Proton Therapy Reduces Normal Tissue Dose in Extended-Field Pelvic Radiation for Endometrial Cancer.

Melody J Xu,Jennifer Vogel,Huifang Zhai,Maura Kirk,Lilie L Lin,Stefan Both,Alisha Maity

doi:10.14338/ijpt-17-00027.1

Abstract

We dosimetrically compared pencil beam scanning (PBS) proton therapy and intensity-modulated radiation therapy (IMRT) for pelvic and para-aortic lymph node disease in endometrial carcinoma and present acute toxicities associated with extended-field PBS. Twenty-five patients with locally advanced endometrial malignancies were enrolled in an image-guided registry study. Seven of these patients were treated with PBS, and 18 patients were treated with IMRT. Organs at risk included pelvic bone marrow (PBM), small bowel (SB), large bowel (LB), rectum, bladder, and kidneys. The IMRT and PBS dosimetric parameters were compared using Wilcoxon rank-sum tests. Compared with IMRT PBM dose-volume histograms, PBS resulted in significantly lower dose volumes from 0 to 26.0 Gy (P < .05) and higher dose volumes from 33.9 to 42.9 Gy (P < .05). Overall, PBS resulted in 22% lower median PBM volume irradiated to 10 Gy (RBE) (PBS 71.3% versus IMRT 93.4%, P < .001) and 14% lower median volume irradiated to 20 Gy (RBE) (PBS 65.1% versus IMRT 79.4%, P < .001). Compared with IMRT, PBS also significantly reduced SB dose volumes from 0 to 27.5 Gy, LB dose volumes from 0 to 31.6 Gy, bladder dose volumes from 0 to 27.3 Gy, and rectal dose volumes from 0 to 7.6 Gy (all P < .05). However, PBS resulted in higher rectal dose volumes compared with IMRT from 26.0 to 48.4 Gy. Grade 3+ hematologic toxicities were present in 2 (11%) IMRT-treated patients and no PBS-treated patients. No grade 3+ gastrointestinal or genitourinary toxicities were present in either treatment group. In endometrial carcinoma, extended-field PBS is clinically feasible, resulting in statistically significant dose reduction to PBM as well as SB, LB, and bladder in the lower dose regions.

Highlights

Extended-field radiation therapy (RT) that includes the pelvis and para-aortic lymph nodes (PALN) is indicated in patients with gynecologic malignancies with suspected or confirmed PALN disease (gross disease, fluorodeoxyglucose (FDG) avid, or pathologically confirmed)
pencil beam scanning (PBS) resulted in 22% lower median pelvic bone marrow (PBM) volume irradiated to 10 Gy (RBE) (PBS 71.3% versus intensity-modulated RT (IMRT) 93.4%, P, .001) and 14% lower median volume irradiated to 20 Gy (RBE) (PBS 65.1% versus IMRT 79.4%, P, .001)
Use of PBS resulted in lower PBM volume irradiated to 10 Gy (V10) and volume irradiated to 20 Gy (V20) compared with IMRT (Table 2)

Summary

Introduction

Extended-field radiation therapy (RT) that includes the pelvis and para-aortic lymph nodes (PALN) is indicated in patients with gynecologic malignancies with suspected or confirmed PALN disease (gross disease, fluorodeoxyglucose (FDG) avid, or pathologically confirmed). There are no clinical reports of proton therapy for pelvic and PALN RT in women with gynecologic cancers. We have previously shown the clinical feasibility, toxicity, and dosimetric advantages of proton therapy for women requiring pelvic RT for gynecologic cancers. Our results demonstrated that pencil beam scanning (PBS) proton therapy is able to significantly reduce dose to normal tissues in the pelvis, the PBM, bladder, and small bowel (SB) compared with IMRT while maintaining adequate target coverage [7]. In an early dosimetric study, we compared IMRT and 2 different proton therapy techniques for PALN irradiation, demonstrating that both proton therapy techniques resulted in statistically significant dose reduction to SB, large bowel (LB), and kidney dose compared with IMRT [8]

Objectives

Methods

Results

Conclusion