1 Angela Kempen February Case Study February 22, 2012 3D Conformal Radiation Therapy for Mucinous Carcinoma of the Breast History of Present Illness: JE is a 45 year-old Caucasian female who underwent a regular scheduled screening, which led to the detection of a right breast cancer. She had a screening mammography that defined an 8 millimeter (mm) irregular density in the right breast at 6 o clock posterior depth. She was referred to the Breast Center. The lesion was non-palapable. When a diagnostic mammography was performed, an irregular 13 mm focal asymmetrical density with an indistinct margin was seen in the right breast at 6 o clock posterior depth. On ultrasound, there was a subtle area of vertically oriented irregular hypoechogenicity in the 6 o clock location, 7 centimeter (cm) from the nipple corresponding to the mammographic density. She had a vacuum-assisted biopsy, with clip placement, that same day. The pathology returned as benign breast tissue with nerve bundles. The surgeon met with the patient and discussed options for management considering this could be benign, breast malignancy, or a different soft tissue malignancy. She elected to have an excisional diagnostic biopsy. During the biopsy, the surgeon felt a suspicious lump and converted the procedure to a formal lumpectomy. The lumpectomy demonstrated a 1.3 cm, grade 1, mucinous carcinoma with 1 cm of intermediate grade ductal carcinoma in situ (DCIS). No peritumoral intralymphatic tumor emboli were found. The anterior invasive tumor margin was 2 mm, inferior margin was 4 mm, and all others < 10 mm. Margins for the DCIS were 6 mm anterior and all other margins were < 10 mm. The tissue was estrogen receptor (ER) 3+ and progesterone receptor (PR) 3+. The patient was staged with a T1c N0 M0 mucinous breast carcinoma. She was referred to medical and radiation oncology for further management. Past Medical History: The patient has mild acne. She has a long smoking history. No significant history of alcohol use. The patient has no previous history of previous malignancies or radiation.
2 Diagnostic Imaging Studies: The patient had a diagnostic mammogram which identified a 13 mm abnormality at 6 o clock in her right breast. She underwent a subsequent ultrasound with abnormal findings correlating to the mammographic finding. A vacuum-assisted needle biopsy identified benign breast tissue with nerve bundles. She underwent a right axillary sentinel lymph node biopsy. A surgical excision was recommended. She underwent a needle-localization open lumpectomy, where a suspicious lump was noted. The procedure was converted from a diagnostic excisional biopsy to a formal lumpectomy, in which the surgeon took extra tissue and performed margin assessment. She had chest x-rays to evaluate any possible metastasis. Family History: The patient has a significant family history. Her mother was diagnosed with breast cancer at age 38, colon cancer at age 59, and lung cancer at 64. She is deceased at age 67. Additionally, her grandmother s sister was diagnosed with breast cancer at a young age. The P53 sequence analysis showed no mutation detected. CHK2 sequence analysis of 1100delC mutation was not detected. The patient s father has a history of diabetes and hypertension. Three of her uncles had skin cancers at ages 68, 63 and 59. Social History: The patient is married and resides with her husband. She has two children. The patient is a current every day smoker, approximately half a pack per day. She works as a technician at Dairyland Power Cooperative. Medications: The patient uses the following medications: bupropion XL and hydrocodone. Recommendations: The Radiation Oncologist recommended post-lumpectomy radiotherapy to the right breast. The logistics of radiation were discussed with the patient, in addition to the utilization of post-lumpectomy radiotherapy to reduce the risk of recurrence. The risks, benefits, side effects, and alternatives were explained. The patient understood the benefit of reduced risk of recurrence and alternatives, including any recommendations from medical oncology. The Plan (Prescription): The plan is for the patient to receive 50.4 Gray (Gy) in 28 fractions, with a boost to the planning treatment volume (PTV) lumpectomy of 10 Gy in 5 fractions using tangential treatment fields. The goal is for 95% of the boost PTV lumpectomy composite to receive 60.4 Gy.
3 Patient Setup/Immobilization: The patient was simulated in the prone position, using the prone breast board, and a wedge cushion under her ankles for support. A treatment planning computed tomography (CT) scan was competed with 2.5 mm slices through the chest region. Anatomical Contouring: The physician drew contours in the treatment planning program, Pinnacle. The physician contoured the right breast, the right breast 0.5 mm skin, the lumpectomy site, and the PTV lumpectomy (lumpectomy + 1.5 cm margin). I contoured the heart, right lung and carina. Beam Isocenter/Arrangement: I placed the isocenter mid-depth in the superior to inferior plane in the breast; however, slightly lateral. The calculation point was placed within the thickest portion of the breast tissue in order to increase coverage in the area closet to the chestwall. The first beam I placed was a right posterior oblique (RPO) at 68 degrees. The second beam placed was a left anterior oblique (LAO) at 258 degrees. I matched the divergence of the posterior field edges of the beams in order to avoid divergence into the chestwall and lungs. Therefore, the beams were not truly parallel-opposed because they were slightly less than 180 degrees apart at the central axis. A photon beam energy of 6 megavoltage (MV) was used for each beam. The same beam arrangements and energies were used for the photon boost. A 0.7 cm margin was placed around the PTV lumpectomy for the boost treatment. Treatment Planning: The physician provided a list of the objectives he would like to achieve to complete this treatment plan, using the Pinnacle treatment planning system. He listed several structures and the corresponding instructions. He required 90-95% of the breast (subtracting a 0.5 cm skin margin) to receive 50.4 Gy, in addition to 95% of the PTV lumpectomy to receive 50.4 Gy. For the boost, he required 95% of the boost PTV lumpectomy to receive 10 Gy, and for 95% of the composite boost PTV lumpectomy to receive 60.4 Gy. Other requirements included 25% or less of the ipsilateral lung to receive 20 Gy, and less than 5% of the heart to receive 25 Gy. After initial placement of the beams, the physician drew blocks to shield the lung. I computed the dose and reviewed the isodose distribution. I contoured in any hot spots, and optimized the plan by creating segments with the step and shoot multi-leaf collimator (MLC) to minimize the hot spots. Since the PTV was in close proximity to the chestwall, it was not adequately covered
4 with the prescription dose. I placed supplemental fields, of 4 Gy each, to boost the chestwall area to the prescription dose. I achieved this by contouring the cold spot located in the PTV, and then adding a field from each beam angle encompassing only this under dosed area. Supplemental fields are a way for the breast to achieve a more homogenous dose distribution to the prescription. The alternative was to move the calculation point; however, this method was creating more hot spots to segment out and decreasing coverage elsewhere within the breast. In addition, moving the calculation point created hotter areas medially and laterally in the breast, where it is not possible to segment them out. The physician evaluated the plan and prescribed to the 99% isodose line. The boost plan utilized the same beam angles and energy. A 0.7cm margin was placed around the PTV lumpectomy cavity. Weighting the RPO beam 53% and the LAO beam 47% optimized the boost plan. I showed him the boost plan and he prescribed to the 100% isodose line. He evaluated the composite and approved the plans. Figure 1: Transverse, Sagittal and Coronal slices of calculation point location
5 Figure 2: Isodose Transverse slices Figure 3: Rpo and Lao supplemental fields
6 Monitor Unit Check: Monitor unit (MU) calculations were performed to verify that the treatment planning computer was calculating properly. MU check takes several factors into consideration. These include: beam energy, field sizes (equivalent square), TMR or PDD, output factor including Sc and Sp, SSDs, physical and effective depths, inverse square, off-axis calculation point, percent isodose lines and dose. It includes all these factors in a calculation to determine the monitor units needed for treatment. The MU result is compared to the computer MU calculation. The difference between the two should result in less than 5%, which it did for this plan. I did hand calculations for each field as well, where the RPO, LAO, RPO supplemental, and LAO supplemental had 1.01%, 1.02%, 1.11%, and 1.10% percent differences respectively. Quality Assurance: A physicist performed a second check of the treatment plan and monitor unit check. It is critical to have an independent set of eyes look over the plan and additional checks. Conclusion: I chose this patient for my case study because it was the first treatment plan I completed on my own. Many breast cases are done at Gundersen Lutheran in the prone position, so I had the opportunity to observe quite a few before attempting to construct a treatment plan individually. From this treatment plan, I gained a better understanding of how tangential fields are set up, in addition to how dose distribution is affected by the placement of the calculation point. I had some assistance with the construction of the supplemental fields, but learned a lot about this technique. I learned a lot from this patient s plan and feel I am capable of creating treatment plans of similar cases in the future.
Figure 4: Dose Volume Histogram 7