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Outcomes of definitive chemoradiation for squamous cell carcinoma of the anus and the effect of radiation technique on hematologic parameters.

580 Background: Chemotherapy-radiation (CRT) is an established therapy for squamous cell carcinoma of the anus. A limiting factor in the successful completion of CRT is bone marrow toxicity. The effect of intensity modulated radiation therapy (IMRT) on marrow toxicity is not well defined. We evaluated the effect of IMRT on the severity of cytopenias for patients receiving CRT. We also explored the influence of cytopenias on disease outcome both pre-CRT or during CRT.


METHODS
43 patients were treated with CRT between 1994-2010. The median delivered dose was 50.4 Gy (range, 32.4-59.4). 31 patients (72%) were treated with IMRT. All patients received concurrent chemotherapy, usually 5FU and mitomycin-C (n = 34, 79%). White blood cell (WBC), hemoglobin (Hg), and platelet counts were recorded pre- CRT, weekly during CRT, and within 7 days post-CRT. Hematologic values were analyzed according to type of RT and for association with treatment outcome.


RESULTS
2-year locoregional failure (LRF) and distant failure were 14% and 14%, respectively. 21 patients required a treatment break due to any cause. In 9 (43%) patients the break was due to hematologic toxicity. 34 patients had complete blood values available. IMRT did not affect the rate of ≥ grade 2 cytopenia (p = 0.64) or median treatment nadirs; Hg (9.1 vs. 8.3 g/dL, p = 0.24), WBC (1.7 vs. 1.2 K/uL, p = 0.95), or platelets (90.5 vs. 61.5 k/uL, p = 0.88). Median time to nadir was not different for WBC (7 vs. 7 days, p = 0.36) or Hg (36 vs. 22 days, p = 0.29), but patients treated with IMRT did have a delayed platelet nadir (33 vs. 14 days, p = 0.01). Hg nadir ≤ 9 g/dL was associated with a higher rate of 2- year LRF (> 9 g/dL 100% vs. ≤ 9 g/dL 73%, p = 0.03). No other hematologic values were associated with LRF.


CONCLUSIONS
In this cohort of patients, nearly 50% of patients required a treatment break, which was related to a cytopenia 43% of the time. IMRT did not appear to have significant impact on acute marrow toxicity, although sample size may limit our power to detect a difference. Low Hg during CRT appears to influence LRF. More detailed dose volume histogram analysis will be useful to further explore how IMRT might influence acute hematologic toxicity, and therefore treatment outcomes. No significant financial relationships to disclose.