Teresa Meier

Magnetic Resonance Imaging-Guided High–Dose Rate Brachytherapy for Cervical Cancer

Introduction Cervical cancer represents 0.8% of all new cancer cases and in 2012 there was an estimated 249,512 women living with cervical cancer in the United States. Concurrent chemoradiation followed by brachytherapy represents the standard of care in patients with International Federation of Gynecology and Obstetrics stage IB2 to IVA tumors (tumors larger than 4 cm or with parametrial involvement). During the first phase of treatment, patients receive external beam radiotherapy (EBRT) to the pelvis specifically targeting the cervix, uterus, and regional lymphatics. Patients typically receive 45-50.4 Gy with concurrentweekly cisplatin over 5weeks. This is followed by brachytherapy where applicators are placed in close proximity to the tumor typically via an intracavitary approach for temporary loading of a radioactive source. Brachytherapy plays a crucial role in the management of invasive cervical cancer. It has a rapid dose fall off allowing the tumor to receive a high dose while relatively sparing nearby structures such as the bladder, sigmoid, and rectum. Brachytherapy delivery options have evolved over time and can be delivered through multiple (typically 5) outpatient procedures using a high–dose rate source or during 2 inpatient stays using a low–dose rate source. By taking advantage of the geometric andphysical properties of brachytherapy, the central principle is to escalate the tumor dose to a curative rangewhileminimizing the dose and toxicity to the surrounding organs at risk (rectum, bladder, and sigmoid). Over time with advances in imaging, brachytherapy treatment planning has evolved tomeet these goals. In the early era, brachytherapy was planned using 2-dimensional images (Fig. 1). Defined points in space were used to evaluate the quality of brachytherapy implants and to estimate the tumor dose and dose to organs at risk. With the widespread use of computed tomography (CT) within radiation oncology departments, CT-based planning (Fig. 2) is now feasible. The

Dosimetric Comparison of Intensity-Modulated Proton Therapy and Volumetric-Modulated Arc Therapy in Anal Cancer Patients and the Ability to Spare Bone Marrow

Purpose Intensity-modulated radiation therapy (IMRT) has been used to spare organs at risk (OARs) in the definitive treatment of anal cancer. However, treatment continues to result in significant hematologic toxicity. In a cooperative trial assessing IMRT (RTOG 0529), the rate of grade 2+ and grade 3+ hematologic toxicity was 73% and 58%, respectively. Intensity-modulated proton therapy (IMPT) has the potential to decrease the integral bone marrow dose and dose to other OARs compared with photon therapy. Patients and Methods Computed tomography datasets of 9 patients with anal cancer previously treated with IMRT, volumetric arc therapy (VMAT), or tomotherapy at our institution were used for comparison. Both VMAT and IMPT plans were created for each patient. The IMPT plans were created using a multi-field optimized, split-target technique. The dose to OARs, including bone marrow, bladder, small bowel, large bowel, femoral heads, and genitalia, were compared using a paired t test. Results The mean bone marrow dose was 17.42 Gy with IMPT plans and 30.76 Gy with VMAT plans (P < .0001). The absolute volume of bone marrow spared 10 and 20 Gy was significantly less with the proton plans. IMPT also showed significant sparing of other OARs, including the small and large bowel, femoral heads, and genitalia. The mean planning target volume receiving at least 95% of the prescribed dose (V95) was similar with IMPT and VMAT plans, 99% and 98%, respectively. Conclusion IMPT can decrease the mean bone marrow dose compared with VMAT plans by minimizing the low dose spill associated with standard photon treatment. Prospective studies assessing proton therapy for anal cancer are ongoing to evaluate the potential for improvement in hematologic toxicity and the acute tolerance of therapy.