ESTRO 36 Abstract Book

S373 ESTRO 36 _______________________________________________________________________________________________

patients) or 50Gy/25fx with simultaneous integrated boost of 60Gy/30fx (node-positive patients). Pulsed dose rate MRI-guided adaptive brachytherapy was given in addition. Follow-up MRI was performed routinely at 3 and 12 months after end of treatment or at clinical indication. PIF was defined as a fracture line with or without sclerotic changes in the pelvic bones. D 50% , and V 55 Gy were calculated for os sacrum and jointly for os ileum and pubis. Patient and treatment related factors including dose were analysed for correlation with PIF. Results Median follow-up was 25 months. Median age was 50 years. Twenty patients (20%) were diagnosed with a median of 2 (range 1-3) PIFs; half were asymptomatic. The majority of the fractures were located in the sacrum (74%). Age was a significant risk factor (p<0.001), and the incidence of PIF was 4% and 37% in patients below and above 50 years, respectively. Sacrum D 50% was a significant risk factor in patients >50 years (p=0.04), whereas V 55Gy of sacrum or pelvic bone were insignificant (p=0.33 and 0.18 respectively). Risk factors are reported in table 1. A dose- response curve for D 50% sacrum in patients >50 years showed that reduction of sacrum D 50% of from 40 Gy EQD2 to 35 Gy EQD2 reduces PIF from 45% to 22% (Figure 1).

Patients with locally advanced cervical cancer (LACC) are at risk for para-aortic lymph node (PALN) metastasis. The current treatment is pelvic concurrent chemoradiotherapy (CCRT) with reported PALN failure rate of 9% by RTOG 90- 01, suggesting that pelvic CCRT might not completely eliminate all microscopic tumours in the PALNs. The pattern of lymphatic spread from the pelvis to the PALN appears orderly. This study aimed to evaluate the role of prophylactic lower PALN irradiation in the era of intensity- modulated radiotherapy (IMRT). Material and Methods We retrospectively assessed 186 patients with stage IB2– IVA cervical cancer and clinically negative PALNs receiving definitive IMRT and concurrent weekly cisplatin (40 mg/m2) during 2004–2013. The standard radiation field was the whole pelvis with a prescribed dose of 50.4 Gy in 28 fractions. Brachytherapy was performed at a dose of 30 Gy in six fractions. The decision to use semi-extended field radiotherapy (SEFRT) or extended field radiotherapy was according to physicians’ discretion. Patients receiving extended field radiotherapy were excluded. The region targeted by SEFRT included the PALNs below the level of the renal vessels. The acute and late toxicities were scored according to the Common Terminology Criteria for Adverse Events, v3.0. Survival outcomes were calculated using the Kaplan-Meier method. Multivariate analyses were performed with Cox regression models. A p-value < 0.05 was considered statistically significant. Results One-hundred-ten and 76 patients received pelvic IMRT and SEFRT, respectively. The patient and tumour characteristics were not significantly different between the two groups. All patients completed the planned radiotherapy, and brachytherapy. The median follow-up time was 58 months (range, 5–124). The failure patterns are shown in Table 1. The 5-year overall survival, disease- free survival, and PALN failure-free survival for SEFRT vs. pelvic IMRT were 85% vs. 74% (p = 0.06), 84% vs. 73% (p = 0.08), and 98% vs. 90% (p = 0.01), respectively. In the subgroup analysis, the 5-year overall survival for SEFRT vs. pelvic IMRT was 81% vs. 59% (p = 0.04) and 87% vs. 82% (p = 0.48) in patients with positive and negative pelvic lymph nodes, respectively (Fig. 1). In the multivariable analysis, SEFRT affected the overall survival (hazard ratio, 0.39; 95% confidence interval, 0.19–0.82; p = 0.01). No patients had severe late genitourinary toxicities, and three and two patients had late grade 3 gastrointestinal toxicities in the SEFRT and pelvic IMRT groups, respectively (p = 0.4).

Conclusion PIF is common after treatment for LACC and is mainly seen in patients > 50 years. Our data indicates that PIFs are not related to lymph node boosts, but to dose and volume associated with irradiation of the elective pelvic target. Reducing prescribed elective dose from 50 to 45 Gy may reduce the risk of PIF considerably. PO-0712 Benefit of semi-extended field radiotherapy in patients with locally advanced cervical cancer J. Lee 1 , Y.J. Chen 1 , M.H. Wu 1 , C.L. Chang 2 , T.C. Chen 2 , J.R. Chen 2 , Y.C. Yang 2 1 MacKay Memorial Hospital, Radiation Oncology, Taipei, Taiwan 2 MacKay Memorial Hospital, Department of Obstetrics and Gynecology, Taipei, Taiwan

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