ESTRO 36 Abstract Book

S586 ESTRO 36 2017 _______________________________________________________________________________________________

Many patients receiving fractionated radiotherapy (RT) for head-and-neck cancer have marked anatomic changes during their course of treatment. We conducted a study to quantify the magnitude of these anatomic changes with systematic CT re-scans done after 1st week and 4th week of treatment. Material and Methods A total of 30 patients with head and neck cancer treated with Intensity modulated radiotherapy are enrolled in the study. All patients underwent re-scans after 1st week and 4th week of radiation. Volumetric changes were analyzed for Right parotid and Left parotid. Results Thirty patients were analyzed. Mean volumes of right parotid at initial, after 5# and after 20# was 21.62, 17.55 and 14.53 cc. Mean reduction volume after 5# and 20# was 4.07 and 7.09 cc. Mean volumes of left parotid at initial, after 5# and after 20# were 22.70, 17.86 and 14.13cc. Mean reduction volume after 5# and 20# is 4.83 Measurable anatomic changes occurred throughout fractionated external beam RT for head-and neck cancers. The data may, therefore, be useful in the development of an adaptive RT strategy that takes into account such treatment-related anatomic changes. Such a strategy would maximize the therapeutic ratio of RT EP-1074 Dose impact using standard head and neck immobilization system in brain tumours M. Rincon 1 , J. Olivera 1 , J. Penedo 1 , I. Prieto 1 , S. Gomez 1 , M. Garcia 1 , J. Luna 1 , D. Esteban 1 , A. Ilundain 1 , J. Vara 1 1 Fundación Jimenez Díaz, Radiotherapy, MADRID, Spain Purpose or Objective To evaluate the dosimetric impact using the standard head and neck immobilization system during the radiotherapy course in patients with brain tumours. Material and Methods 10 cases of glioblastomas patients were analyzed In our department, the standard immobilization system for brain tumours consists of a flat carbon fiber headboard, an acrylic head support and an IMRT reinforced thermoplastic mask. CT in 3-mm slice thickness was obtained. The image fusion of CT/MRI allowed a more correct delineation of the planning target volume (PTV) and the organs at risk (brainstem, chiasm, optic nerves and crystalline lens). Three fiducial marks were placed on the mask: two lateral marks and one on midline. The isocenter was located in the center of the three markers. In all patients two plans were considered: with and without the inmobilization system contoured. The treatment planning was performed using Monaco planning system (version 3.30.01) based on the Monte Carlo algorithm. Six MV photon beams generated from Elekta Synergy Beam Modulator linac equipped with 40 pairs of opposing leaves (4mm thickness at isocenter) were utilized. A double-arc volumetric modulated arc therapy (VMAT) technique was used: one arc from 50º to 180º and another from 180º to 310º, both in the clockwise, avoiding eyes. The target prescription dose was 60 Gy to tumoral bed. The maximum dose in organs at risk brainstem and chiasm, the dose at the isocenter and D95 and Dmean of PTV were compared. The difference errors were analyzed. Results D95 and Dmean with and without the inmobilization system contoured showed differences of 0.7% and 0.6% respectively. The maximun dose in brainstem and chiasm were lower by 0.9% and 0.4%. The dose at the isocenter decreased by 0.5 % Conclusion The dose impact using standard head and neck immobilization system in brain tumours was not and 8.57cc. Conclusion

significant, less than 1 %, even in the worst case where this accessory directly interfered with the treatment beam. With other immobilization systems this attenuation should be measured and implemented into the treatment planning process to diminish it when it was necessary. EP-1075 Role of Diffusion Weighted Imaging in Laryngeal & Hypopharyngeal Cancers treated with Radiotherapy S. Pavamani 1 , S. Thomas 1 , P. Surya 2 , R. Michael 3 , G. Mathew 3 , S. Mathews 3 , S. Balukrishna 1 , M. Sunithi 2 1 Christian Medical College Hospital, Radiation Oncology, Vellore, India 2 Christian Medical College Hospital, Radiology, Vellore, India Purpose or Objective Locally Advanced Squamous Cell Carcinoma of the Larynx & Hypopharynx can be treated with an Organ Preserving approach utilising Concurrent Chemoradiotherapy (CRT), Radical Radiotherapy (RT) or targeted therapy. Due to various reasons, some patients may not respond to this treatment & will eventually need salvage surgery. However, if the outcome of the treatment can be predicted beforehand, this can prevent unnecessary side effects & toxicity. The patient can then be offered surgery upfront. Diffusion Weighted MRI (dWMRI) is an imaging modality wherein an increase in the Apparent Diffusion Coefficient (ADC) in the tumour indicates an increase in the movement of water molecules. This in turn indicates a decrease in the cellularity in the tumour & tumour response. Thus, a rising ADC value during treatment versus Pretreatment ADC values may be used to predict outcomes. The aim of this study was to investigate the role of diffusion weighted MRI derived parameters like ADC, as an imaging biomarker, to predict response to RT in locally advanced squamous cell carcinoma of the larynx and hypopharynx. Material and Methods From May 2014 to August 2015, 19 patients with locally advanced laryngeal & hypopharyngeal malignancies, treated with organ preservation intent with concurrent radiotherapy with Cisplatin (n=14), radiotherapy with Nimotuzumab (n=2) and radical radiotherapy (n=3) were recruited. The patients were all male with predominantly T3 stage. They were assessed for treatment response with dWMRI at baseline, first week, fourth week during RT and at the time of first response assessment at 6 to 8 weeks after RT. The ADC values were compared at different time points and correlated with the treatment response. Results All the 19 patients in the study showed an increasing trend in the ADC values over the chosen 4 different time points. It was observed that an abrupt rise from the pretreatment ADC to the first week ADC was characteristic of complete response while a gradual rise of ADC over the different points suggested a partial treatment response. The patients who responded to chemoradiation therapy had a higher pretreatment ADC than patients with partial response. At the last follow up, 12 patients were disease free, while 5 patients developed recurrence. Four patients with recurrence had shown a partial response while only one had exhibited a complete response during RT. One patient died during treatment of aspiration pneumonia while undergoing CRT & another did not follow up after completion of treatment. Conclusion This study suggests that an abrupt rise in the ADC value in the tumour after one week of treatment may predict complete response & long term tumour control. However this finding needs to be investigated in a larger cohort of 3 Christian Medical College Hospital, Otorhinolaryngology, Vellore, India