Adaptive Radiation Therapy

La radioterapia oncologica, anche grazie agli sviluppi tecnologici degli ultimi anni, costituisce un'arma formidabile per trattare con successo, e spesso guarire, molti tipi di cancro. La disponibilità di immagini ad alto contenuto di informazioni, come quelle della tomografia computerizzata (TC) e della tomografia a risonanza nucleare magnetica (NMR), spesso "fuse" in un'unica immagine, consente di individuare con grandissima accuratezza il target tumorale e gli organi a rischio potenzialmente coinvolti nell'irradiazione. L'uso di sofisticati programmi di calcolo e di simulazione, a sua volta, consente di scegliere, fra i vari tipi di radiazioni, le varie apparecchiature che le producono e le varie tecniche oggi disponibili, quelle più adatte per ogni tipo di tumore.

The purpose of this study was to compare 2 adaptive radiotherapy strategies with helical tomotherapy. A patient having mesothelioma with mediastinal nodes was treated using helical tomotherapy with pretreatment megavoltage CT (MVCT) imaging. Gross tumor volumes (GTVs) were outlined on every MVCT study. Two alternatives for adapting the treatment were investigated: (1) keeping the prescribed dose to the targets while reducing the dose to the OARs and (2) escalating the target dose while maintaining the original level of healthy tissue sparing. Intensity modulated radiotherapy (step-and-shoot IMRT) and 3D conformal radiotherapy (3DCRT) plans for the patient were generated and compared. The primary lesion and nodal mass regressed by 16.2% and 32.5%, respectively. Adapted GTVs and reduced planning target volume (PTV) margins of 4 mm after 22 fractions decrease the planned mean lung dose by 19.4%. For dose escalation, the planned prescribed doses may be increased from 50.0 to 58.7 Gy in PTV1 and from 60.0 to 70.5 Gy in PTV2. The step-and-shoot IMRT plan was better in sparing healthy tissue but did not provide target coverage as well as the helical tomotherapy plan. The 3DCRT plan resulted in a prohibitively high planned dose to the spinal cord. MVCT studies provide information both for setup correction and plan adaptation. Improved healthy tissue sparing and/or dose escalation can be achieved by adaptive planning.

Robustness to obstacles is the most important factor necessary to achieve accurate tumor tracking without fiducial markers. Some high-density structures, such as bone, are enhanced on X-ray fluoroscopic images, which cause tumor mistracking. Tumor tracking should be performed by controlling ‘‘importance recognition’’: the understanding that soft-tissue is an important tracking feature and bone structure is unimportant. We propose a new real-time tumor-contouring method that uses deep learning with importance recognition control. The novelty of the proposed method is the combination of the devised random overlay method and supervised deep learning to induce the recognition of structures in tumor contouring as
important or unimportant. This method can be used for tumor contouring because it uses deep learning to perform image segmentation. Our results from a simulated fluoroscopy model showed accurate tracking of a low-visibility tumor with an error of approximately 1 mm, even if enhanced bone structure acted as an obstacle. A high similarity of approximately 0.95 on the Jaccard index was observed between the segmented and ground truth tumor regions. A short processing time of 25 ms was achieved. The results of this simulated fluoroscopy model support the feasibility of robust real-time tumor contouring with fluoroscopy. Further studies using clinical fluoroscopy are highly anticipated.

Follicular Dendritic cells sarcomais a relatively rare entity with intermediate malignancy. Their evolution is characterized by the frequency of local and/or remote relapses. Due to their rarity, the treatment is not consensual in the literature. We report a rare case of follicular dendritic cells sarcoma of accessory salivary glands in a 45-year-old patient whose progression is favorable after surgery followed by chemo-radiotherapy and review of the literature. Follicular Dendritic cellstumors are rare entities (less than 1% of  malignant  salivary  gland  tumors).  Only  a  few  cases  have  been  reported  in  the  literature  [1-2].  In  addition  to  their  rarity,  these  tumors shows difficulties in the diagnosis of certainty and in the optimal  the  rape  utic  strategy.  We  report  an  exceptional  case  of  follicular dendritic cell sarcoma of submaxillary accessory salivary glands  in  a  45-year-old  man  and  discuss  the  therapeutic  strategy  based on data from the literature. A  45-year-old  patient  with  no  previous  medical  history  who  consulted  for  a  right  latero-cervical  swelling,  increasing  gradually in volume for 3 months, with no pain or other associated otolaryngologic    signs.    The    cervical    ultrasound    showed    a    vascularized  lesion  under  the  right  angulo-mandibular  measured  6.5 cm of major axis. The cervical CT scan showed a right sub-angulo-mandibular tumoallesion develop that the expense of an accessory salivary  gland  of  the  inner  surface  of  the  lowerlip,  mesured  65  x  33mm, with no significant cervical adenopathy or involvement of the parotid glands, Submaxillary or thyroid (Figure 1). The patient had  a  biopsy  excision  of  the  mass.  In  the  macroscopic  study,  it  was  an  encapsulated  mass  mesured  7  cm  of  long  axis,  of  whitish  aspect  quite  homogeneous.  Histologically,  tumorous  proliferation  of  diffuse  architecture  was  described  containing  void  cells  with  invisible  cytoplasmic  boundaries  (Figure  2).  Exercise  margins  were healthy at 1 cm.

Purpose: VERO is a novel platform for image guided stereotactic body radiotherapy. Orthogonal gimbals hold the linac-MLC assembly allowing real-time moving tumor tracking. This study determines the geometric accuracy of the tracking. Materials and methods: To determine the tracking error, an 1D moving phantom produced sinusoidal motion with frequencies up to 30 breaths per minute (bpm). Tumor trajectories of patients were reproduced using a 2D robot and pursued with the gimbals tracking system prototype. Using the moving beam light field and a digital-camera-based detection unit tracking errors, system lag and equivalence of pan/ tilt performance were measured. Results: The system lag was 47.7 ms for panning and 47.6 ms for tilting. Applying system lag compensation, sinusoidal motion tracking was accurate, with a tracking error 90% percentile E 90% < 0.82 mm and similar performance for pan/tilt. Systematic tracking errors were below 0.14 mm. The 2D tumor trajectories were tracked with an average E 90% of 0.54 mm, and tracking error standard deviations of 0.20 mm for pan and 0.22 mm for tilt. Conclusions: In terms of dynamic behavior, the gimbaled linac of the VERO system showed to be an excellent approach for providing accurate real-time tumor tracking in radiation therapy.