Brittanytbutler.weebly.com



Brittany ButlerDOS 711 Case StudyApril 8th, 2018Rare Malignancy of Neural Sheath Tumors in Spinal Canal: a case studyIllness Presentation and Discovery: Seventy-one-year-old male patient, RG, who presented to the emergency room on September 2017 with severe low back and sacral pain for 3 weeks. A computed tomography (CT) pelvis for boney anatomy was performed and revealed some mixed sclerotic and lytic changes in the weight bearing surface of femoral heads. This was considered old appearing changes of avascular necrosis. The patient was admitted to the hospital from this visit. To further evaluate the patient, a magnetic resonance imaging (MRI) lumbar with and without contrast was ordered with a diagnosis of spondylolistheses and osteoarthritis. Findings from this study revealed severe canal narrowing and multiple tumors within the spinal canal. The largest two measures at 1.5 x 1.5 cm in size and 1.7 x 1.4 cm and presented at the level of T12-L1 and L4-L5. The radiologist recommended imaging of the patient’s brain, cervical spine and thoracic spine for further assessment. On the second day of hospital admittance, RG underwent an MRI head, c-spine and t-spine imaging with and without contrast. The head and brain MRI yielded no evidence of neoplasm, a negative result. The MRI t-spine reported spinal cord compression and several enhancing soft tissue nodules within the thecal sac at T12 and L1 levels that may be indicative of metastatic disease. Later that day, a CT chest/abdomen/pelvis with contrast scan was acquired and came back negative for primary malignancy elsewhere in the body. In spinal mass cases such as this one, classification is indistinguishable radiographically, can be further narrowed down with MRI sequencing but can only officially be categorized with tissue biopsy or resection.1 Neurology was consulted for surgery to deal with the primary issue at hand of spinal cord compression.Five days later the patient had back surgery. Laminectomies were performed at the level of T12, L1 and L4 and therefore decompression of the spinal cord but the gross tumor remained. During surgery, there was resection of the 2 dominant enhancing lesions at those levels taken out in en bloc fashion. This was then sent out to pathology, diagnosing the patient from less specific malignant spindle cell tumor to more specific malignant peripheral nerve sheath tumor (MPNST) with focal epithelioid features. Marker results came back positive for S-100 and epithelial membrane antigen(EMA) and negative for chromogranin and desmin. This diagnosis is a sub category of intradural extramedullary lesions that exit along the peripheral nerve.2 This disease tends to affect the young and middle-aged adults and is very rare in comprising only 2% of all sarcomas.3 Numerically, that is 5 people per million each year.3Past Medical History: RG has an extensive past medical history including obesity, benign hypertension with chronic kidney disease(CKD) stage III, idiopathic parkinsonism, degenerative joint disease(DJD) of the lumbar spine, gastral intestinal(GI) bleed secondary to ischemic colitis and pulmonary nodules, to name a few. Patient RG does have a history of a solitary left kidney and aplastic right kidney with diffuse atrophy. Proceeding T12/L1 laminectomies and tumor resection surgery, patient experienced neurogenic bowel and bladder. This resolved during his stay on the rehabilitation unit. Patient at baseline is ambulatory and uses a 2-wheeled walker for long distances. Patient has no prior history of cancer and no prior radiation exposure. RG has no family or personal history of neurofibromatosis, which is when the tumor suppressor, neurofibromin, loses its function. This is noted due to 50% of cases in MPNST occur in correlation to neurofibromatosis and the remainder of the percentage arise sporadically or after radiation therapy.3Social History: Patient is a former smoker of 1 pack per day for 50 years with a quit date on 8/2014. Alcohol use is reported as rarely uses and smokeless tobacco as never used. RG is a retired accountant, married with 2 children. Patients mother deceased at age 55 from pancreatic cancer and had a history of solitary kidney due to injury. Patients father deceased at age 91 with a history of lung disease and was a tobacco smoker. Patient’s brother is alive and well with no major problems reported. Radiation Oncology Consultation: A little over a month after the patient’s laminectomy surgery and after he was recovered, he had his consultation with oncology. Surgery dealt with the immediate problem of cord compression but gross tumor remains. Due to chemotherapy showing no beneficial results in MPNST cases, medical oncology did not recommend. Radiation therapy was presented as an option to control the cancer for a period and delay progression. This course would be palliative as the radiation oncologist felt it was not curable. Benefits, risk and side effects of radiation therapy was discussed with the patient and his wife. There is concern to patient’s single good kidney and avoidance will be strived for in planning. Alternatives were presented to the patient as well, such as observation. Patient wishes to proceed with radiation therapy treatments.Radiation Therapy Prescription: The patient was prescribed radiation at the level of T12 through sacrum. The patient would receive a total dose of 5940 cGy in 33 fractions. The primary volume is from T12 through sacrum, receiving 5040 cGy in 28 fractions. The boost volume is at the level of L2 through sacrum and will receive 900 cGy in 5 fractions. The boost will be performed in a sequential fashion. In this case, treatment prescription dose is challenging due to MPNST rarity and the fact that the PTV is in some parts defined within the spinal cord. Being that the cord is a serial organ, it is difficult to find a balance between healthy portion of the organ sparing and PTV coverage. Therefore, the MD decided the boost treatments superior edge of the field would be just below where the spinal cord ends. Per RTOG protocol, the spinal cord is limited to 4500 cGy as a total maximum dose.4 Intensity modulated radiotherapy (IMRT) was the decided treatment method due to target volumes proximity to critical structures. Narrow margins on tumor volume will also be defined to ensure maximum organ sparing of healthy tissue. It will be planned on volumetric modulated arc therapy (VMAT), Varian’s Rapid Arc Technology, for the IMRT planning with 6 MV beams. Image guided radiation therapy (IGRT) will be performed daily with ExacTrac system. Patient Simulation: Patient undergoes CT simulation scan without intravenous contrast injection or GI contrast agents. Patient is positioned supine with Total Body Fix positioning device (Figure 1). A knee sponge is molded under this device to ensure patient comfort. Patient’s arms are above his head with support from wing board device and triangular sponge placement (Figure 2). Metal bb markers are placed on patient before the scan to be able to correlate user origin on planning system. After CT scan acquired and MD approved, permanent marker drawn on patient to replace bb’s with tegaderm tape placed over. Patient to have isocenter verification done on the day before first treatment. Contouring: CT volumetric data set sent to MIM software for MRI fusion of scan that was performed 4 days prior. Dosimetrist performed fusion utilizing the rigid method to combine the two scans. Fusion approved by MD and sent to Eclipse treatment planning program. MD contours clinical target volume (CTV) and will create planning target(PTV) volume. The cauda equina is defined at mid L1 to sacrum. The spinal cord is contoured as mid L1 through superior portion of the field. The cauda equina and spinal cord are combined to form the PTV. The CTV encompasses the entire spinal canal. A structure was also created with 1.2mm added around the entire cord volume and named “cord 5mm.” Using the Eclipse software, the dosimetrist draws contours that will be reviewed by the MD. This includes the liver, stomach, spinal cord, bowel and left kidney. Treatment Planning: The patient’s treatments will be performed on Varian True Beam Linear accelerator using ExacTrac for daily IGRT. The planning system utilized is Eclipse, version 13. Isocenter is placed in the middle of the total PTV around disk space level of L3/L4 within the patient’s spinal canal (Figure 3). The same isocenter placement will be used for both the primary treatment and boost treatment prescriptions. All beam energies for both plans will be 6MV.The primary treatment to 5040 cGy in 28 fractions includes 4 coplanar and full arcs from 181? to 179?. The arcs started in the clockwise directed and then alternated to counter clockwise and back. The collimator angles are 330?, 350?, 10?, and 30?. These angles gave the best coverage for the longer length of the PTV. Arc 2 and 3 have full modulation range of the multileaf collimators (MLC) due to the X distance being under 15 cm. Even with arc 1 and 4 being over, the MLC patterns were satisfactory in obtaining objectives.All dose constraints, except for cord 5mm structure, given for the primary plan were to be applied to composite and therefore will be discussed later (Figure 5). For the initial 5040cGy plan, the objective was given to have less than 5150cGy for first 28 treatments and/or as low as possible to the cord 5mm structure. This calculates to be less than 102.1% allowance. To obtain this, the dosimetrist tightened his optimization objectives to three upper limits of 0% above 5040 cGy and assigned them the highest priority. He also created a PTV inner ring structure and gave a lower limit of 100% of volume gets 5040 cGy and assigned its priority the same as the PTV volume. This then told the computer to cool the center where the cord was first and to push dose to the outer portion of the ring.The boost treatment to 900 cGy in 5 fractions included 4 coplanar full arcs as well. These alternated from counter clockwise to clockwise from 179? to 181?. The collimator angles were 330?, 30?, 15?, and 345?. Objective dose constraints were set similar to the primary treatment rational. Instead of spinal cord, as it was no longer in boost field, the cauda equina was set with three upper limit objectives of 0% volume above 900 cGy and given the highest priority. There was also an inner ring boost structure created so the spinal canal would receive no more that 102%. For both plans, the patients only viable kidney was given upper limit objectives to limit dose to less than 25% of kidney volume.The composite dose volume histogram (DVH) met all the objectives provided on the MD wish list (Figure 4). For the PTV, the MD wanted 95% receiving prescription dose with less than 105% hot spots. At 5940 cGy, the PTV was covered at 95.97% with hot spot maximum of 4%. The cord structure the MD drew, he wanted the max dose below 5150 cGy for first 28 fractions and it came in at 5126.8 cGy. The left kidney was given an objective of 10% of volume less than 1800 cGy. This was well below being that at 10% volume the dose was 831 cGy. The bowel and stomach maximums were defined at 4500 cGy and they were 1443 cGy and 418 cGy. The liver mean was to be kept below 1000 cGy and came in at 391 cGy. The challenging objective in this case was keeping the PTV above 95% coverage and less than 105% hot but the planning dosimetrist was able to achieve (Figure 6). The patient followed up three months later with an MRI of his total spine. Unfortunately, the results showed multiple enhancing lesions at T10-T11. The progression occurred just superior to treatment field. For this patient’s case, surgery is not an option due to health and chemotherapy has not proven to be effective. Another round of radiation treatment was once again discussed and agreed to by the patient to proceed. A new CT simulation scan would need to be acquired to view more superior portions of the patient’s anatomy. Some considerations will need to be addressed in creating the next plan. A match line will have to be decided as the field would have to abut prior treatment volume. Another consideration will be accounting for the dose already received to the organs at risk. The treatment prescription the MD decided is on was from T10 to T11 at 5040 cGy in 28 treatments. If they would perform VMAT, IMRT beam split or a combination of the two was yet to be decided. Quality Assurance/Physics Check: Our current RadCalc version software is not sophisticated enough to perform calculation second checks on IMRT/VMAT plans. For a second check method, diode measurements are performed by physics. The physics check for the plan was performed using Sun Nuclear Arc Check phantom containing 1 cm spaced diodes. There were several absolute dose points that were compared to planning system’s calculations. For the initial treatment of PTV that was including the entire spinal canal, 1386 diode measurements were made and 92.9% agreed within 3% or 3mm. On the boost portion of the plan, 1006 diode measurements were made and 97.2% agreed within 3% or 3mm. These results between the planned and the measured values are satisfactory and pass the physics check.Conclusion: The rarity of MPNST creates a challenge for radiation therapy oncology providers as there is not an abundance of data as compared to other malignancies. In this patient’s case MPNST was considered the patients primary malignancy and causing spinal cord compression. With the spinal cord being one of the most sensitive organs at risk, and part of the PTV, made this case heightened in striving for accuracy. VMAT planning was ideal for this case as the PTV was circular in shape, making the 360? arcs beneficial in conforming to the target. It also worked to the planner’s advantage that the organs at risk objectives were reasonable to achieve. With the patients only viable kidney being the left, the right kidney dose was not of concern and the constraints on the left were well within achievable range. This case was beneficial to my learning as an intern in that I have not yet had experience with VMAT planning. The concept of why structures were created, such as an inner ring, was not easy to understand at face value. With help from the planning dosimetrist in explaining, I feel I can have a better basic knowledge of these structures and how they aide in meeting the MD objectives.Some concepts I struggled with was initially realizing how all the pieces fit together for this patient. With an extensive medical history, it was challenging to know what was relevant to this disease and what was not beneficial to go into detail. To add to that, this is a rare malignancy that does not necessarily have a workflow, or protocol, and can vary in location throughout the body. I feel after researching this patient, I have increased knowledge of a patient’s overall experience and the challenges that arise for doctors in making the “right” decision when it is not always so black and white. ReferencesRadioed. Spinal Nerve Sheath Tumors. Radiopaedea Website. . Accessed April 3, 2018.Hsu W, Jallo GI. Chapter 100 – Pediatric spinal tumors. Handb Clin Neurol. 2013;112:959-965. M, Demicco EG, Carcia R, et al. Malignant peripheral nerve sheath tumors. Oncologist. 2014;19(2):193-201. Foundation. A prescription template for RTOG protocols. RTOG Foundation Website. . Accessed April 6, 2018.FiguresFigure 1. Full body image of patient in Total body fix with knee sponge support and wing board.Figure 2. Superior view of patient in Total Body fix, wing board with triangular sponges for arm placement.Figure 3. From left to right, axial, 3D representation, coronal and sagittal view of T12-sacrum isocenter.Figure 4. Composite DVH of treatment volumes. StructureInstructionsPTV95% gets Rx dose, >99% gets 95% of Rx dose. Hot spot <5%.LiverMean < 10 GyBowel and stomach<5150cGy in for first 28 treatments, try to get as low as possible.Cord 5mmMax 45 Gy, will accept up to 50 Gy if necessary.L KidneyNot more than 10% of the volume can receive > 18 Gy, V6Gy < 30%.Other Comments5040 cGy/28 fractions using VMAT. Will design boost later. Final doses will be 5940/33 fractions. All dose constraints above for composite except cord5mm which is for initial 28 fx.Figure 5. Radiation oncologist wish list.Figure 6. Composite axial slices from superior to inferior in isodose lines dose distribution. ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download