Application technique

The procedure was conducted under general (Patients 2, 3 and 4) or local anesthesia (Patient 1). Under local anesthesia, we have used 1% Lignocaine after former premedication with Midazolam and Fentanyl. Steel or titanium needle applicators, as well as elastic interstitial applicators were used in brachytherapy. In sites, where it was impossible to drive the applicators through the lesion, needle applicators were used. The applicators had an advantage of being well visible in tomographic examination. A disadvantage was the necessity of conducting the treatment in several stages, which was associated with the need for performing several application procedures, as well as several steps of treatment planning. Elastic applicators were used in cases when it was possible to form an applicator outlet on the other side of the tumor. Due to poor visibility of the placed applicators, it was necessary to apply markers just after the application. After applicators were in place, they remained in the lesion throughout the treatment process. The application was conducted under guidance of CT device located in the operating room and moving on rails. Both, the CT device and the operating table movement were controlled using a console located in the operating room. SOMATOM Sensation OPEN CT device (Siemens AG, Munich, Germany) was used including optional fluoroscopy accessory from Siemens.

Before the commencement of the treatment, CT examination was conducted with or without contrast agent, and then, the image was fused with the previously performed CT or magnetic resonance imaging (MRI) examination. The extent of the tumor was determined on the basis of the conducted examinations and projected on patient’s skin using laser beams. Then, under continuous CT guidance, applicator needle or elastic applicator lead was percutaneously (transdermally) inserted into the tumor in a way facilitating irradiation of the whole tumor area, and simultaneously controlling the position of the needle against the adjacent structures (Figure 1). If it was possible, the applicators were inserted in such a way that their layout in the lesion was possibly most parallel, and their distance from one another as well as from the edge of the tumor was not greater than 2 cm. Technical difficulties were encountered in cases requiring the insertion of an applicator under different angles towards the tomographic image plane. It was associated with the necessity of constant control of needle position at the time of insertion on several tomographic scans simultaneously. Due to little respiratory movement of anatomic structures in head and neck region, CT guided insertion of the needle was precise and relatively safe, despite close vicinity of many important organs. Only the region directly under the needle was not sufficiently visible due to artifacts related to the material, of which the needle was made. Needle applicators were located in the lesion only during each fraction of treatment but elastic applicators, used for their stabilization, remained in the tumor from the beginning of the first to the end of the last fraction (Figure 2).

Computed tomography-guided applicators, next steps (Patient 4)

Patient 4 with applicators

On the completion of a single treatment session, CT scan was performed to plan further treatment, and then, after drawing the clinical target volume (CTV) and organs at risk (OAR), time and place of ionizing radiation source stopping points were planned. BrachyVision v.10 treatment planning system from Varian (Varian Medical Systems, Inc., Palo Alto, CA, USA) was used (Figure 3). Dosimetry parameters were reported according to the guidelines outlined in ICRU Report 58 [4]. The condition for treatment plan acceptance was encompassing the total CTV with a dose constituting 90% of the planned dose (D₉₀). Additionally, the minimum significant dose for local control of the tumor was reported (D₁₀₀). These doses and total doses were converted according to linear quadratic model of biologic effective dose (BED), using the following formula BED = nd (1 + d/(α/β)), where d – fractional dose, n – number of fractions, α/β – alpha/beta ratio, in case of squamous cell carcinoma of head and neck it is 10. In order to compare them with conventional fractioning of 2 Gy, the doses were converted to dose equivalent 2 Gy (DEQ₂) using the following formula: DEQ₂ = BED/(1 + 2/(α/β)). In order to facilitate the evaluation of correlation between the dose and possible future damages, the volume receiving 100% of the prescribed dose was reported, as well as high dose areas receiving 150% of the prescribed dose (V₁₅₀) and 200% of the prescribed dose (V₂₀₀). Biologic effective dose and DEQ₂ were calculated for each fraction.

The image-guided high-dose-rate (IG-HDR) plan for patients. The color code for the isodose color wash is as follows: red 200%, orange 150%, yellow 110%, green 100%, blue 90% (transverse view – left, sagittal view – right)

Due to various locations, doses received by critical organs were also reported. Depending on the type of the organ, either maximum dose (D_max) or dose per 1 cm³ of the organ located in the maximum dose area (D_1cm³) were reported. The doses were converted to BED and to DEQ₂ according to the linear quadratic model, adopting α/β ratio value of 3 for future radiation induced complications.

The treatment was conducted using 24 channel Gammamed Plus device from Varian (Varian Medical Systems, Inc., Palo Alto, CA, USA). After completion of irradiation session, applicators were removed from lesions. If it was necessary, the removal was conducted after premedication with opioid analgesics. Because of the risk of hemorrhage, the surgical procedure was conducted in an operating room equipped with GE OEC 9900 Elite System (GE Health Care, Milwaukee, WI, USA), and offering the possibility of interventional embolization of a damaged vessel by a surgical radiology specialist. After applicators removal, CT scan with contrast was performed in order to rule out potential complications, especially fresh bleeding in the applicator area.