Evrim Tezcanli

Comparison of 3D dose distributions for HDR 192Ir brachytherapy sources with normoxic polymer gel dosimetry and treatment planning system.

Radiation fluence changes caused by the dosimeter itself and poor spatial resolution may lead to lack of 3-dimensional (3D) information depending on the features of the dosimeter and quality assurance of dose distributions for high-dose rate (HDR) iridium-192 ((192)Ir) brachytherapy sources is challenging and experimental dosimetry methods used for brachytherapy sources are limited. In this study, we investigated 3D dose distributions of (192)Ir brachytherapy sources for irradiation with single and multiple dwell positions using a normoxic gel dosimeter and compared them with treatment planning system (TPS) calculations. For dose calibration purposes, 100-mL gel-containing vials were irradiated at predefined doses and then scanned in an magnetic resonance (MR) imaging unit. Gel phantoms prepared in 2 spherical glasses were irradiated with (192)Ir for the calculated dwell positions, and MR scans of the phantoms were obtained. The images were analyzed with MATLAB software. Dose distributions and profiles derived with 1-mm resolution were compared with TPS calculations. Linearity was observed between the delivered dose and the reciprocal of the T2 relaxation time constant of the gel. The x-, y-, and z-axes were defined as the sagittal, coronal, and axial planes, respectively, the sagittal and axial planes were defined parallel to the long axis of the source while the coronal plane was defined horizontally to the long axis of the source. The differences between measured and calculated profile widths of 3-cm source length and point source for 70%, 50%, and 30% isodose lines were evaluated at 3 dose levels using 18 profiles of comparison. The calculations for 3-cm source length revealed a difference of > 3mm in 1 coordinate at 50% profile width on the sagittal plane and 3 coordinates at 70% profile width and 2 coordinates at 50% and 30% profile widths on the axial plane. Calculations on the coronal plane for 3-cm source length showed > 3-mm difference in 1 coordinate at 50% and 70% and 2 coordinates at 30% profile widths. The point source measurements and calculations for 50% profile widths revealed a difference > 3mm in 1 coordinate on the sagittal plane and 2 coordinates on the axial plane. The doses of 3 coordinates on the sagittal plane and 4 coordinates on the axial plane could not be evaluated in 30% profile width because of low doses. There was good agreement between the gel dosimetry and TPS results. Gel dosimetry provides dose distributions in all 3 planes at the same time, which enables us to define the dose distributions in any plane with high resolution. It can be used to obtain 3D dose distributions for HDR (192)Ir brachytherapy sources and 3D dose verification of TPS.

Monitoring the Maintainability of Deep Inspiration Phase with Cine Acquisition in Patients with Left-Sided Breast Carcinoma Receiving Radiotherapy

Objectives: This prospective study aimed to investigate whether left-sided breast carcinoma patients could maintain deep inspiration (DI) during radiotherapy in order to reduce exposed heart volume. Methods: Twenty-one patients with left breast carcinoma receiving adjuvant breast radiotherapy were included in this study. Breath hold time was monitored using the cine acquisition mode (CAM) of a linear accelerator during treatment in every fraction. Simulated kV and treatment field images were compared to determine whether the patient could achieve the same “breath holding level” (BHD). Maintenance of BHD during beam on time was referred as “maintenance of intrafraction breath holding level” (BHM), and chest wall displacement during each treatment was measured in order to verify the BHM. Furthermore, the relation between treatment time and patient compliance was studied. Results: Sixteen patients were treated according to the deep inspiration breath hold (DIBH) protocol while 5 patients, excluded due to noncompliance, received their treatment without breath control. For the patients treated with DIBH protocol, maximum heart doses without breath control and DI phases were 3044 cGy and 1347 cGy, while mean heart doses were 348 cGy and 239 cGy, respectively. Median BHD and BHM displacements were 0.2 cm (0– 0.86 cm) and 0.07 cm (0–0.31 cm), respectively. BHD differences were <0.4 cm in all but 2 patients. Treatment time did not affect patient compliance. Conclusions: DI phase was successful in reducing heart dose and 76.2% of the patients were eligible for DIBH. Treatment during moderate DI phase can be used for selected left-sided breast carcinoma patients and CAM could monitor safe execution.

Tumor-stage mycosis fungoides of the vulva successfully treated with local low-dose radiotherapy

Mycosis fungoides (MF) is the most common type of primary cutaneous T‐cell lymphoma. According to the proposed guidelines for MF, skin‐directed therapies are the treatment of choice for patients with limited stage disease. We present a case of early‐stage MF, who progressed to tumor‐stage MF during the postpartum period, showing a solitary ulcerated tumor on the vulva, which was successfully treated with local response‐based, low‐dose radiotherapy.

SU‐F‐J‐129: Verification of Geometric and Dosimetric Accuracy of Respiratory Management Systems Using Homemade Phantom

PURPOSE Different placements of Infrared Cameras (IRC) in CT and treatment rooms can cause gating window level (GWL) variations leading to differences between GWL used for planning and treatments. Although, Varian Clinac DHX-OBI sytem and CT are equipped with the same kind of IRC, Truebeam STx (TB) has a different type of IRC known as banana type. In this study; geometric and dosimetric accuracy of respiratory management system (RPM) for different machines were investigated with a special homemade phantom. METHODS Special phantom was placed on the respiratory simulator machine and a CT data set was obtained at the end of the expirium phase (EOE). Conformal and IMRT plans were generated on the EOE CT image series for both DHX-OBI and TB LINACs while a VMAT plan was generated only for TB.The acquired respiratory graphs in the CT were directly sent to DHX-OBI system, and they were converted with software before sending to TB. EBT3 films were placed inside the phantom and were irradiated using RPM system with two machines for different plans. Planar dose distributions were compared with gamma analysis (GA) method (3mm, %3) to evaluate planned-measured dose differences. In addition, radio-opac marker was placed in the center of the phantom to evaluate the geometric accuracy of treatment field with gated flouroscopy (GF). RESULTS There were no shifts detected between planning and treeatment GWL for both DHX-OBI and TB. Difference on the GF image between digital graticule and radio-opac marker was <1mm for TB and 1mm for DHX-OBI. Although, GA agreement was 97% for conformal and IMRT techniques in TB, it was 96% for VMAT technique. While GA agreement was 98% for conformal technique in DHX-OBI, IMRT was 95%.ConclusionThis study showed that RPM can be used accurately in spite of different IRC placements or different types of ICR used.

SU-E-J-75: Importance of 4DCT for Target Volume Definition in Stereotactic Lung Radiotherapy

PURPOSE We aimed to investigate the importance of 4DCT for lung tumors treated with SBRT and whether maximum intensity projection (MIP) and free breathing (FB) images can compansate for tumor movement. METHODS Six patients with primary lung cancer and 2 patients with lung metastasis with a median age of 69.5 (42-86) were included. Patients were positioned supine on a vacuum bag. In addition to FB planning CT images, 4DCT images were obtained at 3 mm intervals using Varian RPM system with (Siemens Somatom Sensetion 64). MIP series were reconstructed using 4DCT images. PTV-FB and PTV-MIP (GTV+5mm) volumes were contoured using FB and MIP series, respectively. GTVs were defined on each of eight different breathing phase images and were merged to create the ITV. PTV-4D was generated with a 5 mm margin to ITV. PTV-MIP and PTV-4D contours were copied to FB CT series and treatment plans for PTV-MIP and PTV-FB were generated using RapidArc (2 partial arc) technique in Eclipse (version 11, AAA algorithm). The prescription dose was 5600cGy in 7 fractions. ITV volumes receiving prescription dose (%) and V95 for ITV were calculated for each treatment plan. RESULTS The mean PTV-4B, PTV-MIP and PTV-FB volumes were 23.2 cc, 15.4cc ve 11cc respectively. Median volume of ITV receiving the prescription dose was 34.6% (16.4-70 %) and median V95 dose for ITV was 1699cGy (232cGy-5117cGy) in the plan optimized for PTV-FB as the reference. When the plan was optimized for PTV-MIP, median ITV volume receiving the prescription dose was 67.15% (26-86%) and median V95 dose for ITV was 4231cGy (1735cGy-5290cGy). CONCLUSION Images used in lung SBRT are critical for treatment quality; FB and MIP images did not compensate target movement, therefore 4DCT images should be obtained for all patients undergoing lung SBRT or the safety margins should be adjusted.

The Great Mimicker: Zona Zoster at the Mastectomy Site Causing Contralateral Intramammary Lymph Node Enlargement

Zona zoster is rarely observed in patients with malignancy; when present, it follows a dermatomal fashion. Involvement of widely separated regions is very rare. Hereby, zona zoster causing enlarged intramammary lymph nodes (IMLN) in the opposite breast is reported for the first time in literature. The masses were hypoechoic on US with no hilum and hypervascular on color Doppler US. MRI showed hypointense masses with type 3 time-intensity curve and adjacent vessel sign. The complete regression of the nodes after the antiviral therapy confirmed the diagnosis. In breast cancer patients, IMLN enlargements may mimic breast cancer metastasis, and zona zoster infection of the mastectomy site may present with contralateral IMLN enlargement due to altered lymphatic drainage. When breast US is not sufficient for the differential diagnosis, breast MRI may warrant proper diagnosis, and prevent unnecessary biopsies. Antiviral treatment with followup would be sufficient for management.