1157 Neoplasma 2020; 67(5): 1157–1163 doi:10.4149/neo_2020_191229N1350 Improved survival in patients with FDG-PET/CT-based radiotherapy treatment planning for squamous cell anal cancer R. LOHYNSKA 1,4, *, E. MAZANA 1 , A. NOVAKOVA-JIRESOVA 1 , M. JIRKOVSKA 2 , A. NYDLOVA 2 , T. VESELSKY 3 , B. MALINOVA 2 , T. BUCHLER 1 , H. STANKUSOVA 2 1 Department of Oncology, First Faculty of Medicine of Charles University and omayer Hospital Prague, Czech Republic; 2 Department of Oncology, Second Faculty of Medicine of Charles University and Motol Hospital, Prague, Czech Republic; 3 Department of Medical Physics, Motol Hospital, Prague, Czech Republic; 4 First Faculty of Medicine of Charles University and Na Bulovce Hospital Prague, Institute of Radiation Oncology, Czech Republic *Correspondence: radka.lohynska@ſtn.cz Received December 29, 2019 / Accepted February 6, 2020 e aim of this retrospective analysis was to evaluate the impact of FDG-PET/CT-based target volume definition on locoregional control and survival, compared to conventional CT-based target volume definition and dose prescription. One hundred and twenty-two patients with squamous cell anal cancer were treated with curative radiotherapy (RT) alone (27%) or with RT with concurrent chemotherapy (73%) and analyzed. Forty-six percent had the early disease (stage I+II) and 54% were stage III. FDG-PET/CT-based staging was performed in 21% of the patients. e mean follow-up time was 60 months. Other risk factors affecting survival were investigated. According to initial staging in both groups (FDG-PET/ CT and conventional CT) were 10% of stage IV disease, and they were excluded from radical radiotherapy and treated with palliative intent. Ninety-two percent of the patients achieved complete remission. Significant favorable factors in univariate analysis associated with disease-free survival (DFS) were PET/CT staging, T1/2 and N0 stage, and clinical stage I and II. Locoregional control (LRC) correlated with the T1/2 stage and initial performance status (PS) 0. ere were no significant factors affecting overall survival (neither in univariate nor multivariate analysis). In multivariate analysis, the factor associ- ated with better DFS was PET/CT staging and for LRC, PS 0 and concomitant chemoradiation. Acute toxicity was increased in the concurrent chemo-radiotherapy group. Two-, five- and ten-year overall survival rates were 83%, 69%, and 60%; disease-free survival rates were 76%, 73%, 73%; local control rates were 91%, 90%, and 90% and colostomy-free survival was 89%, 86%, and 81%, respectively. PET/CT staging allowed targeted dose escalation to the primary tumor and nodal metastases while decreasing dose to uninvolved regions, resulting in significantly improved DFS without compromising locoregional control. Key words: anal carcinoma, PET/CT, survival, radiotherapy, chemotherapy, prognostic factors Squamous cell carcinoma is the most common type of anal cancer, with rising incidence but a stable mortality rate over the past 20 years [1]. Improved treatment outcomes are achieved due to diagnostic and therapeutic advances based on a multidisciplinary approach. Surgical resection alone (with 5 mm safety margin) is appropriate in Tis lesions and small perianal cancers (T1 N0 M0 G1 tumors). e majority of cases are diagnosed in advanced stages requiring curative radiotherapy (RT). e Radiation erapy Oncology Group (RTOG) 98-11 [2], ACT II [3], ACCORD 3 [4], and other trials [5, 6] led to an adoption of concurrent chemo- radiation as the standard treatment [7–9]. Salvage surgery has been reserved for non-responders or local recurrence. Chemotherapy alone is applied in metastatic or recurrent inoperable disease. Achieving local control is a major predictor of treatment outcome. Different RT protocols are associated with varying levels of acute and late toxicity affecting the quality of life. e introduction of intensity modulated RT (IMRT) signifi- cantly reduced these toxicities [10, 11] and minimized treat- ment breaks. A strong emphasis has been placed on accurate gross tumor volume (GTV) definition. GTV is defined based on clinical findings (DRE) and tumor imaging by endoscopic and radiological methods including CT and MRI. Elective lymph node CTV delineation is based on well-defined guide- lines [12]. Margin definition depends on motion control and set up variations among site protocols. Recently, the role of 18-fluorodeoxyglucose positron emission tomography (PET) with computed tomog- raphy (CT) in clinical staging has been evaluated [13, 14].