Brachyvision

Brachytherapy (BRT) dose planning and optimization was based on medical images obtained from Acuity simulator (Varian Medical Systems, Palo Alto, USA). Two orthogonal two-dimensional topographical images (2D-keV) were produced, and CT images were obtained through CBCT. The slice thickness was 0.2 cm, and the pixel size was 0.088 cm × 0.088 cm. All images were made within a single imaging session for a patient set-up used in BRT, with an applicator placed inside the uterine cavity and a catheter placed in the bladder. Based on the 2D-keV images, a treatment plan was made for iridium-192 source (¹⁹²Ir) with radiation energy of 0.397 MeV (treatment planning system BrachyVision version 11; Varian Medical Systems, Palo Alto, USA, algorithm TG-43). Dose distributions were calculated for a homogeneous medium, with density equivalent to that of water. The 2D-keV images were merged with the CBCT images using the rigid registration method with a particular focus on bone anatomy compatibility [11 (link)]. Then, the planned dose distributions (based on the 2D-keV images) were copied onto the CBCT images. The bladder was contoured on the CBCT images.

The following briefly describes the established HDR prostate brachytherapy treatment procedure at Sir Charles Gairdner Hospital (SCGH), Perth, Western Australia. The prescribed dose of 19.5 Gy is delivered over three fractions as a boost following external beam radiation therapy. The time between fractions is at least 6 h. In an operating theatre, 15–20 titanium 16 gauge afterloading catheters are inserted transperineally into the prostate under TRUS and fluoroscopy guidance. Four fiducial gold markers are also inserted transperineally into the prostate (two at the base and two at the apex of the prostate) using a biopsy needle. A silicone catheter is inserted through the urethra, and radiopaque packing is inserted into the rectum. CT images are obtained with the Toshiba Aquilion LB after the patient's recovery from anaesthesia. The SCGH HDR brachytherapy protocol is followed, that is helical scan, 2 mm slice thickness, 32 cm diameter field of view (FOV). A CTV and OARs (rectum and urethra) are contoured and fiducial markers and catheters are identified with the treatment planning system BrachyVision™ (version 10 and later version 13.7, Varian Medical Systems, Palo Alto, CA, USA). The dose is delivered with a single Ir‐192 source through the titanium catheters with the GammaMedplus™ iX HDR/PDR Brachytherapy Afterloader (Varian Medical Systems, Palo Alto, CA, USA).

All the patients were contoured, planned, and evaluated by a single evaluator to minimize interpersonal variations. All plans were optimized and calculated using Varian BrachyVision (version 13.0), which has both standard TG-43 formalism, and Acuros^® BV (version 1.4.0) developed by Transpire, Inc., Gig Harbor, Washington, USA, which was integrated into Eclipse treatment planning system (Varian Medical Systems Inc., Palo Alto CA, USA). Planned treatments were executed in GammaMedPlus^® iX (Varian Medical Systems Inc., Palo Alto CA, USA), with a maximum activity of 370 GBq ¹⁹²Ir stepping radioactive source to deliver the prescribed dose with decay correction. HDR brachytherapy plans were firstly performed using TG-43 formalism and inverse planning adaptive volume optimization. This was achieved with specific objectives for target volume and normal tissue sparing, followed by GBBS algorithm-based calculation (Acuros^® BV). During planning, surface mould brachytherapy with catheter flap calculation resolution was set to 1 mm as a standard to provide the best output. Similarly, the matrix grid was identically ensured in both the calculation methods. Both EBRT and HDR surface mould brachytherapy plans were evaluated at the same time in order to arrive at a conclusion on organ dose-limiting and to evaluate skin dose.

Both the BRT plans created in the BrachyVision planning system and the EBRT plans (Eclipse planning system) were exported to the RaySearch treatment planning system (version 9A), where image registration and dose distribution mapping procedures were carried out. When performing those procedures, the following data were used:

– for BRT plans, dose distribution and CBCT images with bladder contour;

– for EBRT plans, CT images with bladder contour.

To evaluate the correctness of data migration, a comparison was made between volumes of the bladder contoured in Varian systems (BrachyVision, Eclipse) and the same volumes, which were determined based on contours of those structures imported and reconstructed in the RaySearch system. These were:

– for BRT plan migration (BrachyVision → RaySearch), bladder volume calculated on the basis of the contour made in CBCT images;

– for EBRT plan migration (Eclipse → RaySearch), bladder volume calculated on the basis of the contour made in CT images.

Protocol of operations performed in the RaySearch system was as follows:

– registration of CT images (from EBRT plan) and CBCT image registration (from BRT plan);

– propagation of the bladder contour based on CBCT images (BRT) and its transfer to CT images (EBRT);

– mapping of dose distributions from the BRT plan in CT images (EBRT), according to the registration result.

Postoperative MRI and thin-cut, non-contrast CT scan were obtained prior to discharge. Commercially available treatment planning software (BrachyVision, Varian, Palo Alto, CA) was used post implant to verify 60 Gy at the 0.5 cm depth. No additional post-implant planning was routinely undertaken. Follow-up visits and imaging varied according to clinical need (typically every 3 months for the first year and every 4–6 months thereafter). An example case is shown in Figure 2.

After each insertion and subsequent recovery from sedation, the patient underwent CT simulation (3 mm slice) via Philips Brilliance CT simulator (Philips Healthcare, Inc., Andover, MA) for CT based treatment planning using the software Brachyvision (Varian Medical Systems, Inc., Palo Alto, CA). All patients were scanned in the supine position.