Jesse Conterato, BA&Sc. RSNA 2016 Assessment of Acute Toxicity in Prostate Cancer Patients using Hydrogel Spacer During Proton Therapy Jesse Conterato, BA&Sc. RSNA 2016

Hydrogel Spacers: MRI Comparison Absorbable polyethylene glycol hydrogel spacers are injected into the peri-rectal space. Moves the anterior rectal wall outside of high dose volumes Without Spacer With Spacer Axial View Rectum Hydrogel Spacer Sagittal View Prostate Pinkawa et al. WJCO 2015

Hydrogel Spacers During Proton Therapy? Prospective IMRT trials demonstrate advantage of hydrogel spacer during treatment for prostate cancer: Rectal dose reduction Severity of rectal toxicity reduced (Song et al. 2013, Mariados et al. 2015, Uhl et al. 2014) Mariados et al. Int J Radiation Oncol Biol Phys 2015 Few studies have examined the use of hydrogel spacers in patients treated with proton therapy

Purpose To evaluate the acute toxicity outcomes in prostate cancer patients treated with definitive proton beam radiotherapy (PBRT) with a hydrogel spacer (HS) in place

Methods Retrospective review of prostate cancer patients undergoing definitive PBRT at a single institution Patient data collected from: Prospective Proton Collaborative Group Registry Our institutional Advancements Through Outcomes Measures protocol 63 consecutive patients with hydrogel spacer in place Treatment era: April 2015 – February 2016 All patients completed treatment of 79.2 Cobalt Gray Equivalent (CGE) in 44 fractions Acute Toxicity was defined as occurring during the PBRT treatment period

Methods and Patient Characteristics Toxicity was prospectively assessed weekly during PBRT and scored according to CTCAE v4.0 in 6 genitourinary (GU) and 4 gastrointestinal (GI) categories: GU: Urinary Tract Pain, Urinary Frequency, Urinary Retention, Urinary Incontinence, Urinary Urgency, Hematuria GI: Fecal Incontinence, Rectal Hemorrhage, Proctitis, and Diarrhea.

Methods and Patient Characteristics

Results: Spacer Placement Safety No infections were observed after hydrogel injection, performed under trans-rectal ultrasound guidance Prostate Prostate Prostate Prostate Müller et al. Radiol Oncol 2016

Results: Overall GU Toxicity Most common forms of Grade 2 GU toxicity: Urinary frequency, retention, and urgency Grade 3 GU toxicity: During PBRT, one patient experienced GR3 urinary tract pain while being treated for UTI One patient, with prostate volume of 253.014 mL, underwent Green Light procedure for urinary retention prior to starting PBRT

Results: Overall GI Toxicity Grade 2 Toxicities: One patient experienced GR2 Fecal Incontinence during PBRT One patient with pre-existing hemorrhoids experienced GR2 Rectal Hemorrhage and was treated with Proctocream

Results: GU Toxicity by Proton Target Change in GU Toxicity Score No Increase 1 GR Increase 2 GR Increase Prostate Only 7% 79% 14% Prostate and Seminal Vesicles 19% 58% 22% Prostate, Seminal Vesicles and Pelvic Nodes 31% 62% 8%

Results: GI Toxicity by Proton Target Change in GI Toxicity Score No Increase 1 GR Increase 2 GR Increase Prostate Only 71% 21% 7% Prostate and Seminal Vesicles 78% 22% 0% Prostate, Seminal Vesicles and Pelvic Nodes 62% 38%

Conclusion The use of hydrogel spacers during definitive PBRT for prostate cancer resulted in acceptably low rates of acute GU and GI toxicity Additional follow-up is needed to assess effects of hydrogel spacer placement on late rectal toxicity

Acknowledgements Lisa McGee, MD William Hartsell, MD Dean Conterato, MD Vinai Gondi, MD John Chang, MD Shae Gans, CMD Megan Dunn, PhD, MSHS Steven Laub, MMP Chicago Proton Center Staff Proton Collaborative Group

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