Presentation on theme: "Treatment delivery from the patient perspective: potential indication, set-up and organ motion issues at CNAO Piero Fossati ESF Exploratory Workshop on."— Presentation transcript:
Treatment delivery from the patient perspective: potential indication, set-up and organ motion issues at CNAO Piero Fossati ESF Exploratory Workshop on Advanced Instrumentation for Cancer Diagnosis and Treatment Oxford, United Kingdom, 23 – 26 September 2008
We all know how nice it is to have the Bragg peak Goitein et al, Physics today, 2002Courtesy of Dr. Ando, NIRS
We all know how nice it is to have a high RBE (and only where you need it) Vertebral osteosarcoma 7 years later CIRT Imai et al., Lancet Oncology 2006
We can hope in good clinical results if we are able to deliver this radiation, with nice physical and biological properties, to the target We have to know where the target is No matter how good our beam, if the target is not where we thought we will not kill the tumor
Why should the target be elsewhere? Mispositioning (interfraction) Organ motion (intrafraction) Shape change (interfraction)
Steeper gradients Dose distribution heavily dependent on tissue density Hypofractionation This issues are much more critical in hadrontherapy (compared to photons RT) because of:
Organ motion is even more critical when active scanning is used (risk of hot and cold spots): For the CNAO delivery system spot size will be of millimiters (4 - 10) and time scale will be of milliseconds.
What has been done until now ? What do we plan to do at CNAO ? What would we like to do but do not know how?
Delivery system at CNAO Fixed vertical and horizontal beams Active spot scanning (no passive spread beam)
1 - Precise positioning Always an issue (for all body sites) Need of fixation devices Need of position verification devices Need of 6 DOF position correction devices The only issue for some body district (limb, head, spine ?) Time consuming
Precise positioning We believe that for “fixed” body sites a orthogonal KeV X-Ray imaging coupled to a robotic positioning device is necessary and sufficient. Head and body masks, personalized cushions, bite blocks and all such devices employed in high precision photons RT can be straightforwardly transferd to hadrontherapy
2 Shape change Tumor shrinkage Weight loss or gain Dependent on tumor biology Relatively easy to cope with through close clinical monitoring of the patient and frequent off line imaging (e.g. each week for gynecological malignancy) Too late if discovered in the treatment room (a check is anyway most necessary)
3 Organ motion The real problem Due to peristalsis, swallowing, heartbeat, vessels pulsation but especially BREATHING Affects lung treatments, liver treatments, and to a lesser extent all abdominal and pelvic treatments. If the patients is in supine position (as may be necessary without a gantry) it may also affect retroperitoneal treatments
Breathing A complex caotic phenomenon Intervals of more or less regular breathing that each 5- 15 minutes change pattern and through a highly unpredictable phase reach a new temporary steady state No reliable correlation betwen body surface and internal displacement during change of patterns Frequency, Tidal volume, relative role of thoracic muscles and diaphragm and end expiration volume are among the parameters that can change in minutes Elevated inter-patient and intra-patient variability Pain and emotional status can influence breathing pattern Displacements up to 3-4 cm can take place Not possible to predict a priori direction and amplitude of a lung nodule displacement
How to deal with respiratory organ motion Breathhold, gating, tracking, coaching, abd. pressure Whichever you choose you need to measure motion (target position or surrogate marker) Once you know how the target moves you can steer the beam, or decide to enlarge the irradiated volume (a simple CTV PTV approach is not adequate) It is mandatory to check what you are doing (a real time, in vivo dosimetry would be appreciated) Robustness of the treatment plan should be considered (ideally as a parameter for inverse planning optimization) Everything should happen in real time
Strategies Breath hold: requires active cooperation, you cannot avoid measuring target position (to be sure it is performed correctly) Gating: (in my opinion probably the best solution) Tracking: much more complicated with only a small gain on time efficiency
Measuring target displacement Breathing is a caotic phenomenon Surrogate markers: air flow, body surface position (simple 1D marker option cfr NIRS, or optoeletronic surface reconstruction with or without passive markers) Measuring the real thing: implanted markers and fluoroscopy, or frequent X- ray (how often ?)
Surrogate markers Only the phase… probably not enough for spot scanning (and for stack layer?)
More advanced surface reconstruction Body markers Surface reconstruction
From the camera images to the surface or marker position From the marker position to the target position How many msec ? At the end it is only a guess (caotic behaviour, hysteresis) NOT ENOUGH
You have to look at what you do Fluoroscopy (radioprotection issues) Periodic x-ray check during dose delivery to verify the external internal model, i.e. you trust the model for a short time between cheks (how often have I to check ? Regular interval vs. adaptive interval cfr. Isaksson et al, Med Phys 2005)
What has been done until now (by us)? X-ray Exac trac with a custom made BH system (together with EIO and Politecnico di Milano). Accuray Synchrony (together with CDI) ….. not precise enough for spot scanning What do we plan to do at CNAO ? ?? …. In the beginning only fixed targets
What would we like to do but do not know how? Approach similar to Accuray synchrony but with better surface detection and adaptive chek intervals (optimizing what already exist) Problem our orthogonal X ray flat panels cannot be both in position when the terapeutic beam is on Something new??
Can we detect in real time without extra dose to the patient the position of a lung nodule ? Can we avoid invasive fiducial marker placement ? (I believe NO) Could we measure the position of an implanted marker in some other way ? Maybe measuring the influence of an implanted coil on an external magnetic field makes sense or is it only an ignorant’s dreor measuring the change in electric capacitance? Is anybody working on this? Does it am? Would it work with a ion beam on?
If you have an idea you like be sure somebody else had already had it quite a while ago ! Meas. Sci. Technol. 19 (2008) 024006 (9pp) doi:10.1088/0957-0233/19/2/024006 Tracking of internal organ motion with a six degree-of-freedom MEMS sensor: concept and simulation study Manuel Bandala and Malcolm J Joyce 30 mm × 20 mm × 10 mm
Implantable with 14 gauge needle Accuracy 0.2 mm Read out rate 10 Hz Not yet tested in clinics Balter et al, IJROBP 2005
We are the ones who could benefit most of such sensors Hadrontherapy as a community should support those researches Probably not too ambitious a goal but investment and focusing are required
Steering the beam is easier than measuring the motion Novel approaches are welcome We should strive for a continuous real time measurment of the target position At present I believe we need implanted markers In the end active spot scanning may turn out to be simply not the best way to treat lung and liver and we may have to go back to passive spreading
Quality assurance and in vivo dosimetry Organ motion is difficult to deal with, we have to check what we are doing and how effective it is In vivo dosimetry is mandatory In vivo dosimetry can detect also shape changes that eluded clinical monitoring
What has been done until now (not by us)? In beam PET In beam PET (cfr. FP7 call) AQUA What do we plan to do at CNAO ?
Those approaches have much in common: They mesure something that would have happened anyway (and so no extra dose is delivered to the patient) If the result is positive you can be sure that everything went well, if it is negative you are not sure of what went bad The signal that can be detected bears less information respect to the actual dose distributions and therefore cold spots may be masked by a blurring effect You know the result after the treatment session is ended, for hypofractionated treatments it may be too late
What would we like to do but do not know how? When a fiducial marker is inserted, have a dosimeter inside it (it should be read without extracting the fiducial from the patient body). Science fiction ? Have a proton portal imaging (or part of it) to check position during dose delivery
Proton portal imaging ? (CNAO can accelerate C12 to 400 MeV/u so protons could be much faster) Would it be possible to put the Bragg peak beyond the patient and measure the range without delivering a high dose ?