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World Journal of Surgical, Medical
and Radiation Oncology Review Open Access Time for Change in Particle Therapy of Intraocular Tumors Tarek Halabi Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. anatomical sites: Introduction Suturing of radio‐opaque markers for subsequent X‐ray localization of intraocular tumors [1, 2] continues to be the standard of care in particle therapy. Well over weeks before treatment, four tantalum rings (also referred to as clips, washers, markers, or fiducials) are sutured to the outer surface of the sclera. During treatment simulation (an exploratory dry run of sorts) orthogonal X‐rays are taken, allowing 3D reconstruction of the tantalum ring positions. Knowing the geometric relationship between tumor/eye model and rings then allows for the 3D localization needed for proton therapy irradiation. With tumor regrowth in less than 5% of treated patients [3] why change the decades‐
old, established ring suturing approach? More importantly, are there alternatives to begin with? While there may not be much room for further improvement in tumor control, I argue that there may still be plenty of room for improvement in complication rates. The first reason for this appeals to the relatively small size of intraocular tumors compared with other (1)
Where V is the irradiated volume (or area if you prefer) and r is its radius. In words, the percentage decrease in irradiated volume that we would gain from a reduction in radiation margin is inversely proportional to size. At 3 mm, radiation margins at our institution for intraocular tumors are similar to those used for other anatomical sites. The second reason for suspecting room for improving complication rates is a tricky one, and I’m often misunderstood when presenting it. It is a two‐point argument. The first, and most controversial point is this: we simply do not know that full dose coverage of the full intraocular tumor volume is a necessary condition for preventing intraocular tumor regrowth. Therefore, the observed regrowth rate among treated patients does not necessarily accurately reflect the degree to which we deliver full dose to full tumor volumes. The second point is that we are no better at avoiding normal tissue than we are at fully irradiating the full tumor volume. Errors and uncertainties fall just as well on both sides of the challenge. The observed low rates of regrowth no more accurately reflect our ability to avoid normal tissue than they do our ability Address for correspondence and Reprint requests to: Tarek Halabi, PhD, Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114. ©2013 Halabi T et al. Licensee Narain Publishers Pvt. Ltd. (NPPL) Submitted: April 16, 2013; Accepted May 07, 2013; Published: May 09, 2013 26 dV /dr ∝ 1/r; V
http://www.npplweb.com/wjsmro/content/2/4 World J Surg Med Radiat Oncol 2013;2:26‐30 ability is inconsequential given the rates themselves, the former is very much of consequence. My suspicion of errors or uncertainties is rooted in the heavy reliance on human visualization, memory, communication, transcription, computation, and drawing (Table 1). In the Operation Room, the ophthalmologist must visually access very posterior areas of the eye, pulling and tugging to reach one area at a time. He/she must mentally register tumor shadows via transillumination at different light source positions (Figure 1 (a)). He/she must then mentally form the intersection of these shadows, pull, tug, and repeat since not all areas may be visually accessed at once. Suturing rings to posterior areas of the eye is awkward. The clips are not coded, but must be mentally numbered according to their location within the chosen suturing pattern. Measurements are taken with a caliper, reported, and transcribed, of distances in‐
between rings, between ring edges and tumor, and between ring edges and limbus. Finally, hand drawings are made of the tumor outline and ring positions (Figure 1 (b)). The relationship between tumor outline and ring positions is crucial because it is the latter that can be reconstructed in 3D space using orthogonal X‐ray images at the proton facility. One week later, the findings are communicated to the radiation oncologist during chart rounds. Let us also not forget patient discomfort and anxiety caused by the suturing procedure. Not having to schedule the OR visit would also shorten the treatment schedule, thereby affording some savings in travel costs for many patients. Patients seeking such treatment often travel from distant locations. This is not just because of the limited number of particle therapy centers in the world; those numbers have been rising, but the new centers have struggled to initiate such eye treatments, precisely because of the difficulty in gaining the expertise necessitated by the above described reliance on human performance. Figure 1: Ring suturing approach to proton treatments of intraocular tumors. (a) Transillumination performed during ring suturing procedure in Operating Room. (b) Drawings and transcriptions made during ring suturing procedure in Operating Room. (c) Patient setup for proton treatment (or treatment simulation) at the proton facility. Occurs after ring suturing procedure to irradiate the full tumor. And while the later 27 Particle Therapy for Intraoccular tumors http://www.npplweb.com/wjsmro/content/2/4 World J Surg Med Radiat Oncol 2013;2:26‐30 Halabi T et al. Table 1: Heavy reliance of suturing procedure on human performance Task Memory Communication
Tran x illumination Transcription
Ring visualization x x x
Relation between tumor and rings x x x
Chart rounds x x x
Most underappreciated, I think, are potential reductions and simplifications of the 28 Computation
Drawing x
Description
Must mentally form the intersection of the tumor shadows formed at different light source positions. This intersection may have to be obtained one region at a time as different areas of the eye can be visually accessed one at a time. Rings are indistinguishable. Each must be mentally as‐signed a number according to location, given chosen placement pattern. May not be able to visually access all rings at once. Ophthalmologist measures and reports distances in‐
between rings and between rings and limbus to transcriber. Using the known diameter of a ring, ophthalmologist estimates distances from ring edges to tumor, and reports them to transcriber. Transcriber and (later) ophthalmologist draw the tumor and rings with pen and pa‐per. Delineation and prescription are traditionally the radiation oncologist’s domain. Ophthalmologist and transcriber must then communicate their findings to the radiation oncologist one week later during chart rounds. current workload and workflow. Proton therapy of intraocular tumors is an extremely http://www.npplweb.com/wjsmro/content/2/4 World J Surg Med Radiat Oncol 2013;2:26‐30 Table 2: Work required by suturing procedure per patient Personnel work 1 anesthesiologist 1 ophthalmologist 1 resident 1 planner 1 patient anesthesia tim
e 1 hr
Suturing proc.
1 hr
Suturing proc.
transcription‐n
sleep 1 hr
1 hr
1 hr
2 OR assistant equipment 2 hr
handling etc. 1 planner ring digitization 0.5 and modeling hr Scheduling scheduling and 0.5 assistants communications hr 2 planners, 2 Communicate‐on 3 ophthalmologists
of findings hrs , 2 rad. during chart Oncologists rounds Total 11 hrs interdisciplinary affair, with many personnel involved. From each individual’s perspective the suturing procedure seems to require only an hour or so of time. When one considers however, the cumulative amount of work involved as shown in Table 2, and the degree of training of those carrying it out, the picture is really a staggering one. Recent technological advances in 3D cameras have led some to re‐examine the invasive suturing procedure [4]. Less attention, if any, however has been paid by physicist in radiation therapy to advances in Optical Coherence Tomography of the eye [5]. Here, one possibility is to mount an OCT device on a 2D dial that itself is mounted on the proton beam nozzle shown in Figure 1 (c). As is typical with dedicated proton beam‐lines for eyes, such nozzles do not rotate. The nozzle can, however, retract and extend if it needs to. 29 Table 3: Attractive features of OCT as a replacement for the ring suturing procedure Particle Therapy for Intraoccular tumors Feature
Comment
resolution
Ability to display intraocular tumor features is well documented [6]. In fact, OCT’s resolution, ῀µm , is well beyond what is customary in radiation oncology compactness
This is desirable since the idea is to mount the device on a 2D dial that itself is mounted to the beam‐line. High resolution handheld OCT devices with 3D reconstruction capability have already been developed [7]. field of view
Eye tumors vary greatly in basal area, height, and location. Wide field of view and focus range are therefore highly desirable. Whole eye imaging with OCT has been reported by [8]. The treatment planning process specifies a patient gaze direction, relative to the proton beam axis, given by polar and azimuthal angles. The OCT device is rotated to coincide with this direction so that it can peer through into the eye and image it. The treatment planning system “informs” the OCT system of what to expect for tumor geometry at its location. The OCT device then confirms that the tumor is in the expected position and orientation, or suggests patient translations or rotations of gaze direction to better fit the planned geometry. OCTs have adjustable internal LED’s, to help guide patient gaze. Table 3 summaries attractive features of OCT as a replacement for the ring suturing procedure. The novel application of OCT technology in particle therapy requires special attention to several requirements. For example, http://www.npplweb.com/wjsmro/content/2/4 World J Surg Med Radiat Oncol 2013;2:26‐30 Halabi T et al. [4].
one now needs to obtain voxel coordinates relative to a known frame of reference (initially that of the device). Also of relevance in this application are facilities to contour structures on scans and to input and output large field of view scans and structures in DICOM format. [5].
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Goitein M, Miller T. Planning proton therapy of the eye. Med Phys. 1982;10:275– 283. [Pubmed]. Gragoudas ES, Goitein M, Verhey L, Munzenreider J, Suit HD, Koehler A. Proton beam irradiation. An alternative to enucleation for intraocular melanomas. Ophthalmology. 1980;87:571–581. [Pubmed]. Gragoudas ES, Lane AM, Munzenreider J, Egan K, Li W. Long‐term risk of local failure after proton therapy for choroidal/ciliary body melanoma. Trans Am Ophthalmol Soc. 2002;100:43–50. [Pubmed]. [7].
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Fassi A, Riboldi M, Forlani CF, Baroni G. Optical eye tracking system for non‐invasive and automatic monitoring of eye position and movements in radiotherapy treatments of ocular tumors. Optical Society of America. 2012;51:2441–2450. [Pubmed]. Schuman J, Puliafito C, Fujimoto J, Duker J, editors. Optical Coherence Tomog‐raphy of Ocular Diseases. Slack Incorporated; 2012. Say EA, Shah SU, Ferensczy S, Shields CL. Optical Coherence Tomography of Retinal and Choroidal Tumors. Journal of Ophthalmology. 2011;2011. [Pubmed]. Houston SK, Murray TG, Wolfe SQ, Fernandes CE. Current update on retinoblastoma. International Ophthalmology Clinics. 2011;51:77–
91.[Pubmed]. Dai C, Zhou C, Fan S, Chen Z, Chai X, Ren Q, et al. Optical Coherence Tomogra‐phy for Whole Eye Segment imaging. Optical Society of America. 2012;20:6109‐15.[Pubmed]. World Journal of Surgical, Medical
and Radiation Oncology
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