Sparing healthy lung by focusing the radiation beam flow onto the emphysematous regions in the treatment of lung cancer.

INTRODUCTION: Currently, routine radiotherapy (RT) planning for locally advanced lung cancer (LC) does not take into consideration the functional state of the lung. The goal of this study was to determine if it is technically feasible to integrate the sites of pulmonary emphysema (PE) into the RT planning process. METHODS: Ten patients with LC and PE treated with helical Tomotherapy© were retrospectively included. After extraction by Myrian© software based on diagnostic CT (DCT), the PE data were transferred to the treatment planning system (TPS). PE-optimized plans were performed for patients with significant PE, where the dose was focused onto the PE. We compared the PE-optimized RT plans to the initial RT plans. RESULTS: The median dose to the planning target volume (PTV) was 52 Gy (range, 36-66) in fractions of 2-3 Gy. The median PE volume was 220 cm3 (range: 12-1394), and six patients were eligible for a PE-optimized RT plan. Considering the lung without PE, the V20 and V30 variations were not significant (P > 0.05), the V5 decreased from 50% to 44% after re-planning (P < 0.05). The mean PTV D98 was 50 Gy versus 48 Gy (P < 0.05). CONCLUSION: Focusing the RT beam flow on the PE structure rather than the healthy lung appears feasible, and may be a promising technique to help preserve pulmonary function and minimize RT-related pulmonary toxicity.

Retrospective feasibility study of simultaneous integrated boost in cervical cancer using Tomotherapy: the impact of organ motion and tumor regression.

BACKGROUND: Whole pelvis intensity modulated radiotherapy (IMRT) is increasingly being used to treat cervical cancer aiming to reduce side effects. Encouraged by this, some groups have proposed the use of simultaneous integrated boost (SIB) to target the tumor, either to get a higher tumoricidal effect or to replace brachytherapy. Nevertheless, physiological organ movement and rapid tumor regression throughout treatment might substantially reduce any benefit of this approach. PURPOSE: To evaluate the clinical target volume - simultaneous integrated boost (CTV-SIB) regression and motion during chemo-radiotherapy (CRT) for cervical cancer, and to monitor treatment progress dosimetrically and volumetrically to ensure treatment goals are met. METHODS AND MATERIALS: Ten patients treated with standard doses of CRT and brachytherapy were retrospectively re-planned using a helical Tomotherapy - SIB technique for the hypothetical scenario of this feasibility study. Target and organs at risk (OAR) were contoured on deformable fused planning-computed tomography and megavoltage computed tomography images. The CTV-SIB volume regression was determined. The center of mass (CM) was used to evaluate the degree of motion. The Dice's similarity coefficient (DSC) was used to assess the spatial overlap of CTV-SIBs between scans. A cumulative dose-volume histogram modeled estimated delivered doses. RESULTS: The CTV-SIB relative reduction was between 31 and 70%. The mean maximum CM change was 12.5, 9, and 3 mm in the superior-inferior, antero-posterior, and right-left dimensions, respectively. The CTV-SIB-DSC approached 1 in the first week of treatment, indicating almost perfect overlap. CTV-SIB-DSC regressed linearly during therapy, and by the end of treatment was 0.5, indicating 50% discordance. Two patients received less than 95% of the prescribed dose. Much higher doses to the OAR were observed. A multiple regression analysis showed a significant interaction between CTV-SIB reduction and OAR dose increase. CONCLUSIONS: The CTV-SIB had important regression and motion during CRT, receiving lower therapeutic doses than expected. The OAR had unpredictable shifts and received higher doses. The use of SIB without frequent adaptation of the treatment plan exposes cervical cancer patients to an unpredictable risk of under-dosing the target and/or overdosing adjacent critical structures. In that scenario, brachytherapy continues to be the gold standard approach.