Image demonstrates a comparison of standard photon therapy (left) to proton therapy (right)
Figure 1: The green colorwash demonstrates the 20 Gy isodose line for a five non-opposed co-planar field IMRT plan (left) compared to a two field IMPT plan (right) that were both prescribed to 50.4 Gy. It is obvious that the mean heart dose is substantially less, but in this case the maximum dose to the aortic valve prior to a planned replacement is less than four Gy.

Radiation oncologists at the Roberts Proton Therapy Center have developed protocols, techniques and approaches expressly for patients who have complications that might alter the efficacy of, or preclude, radiotherapy. These complex presentations typically involve the presence of cancer in proximity to radiosensitive organs and comorbidities that necessitate dose reduction.

Standard cancer radiotherapy involves an intricate balance to determine the minimum exposure required to treat malignancy without toxicity to nearby normal tissues. On one hand, overexposure to standard radiotherapy may increase the risk of adverse events. Efforts to minimize radiation exposure, on the other hand, may result in inadequate dose delivery, increasing the risk of cancer recurrence.

The benefits of radiotherapy are diminished when patients have comorbidities that may be exacerbated by significant radiation exposure. Although not ideal candidates for standard radiotherapy, these complex patients may benefit from proton therapy, which can preserve the therapeutic ratio and deliver safe treatment.

Among the important properties of proton therapy is a rapid dose fall off at the distal edge of the target (Bragg-Peak effect), a characteristic that allows for significant reductions in integral dose to normal organs by comparison to standard photon therapy (Figure 1). [1] In addition, proton therapy permits conformal, precision treatment delivery, improved dose homogeneity and the opportunity for dose escalation to achieve optimal radiation dosing to the target lesion.

Case Study

Mr. G, a 68-year-old man, was referred to the Roberts Proton Therapy Center for post-operative radiotherapy after he was found to have mediastinal lymph node involvement at the time of his lobectomy, where the initial PET/CT showed no evidence of abnormal lymph nodes. Typically, it is recommended that patients diagnosed with stage III lung cancer undergo sequential chemotherapy followed by radiation.

Mr. G’s case was made more challenging, however, by a diagnosis of symptomatic severe aortic stenosis prior to surgery. As a temporizing measure, Mr. G then had a valvuloplasty with a planned valve replacement to follow the completion of his treatment for cancer. In addition to aortic stenosis, Mr. G’s condition was complicated by the presence of atrial fibrillation and rapid ventricular rate (RVR) during his original lobectomy. Post-operative radiotherapy in this situation has been a challenge causing real morbidity and mortality in the past.

Improvements in techniques over the last decade have improved the safety of this treatment, but in Mr. G’s case, there were several incentives for a reduction in radiation dose. Because the disease to be targeted was located in the mediastinum, a substantial decrease in dose to the heart would be appropriate. A further diminishment in dose to the aortic valve was required to decrease complications arising from the anticipated valve replacement post-radiotherapy. The presence of atrial fibrillation and RVR at his prior surgery also mandated dose reduction.

A multidisciplinary discussion with Mr. G’s cardiac surgeon then took place to determine which areas of the vasculature should be avoided to minimize this risk. Mr. G received radiotherapy at the Roberts Proton Center for five and a half weeks, with minimal dosing to his heart and nearly no dose to the area of the aorta valve. Three weeks after the conclusion of radiotherapy, he had a transaortic valve replacement (TAVR) procedure to correct his aortic stenosis.

At his one-year follow-up, he noted no deterioration in his capacity for normal daily activity. No evidence of cancer recurrence was noted at this time.

 

ACCESS

Penn Radiation Oncology
Perelman Center for Advanced Medicine
Concourse Level
3400 Civic Center Boulevard
Philadelphia, PA 19104

Published on: March 19, 2018

References

1. Chang JY, Jabbour SK, De Ruysscher D, et al. Consensus Statement on Proton Therapy in Early-Stage and Locally Advanced Non–Small Cell Lung Cancer. Rad Oncology 2016;95:505–516.

About Penn Radiation-Oncology

As a national leader in basic science, translational research and clinical trials, and one of the largest and most respected programs in the world, Penn Radiation Oncology offers a variety of innovative treatment options to patients with cancer, as well as the latest treatment options--including proton therapy--before they are widely available elsewhere.

Penn Faculty Team

Steven Joel Feigenberg, MD

Chief of Thoracic Service, Perelman Center for Advanced Medicine

Vice Chair of Clinical Research, Department of Radiation Oncology

Professor of Radiation Oncology at the Hospital of the University of Pennsylvania

Abigail T. Berman, MD, MSCE

Associate Director, Clinical, Penn Center for Precision Medicine

Assistant Professor of Radiation Oncology at the Hospital of the University of Pennsylvania

Keith Cengel, MD, PhD

Associate Professor of Radiation Oncology at the Hospital of the University of Pennsylvania

William Levin, MD

Medical Director, Penn Radiation Oncology Network

Associate Professor of Clinical Radiation Oncology

Samuel D. Swisher-McClure, MD, MSHP

Assistant Professor of Radiation Oncology at the Hospital of the University of Pennsylvania

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