A case report on bilateral partial breast irradiation using SAVI.

To assess dosimetric parameters in a case study where bilateral accelerated partial breast irradiation (APBI) is delivered using a strut-adjusted volume implant (SAVI) device. A 59-year-old female received APBI in both breasts over 5 days, with fractions of 3.4 Gy twice daily. A Vac-lok system was used for immobilization, and a C-arm was used for daily imaging. We generated dose-volume histograms (DVHs) for the brachytherapy plans to derive several important biologic factors. We calculated the normal tissue complication probability (NTCP), equivalent uniform dose (EUD), and tumor control probability (TCP) using the Lyman-Kutcher-Burman model parameters α = 0.3 Gy(-1), α/ß = 4 Gy, n = 0.1, and m = 0.3. In addition, we assessed the dose homogeneity index (DHI), overdose index, and dose nonuniformity ratio. D95 was >95% and V150 was <50 mL for both breasts. The DHIs were 0.469 and 0.512 for the left and right breasts, respectively. The EUDs (normalized to 3.4 Gy b.i.d.) were 33.53 and 29.10 Gy. The TCPs were estimated at 99.2% and 99.9%, whereas the NTCP values were 4.2% and 2.57%. In this clinical case, we were able to quantify the dosimetric parameters of an APBI treatment performed with a SAVI device.

RapidArc quality assurance through MapCHECK.

The purpose is to devise a patient-specific quality assurance procedure for RapidArc radiotherapy using the MapCHECK detector array. We use our existing MapCHECK system and a Solid Water phantom with an embedded ion chamber to develop a quality assurance procedure for RapidArc treatment after commissioning. The ion chamber used to measure the absolute dose is surrounded by 6 cm layers of solid water on the anterior and posterior sides. Partial arcs derived from the treatment planning system were used with MapCHECK to determine the actual shape of the dose and correct for the angular dependence. The ion chamber measurements were within 1% of the absolute doses predicted by the Eclipse treatment system. When using a partial arc from 60° to 300° on the MapCHECK array (gamma index <1: 3%, 3 mm, 10% threshold), we obtain a 97.52% average passing rate. A combination of ion chamber phantoms, partial arcs and the MapCHECK system can be used for quality assurance of RapidArc therapies.

Dosimetric parameters in partial breast irradiation through brachytherapy.

The objective of this work is to evaluate biological models and dose homogeneity in a new partial breast irradiation method, the MammoSite RTS. The study is based on 11 patients who received the therapy. For each patient, we determined the dose volume distribution delivered to the breast. Based on these data, we estimate some important biological parameters. Eleven patients with early-stage, invasive, ductal breast cancer were treated using MammoSite RTS brachytherapy, which delivers radiation through a balloon placed in the lumpectomy bed. The radiation was provided by an Iridium-192 source, and 340 cGy were delivered per fraction twice daily. We calculated some commonly used dosimetric parameters, and evaluated the biological parameters tumor control probability (TCP) and normal tissue complication probability (NTCP). We also looked for correlations among these parameters. The average equivalent uniform dose (EUD), NTCP, and TCP were 43.66 Gy, 47.95%, and 91.78%, respectively. The coefficient of variation (CV) among the patients was very low for all 3 parameters. Two dose homogeneity indices (DHI and the S-index) are strongly correlated (r = -0.815). The area under the dose-volume histogram (DVH) and the treatment volume (TXV) also showed a strong correlation (r = 0.995, p < 0.0001). A simplified logit Poisson-EUD model is suitable for determining NTCP and TCP. Other factors such as the area under the DVH and dose homogeneity indices are also useful in planning radiotherapy treatments for early breast cancer.

A Bland-Altman analysis of the bias between computed tomography and ultrasound prostate volume measurements.

This study assesses the agreement between computed tomography (CT) measurements of prostate volume and those obtained by ultrasound (US), a well-established non-invasive technique. Twenty-six patients aged between 58 and 74 years were evaluated for prostate seed implant therapy using both CT and US measurements. The level of agreement between these 2 methods, which were strongly correlated (R2 = 0.828; p < 0.0001), was determined through Bland-Altman analysis. The mean prostate volume (+/- one standard deviation) of the sample was 31.8 +/- 10.5 cc for the CT method and 27.0 +/- 8.2 cc for the US method. The prostate volumes obtained by CT were, on average, 17% larger than the corresponding volumes determined by US. The average bias between the 2 imaging methods is 4.80 cc or 15%, which is significantly larger than the clinically acceptable margin of 10%.