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BRIEF COMMUNICATION
Year : 2015  |  Volume : 11  |  Issue : 2  |  Page : 479-481

Living with the Elekta Compact: Limitations and ways around them


1 Radiation Oncologist, Westbank Health and Wellness Institute, Howrah, West Bengal, India
2 Medical Physicist, Westbank Health and Wellness Institute, Howrah, West Bengal, India

Date of Web Publication7-Jul-2015

Correspondence Address:
Suman Mallik
Westbank Health and Wellness Institute, 120/1 Andul Road, Howrah, West Bengal - 711 103
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-1482.139605

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 > Abstract 

Elekta AB, Sweden has recently propagated the Elekta Compact - a low-cost, small-footprint, single energy (6MV), linear accelerator, in India. The absence of electron beams and the inability to seamlessly deliver inverse planned intensity modulated radiotherapy (IMRT) segments, mean that some out-of-the-box thinking is mandatory for the full range of required treatments in different clinical settings, but is ultimately very rewarding. Our department started off in July 2011, with the Elekta Compact, equipped with MLCi2 and a camera-based electron portal imaging device. For head-neck cancers, we have successfully utilized a 3D conformal class-solution of eight-to-nine oblique beams, with multiple segments, to deliver an adequate dose to the posterior neck, respecting spinal cord tolerance. Parotid gland sparing is possible in selected node-negative hypopharyngeal/laryngeal cancers. For prostate cancers, we have developed a forward-planned IMRT protocol to routinely deliver 76-80 Gy to the prostate, with margins, while conforming to the same rectal dose-volume constraints as in inverse IMRT. Response and tolerance have been excellent so far. In head-neck cancers, the majority (71%) of patients was locally advanced; however, complete response was achieved in 75% of the cases. Grade 3 acute toxicities were seen in only 7% of the cases and compliance overall was excellent, with no patients requiring a gap in treatment. We achieved biochemical control in 100% of the prostate cancer patients; no patients had grade 3 acute toxicities, and with a median follow-up of 12 months, have yet to see any late rectal bleeding. Although engineered for simplicity and versatility, the Compact requires some innovative thinking by clinicians/physicists to optimize the full range of its possibilities. However, upgrades like inverse IMRT delivery, which are in the pipeline, are urgently needed for it to be viable, especially in a single-accelerator department.

Keywords: Conformal RT, Elekta Compact, forward plan intensity modulated radiotherapy


How to cite this article:
Goswami J, Mallik S, Adhikary A, Das S, Pal B. Living with the Elekta Compact: Limitations and ways around them. J Can Res Ther 2015;11:479-81

How to cite this URL:
Goswami J, Mallik S, Adhikary A, Das S, Pal B. Living with the Elekta Compact: Limitations and ways around them. J Can Res Ther [serial online] 2015 [cited 2019 Nov 23];11:479-81. Available from: http://www.cancerjournal.net/text.asp?2015/11/2/479/139605


 > Introduction Top


Elekta AB, Sweden has recently propagated the Elekta Compact, a single energy (6MV) linear accelerator, in India. The target centers for the new machine have been new centers in smaller towns and older centers looking to switch from telecobalt machines. The advantages of the Elekta Compact are its low course and small footprint, but it also has some disadvantages like the absence of electron beams and the inability to seamlessly deliver inverse planned intensity modulated radiotherapy (IMRT) segments. As a result, some treatments, such as those of head-neck cancers and prostate cancers are challenging, but can be successfully negotiated.


 > Materials and methods Top


Our department started off in July 2011, with an Elekta Compact, equipped with an MLCi2 multi-leaf collimator head and camera-based electron portal imaging device (EPID). We use the Computerized Medical Systems (CMS)/Focal treatment planning software and the MOSAIQ record-and-verify system, while image matching for the electronic portal imaging device (EPIDs), is done with the iViewC software.

For head-neck cancers, we have successfully utilized a 3D conformal class-solution of eight to nine main beams, mainly oblique, with multiple segments, to deliver an adequate dose to the posterior neck, respecting spinal cord tolerance. The paired anterior oblique beams treat the entire planning target volume (PTV), whereas, in the two pairs of posterior oblique beams and direct anterior/posterior beams, the spinal cord is blocked by multileaf / (MLCs) [Figure 1]. The planned dose to the PTV of the primary and enlarged nodes is 66-70 Gy/33-35#, with doses to the electively radiated nodes varying between 50 and 60 Gy, depending on the tumor subsite and stage [Figure 1]. Average time cost (planning time) for each plan was 84 min (standard deviation (STDEV) 28 min) and average treatment time was 19 min (STDEV 7 min) for head and neck patients.
Figure 1: Class solution of the beam arrangement and resultant isodose of a head and neck plan

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Parotid gland sparing is only attempted in selected T1-T2, N0, M0 hypopharyngeal/supraglottic cancers, where it is possible to restrict the average parotid dose to 25 Gy or less and the dose to 50% volume of the parotid glands, to 30 Gy or less. [1]

For prostate cancers, we have developed a forward-planned IMRT protocol using five equispaced main beams (0, 72, 144, 216, and 288 degrees), again with multiple segments, some treating the entire PTV, while in others, the rectum is blocked by MLCs [Figure 2]. The planned dose to the prostate with margins is 76- 80 Gy/38-40# [Figure 2], while the dose to the pelvic nodes (if irradiated) is 50 Gy/25#. The dose-volume constraints used for the urinary bladder and rectum are those suggested by the Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) group. [2] Average time cost (planning time) for each plan was 128 min (STDEV 42 min) and average treatment time was 17 min (STDEV 6 min) for prostate patients.

Quality assurance (QA) plans were created on the treatment planning system, copying the beams included in the patient's treatment plan on the data set of IMatrix phantom (IBA). The fluence map of the transaction processing system (TPS) data was compared with the fluence map created by treatment fields on the IMatrix Phantom, on the treatment machine, using the IMRT QA software. Gamma and distance to agreement (DTA) were verified keeping the passing criterion at >95% of the pixel value.
Figure 2: Class solution of the beam arrangement and resultant isodose of a prostate and pelvic node plan

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 > Results Top


Response and tolerance have been excellent so far.

In head-neck cancers, the majority (71%) of patients were locally advanced. Complete response was achieved in 75% of the cases. Grade 3 acute toxicities were seen in only 7% of the cases. Compliance overall was excellent, with no patients requiring a gap in treatment [Table 1].
Table 1: Demography and response to treatment in patients with head and neck malignancy


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Parotid sparing was possible in the cases mentioned above, as shown in the dose-volume histogram (DVH) analysis of a sample plan [Figure 3].
Figure 3: Dose-volume histogram of a head and neck 3DCRT plan with parotid sparing

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We achieved biochemical control in 100% of the prostate cancer patients. No patient had grade 3 acute toxicities.With a median follow-up of 12 months, we have yet to see any late rectal bleeding [Table 2].
Table 2: Demography and response in patients with carcinoma prostate

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Dosimetrically, the forward-planned IMRT plans were able to achieve the same dose-volume constraints as would have been desired with the inverse-planned IMRT, as shown in the DVH analysis of a sample plan [Table 3].
Table 3: DVH analysis of a prostate plan (prostate dose 76 Gy in 38 fractions, nodal dose 50 Gy in 25 fractions)

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 > Conclusion Top


Although engineered for simplicity and versatility, the Compact requires some innovative thinking by clinicians/physicists to optimize the full range of its possibilities. It can still be made to execute the vast majority of treatments necessary in the Standard Radiotherapy Department. However, upgrades like the inverse IMRT delivery, which are said to be in the pipeline, are urgently needed for it to be viable, especially in a single-accelerator department.

 
 > References Top

1.
Deasy JO, Moiseenko V, Marks L, Chao KS, Nam J, Eisbruch A. Radiotherapy dose-volume effects on salivary gland function. Int J Radiol Oncol Biol Phys 2010;76 3 Suppl:S58-63.  Back to cited text no. 1
    
2.
Marks LB, Yorke ED, Jackson A, Ten Haken RK, Constine LS, Eisbruch A, et al. Use of Normal Tissue Complication Probability Models in the Clinic. Int J Radiol Oncol Biol Phys 2010;76 3 Suppl:S10-9.  Back to cited text no. 2
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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