients undergoing external beam radiation therapy for carcinoma of the prostate on three different therapy units are presented. Field shaping during treatments was accomplished either by multileaf collimation or by cerrobend blocking. A deviation of less than ±4% between the measured and prescribed patient doses was observed. The results indicate that the diodes exhibit excellent linearity, dose reproducibility, minimal anisotropy, and can be used with confidence for patient dose verification. Furthermore, diodes render real time verification of dose delivered to patients.     

Dosimetric effect of external beam planning preceding combined high-dose-rate brachytherapy of the prostate

Purpose

The sequencing of external beam radiotherapy (EBRT) and a high-dose-rate brachytherapy (HDRB) boost is often interchangeable in clinical practice. When given before EBRT, HDRB could induce volume alterations in the prostate, which may have significant implications for EBRT dosimetry. We aimed to assess the influence of HDRB on prostate volume and, hence, prostate dosing via subsequent EBRT.

Methods and Materials

Fifteen men had both pre- and post-HDRB CT performed followed by EBRT. After deidentification, the clinical target volume (CTV) was defined on each CT by a single-blinded observer. Volumes were compared for the pre- and post-HDRB scans in each patient. Radiotherapy planning was performed using the prebrachytherapy volumes aiming for the planning target volume (PTV) to be covered by 43.7 Gy. After soft-tissue coregistration, this plan was also applied to the postbrachytherapy volumes.

Results

Median volume increase was 35.4% for the CTV after HDRB. No patient experienced a decrease in CTV volume (range, 0-79% volume increase; p-value < 0.001). Median volume increase was 26.1% for the PTVs, with no volume decrease observed (range, 8-56%; p < 0.001). PTV proportion achieving dose target (V43.7 Gy) decreased by median of 7% (range, 0-21.5%; p = 0.004). The minimum dose to the PTV (D₁₀₀%) decreased by a median of 6 Gy (range, 0.5-16 Gy; p < 0.001).

Conclusions

Insertion of HDRB catheters exerts substantial acute volumetric distortion on the prostate. EBRT planning performed on the basis of pre-HDRB imaging only inherently risks underdosing tumor. Planning adjustments based on repeat CT, or dedicated post-HDBT planning, is warranted for men managed with HDRB before EBRT.     

Beta-particle dosimetry in radiation synovectomy

Beta-particle dosimetry of various radionuclides used in the treatment of rheumatoid arthritis was estimated using Monte Carlo radiation transport simulation coupled with experiments using reactor-produced radionuclides and radiachromic film dosimeters inserted into joint phantoms and the knees of cadavers. Results are presented as absorbed dose factors (cGy-cm²/MBq-s) versus depth in a mathematical model of the rheumatoid joint which includes regions of bone, articular cartilage, joint capsule, and tissue (synovium) found in all synovial joints. The factors can be used to estimate absorbed dose and dose rate distributions in treated joints. In particular, guidance is provided for those interested in (a) a given radionuclide's therapeutic range, (b) the amount of radioactivity to administer on a case-by-case basis, (c) the expected therapeutic dose to synovium, and (d) the radiation dose imparted to other, nontarget components in the joint, including bone and articular cartilage.     

Patient safety in external beam radiation therapy

OBJECTIVE: External beam radiation therapy is a highly effective treatment for many types of cancer and other diseases, but incorrect delivery of the high doses necessary for tumor control can cause serious normal tissue complications, and geographic misses of the tumor can cause tumor recurrence. CONCLUSION: Benefits and risks of the explosive technologic growth of the last three decades will be described, as will efforts to reduce treatment errors and ensure safe effective treatment.     

Combined transperineal implant and external beam radiation for the treatment of prostate cancer: a large patient cohort in the community setting

Purpose

Treatment of prostate cancer using higher doses of external beam radiation (EBRT) has been shown to improve results, but there are toxicity concerns with further dose escalation. A treatment option to safely increase total dose to the prostate includes combination therapy using EBRT and low-dose-rate transperineal brachytherapy seed implant. Our purpose was to report the results of combined modality therapy from a single institution in the community setting.

Methods and Materials

Retrospective review from single institution in the community setting. All patients were treated with a combination of EBRT followed by low-dose-rate brachytherapy seed placement.

Results

A total of 824 patients were analyzed with a median followup of 5.5 years, all censored patients had a minimum followup of 2 years. A total of 588 patients received hormone therapy before or concurrent with the radiation. Three hundred twenty-nine patients had low-risk disease, 300 patients had intermediate-risk disease, and 195 patients had high-risk disease. Five-year overall survivals were 86.1%, 85.0%, and 82.5% for low-, intermediate-, and high-risk patients. Five-year actuarial biochemical relapse-free survivals (bRFSs) were 85.4%, 83.2%, and 79.6% for low-, intermediate-, and high-risk patients. High-risk patients who received hormonal therapy had an improved bRFS vs. patients not receiving hormones.

Conclusions

Combination treatment using brachytherapy and EBRT is well tolerated, with acceptable overall survival and bRFS rates and should be considered a standard treatment option for patients. Hormones should be considered for high-risk patients.     

调强适形放射治疗剂量验证中CT密度值的校准分析

目的 基于调强适形放射治疗(IMRT)验证体模,分析放射治疗计划系统中CT密度转换曲线在IMRT剂量验证中的影响,并加以校准.方法　利用CT电子密度体模刻度计划系统中的CT密度转换曲线,取12例鼻咽癌患者的IMRT计划,分别移植至IMRT验证体模,计算剂量分布,并于剂量均匀处放置测量点,利用电离室测量出其实际剂量.将I...     

瓦里安呼吸门控实时位置管理系统对放射治疗计划剂量学的影响

目的 研究瓦里安呼吸门控实时位置管理(RPM)系统对放射治疗计划剂量学的影响。方法 回顾性选取40例胸腹部肿瘤放疗计划,采用质量控制运动模体产生呼吸门控信号,选取呼气末30%~60%稳定时相作为呼吸门控窗,在Edge加速器RPM呼吸门控模式下对上述计划进行Portal Dosimetry(PD)系统剂量验证,采用不同的γ通过率标准进行剂量分析,并分析其γ值的分布特点,与非门控模式下验证结果进行对比。结果 在RPM呼吸门控模式下,对于不同均整器模式下的调强放射治疗计划(IMRT)或容积调强放射治疗计划(VMAT),采用γ(3%,3 mm)或(3%,2 mm)标准,所有计划通过率均在95.5%以上,采用更严格的γ(2%,2 mm)标准,所有计划通过率均在90%以上,符合美国医学物理师学会(AAPM)推荐的临床治疗标准。非门控模式下剂量验证结果通过率略优于呼吸门控模式下验证结果,两种模式下差异具有统计学意义(3%/3 mm,Z=-1.45;3%/2 mm,Z=-2.86;2%/2 mm,Z=-3.70;1%/1 mm,Z=-4.52, P<0.05)。两种模式下计划验证结果γ值的最小值、最大值及γ＞1.5的份额差异不明显,但非门控模式下γ的平均值及标准偏差总体更小。结论 RPM呼吸门控技术引入带来的剂量影响在临床可接受范围内,该门控模式下计划执行是安全可靠的。     

腮腺动态显像评价鼻咽癌放疗对腮腺功能的影响

目的 探讨腮腺动态显像评价鼻咽癌放疗对腮腺功能影响的价值。方法 21例鼻咽癌患者分别于放疗前、后行放射性核素腮腺动态显像,计算腮腺摄取指数(UI)、酸刺激后的分泌率(ER)、分泌指数(EI)等半定量指标以评价放疗前后腮腺功能的变化。结果 放疗后与放疔前比较,所有患者UI、ER、EI均显著下降,t值分别为56.65、41.34、30.69,P<0.001,腮腺摄取与分泌功能均明显受损,与患者临床口干症状相符。结论 腮腺动态显像是一种评价鼻咽癌放疗对腮腺功能的影响的有用方法,具有临床应用价值。     

A comparison of small-field tissue phantom ratio data generation methods for an Elekta Agility 6 MV photon beam

Tissue-phantom ratios (TPRs) are a common dosimetric quantity used to describe the change in dose with depth in tissue. These can be challenging and time consuming to measure. The conversion of percentage depth dose (PDD) data using standard formulae is widely employed as an alternative method in generating TPR. However, the applicability of these formulae for small fields has been questioned in the literature. Functional representation has also been proposed for small-field TPR production. This article compares measured TPR data for small 6 MV photon fields against that generated by conversion of PDD using standard formulae to assess the efficacy of the conversion data. By functionally fitting the measured TPR data for square fields greater than 4 cm in length, the TPR curves for smaller fields are generated and compared with measurements. TPRs and PDDs were measured in a water tank for a range of square field sizes. The PDDs were converted to TPRs using standard formulae. TPRs for fields of 4 × 4 cm² and larger were used to create functional fits. The parameterization coefficients were used to construct extrapolated TPR curves for 1 × 1 cm², 2 × 2-cm², and 3 × 3-cm² fields. The TPR data generated using standard formulae were in excellent agreement with direct TPR measurements. The TPR data for 1 × 1-cm², 2 × 2-cm², and 3 × 3-cm² fields created by extrapolation of the larger field functional fits gave inaccurate initial results. The corresponding mean differences for the 3 fields were 4.0%, 2.0%, and 0.9%. Generation of TPR data using a standard PDD-conversion methodology has been shown to give good agreement with our directly measured data for small fields. However, extrapolation of TPR data using the functional fit to fields of 4 × 4 cm² or larger resulted in generation of TPR curves that did not compare well with the measured data.     

Interstitial brachytherapy in the management of persistent head and neck disease after definitive external beam radiation therapy

PurposePersistent disease after definitive external beam radiation therapy for head and neck (H&;N) malignancies negatively impacts survival. In this series, the effectiveness of low-dose-rate brachytherapy in the management of persistent H&;N disease is explored.MethodsAll patients who received brachytherapy for persistent H&;N disease between 1987 and 2002 were identified. Tumor and treatment characteristics and toxicities were recorded. Progression-free survival and overall survival estimates were generated. The influence of prognostic factors was determined.ResultsTwelve patients were analyzable. Brachytherapy was given curatively (n = 4) in patients not amenable to surgery or in combination with surgical dissection to avoid carotid resection (n = 8). Seven patients had disease progression with a median time to progression of 11 months (95% confidence interval: 0–22.9). The only negative prognostic factor was time to re-treatment (brachytherapy >4 months) after definitive treatment (p = 0.003). Overall survival at 1 and 5 years was 50% and 21%, respectively. Toxicity was limited to one major complication (fistula) and five minor toxicities: low-grade radionecrosis (n = 2), cellulitis (n = 1), and wound dehiscence (n = 2).ConclusionIn patients with persistent disease, brachytherapy is an appealing re-treatment alternative. When combined with neck dissection, brachytherapy yields less morbidity than the surgical alternative of carotid resection.     

Real-time light dosimetry for intra-cavity photodynamic therapy: Application for pleural mesothelioma treatment

Complete and homogeneous illumination of the target is necessary for the success of a photodynamic therapy (PDT) procedure. In most applications, light dosimetry is done using detectors placed at strategic locations of the target. In this study we propose a novel approach based on the combination of light distribution modeling with spatial localization of the light applicator for real time estimation and display of the applied dose on medical images. The feasibility approach is demonstrated for intrapleural PDT of malignant pleural mesothelioma.     

Radiation therapy dosimetry system

New therapeutic treatments generally aim to increase therapeutic efficacy while minimizing toxicity. Many aspects of radiation dosimetry have been studied and developed particularly in the field of external radiation. The success of radiotherapy relies on monitoring the dose of radiation to which the tumor and the adjacent tissues are exposed. Radiotherapy techniques have evolved through a rapid transition from conventional three-dimensional (3D) conformal radiation therapy to intensity-modulated radiation therapy (IMRT) treatments or radiosurgery and robotic radiation therapy. These advances push the frontiers in our effort to provide better patient care by improving the precision of the absorbed dose delivered. This paper presents state-of-the art radiation therapy dosimetry techniques as well as the value of integral dosimetry (INDOS), which shows promise in the fulfillment of radiation therapy dosimetry requirements.     

Radical external beam radiation therapy for prostate carcinoma

Between 1970 and 1978, 202 patients with carcinoma of the prostate were treated with radical external beam radiation with curative intent. Intracapsular disease was present in 38% and the remaining 62% had disease extending through the prostatic capsule. The overall survival is 72% at five years, and despite the large number of patients with advanced disease the five-year disease-free survival is 46%. Significant prognostic factors include: i) tumor, grade, ii) extent of primary disease, iii) procedure done to determine diagnosis (TURP vs. needle biopsy) and iv) tumor dose. There was a significant improvement in survival at a minimum dose of 5000 Gy. Prostate carcinoma is radiosensitive and a dose-response relationship in treatment has been demonstrated by this review.     

Dosimetric considerations of water-based bolus for irradiation of extremities

The dosimetry of high-energy photon beams in the treatment of superficial lesions occurring in extremities was examined. Large parallel-opposed fields with different photon beam energies were used. The extremity was immersed in water contained in a commercially available plastic wastebasket. The water bolus serves to even out the surface irregularities of the extremities and to remove the skin sparing effect. A polystyrene block was placed at the floor of the wastebasket to ensure that the extremity was encompassed in the radiation fields. The photon beam energies considered were 4 MV, 6 MV, 10 MV, and 24 MV. The results show that the dose distributions are more homogeneous with higher photon beam energies. The isodose lines are more constricted at mid-plane for low energy photon beams. Higher energy photon beams, 10 MV and up would be preferable for the treatment of superficial lesions of the extremities immersed in water bolus contained in a typical wastebasket size.