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Charles Poole
May Case Study
May 31, 2012
Intensity Modulated Radiotherapy of Ductal Carcinoma in Situ (DCIS) of the Left Breast
History of Present Illness: Patient JK is a 66 year old female who underwent a routine
mammogram screening in mid-September 2009. The mammogram screening revealed a cluster
of calcifications in the upper outer quadrant of the left breast. Subsequently, a stereotactic needle
biopsy revealed a high grade, non-invasive, ductal carcinoma in situ (DCIS) that was estrogen
receptor (ER) and progesterone receptor (PR) positive. For patients with positive receptors for
the hormones estrogen and progesterone, approximately two out of three breast cancer growths
may be facilitated by estrogen.1 Several anti-estrogen approaches to block the effects of estrogen
such as Tamoxifen are being used to treat hormone receptor-positive breast cancers.1 Patients
with receptor-positive tumors are more likely to respond to hormonal therapies and have better
outcomes than receptor negative patients.2 In late September 2009, JK underwent a wirelocalized tumor lumpectomy of the left breast with the greatest dimension reported as 1.3 cm
which demonstrated no invasive disease. The surgical margins were negative with the closest
margin reported at 0.5 cm. No sentinel lymph node or axillary lymph nodes were reported.
Postoperatively, the lumpectomy specimen confirmed the initial biopsy findings and JK was
diagnosed with high grade, non-invasive DCIS involving the left breast which was ER and PR
positive. Upon further evaluation from a multi-disciplinary tumor board, it was recommended to
JK that radiation therapy be considered as the primary treatment for her diagnosis. The medical
oncologist also discussed with JK the use of Tamoxifen due to the patients ER and PR positivity.
The patient weighed the risks and benefits of this drug and ultimately decided against
incorporating Tamoxifen into her treatment regimen.
In mid-October 2009, the patient was referred to radiation oncology for consultation of
post-operative irradiation to the left breast. The radiation oncologist discussed various treatment
regimens with JK, such as partial breast irradiation and whole breast irradiation. The radiation
oncologist recommended radiation treatment to the entire left breast with an additional radiation
boost treatment to the tumor bed as the standard of care for this early diagnosis. The treatment
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benefits and side effect complications were discussed and JK elected to proceed with radiation
treatment.
Past Medical History: JK has a past medical history of hypertension, migraine headaches, and
urinary incontinence. The patient’s surgical history includes bi-lateral carpal tunnel surgery,
cholecystectomy, an endoscopic retrograde cholangiopancreatography (ERCP) for retained
gallstones following cholecystectomy, and an appendectomy. In addition, the patient reported
undergoing open heart surgery for repair of an atrial septal defect. The patient also reported that
at age 32 she underwent a total abdominal hysterectomy with bi-lateral salpino-oophorectomy
and began using estrogen vaginal cream recommended by her physician at the time. JK states no
allergies or reactions to medications, food, or latex.
Social History: JK is a retired nurse from a regional medical center in the Midwest and lives in a
small rural farming community. JK is married and a lifetime non-smoker and has never used
tobacco. JK states she does not drink alcohol and denies any drug use. In addition, the patient
reported a prevalent history of cancer in her extended family and stated her brother was
diagnosed with metastatic breast cancer around 40 years of age. In addition, JK had one daughter
that was diagnosed with an astrocytoma at age 21.
Medications: JK uses the following medications: Colace, Citrucel, omeprazole, atenolol,
Hyzaar, amitriptyline at night, amlodipine, Enablex, meclizine, folic acid, docusate sodium,
multi-vitamin, calcium, vitamin D, and fish oil.
Diagnostic Imaging: In September of 2009, JK underwent a routine mammogram screening
which revealed a cluster of calcifications in the upper outer quadrant of the left breast. A
stereotactic needle biopsy was performed in the suspected calcified region of tissue within the
left breast. Pathology from this biopsy concluded the suspicious calcified tissue was a high
grade, non-invasive, DCIS that was ER and PR positive. A lumpectomy was performed with the
greatest dimension of the tumor reported as 1.3 cm with no positive margins reported. The
sentinel and axillary lymph nodes were not reported or dissected. Pathology from the
lumpectomy tissue in the left breast confirmed a diagnosis of DCIS.
Recommendations: The radiation oncologist reviewed the patient’s surgical history and
pathology reports and recommended JK undergo postoperative radiation therapy to the left breast
using an intensity modulated radiation therapy (IMRT) plan. This would be followed by a boost
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plan utilizing an enface electron beam targeting the tumor bed site within the left breast. The
recommendation to use IMRT for the initial plan was to achieve a homogeneous dose
distribution throughout the left breast volume while sparing normal structures such as the heart
and left lung that are located in proximity to the left breast volume. IMRT may lessen the
radiation toxicity effects to portions of the underlying lung and heart volumes by offering more
degrees of freedom in the planning process.3 Dose homogeneity with conventional threedimensional conformal radiotherapy (3DCRT) may be worse in patients with large breast
volumes and hotspots may increase within the target and surrounding normal tissues.3 IMRT
offers the ability of improved dose homogeneity and decreased normal tissue irradiation.3
The Plan (prescription): The radiation oncologist’s recommendation for JK was to utilize
IMRT for the left breast primary treatment. In addition, a boost region involving the tumor bed
region within the left breast was recommended by the radiation oncologist to be treated after the
left breast region was treated. The boost plan would utilize an enface electron beam targeting the
tumor bed. The prescription dose for the initial left breast IMRT plan was 46.8Gy at 1.8Gy per
fraction for 26 fractions. The dose for the left breast IMRT plan was prescribed to a left breast
volume that the radiation oncologist contoured as a target volume. The boost prescription dose to
the tumor bed region was 12.6Gy at 1.8Gy per fraction for seven fractions. The composite dose
to the left breast tumor bed region was 61.2Gy. For the evaluation of this case study, only the
primary left breast IMRT treatment technique will be discussed.
Patient Setup / Immobilization: JK underwent a computed tomography (CT) simulation scan
for radiation therapy treatment in October 2009. The patient was placed on the CT simulation
couch in the supine position with her left arm raised and positioned above her head on a MedTec, Inc. breast board immobilization device (Figure 1). The breast board was inclined 15° and
the patient’s head was turned to the right and supported with a breast board headrest (Figure 2).
The patient had a sponge under her knees for support and her right arm was at her side for
comfort. The radiation oncologist identified the superior, inferior, medial, and lateral regions of
the left breast tissue on the skin surface with BB’s. Also, the lumpectomy scar was outlined on
the patient’s skin surface by the physician with CT wire to identify the location of the scar on the
CT simulation scan.
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Anatomical Contouring: Once the CT simulation scan was complete, the CT dataset was
transferred into the Philips Pinnacle3 8.0m radiation treatment planning system (TPS). The left
breast volume was contoured on the TPS by the radiation oncologist and included the superior
portion of breast tissue extending through to the inferior portion of breast tissue. The tumor bed
was also contoured by the physician. The identification of the tumor bed proved challenging for
the radiation oncologist. Postsurgical seroma changes within the breast tissue are difficult at
times to identify. The radiation oncologist verified the location and size of the tumor bed from
previous operative reports, the seroma from the lumpectomy procedure, and the location of the
scar that was wired at the time of simulation. In addition, the left breast volume was adjusted 0.4
cm inside from the skin surface to avoid excessive dose to the patient’s left breast skin surface.
The medical dosimetrist contoured organs at risk (OR) which included the left and right lungs, a
total lung volume, the heart, carina, and normal tissue. The radiation oncologist reviewed the OR
and final adjustments were made to proceed with radiation treatment planning. The medical
dosimetrist was given a prescription objective sheet to begin treatment planning.
Beam Isocenter / Arrangement: An isocenter was placed by the medical dosimetrist in the left
chest wall adjacent to the left lung. The placement of the isocenter corresponded approximately
to the mid-plane depth of the medial and lateral tangential beams and the center of the superior
and inferior extents of the left breast volume (Figure 3). The left breast IMRT plan utilized four
coplanar tangential photon fields arranged at gantry angles of 313°, 338°, 113°, and 138°
(Figures 4-6). Each of the four fields utilized a 6 MV beam energy due to the location of the left
breast volume in relation to the skin surface. There was no collimator or couch rotation
associated with any of the four IMRT fields. The medical dosimetrist assigned the prescription to
the four fields and entered the left breast IMRT objectives in the IMRT module of the TPS. The
TPS determined and automatically adjusted the field sizes of each beam in relation to the
treatment objectives in order to accomplish the desired dose distribution around the target
volume (Figure 7).
Treatment Planning: The radiation oncologist outlined dose objectives to the left breast target
volume and OR dose constraints for this plan. The objectives of the IMRT plan were to reduce
the radiation toxicity to the heart and left lung while maintaining a homogeneous dose
distribution throughout the left breast and limiting radiation dose to the OR (Figures 8-14). For
the left breast volume, a uniform, minimum, and maximum dose objective corresponding with
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the prescribed dose were entered into the IMRT module of the TPS. In addition, the OR dose
constraints were entered into the IMRT module of the TPS for plan optimization. The OR
constraints of the plan included: the heart maximum dose was to be less than 50Gy and the
volume at 30Gy (V30) was to be less than 10%, the left lung volume at 20Gy (V20) was to be
less than 17% or as low as possible. A normal tissue objective was used to control peripheral
dose outside of the left breast target volume. The TPS utilized the direct machine parameter
optimization (DMPO) feature with 50 segments to accomplish the IMRT objectives and
parameters. Once adequate prescription dose coverage was achieved to the left breast volume,
the medical dosimetrist reviewed the OR doses, the isodose lines, and the dose volume histogram
(DVH) (Figure 15). The radiation oncologist also reviewed this plan and assigned a
normalization of 97% for the treatment plan. The monitor units were reviewed and a second
check was completed with a quality assurance (QA) computer program. The monitor units were
within tolerance for this IMRT plan.
Conclusion: This plan presented the medical dosimetrist with some challenges utilizing IMRT
for left breast treatment. One challenge was maintaining a daily reproducible setup of the patient.
In the patient setup, the left arm was raised above the head and the patient was on an inclined
breast board. This proved very challenging for the radiation therapists and the medical
dosimetrist to reproduce this setup consistently day to day. With IMRT, treatment plans are very
conformal and a homogeneous dose distribution can be achieved throughout the target volume.
However, if the patient position is slightly off-set everyday due to setup variations a geometric
miss may occur in target area. Other challenges this plan presented were related to target volume
movement from patient respiration and possible swelling of breast tissue during treatment. The
field aperture for each IMRT beam was opened 3.0 cm in order to account for breathing motion,
swelling, and setup variation. This margin adequately accounts for all these variables without
compromising the treatment plan. With some minor adjustments, the IMRT technique for the
treatment of breast cancer yields a plan whose dosimetric conformity and reduction of hot spots
is exceptional without compromising the practicality of a clinically reproducible setup.
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Figure 1: Patient position on a Med-Tec, Inc. breast board at CT simulation.
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Figure 2: Patient position from CT simulation.
Figure 3: Isocenter placement.
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Figure 4: Isocenter placement in the axial view.
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Figure 5: Isocenter placement in the sagittal view.
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Figure 6: Isocenter placement in the coronal view.
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Figure 7: Field sizes determined automatically by the TPS.
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Figure 8: IMRT dose distribution of the left breast.
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Figure 9: IMRT dose distribution of the left breast.
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Figure 10: IMRT dose distribution of the left breast.
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Figure 11: IMRT dose distribution of the left breast.
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Figure 12: IMRT dose distribution of the left breast.
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Figure 13: IMRT dose distribution of the left breast.
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Figure 14: IMRT dose distribution of the left breast.
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Figure 15: Dose Volume Histogram (DVH).
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References
1. Breast cancer hormone therapy. American Cancer Society.
http://www.cancer.org/Cancer/BreastCancer/DetailedGuide/breast-cancer-treating-hormonetherapy. 2012.
2. Uschold GM, Zhang H. Breast Cancer. In: Washington CM, Leaver D, eds. Principles and
Practice of Radiation Therapy. 3rd ed. St. Louis, MO: Mosby-Elsevier; 2010: 866-894.
3. Schubert L, Gondi V, Cannon G, et al. Dosimetric comparison of left-sided whole breast
irradiation with 3DCRT, forward-planned IMRT, inverse-planned IMRT, helical
tomotherapy, and topotherapy. Radiother Oncol. 2011;100(2):241-246.