ESTRO 36 Abstract Book

S593 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective To assess xerostomia patterns in patients requiring significant parotid inclusion in target volumes for treatment of locally advanced head and neck cancers. Material and Methods 30 patients (male = 20, female = 10) with head and neck cancers (oral cavity = 6, oropharynx = 8, nasopharynx = 3, larynx = 7) of AJCC stage II = 4, III = 12, and IV = 14 who were treated with radical chemo radiation from August 2013 – September 2015 and received significant parotid dose (more than 22 Gy Dmean) were analyzed retrospectively at 3, 6 and 12 months post completion of treatment. They received an external radiotherapy dose of 69.34 Gy EQD2 (to HR-CTV, mean HI – 0.13, mean CI – 0.99) using SIB-IMRT by VMAT technique. Their xerostomia patterns were recorded based on subjective complaints (Grade 1 = slight dryness, Grade 2 = moderate dryness, Grade 3 = complete dryness, Grade 4 = fibrosis). Results 1 patient died during treatment due to aspiration and 1 patient developed a second primary in lung at 10 months. The mean of Dmean to right parotid was 43.95 Gy (23- 51.2) to a mean volume of 16.71 cc (9-30.2) while for the left parotid it was 43.6 Gy (23.1-58.2) to a mean volume of 16.9 cc (7.7-26.3). The mean spared right parotid (outside PTV) Dmean was 23.1 Gy (30.2-69.2% of whole parotid volume, mean volume 42.5%) while for the left parotid it was 26.3 Gy (22-65% of whole parotid volume, mean volume 48.7%). At 3 months of completion of treatment Grade 2 and 3 xerostomia were seen in 2 (6.9%) and 27 (93.1%) patients respectively. At 6 months Grade 2 and 3 xerostomia were seen in 12 (41.3%) and 17 (58.7%) patients respectively. While at 12 months Grade 1, 2 and 3 xerostomia were seen in 7 (24.1%), 16 (55.2%) and 6 (20.7%) respectively. 1 patient had a stable residual disease. Conclusion Significant parotid inclusion in target volumes for locally advanced cases had a reversible loss of parotid function at 12 months of completion of treatment. However, loss of function was irreversible when the Dmean was greater than or equal to 50 Gy. EP-1079 Carotid blowout syndrome after reirradiation with particle therapy in the head and neck region J.E. Dale 1 , S. Molinelli 2 , E. Ciurlia 2 , O. Dahl 1,3 , P. Fossati 2,4 1 Haukeland University Hospital, Department of oncology, Bergen, Norway 2 CNAO Foundation, Pavia, Italy 3 University of Bergen, Department of clinical science, Bergen, Norway 4 European Institute of Oncology IEO, Milano, Italy Purpose or Objective Carotid blowout syndrome (CBS) is a serious complication to treatment of neoplasms in the head and neck (H&N) region. Surgery, infection, necrosis and tumor properties are the most significant risk factors, but the rate of CBS is also affected by properties of radiotherapy (RT). Rates seem to increase in hypofractionated or accelerated hyperfractionated regimens. We here investigate the cumulative doses received by the carotid artery (CA) and CBS-rate in a cohort of patients reirradiated with particle therapy in the H&N region. Material and Methods Dosimetric information, medical records and tumor characteristics of 49 patients were collected. CT, structure set and dose files were available for 32 patients, making it possible to perform deformable image and dose registration to allow plan summation and extract precise cumulative dose statistics for the CA. For the remaining 17 patients a reliable approximation of the cumulative

dose to the CAs was made by comparing printed CT-slices with isodose curves from the previous RT courses with the dose distribution from the reirradiation. Corresponding EQD2 was calculated with an α/β-ratio=3. Results Forty-four patients had received 1 prior RT course, while 5 had received 2 prior RT courses. Ten patients received reirradiation with proton RT and 39 with carbon ion RT (CIRT). In the 49 patients a total of 74 CAs had been reirradiated to a median cumulative Dmax EQD2 of 106 Gy (RBE) (range: 25-167 Gy (RBE)). Details are presented in TABLE 1 and FIGURE 1 . Median time between 1 st and final RT was 29 months (range: 3-205 months). Median time of follow-up was 10 months (range: 1-41 months). Two patients (4%) experienced profuse oronasal bleeding at 6 and 8 months after reirradiation, both fatal. Cumulative Dmax EQD2 for these patients CAs were 130 and 107 Gy (RBE), respectively. Both had recurrent tumors completely surrounding the CA. The first patient had undergone surgery close to the CA prior to the reirradiation. At the time of bleeding he performed a CT-angiogra phy revealing a pseudoaneurysm on the CA, making the diagnosis of CBS highly probable. The second patient had a recurrent tumor at the site of bleeding. Autopsy was refused, making it impossible to ascertain if the bleeding was due to CBS or from pathological tumor vessels. If we attribute both cases to CBS, the CBS-rate for reirradiated CAs was 2.7% (95% CI 1.0-6.4%).