Intensity Modulated Radiation Therapy for Squamous Cell Carcinoma of the Penis

Transcription

1 1 Louise Francis September Case Study September 23, 2011 Intensity Modulated Radiation Therapy for Squamous Cell Carcinoma of the Penis History of Present Illness: JM is a 56 year-old African American gentleman who initially presented to the emergency room with a one month history of an enlarging painful lesion on the tip of his penis, as well as a painful large mass in the right inguinal region. He underwent a CT scan of the abdomen and pelvis which revealed an abnormally enhancing penile glans with an abnormally enhancing urethra mass of 3.5 cm. Also noted was a large right inguinal and groin mass compatible with a matted group of necrotic lymph nodes with some suspicious lymph nodes superior and inferior as well. The patient was scheduled to have surgery a month later. At the time of surgery a partial penectomy, bilateral ilioinguinal lymphadenectomy, bilateral pelvic lymphadenectomy and muscle and skin graft were performed. The penile tumor measured 2.2 x 2 x 1.5 cm and involved the glans, foreskin, mucosal surface and penile urethra. The pathology revealed squamous cell carcinoma of the penis with one of eleven lymph nodes positive, thus staging the patient as T3 N1 Mx. Past Medical and Surgical History: The patient suffers from arthritis and noted having increased difficulty walking, coupled with groin pain, prior to surgery. He has a history of allergies and is currently not taking any allergy medication. Patient states that he was told that he had an irregular heartbeat during a prior emergency room visit, but has no current heart issues. The patient had a history of gonorrhea about twenty years ago and admits to being treated several times for this ailment. His past surgical history includes being circumcised at the age of eighteen and having some sort of groin operation in the 1970s. Patient also has a history of a gunshot wound in 1980, with the bullet remaining intact. There is no history of prior radiation therapy. Family History: Patient states that both parents died from lung cancer around the age of fifty nine years-old. An aunt had a female cancer in her fifties, details are unknown. Social/Sexual History: The patient started smoking at the age of eighteen and smoked at least 1.5 packs per day, but quit in September Regular alcohol use, 3 to 4 times per week (either a couple of quarts or a 6-pack of beer with intermittent vodka and gin); denies hospitalization or withdrawal from alcohol in the past. The patient started smoking crack cocaine in 1988 and had done so several times per week, but quit in August Patient

2 2 adamantly denies any IV drug use or any other drug use. Patient admits to having had unprotected sex with partners in the past (men and women), but is currently not sexually active. Sexual encounters were usually unprotected. Patient denies HIV testing, but is interested in having this done. Medications: The patient currently takes stool softeners and Percocet as needed. Diagnostic Imaging: The patient had both a pre and post-operative chest x-ray that were both within normal limits, with the exception of a bullet fragment in the right posterior soft tissue, over the right flank. A pre-operative CAT scan of the abdomen/pelvis with contrast revealed an abnormal penis, an abnormal enhanced glans and abnormal enhancing urethra back to the region of the prescrotal junction. The scan also revealed an irregular necrotic mass in the right groin, compatible with a group of necrotic lymph nodes, measuring 4.9 x 4.3 cm. The overlying skin showed evidence of thickening as well. There was also another small peripherally enhancing lymph node slightly superior and lateral to the primary mass, as well as another lymph node caudal to the primary mass. Post-operative exams included both a right and left thigh ultrasound to evaluate bilateral lower extremity edema. This exam was performed to rule out lymph congestion versus seroma formation. The final report stated that the edema was consistent with a resolving hematoma, seroma or possible lymphoceles. Oncologist Recommendation: The Radiation Oncologist reviewed with the patient treatment options for management of his T3 N1 Mx penile cancer. The patient s options included primary chemotherapy, primary radiation therapy, concurrent chemoradiation therapy or no adjuvant treatment besides pain control.the risk and benefits of all options were explained to the patient. He expressed understanding of his options and elected to have only radiation therapy. The patient was given an appointment to return for simulation following further post-surgical wound healing and edema resolution. Simulation/Immobilization: The patient was simulated supine on an egg crate cushion with his arms raised above his head resting on a wing board (with cushions) for support.the patient s legs were positioned frogged legged (heels together and drawn towards buttocks) with angle sponges for support, comfort and reproducibility. This leg position was chosen in order to decrease the amount of skin reaction in the bilateral inguinal folds. A treatment planning CT scan was then performed using 3 mm slices of the abdomen pelvis area. These images were transferred to the Phillips ADAC Pinnacle treatment planning system.

3 3 Anatomical Contouring: The physician contoured the pelvic nodal volumes, GTV1, GTV2 right, GTV2 left and the penile stump. The dosimetrist contoured the small bowel, bladder, rectum, posterior rectum, right femoral head and neck, left femoral head and neck and expanded the physician contoured items per his instructions. Given the patient s extensive pelvic surgery, it was requested that the physician review the completed contours and expansions. This allowed for volume adjustments, thus sparing as much structures of interest as possible, i.e., small bowel and rectum. Following this, the nodal volumes, GTV1, right and left GTV2(s) and the penile stumped were grouped as PTV1, PTV2 and PTV3. Figure 1: Isocenter Placement Beam Arrangement: The isocenter, placed at time of simulation, was midline and 2 cm inferior to the symphisis pubis when viewed from the anterior (Figure 1). From the lateral view, it was placed 1 cm anterior to and 2 cm inferior to the symphisis pubis. The physician voiced concerns regarding complications and requested that the daily treatment dose not be above 1.8 Gray (Gy) per fraction per day for the initial plan, but that the subsequent boost plans should be 2Gy

4 4 per fraction per day. He then decided that the patient would receive three sequential IMRT plans. The Initial IMRT plan for PTV1 (45Gy) consisted of seven 6MV beams at the following gantry angles: 180 0, 230 0, 280 0, 330 0, 30 0, 80 0 and (Figure 2). The Initial Boost IMRT plan for PTV2 (55Gy) consisted of a five field 6/18 MV mixed beam IMRT plan of gantry angles: 180 0, 252 0, 324 0, 36 0 and (Figure 3). The Final Boost IMRT plan for PTV3 (65Gy) consisted of a five field 6/18 MV mixed beam IMRT plan of gantry angles: 180 0, 240 0, 324 0, 30 0 and (Figure 3). For all fields, the pedestal angle was 0 0 and the collimator angle Figure 2: PTV (45Gy) beam arrangement.

5 5 Figure 3: PTV2 and PTV3 beam arrangement Treatment Planning: The following IMRT plans were done utilizing version 9 of the ADAC Pinnacle treatment planning system. I was given the constraints for the overall IMRT plan (total dose of 65Gy) and scaled the doses for each stage of treatment planning. The initial IMRT plan delivered a dose of 45Gy to PTV1 at 1.8Gy x 25 fractions (Figure 4). PTV1(45Gy) was defined as nodes plus 1 cm expansion, GTV1 plus 1 cm expansion and the penile stump. Of note, the penile stump was treated with 5mm of bolus for the entire course of treatment to ensure to superficial dose (see Figure 10). I listed PTV1 (45Gy) minimum dose as being 45.5Gy and maximum dose no greater than The bladder and rectum constraints were listed as 26.5Gy allowed to 50% of both volumes. The right and left femurs were not to exceed doses of 34.5Gy to 1% of their volume. Since PTV1 was generally anterior to the aforementioned structures, meeting the objective values for the initial planning was not difficult. There was a portion of small bowel that overlapped with PTV1. In an effort to reduce the amount hot spots in this area, I gave the small bowel a maximum dose constraint of 44.5Gy. The Initial Boost IMRT plan delivered an additional dose of 10Gy to PTV2 at 2Gy x 5 fractions bringing this area s total dose to 55Gy (Figure 5). PTV2 (55Gy) was defined as GTV2 (right and left), plus 0.5cm expansion and the penile stump. The PTV2 minimum dose was listed as 10.1Gy and the maximum dose no greater than 10.8Gy. The bladder and rectum constraints were listed as 6Gy maximum dose allowed to 50% of both volumes. The right and left femur constraints were set at 5Gy maximum dose allowed to 1% of both volumes. The overlapping portion of small bowel with PTV2 was eliminated to create a PTV2 minus small bowel structure. My rational for doing this was because the composite treatment objective for the small bowel was not to exceed 50Gy to 1%

6 6 of the structure. The Final Boost IMRT plan delivered an additional dose of 10Gy (Figure 6) to PTV3 (65Gy) at 2Gy x 5 fractions bringing this area s total dose to 65Gy. PTV3 (65Gy) was defined as GTV2 (right only) with 0.5cm expansion and the penile stump. The PTV3 minimum dose was listed as 10.1Gy and the maximum dose was no greater than 10.8Gy. The bladder and rectum dose constraints were the same as the Initial Boost (both IMRT plans went to 10Gy). The current field arrangement positioned all beams away from the left femur leaving the right femur constraint as 5Gy maximum dose to 1% of the volume. The PTV3 volume also overlapped with the small bowel, thus necessitating the creation of a PTV3 minus small bowel volume. Figure 4: PTV1 (45Gy) with isodose distribution. Figure 5: PTV2 (55Gy) isodose distribution.

7 7 Figure 6: PTV3 (65Gy) isodose distribution. Physics Second Checks: The departmental Quality Assurance (QA) procedure for checking IMRT plans includes sending a QA copy of the plan to ARIA (a record and verify system by Varian Medical) and performing a Monte Carlo dose verification. Once the QA copy is present in ARIA, the plan is delivered and each beam s fluence is measured. The overall percent difference for all three plans was less than 1.8%. Fluence patterns for each individual beams were measured using the Electronic Portal Imaging Device (EPID) and compared against the calculated fluence patterns from the treatment planning system. The Monte Carlo dose verification involves recalculating the beams using Monte Carlo software and applying the results to a water phantom. The results of this verification should agree with Pinnacle s dose calculation within 3%. If this does not occur, monitor units would be scaled accordingly. All IMRT plans were within acceptable ranges. Conclusion: The challenge of planning a sequential IMRT plan versus a simultaneous integrated boost IMRT is being able to control the peripheral doses. If each individual sequential plan is maximized as if it were standing on its own, when a composite (Figure 7) is done, adjustments may be needed so that the overall composite constraints will not be exceeded. I had to do a few plan revisions to ensure that the small bowel dose was not exceeded. Such adjustments may come at the risk of the physician electing to compromise coverage on the tumor. The Dose Volume Histogram (DVH) reflects the composite plan (Figures 8 and 9). The overall PTV1 coverage to 45Gy was 99.9%. Coverage for PTV2 to 55Gy was 98.6% and for PTV3 to 65Gy, 94.7%. The objective value to 50% of the rectum was 39Gy, 25.1% was achieved. The objective value to 50% of the bladder was 39Gy, 25% was achieved. The objective value to 50% of the small bowel was 1%, 0.9% was

8 8 achieved. The objective value to 1% of each femur was 50Gy. No portion of the left femur received this amount, but 5.4% of the right femur received 50Gy. The physician was informed of this and deemed it acceptable. Given that the Final Boost IMRT plan was focused to the right inguinal pelvic area, it was expected that the overall right femur objective of 50Gy to 1% of femur volume might be slightly exceeded.

9 Figure 7: Composite IMRT plan dose distribution to 65Gy. 9

10 10 Figure 8: Composite DVH I Figure 9: Composite DVH 2

11 11 Figure 10: Bolus placement over penile stump Figure 11: Wire outlining muscle/skin flap and inguinal wire (both denoting inguinal nodal disease from CT report).