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Jesse Speedy

Case Study

March 3, 2017

Pediatric Nodal Therapy per ARST0331 Protocol

History of Present Illness: A 13 year old white male was recently diagnosed with stage 1 grade

2B embryonal rhabdomyosarcoma of the right testicle. The patient initially presented a right

testicular torsion in September of 2016. After MRI and CT imaging there was suspicion of

malignancy and the patient underwent a hemiscrotectomy and surgical excision. Pathological

examination presented a diagnosis of embryonal rhabdomyosarcoma with negative bone marrow

biopsy. Shortly thereafter a staging PET scan revealed a suspicious retroperitoneal lymph node at

the level of the aortic bifurcation. Upon this finding the patient underwent further lymph node

dissection of the retroperitoneal nodes and spermatic cord. Biopsy showed one positive node the

peritoneum. The most distal node and para-aortic, paracaval, right pericaval, and intra-aortic

caval nodes were all negative for metastatic disease confirming a stage IIb low risk

rhabdomyosarcoma.

In January 2017 the patient and his accompanying family were referred to radiation

oncology. Per the ARST03311 protocol the patient had completed his fourth cycle and 10th week

of VAC (vincristine, dactinomycin, cyclophosphamide) and was ready for evaluation for local

control of disease via radiation therapy. The patient and his mother were educated about the

benefits and possible early and late reactions resulting from pelvis and nodal treatment. Both

patient and mother agreed to continue with the protocol approach and undergo radiation therapy.

Past Medical History: Patient has a history of Asperger’s syndrome, ADHD, bipolar disorder,

right orchiectomy with hemiscrotectomy, bone marrow biopsy, and scrotal exploration.

Social History: Pt has been Baker-acted twice for harming his sister. Patient is in seventh grade

but is currently out of school. Maternal grandmother was diagnosed with breast cancer and heart

disease. Both maternal and paternal sides of family suffer from depression, anxiety, and bipolar

disorder.

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Medications: Zofran, sodium bicarbonate, singulair, sertraline, olanzapine, megestrol, Fioricet,

ferrous sulfate, Emla, clonidine, Bactrim.

Diagnostic Imaging: MRI and CT on September 22, 2016 revealed a suspicious area in right

inguinal region. Inguinal exploration, excision of additional tissue, and a hemiscrotectomy were

performed. Pathological examination presented a diagnosis of embryonal rhabdomyosarcoma

and bone marrow biopsies were negative for malignancy. A follow up PET scan was performed

on September 29, 2016 which revealed a 1.1cm nodal area of interest. On October 17, 2016, a

retroperitoneal lymph node dissection, spermatic cord dissection, and biopsy were performed.

One positive lymph was found in the spermatic cord all other nodal dissections were negative.

Radiation Oncologist Recommendations: Patient will undergo 3D conformal nodal therapy

following the ARST 0331 protocol (group 2) for embryonal rhabdomyosarcoma patients. He will

begin radiation per the protocol after 4 cycles of VAC chemotherapy at 13 weeks from start of

the protocol. Patient will receive further chemo after radiation as dictated by the protocol.

Treatment will utilize LAO and RPO 10Mv fields. The doctor viewed a four field plan

but decided against it because the improvement in dose distribution was negligible and dose to

critical structures such as kidneys and liver was not markedly improved. The physician also

considered IMRT planning but was concerned about the volume of tissue receiving low dose.

The Plan (prescription): The Oncologist will treat the patient’s spermatic cord, para-aortic,

obturator and inguinal nodes to 41.4 Gy in 23 fractions. A .5cm bolus is to be used for daily

treatment. The first three fractions will utilize cone beam imaging, after the initial 3 fractions the

patient will receive daily kVkV imagining with cone beam imaging verification done once a

week. Additionally, the patient will undergo daily sedation due to his developmental disabilities.

This is due to the fact that the patient was unable to remain still for his initial CT simulation

which had to be cancelled and rescheduled with sedation.

Patient Setup/Immobilization: Initially a CT simulation was attempted in late Jan 2017 but was

unable to be completed due to patient non-compliance. A second simulation was completed in

early February with the addition of sedation. Patient was positioned supine, head first, arms

above head resting on a wingboard with “A” headrest. A dual-leg immobilizer was used to

stabilize the patient’s legs and pelvis. During the simulation the physician marked the patient’s

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surgical scar and facilitated the manufacture of a custom 5.cm bolus. Scan length was 209 slices

and .3cm slice thickness was used for the simulation CT scan.

Anatomical Contouring: After CT simulation the treatment planning scan was sent to Pinnacle

treatment planning system. The patient’s prior PET scan from October 2016 was fused with the

treatment planning CT to aid the physician in setting the treatment field. A “dog leg” field was

drawn by the physician to include the primary tumor surgical site, areas in occult disease and

possibly involved lymph drainage routes. The physician delineated nodes and areas of concern

but did not specify a PTV or CTV, rather his concern lied more in treating the entire volume to

his 100% isodose coverage. Critical structures in or near the treatment fields were contoured by

the dosimetrist including; the right and left kidney, rectum and bowel, liver, stomach, spinal cord

and .5cm margined cord.

Beam Isocenter/Arrangement: The patient was treated on a Varian 23IX OBI linear

accelerator. A 10-degree left anterior oblique (LAO) and 190-degree right posterior oblique

(RPO) using 10Mv energy administered the treatment plan. No collimator or couch rotation was

used. A custom blocked LAO field was a lengthy 39.26cm long and 15.91cm wide. The custom

blocked RPO field was 38.8cm long and 15.91 cm wide. Both field block patterns were custom

drawn by the radiation oncologist. The physician also placed the treatment isocenter at the

patient’s mid sagittal plane along the X-axis along the spinous processes of the vertebral bodies,

at the junction of L5-S1 along the Y-axis, and slightly anterior to mid-separation depth along the

Z-axis.

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Figure 1. Attached are the physician delineated field DRRs.

Figure 2. Attached is a 3D rendering of the patient external contour with field shown on skin.

Treatment Planning: Pinnacle TPS V14.0 was used to create a 3D conformal treatment plan.

The prescription in Pinnacle was set to 1.8Gy daily for 23 fractions for a total of 41.4Gy. The

plan dose grid was set to .3cm resolution. After the physician placed the treatment beams and

fields a dosimetrist placed a calc point to maximize field coverage while reducing hotspot.

Additionally, 10Mv energy was used to reduce the amount of 110% isodose on the plan. An even

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50/50 field weighting produced the best result in terms of field coverage and hotspot reduction.

Four control points per field were able to minimize the amount of 105% isodose and reduce

global max to 44.6Gy at 107% of Rx. The LAO was calculated to deliver 98 monitor units (MU)

and a dose rate of 400 and the RPO delivered 103 MU at a dose rate of 400. Overall plan

coverage was assessed by the physician. The plan was normalized to the 100% isodose line and

maximum 100% isodose field coverage was the planning goal specified by the physician.

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Figure 3. Attached above are axial slices of plan coverage shown in 5 slice intervals.

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Figure 4. Axial, sagittal, and coronal isodose views with added skin rendering.

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Firgure 5. Attached above is the plan dose volume histogram (DVH). Critical structure tolerance was designed according to the ARST0331 protocol. Rectum and Cord max was specified as 4500cGy. The kidney V50 was 2400cGy. Bowel V50 was 4500cGy. All structures met the protocol guidelines. Other structured not specified in the protocol were requested to by the doctor and met his personal specifications.

Quality Assurance/Physics check: After the initial Pinnacle MU calculation, a second check

was performed utilizing the Diamond Calc program. The Diamond Calc second check monitor

unit verification was determined to be within the 5% differential tolerance of the initial Pinnacle

calc. A Diamond report was uploaded into the patient treatment plan and reviewed and approved

by a physicist to ensure accuracy.

Conclusion: Treatment of protocol pediatric patients can prove to be a challenging experience

for medical dosimetrists. Critical structures appear differently and are more cramped in a

pediatric patient. This can present contouring challenges to a dosimetrist who is unfamiliar with

the variances of pediatric anatomy. The introduction of a protocol can present additional

challenges. Critical structures must be contoured per the protocol and constraints must be met as

well as is reasonably achievable based on treatment area and field boundaries. In this case the

physician desired to be actively involved in the planning process and requested several beam

configurations before he was satisfied with the result. As mentioned, more beams such as an

attempted four field arrangement did not improve field coverage and increased low dose to

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healthy tissues. The length of the treatment fields also provided challenges. The differences in

patient separation thickness made it hard to achieve a uniform dose. However, with the use of

carefully placed control points an optimal result was achieved. The only areas of less than 100%

coverage were near the bowel due to presence of air in the bowel and near the femoral heads. In

each case the 98% isodose line still provided field coverage which satisfied the physician.

Protocol patients can be challenging to the dosimetrist and a pediatric protocol patient can

present further challenges. However, thoughtful planning and a willingness to listen and

accommodate the physician can prove to be a great learning experience.

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References:

1. Walterhouse D, Pappo A, Meza Jane et al. Shorter-Duration Therapy Using Vincristine,

Dactinomycin, and Lower-Dose Cyclophosphamide With or Without Radiotherapy for Patients

With Newly Diagnosed Low-Risk Rhabdomyosarcoma: A Report From the Soft Tissue Sarcoma

Committee of the Children's Oncology Group. J Clin Oncol. 2014;32(31) 3547-3552.

http://dx.doi.org/10.1200/JCO.2014.55.6787

2. Malempati S, Hawkins D, Rhabdomyosarcoma: Review of the Children’s Oncology Group

(COG) Soft-Tissue Sarcoma Committee Experience and Rationale for Current COG Studies.

Pediatr Blood Cancer. 2012;59(1)5-10. http://dx.doi.org/10.1002/pbc.24118

3. Chao KS, Perez C, Brady L. Rhabdomyosarcoma. In Radiation Oncology Management

Decisions. 3rd Philadelphia, PA: Lippincott Williams and Wilkins; 2011: 755-763.