Comparing gamma knife and cyberknife in patients with brain metastases.

The authors compared the relative dosimetric merits of Gamma Knife (GK) and CyberKnife (CK) in 15 patients with 26 brain metastases. All patients were initially treated with the Leksell GK 4C. The same patients were used to generate comparative CK treatment plans. The tissue volume receiving more than 12 Gy (V12), the difference between V12 and tumor volume (V12net), homogeneity index (HI), and gradient indices (GI25, GI50) were calculated. Peripheral dose falloff and three conformity indices were compared. The median tumor volume was 2.50 cm3 (range, 0.044-19.9). A median dose of 18 Gy (range, 15-22) was prescribed. In GK and CK plans, doses were prescribed to the 40-50% and 77-92% isodose lines, respectively. Comparing GK to CK, the respective parametric values (median ± standard deviation) were: minimum dose (18.2 ± 3.4 vs. 17.6 ± 2.4 Gy, p = 0.395); mean dose (29.6 ± 5.1 vs. 20.6 ± 2.8 Gy, p < 0.00001); maximum dose (40.3 ± 6.5 vs. 22.7 ± 3.3 Gy, p < 0.00001); and HI (2.22 ± 0.19 vs. 1.18 ± 0.06, p < 0.00001). The median dosimetric indices (GK vs. CK, with range) were: RTOG_CI, 1.76 (1.12-4.14) vs. 1.53 (1.16-2.12), p = 0.0220; CI, 1.76 (1.15-4.14) vs. 1.55 (1.18-2.21), p = 0.050; nCI, 1.76 (1.59-4.14) vs. 1.57 (1.20-2.30), p = 0.082; GI50, 2.91 (2.48-3.67) vs. 4.90 (3.42-11.68), p < 0.00001; GI25, 6.58 (4.18-10.20) vs. 14.85 (8.80-48.37), p < 0.00001. Average volume ratio (AVR) differences favored GK at multiple normalized isodose levels (p < 0.00001). We concluded that in patients with brain metastases, CK and GK resulted in dosimetrically comparable plans that were nearly equivalent in several metrics, including target coverage and minimum dose within the target. Compared to GK, CK produced more homogenous plans with significantly lower mean and maximum doses, and achieved more conformal plans by RTOG_CI criteria. By GI and AVR analyses, GK plans had sharper peripheral dose falloff in most cases.

A comparison of the biological effective dose of 50-kV electronic brachytherapy with (192)Ir high-dose-rate brachytherapy for vaginal cuff irradiation.

PURPOSE: Advantages for electronic brachytherapy (EBT) of the vaginal cuff include decreased physical dose to the bladder and rectum. Here we compare (192)Ir with EBT using biological effective dose (BED) to account for the different radiobiological effectiveness (RBE) predicted for low-energy x-rays. METHODS AND MATERIALS: Fifteen data sets from five consecutive postoperative endometrial cancer patients treated with EBT were analyzed. Treatment planning was performed using PLATO software. The dose was prescribed as 21Gy in three fractions to a depth of 0.5cm. Physical dose, BED(3), and BED(10) were evaluated for the mucosa, bladder, and rectum. An RBE value of 1.5 was used for BED calculations. RESULTS: Mucosal physical dose is 28.4% greater with EBT (36.6 vs. 28.5Gy, p<0.05). However, the BED(10) is increased by 79.1% (55.6 vs. 99.6Gy, p<0.05) and the BED(3) by 71.5% (118.8 vs. 203.7Gy, p<0.05). The physical dose (dose to 50% volume of the organ) to the bladder (9.3 vs. 6.6Gy, p<0.05) and rectum (7.2 vs. 4.2Gy, p<0.05) are reduced with EBT. BED(3) to the rectum and bladder are also reduced but to a lesser extent (13 vs. 8.3Gy, p<0.05; 18.9 vs. 14.7Gy, p=0.06, respectively). CONCLUSIONS: BED takes into account the higher RBE of low-energy photons generated with EBT and provides a more accurate estimate of the biological effect. When using EBT, physical dose may underestimate the biological effect on the vaginal mucosa and overestimate the benefit for the bladder and rectum. Dose adjustment for EBT based on BED should be considered.

Interface dosimetry for electronic brachytherapy intracavitary breast balloon applicators.

In this study, we evaluate the attenuation of the dose due to barium-impregnation in the region between the surface of an electronic brachytherapy (EBT) balloon applicator for accelerated partial breast irradiation (APBI) and the prescription point at 1 cm depth in tissue. To perform the study, depth dose curves were calculated using a general purpose multi-particle transport code (FLUKA) for a range of balloon wall thicknesses with and without barium impregnation. Numerical data were verified with experimental readings using a parallel plate extrapolation ionization chamber for different wall thicknesses. Depth dose curves computed using both numerical and experimental methods show a 6.0% attenuation of the dose at the 1.0 cm prescription line due to the impregnation of barium in the balloon material, which agrees well with the manufacturer's specification. By applying this single attenuation factor, dose calculations throughout the entire planned volume are uniformly affected. However, at the balloon surface, attenuation on the order of 18.0% is observed. The AAPM TG-43 source data currently incorporated in commercially-available treatment planning systems do not account for the variable dose distributions attributable to balloon wall attenuation. Our results show that variable attenuation factors that may have clinical significance should be applied in order to determine near-surface dose distributions when using barium impregnated balloons for intracavitary breast brachytherapy. Dose distributions at distances greater than 1 cm from the surface of the balloon appear to be accurately represented without further modification.

Exploring the potential of mixed-source brachytherapy for the treatment of cervical cancer using high-dose rate 192Ir and/or 50 kV electronic sources.

PURPOSE: In this study, computer modeling was used to compare the relative doses with the bladder, rectum, and bowel when two different brachytherapy modalities were used to treat cervical cancer with a tandem and ovoid applicator. A standard high-dose rate (HDR) (192)Ir treatment plan was compared with a "mixed-source" brachytherapy (MSB) treatment plan in which a 50 kV electronic brachytherapy X-ray source was substituted for (192)Ir as the tandem source. METHODS AND MATERIALS: A total of 15 three-dimensional CT data sets from cervical cancer patients previously treated with tandem and ovoid applicator were evaluated for the study. Bladder, rectum, bowel, and target volumes were contoured and separate treatment plans were created for MSB and HDR (192)Ir applications. Dose-volume histograms were analyzed for each organ at risk. RESULTS: The mean %V(25) for the bladder was 43% vs. 70% for MSB and HDR (192)Ir methods, respectively. Similarly, for the rectum mean %V(25) was 34% vs. 48% for MSB and HDR (192)Ir. For the bowel, the mean %V(25) was 28% vs. 43% for the MSB and HDR (192)Ir methods, respectively. In 16 of 45 organs at risk, %D(2 cc) values were higher for MSB than HDR (192)Ir. CONCLUSIONS: MSB is capable of providing target coverage to the cervix, uterus, and paracervical regions equivalent to that provided by HDR (192)Ir, while significantly reducing the overall dose to the bladder, rectum, and bowel. This reduction is associated with small regions of increased dose in a significant proportion of patients.

Using baldrige performance excellence program approaches in the pursuit of radiation oncology quality care, patient satisfaction, and workforce commitment.

The Malcolm Baldrige National Quality Improvement Act was signed into law in 1987 to advance US business competitiveness and economic growth. Administered by the National Institute of Standards and Technology, the Act created the Baldrige National Quality Program, recently renamed the Baldrige Performance Excellence Program. The comprehensive analytical approaches referred to as the Baldrige Healthcare Criteria, are very well-suited for the evaluation and sustainable improvement of radiation oncology management and operations. A multidisciplinary self-assessment approach is used for radiotherapy program evaluation and development in order to generate a fact-based, knowledge-driven system for improving quality of care, increasing patient satisfaction, enhancing leadership effectiveness, building employee engagement, and boosting organizational innovation. This methodology also provides a valuable framework for benchmarking an individual radiation oncology practice's operations and results against guidelines defined by accreditation and professional organizations and regulatory agencies.