Gastrointestinal Cancer

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SU_5_2043 - Location-Specific Skin Dosimetry Is Associated With Treatment Breaks and Duration In Concurrent Chemoradiotherapy For Anal Cancer

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Location-Specific Skin Dosimetry Is Associated With Treatment Breaks and Duration In Concurrent Chemoradiotherapy For Anal Cancer
M. S. Susko1, A. Laffan2, L. Parsons1, E. Feldman1, R. Shih3, M. Feng1, A. Venook4, C. Atreya4, V. L. Katherine4, and M. Anwar1; 1Department of Radiation Oncology University of California, San Francisco, San Francisco, CA, 2University of California - San Francisco, San Francisco, CA, 3University of California - Berkeley, Berkeley, CA, 4Department of Internal Medicine, Division of Hematology Oncology University of California- San Francisco, San Francisco, CA

Purpose/Objective(s): Chemoradiotherapy is curative for anal cancer, however unplanned treatment breaks (UpTB) due to treatment-related toxicity can have a detrimental effect on patient outcomes. A priori knowledge of at-risk patients could promote closer patient observation and earlier interventions, minimizing break duration. We introduce a simple method for identifying patients at risk of UpTB using location-specific skin dosimetry on the first day of treatment. This method can serve as a comparison between delivered dose and pre-treatment dosimetric characteristics to identify patients at risk of treatment break.

Materials/Methods: Patients treated between 2014-2017 for anal cancer at a single institution, were retrospectively analyzed for pre-treatment characteristics, dosimetric parameters and treatment characteristics which resulted in treatment breaks. Patients were treated with definitive intent chemoradiation (5FU/MMC 84.6%, other 15.4%) and prior to delivery of the first fraction either thermoluminescent dosimeters (TLD) or optically stimulated luminescence dosimeters (OSLD) placed in standardized locations (anus, gluteal folds, sacrum, perineum, inguinals, external genitalia) to measure actual dose received to these areas.

Results: Thirty-nine patients were available for analysis including 23 men and 16 women, and 82% (32) had skin dosimetry. The median age of the patients was 59 years (IQR: 54-65) and the median radiation dose was 55.8 Gy (IQR: 54-56) in 30 fractions. Twenty-one patients (54%) had an UpTB, with the median break duration of 7 calendar days (IQR: 4-13). Breaks occurred at a median of 35 calendar days (IQR: 22-36) into treatment. 57% (N=12) of patients with an UpTB had an upper-sacral dose (USD) >100 cGy/day. These patients experienced a median break of 13 days, versus 4 days (N=9) for those < 100 cGy/day. Median UpTB for all patients with USD < or > 100 cGy/day was 0 vs 9.5 days, respectively. In patients who received a break, analysis of the TLD/OSLD data revealed there was a significant association between break duration and fractional radiation dose p<0.001 respectively, increasing at approximately 1 day/ 10 cGy increase in USD. Analysis of 7 additional TLD/OSLD sites, including anal dose, was not significantly associated with UpTB.

Conclusion: Treatment breaks during radiation for anal cancer are common for patients with USD > 100 cGy with the median duration of the break in this cohort of 7 calendar days. Per fraction TLD/OSLD radiation dose at the superior aspect of the sacrum and gluteal folds were associated with treatment break duration. Given the uncertainty of dose at the skin surface, the use of TLD/OSLD provides additional information to pre-treatment dosimetric data in ongoing assessment of patients at risk of UpTB. This data could be used prospectively to identify patients at risk for prolonged break on the first day of treatment, allowing for enhanced support measures to be implemented proactively.

Author Disclosure: M.S. Susko: None. A. Laffan: None. R. Shih: None. M. Feng: Research Grant; Celgene, Prostate Cancer Foundation. Honoraria; Reflexion. Consultant; Medivation/Astallas. Speaker's Bureau; Medivation/Astallas. Advisory Board; Medivation/Astallas, GenomeDx, Nanostring, Myriad. Travel Expenses; GenomeDx, Prostate Cancer Foundation, ASTRO. Partnership; PFS Genomics. Patent/License Fees/Copyright; PFS Genomics. Chair; NRG. 2014 Meeting Track Chair, Biology Sessions; ASTRO. V. Katherine: None. M. Anwar: None.

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