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The challenge when considering curative or aggressive local control of previously irradiated recurrent tumors is that photon beam radiotherapy (including intensity-modulated radiation therapy or IMRT), carries significant risk for organs at risk from the cumulative effects of radiation.

Unlike photon beam radiotherapy, protons deposit the bulk of their energy only at the end of their path. Thus, proton radiotherapy may offer potential dosimetric and clinical advantages compared to photon radiation in patients experiencing recurrent cancers.

PRT dose distribution for recurrent rectal adenocarcinoma
Fig. 1: PRT dose distribution for recurrent rectal adenocarcinoma. (A) PRT (B) IMRT (C) PRT + Prior Treatment

The first phase of the current study at Penn studies the feasibility of re-irradiation in each of the cohorts. In cohorts where feasibility has been verified, patients can then be enrolled in the second registration phase of the study. The study evaluates patients for both acute and late toxicity.

For more information about this study, contact: John Plastaras, MD, PhD at 215-615-3714 or

The initial findings from a prospective dosimetric analysis of PRT versus IMRT in pelvic tumors were presented at the 53rd annual meeting of the American Society for Therapeutic Radiology and Oncology in October 2011.

Prospective Trial of Proton Re-Irradiation of Recurrent Pelvic Tumors: Dosimetric Analysis

Objectives: To provide an initial dosimetric analysis of PRT versus IMRT in pelvic tumors and an acute adverse effects profile for these patients. The primary endpoints were feasibility and acute toxicity.

Methods: All patients (N=10) were adults with solid tumor recurrences in or near prior radiation fields treated at least three months prior to entering the study. Malignancies included rectal adenocarcinoma, sarcoma and cervical carcinoma. Patients were further stratified by treatment volume as either low volume CTV (<250 cc, n=6) or high volume CTV (>250 cc, n=4). Fifty percent of patients received concurrent chemotherapy as 5-FU-based treatment (N=4) or cisplatin (N=1). IMRT plans were generated for backup purposes, and were optimized to deliver the same biologically equivalent dose as the PRT plans. IMRT and PRT plans were compared.

Results: Early findings suggest that in the prospective setting, PRT for the re-irradiation of recurrent pelvic malignancies reduces dose to many critical OARs when compared with intensity-modulated radiotherapy (IMRT) including bowel dose.

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

Abramson Cancer Center
Penn Presbyterian Medical Center
Medical Arts Building, Suite 103A
51 N 39th Street
Philadelphia, PA 19104

Published on: June 13, 2016

Penn Faculty Team

James Metz, MD

Chair, Radiation Oncology

Henry K. Pancoast Professor of Radiation Oncology

John P. Plastaras, MD

Chief, Gastrointestinal/Hematologic Service, Radiation Oncology

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

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