Case description

The patient is a 53-year-old female who presented with a large unresectable leiomyosarcoma of the uterus. The patient had advanced disease at diagnosis and progressed through initial chemotherapy (six cycles of Adriamycin, seven of docetaxel/gemcitabine). She underwent debulking surgery, but soon after developed a bulky pelvic recurrence. When her pain dramatically increased, she underwent imaging which noted increase in the size of her pelvic disease and hydronephrosis secondary to the mass causing obstruction of the ureter. She was also noted to have progression of metastatic disease with noted lung disease. At this juncture, radiation oncology was contacted for consideration of palliative pelvic radiation.

The clinical target volume (CTV) and the organs at risk (spinal cord, liver, kidneys, pancreas, bowels) were contoured on the treatment planning CT scan. Considering the size (945 cc) and extensive nature of the CTV, we opted for a crossfire GRID ^{Reference Pokhrel, Bernard and Mallory10,Reference Pokhrel, Halfman and Sanford11} treatment plan. Based on the CTV, we created a 3D plan with 6 evenly spaced radiation beams (gantry angles of 30, 90, 150, 210, 270 and 330 degrees, all with collimator angle 90 degrees) with 6× or 10× energy. Each beam had a static MLC pattern consisting of 1 cm wide, alternating open and closed strips, the MLC opening constrained to the CTV. The resulting dose distribution consists of cylindrical high-dose areas in the sagittal and coronal planes, separated by areas of lower dose (see Figure 1). We prescribed 18 Gy to the isocenter. The dose-volume histogram is shown in Figure 2. The mean dose to the CTV was 11·3 Gy and 10%/50%/90% of the CTV received at least 16 .0/10·4/8·2 Gy. The minimum and maximum CTV doses were 3·5 Gy and 19·0 Gy. All single fraction SBRT normal tissue dose limits of American Association of Medical Physicists Task Group 101, ^{Reference Benedict, Yenice and Followill12} shown in Table 1, were met. The treatment plan was verified by performing an independent monitor unit calculation and a dose measurement using an ArchCheck diode array (Sun Nuclear, Melbourne, FL).

Figure 1. The isodose distribution in the axial (a; CTV contour in green), coronal (b) and sagittal (c) planes. The cylindrical GRID high-dose areas are formed perpendicular to the axial plane.

Figure 2. The dose-volume histogram of the GRID plan.

Table 1. The AAPM Task Group 101 single fraction dose limits for the organs relevant to this case (all limits were met by the plan).

The patient was positioned using a cone beam CT (CBCT) with a soft tissue match to the pelvic mass. The treatment time, from the beginning of the CBCT acquisition to the end of the last treatment field, was 12 min. Despite being in considerable pain, the patient was able to tolerate the treatment of this duration easily. Three weeks after the GRID treatment, a new treatment planning CT was acquired to complete a planned split course of palliative radiation. An EBRT plan, having two intensity-modulated arcs and a prescription dose of 4 Gy × 5 to an EBRT CTV of 524 cc, was created. The treatments were delivered four weeks after the initial GRID treatment.

The patient initiated additional systemic therapy (Pazopanib) after her course of radiation and was followed with surveillance CT imaging to assess response to therapy and to assess for metastatic progression. The primary tumour volume treated with SFRT decreased substantially from 945 cc at time of treatment to 276 cc at 5·5 months and further to 17 cc at 8·5 months (Figure 3). Her abdominal symptoms remained well controlled after radiation requiring no further oral pain medications. Based on the follow-up notes of physicians (1 month post-treatment until the death of the patient), the radiation therapy did not result in any acute toxicity. Her hydronephrosis was managed with stent placement when identified and secondary to stent placement and the decrease in tumour volume did not return. At 8·5 months post-treatment, a mass in the pancreatic tail, likely a new metastasis, was identified. At 9 months post-treatment, the patient died from progression of her metastatic disease in the lungs, but the primary tumour site had still not shown evidence of local progression.

Figure 3. The CTV at treatment (green) and at the 8·5-month follow-up (magenta). Top row: 8·5 month-follow-up CT (A axial, B sagittal and C coronal plane), bottom row: planning CT (D axial, E sagittal and C coronal plane). The volume of the tumour shrunk from 945 to 17 cc.