ISSN: 2640-7566
International Journal of Radiology and Radiation Oncology
Review Article       Open Access      Peer-Reviewed

Volumetric Modulated Arc Therapy versus Intensity Modulated Radiation Therapy in the Treatment of Prostate Cancer: A Systematic Literature Review

Issam Lalya1*, Noha Zaghba1, Khalid Andaloussi-Saghir1, Mohamed Elmarjany1, Laila Baddouh2, Keltoum Dahmani2, Khalid Hadadi1, Hassan Sifat1 and Hamid Mansouri1

1Radiation Therapy Department, Military Teaching Hospital Mohammed V, University Mohammed V Souissi, Rabat, Morocco
2Department of Radio physics, Military Teaching Hospital Mohammed V, University Mohammed V Souissi, Rabat, Morocco
*Corresponding author: Issam Lalya, Radiation Therapy Department, Military Teaching Hospital Mohammed V, University Mohammed V Souissi, Rabat, Morocco, Tel: +212 661572770; E-mail: issamlalya@yahoo.fr
Received: 02 June, 2016 | Accepted: 21 June, 2016 | Published: 22 June, 2016

Cite this as

Lalya I, Zaghba N, Andaloussi-Saghir K, Elmarjany M, Baddouh L, et al. (2016) Volumetric Modulated Arc Therapy versus Intensity Modulated Radiation Therapy in the Treatment of Prostate Cancer: A Systematic Literature Review. Int J Radiol Radiat Oncol 2(1): 015-020. DOI: 10.17352/ijrro.000014

Aim: provide evidence concerning advantages of volumetric modulated arc therapy over intensity modulated radiation therapy.

Background: external beam radiation therapy is a major treatment modality of prostate cancer; especially in high and intermediate risk categories in combination with androgen deprivation therapy. The advent of new techniques of irradiation such as intensity modulated radiation therapy (IMRT) improved significantly the biochemical free survival by allowing dose escalation without enhancement of related toxicities. Volumetric modulated arc therapy (VMAT) is a circular technique delivering radiation dose using one or multiple arc of 360° around the target volumes.

Methods: We collected all dosimetric studies comparing VAMT versus IMRT, published in PubMed indexed journals between 2008 and 2015. Parameters of comparison were dose volume histograms for target volumes and organs at risk, number of monitors units and treatment time.

Results: Globally, the target volumes coverage and organ at risk protection were similar between the two techniques. VMAT has the advantage to reduce significantly the number of monitor units and treatment time.

Conclusion: VMAT is a very efficient technique of radiation therapy, and should be preferred in the treatment of prostate cancer.

Background

Prostate cancer is the leading cancer in men after the age of 50; he is a real public health problem. According to the data of 2005 cancer registry of the Rabat region (RECRAB), prostate cancer is the second most common cancer in men after lung cancers with standardized incidence to the world population of 23,3/100000 inhabitants. US data from the SEER program show a ten-years relative survival of 91.7 %. The relative five-years survival is 100 % for localized (80% of diagnoses) and loco regional (12 % of diagnoses) stages, and 30.6 % for metastatic disease [1].

External beam radiation therapy is indicated in the treatment of low-risk patients, with results comparable to surgery and brachytherapy [2]. It also has a place in treating intermediate-risk forms where it can be combined with short androgen therapy (3 to 6 months) [3-5], and high-risk patients combined to 2-3 years androgen therapy [6]. The benefit of dose escalation has been proven by several randomized trials, showing a better disease-free survival with high doses radiation (74-80 Gy) compared to conventional radiation doses (68 to 70Gy) [7-12]. This dose escalation was made possible by the advent of new radiation techniques such as IMRT, allowing concave dose distributions around target volumes while sparing the rectum and bladder [13-17]. Dosimetric comparison between IMRT and 3D conformal radiation therapy shows a significant decrease in the dose in the rectum and bladder with improved conformation to the target volumes [18,19]. IMRT typically uses five to seven static fields converging towards an isocenter located at the target volume, and the inverse planning system allow by introducing different constraints dose/volume, a very optimized dose distribution [20]. In IMRT technique by static beams, motion of the MLC leaves may occur continuously (sliding window technique) or sequentially (step and shoot technique) [21,22]. The term VMAT or volumetric modulated arc therapy was introduced for the first time in 2008 by Karl Otto, to designate a new circular irradiation technique, which is the evolution of the intensity modulated arc therapy (IMAT) introduced by Yu in 1995 [23]. A displacement of the MLC leaves with variable speed, a rotational displacement of the gantry with variable speed, a variation of the dose rate and a rotation of the collimator, characterize VMAT technique.

Data on the potential benefits of VMAT compared to IMRT are few. Our work proposes through a systematic literature review to collect all the comparative studies published. Three types of comparison criteria will be discussed:

• Criteria related to the target volumes coverage and protection of organs at risk

• Efficiency criteria

• Economic criteria

Methods

The literature search was conducted by the systematic interrogation of the Pub Med database from 2008 to 2015, the key words used were: Volumetric modulated arc therapy (VMAT) versus Intensity modulated radiation therapy (IMRT), dosimetric comparison, prostate cancer. The literature search was limited to publications in English or French. Studies presented as abstracts or oral presentation in international conferences but not published were excluded.

The studied comparisons were: VMAT (SA = single arc, DA = Double arc, CDR = constant dose rate, VDV = variable dose rate) versus IMRT (SW = sliding window or SS = Step and shoot).

The comparison parameters were:

• Dose Volume Histograms for PTV

• Dose Volume Histograms for OAR

• Number of monitor units

• Treatment time.

Results

29 dosimetric studies met our selection criteria; their results are summarized in Table 1. In general VMAT and IMRT have provided similar coverage of target volumes while respecting the constraints for organs at risk. The number of monitor units and treatment time were significantly reduced with VMAT.

Discussion

A-Coverage of target volumes

In all published dosimetric studies, VMAT technique has allowed coverage of target volumes, acceptable and comparable to that provided by conventional IMRT using fixed or stationary fields. However, the results concerning homogeneity and conformity are more controversial, since some studies report better homogeneity and conformity with VMAT [31,34], while others are more in favor of IMRT [32,36]. It is important to remember that these differences rather insignificant are inherent to many factors:

• The number of arcs used in VMAT treatment plans (usually with better homogeneity and improved conformity with multiple arcs)

• The optimization method used for VMAT plans

• The number of beams used for IMRT, a high number of beams generally allows better results [31,32]

• Expertise of the radio physics team

B-Protection of organs at risk

In the study of Palma et al. [24], as well as VMAT and IMRT resulted in a significant reduction of the dose to OAR compared to 3D conformal radiation therapy, these doses were lowest with VMAT. The comparative study of the Memorial Sloan Kettering Cancer Center [25], reported a significant reduction of the dose to the rectum and the rectum-NTCP by 1.5%, the doses to the bladder and the femoral heads were also reduced but not significantly. Similar results were reported by Hardcastle et al. [26], with reduced doses to the rectum and therefore a lower rectum-NTCP with VMAT versus IMRT (7F, SS). In a Danish study [27], the VMAT technique has reduced doses to the rectum and bladder compared to IMRT (SW). Ost et al. [28], have compared VMAT with three techniques of IMRT (3F, 5F, 7F-SS), for prostate radiotherapy with a simultaneous integrated boost to the intraprostatic lesion defined by MRI spectroscopy, VMAT in this study compared to the three IMRT techniques has reduced the dose to the rectum, this reduction was statistically significant for the volumes receiving doses between 20 and 50 Gy (p <0.001). In Weber et al. study [29], comparing VMAT with IMRT (5F, SW) and proton therapy for recurrent prostate cancer after radiation therapy, VMAT and proton therapy allowed a better sparing of OAR compared to IMRT. In a study of 292 patients, the mean doses to the rectum and bladder were lower with VMAT compared with IMRT (7F, SW), especially in the volumes of high doses [30]. However, the results of many studies have shown that IMRT allow a better OAR sparing compared to VMAT [31-34].

C-Peripheral Lower doses or bath doses

The results of comparative studies concerning the integral dose are conflicting, some studies show no difference between the two techniques [26,28], while others report higher levels of whole body integral dose with VMAT compared with IMRT [31]. This difference would be the fact that the full dose, do not depend only on the number of MU, but also significantly on the size of the target volume, shape and dimensions of the opening of the collimator. It is important to note that the dose distributions obtained by VMAT compared with IMRT, generally show higher volumes receiving low doses in the periphery, this is due to the fact that VMAT dose is delivered on an entire 360 degree arc. However, the increased conformity obtained with intensity modulation techniques including VMAT, reduces high doses in healthy tissue outside the target volume [53].

D-Number of Monitor Units (MU) and treatment time

In published dosimetric studies, VMAT treatment plans generally use less MU (up to 65 % less) compared to IMRT by stationary fields (SS and SW) [25,26,31]. This significant reduction in the number of MU theoretically reduce the whole body integral dose, with consequently less risk of radiation induced carcinogenesis and thus second cancers, which represents the major concern with any technique of modulation of intensity, however, data on the whole body integral dose are contradictory, especially since it does not depend uniquely on the number of MU.

Prolongation of the treatment time has been identified as one of the major drawbacks of conventional IMRT with stationary fields. In some locations, the time required to deliver a fraction of a complex IMRT plan can go beyond 15-30 min [54-56]. This disadvantage has often been accepted as an inevitable consequence of the high conformation to the target volume provided by IMRT. The prolongation of the treatment time has several negative consequences:

- At the institutional level: limitation of the number of patients who can be treated by treatment unit.

- Patient discomfort with increased risk of movement of the tumor or the patient during treatment [57].

- Increased machine time required for quality assurance of complex IMRT plans.

- In radiobiological point of view: some authors have suggested that increasing the treatment time, allow tumor cells to repair radio-induced DNA damages and then their proliferation [58,59].

Thus the major impact of the reduction in the number of MU, is probably the significant reduction of the treatment time that passes from 1-1.5 min with a VMAT plan to 5-10 minutes with IMRT plan with 5-7 beams [35, 60-62], the reduction in treatment time allow not only to treat more patients, but also to treat them with more comfort and less intra-fraction tumor as well as organs at risk movements including bladder and rectum.

E-Economic advantage

Reducing both the number of MU and treatment time, implies a cost reduction related to VMAT technique. This hypothesis has been validated by an Australian study, which demonstrated that the technique of VMAT saves on average 174 DAU per patient, compared to IMRT, which is equivalent to a reduction of the cost of about 34%. Indeed, the real economy is much greater, since only the cost related to the nursing staff has been calculated in this study, not the additional cost related to time and to administrative and nursing staff needed to maintain the activity of radiotherapy department with treatments as long as those of IMRT, nor the logistics cost for the construction of new buildings and installation of new machines to treat the same number of patients in a timely manner. According to the same study, VMAT is logistically and economically equivalent to the RC-3D, with the dosimetric advantages of IMRT [44].

Conclusions

Results of dosimetric studies comparing IMRT and VMAT, should be interpreted with caution, given the number of bias, including the expertise of the radio physics team, the dosimetric advantage of one technique over the other may simply be due to a long learning curve of the medical physicist, which allows him an important mastery of technique, by against, treatment plans made by a team at the beginning of learning naturally suffer of many imperfections, incorrectly deducted to the technique.

Thus at the current state of knowledge, we cannot decide on the superiority of one technique over the other for coverage of target volumes and protection of organs at risk. However, the most plausible benefits of VMAT compared with IMRT are obviously the significant reductions in the number of MU and treatment time, with all the impact that can have:

- Patient comfort.

- The comfort of the healthcare team.

- Treatment accuracy by reducing per fraction movements.

- Reducing the cost of treatment.

- The treatment of more patients in optimal time.

  1. Salomon L, Azria D, Bastide C, Beuzeboc P, Cormier L, et al. (2010) membres du CCAFU (2010) Recommandations 2010. Cancer de prostate. Prog Urol 20: S217-251 .
  2. D'Amico AV, Whittington R, Malkowicz SB, Schultz D, Blank K, et al. (1998) Biochemical outcome after radical prostatectomy, external beam radiation therapy, or interstitial radiation therapy for clinically localized prostate cancer. JAMA 280: 969-974 .
  3. Laverdière J, Gomez JL, Cusan L, Suburu ER, Diamond P, et al. (1997) Beneficial effect of combination hormonal therapy administered prior and following external beam radiation therapy in localized prostate cancer. Int J Radiat Oncol Biol Phys 37: 247-252 .
  4. D'Amico AV, Manola J, Loffredo M, Renshaw AA, DellaCroce A, et al. (2004) 6-month androgen suppression plus radiation therapy vs radiation therapy alone for patients with clinically localized prostate cancer: a randomized controlled trial. JAMA 292: 821-827 .
  5. Denham JW, Steigler A, Lamb DS, Joseph D, Mameghan H, et al. (2005) Short-term androgen deprivation and radiotherapy for locally advanced prostate cancer: results from the Trans-Tasman Radiation Oncology Group 96.01 randomised controlled trial. Lancet Oncol 6: 841-850 .
  6. Bolla M, Collette L, Blank L, Warde P, Dubois JB, et al. (2002) Long-term results with immediate androgen suppression and external irradiation in patients with locally advanced prostate cancer (an EORTC study): a phase III randomised trial. Lancet 360: 103-106 .
  7. Pollack A, Zagars GK, Smith LG, Lee JJ, von Eschenbach AC, et al. (2000) Preliminary results of a randomized radiotherapy dose-escalation study comparing 70 Gy with 78 Gy for prostate cancer. J ClinOncol 18: 3904-3911 .
  8. Zietman AL, DeSilvio ML, Slater JD, Rossi CJ Jr, Miller DW, et al. (2005) Comparison of conventional-dose vs high-dose conformal radiation therapy in clinically localized adenocarcinoma of the prostate: a randomized controlled trial. JAMA 294: 1233-1239 .
  9.  Dearnaley DP, Hall E, Lawrence D, Huddart RA, Eeles R, et al. (2005) Phase III pilot study of dose escalation using conformal radiotherapy in prostate cancer: PSA control and side effects. Br J Cancer 92: 488-498 .
  10. Peeters ST, Heemsbergen WD, Koper PC, van Putten WL, Slot A, et al. (2006) Dose-response in radiotherapy for localized prostate cancer: results of the Dutch multicenter randomized phase III trial comparing 68 Gy of radiotherapy with 78 Gy J ClinOncol 24: 1990-1996 .
  11. Beckendorf V, Guérif S, Le Prisé E, Cosset JM, Lefloch O, et al. (2004) The GETUG 70 Gy vs. 80 Gy randomized trial for localized prostate cancer: feasibility and acute toxicity. Int J Radiat Oncol Biol Phys 60: 1056-1065 .
  12. Beckendorf V, Guerif S, Le Prise E, Cosset J, Bougnoux A, et al. (2008) 70 Gy versus (vs) 80 Gy Dose Escalation Getug 06 French Trial for Localized Prostate Cancer: Mature Results. Int J Radiat Oncol Biol Phys 72: S96-S97 .
  13. Ling CC, Burman C, Chui CS, Kutcher GJ, Leibel SA, et al. (1996) Conformal radiation treatment of prostate cancer using inversely-planned intensity-modulated photon beams produced with dynamic multileaf collimation. Int J Radiat Oncol Biol Phys 35: 721-730 .
  14. Damen EM, Brugmans MJ, van der Horst A, Bos L, Lebesque JV, et al. (2001) Planning, computer optimization, and dosimetric verification of a segmented irradiation technique for prostate cancer. Int J Radiat Oncol Biol Phys 49: 1183-1195 .
  15. De Meerleer GO, Vakaet LA, De Gersem WR, De Wagter C, De Naeyer B, et al. (2000) Radiotherapy of prostate cancer with or without intensity modulated beams: a planning comparison. Int J Radiat Oncol Biol Phys 47: 639-648 .
  16. Martinez AA, Yan D, Lockman D, Brabbins D, Kota K, et al. (2001) Improvement in dose escalation using the process of adaptive radiotherapy combined with three-dimensional conformal or intensity-modulated beams for prostate cancer. Int J Radiat Oncol Biol Phys 50: 1226-1234 .
  17. Su AW, Milano MT, Jani AB (2005) IMRT versus conventional whole pelvis radiotherapy for prostate cancer: planning comparison and analysis of acute toxicity. Int J Radiat Oncol Biol Phys 63: S312-S313 .
  18. Liu YM, Shiau CY, Lee ML, Huang PI, Hsieh CM, et al. (2007) The role and strategy of IMRT in radiotherapy of pelvic tumors: dose escalation and cri- tical organ sparing in prostate cancer. Int J Radiat Oncol Biol Phys 67: 1113–1123 .
  19. Luo C, Yang CC, Narayan S, Stern RL, Perks J, et al. (2006) Use of benchmark dose-volume histograms for selection of the optimal technique between three- dimensional conformal radiation therapy and intensity-modulated radiation therapy in prostate cancer. Int J Radiat Oncol Biol Phys 66: 1253–1262 .
  20. Chauvet I, Gaboriaud G, Pontvert D, Zefkili S, Giraud P, et al. (2004) Constraints and dosage for prostate cancer patients treated with conformal radiotherapy and intensity modulated radiation therapy. Cancer Radiother 8: 337–351 .
  21. Galvin JM, Chen XG, Smith RM (1993) Combining multileaf fields to modulate fluence distributions. Int J Radiat Oncol Biol Phys 27: 697–705 .
  22. Webb S (1992) Optimization by simulated annealing of three-dimensional, conformal treatment planning for radiation fields defined by a multileaf collimator: II. Inclusion of two-dimensional modulation of the x-ray intensity. Phys Med Biol 37: 1689–1704 .
  23. Yu CX (1995) Intensity-modulated arc therapy with dynamic multileaf collimation: an alternative to tomotherapy. Phys Med Biol 40: 1435–1449 .
  24. Palma D, Vollans E, James K, Nakano S, Moiseenko V, et al. (2008) Volumetric modulated arc therapy for delivery of prostate radiotherapy: comparison with intensity-modulated radiotherapy and three-dimensional conformal radiotherapy. Int J Radiat Oncol Biol Phys 72: 996–1001 .
  25. Zhang P, Happersett L, Hunt M, Jackson A, Zelefsky M, et al. (2010) Volumetric modulated arc therapy: planning and evaluation for prostate cancer cases. Int J Radiat Oncol Biol Phys 76: 1456–1462 .
  26. Kjaer-Kristoffersen F, Ohlhues L, Medin J, Korreman S (2009) RapidArc volumetric modulated therapy planning for prostate cancer patients. Acta Oncol 48: 227–232 .
  27. Hardcastle N, Tome WA, Foo K, Miller A, Carolan M, et al. (2011) Comparison of prostate IMRT and VMAT biologically optimised treatment plans. Med Dosim 36: 292–298 .
  28. Ost P, Speleers B, De Meerleer G, De Neve W, Fonteyne V, et al. (2011) Volumetric arc therapy and intensity- modulated radiotherapy for primary prostate radiother- apy with simultaneous integrated boost to intraprostatic lesion with 6 and 18 MV: a planning comparison study. Int J Radiat Oncol Biol Phys 79: 920–926 .
  29. Weber DC, Wang H, Cozzi L, Dipasquale G, Khan HG, et al. (2009) RapidArc, intensity modulated photon and proton techniques for recurrent prostate cancer in previously irradiated patients: a treatment planning comparison study. Radiat Oncol 4: 34 .
  30. Kopp RW, Duff M, Catalfamo F, Shah D, Rajecki M, et al. (2011) VMAT vs 7-field IMRT: Assessing the dosimetric parameters of prostate cancer treatment with a 292-patient sample. Med Dosim 36: 365-372 .
  31. Yoo S, Wu QJ, Lee WR, Yin FF (2010) Radiotherapy treatment plans with RapidArc for prostate cancer involving seminal vesicles and lymph nodes. Int J Radiat Oncol Biol Phys 76: 935–942 .
  32. Wolff D, Stieler F, Welzel G, Lorenz F, Abo-Madyan Y, et al. (2009) Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D- conformal RT for treatment of prostate cancer. Radiother Oncol 93: 226–233 .
  33. Tsai CL, Wu JK, Chao HL, Tsai YC, Cheng JC (2011) Treatment and dosimetric advantages between VMAT, IMRT, and helical tomotherapy in prostate cancer. Med Dosim 36: 264–271 .
  34. Rao M, Yang W, Chen F, Sheng K, Ye J, et al. (2010) Comparison of Elekta VMAT with helical tomotherapy and fixed field IMRT: plan quality, delivery efficiency and accuracy. Med Phys 37: 1350–1359 .
  35. Shaffer R, Morris WJ, Moiseenko V, Welsh M, Crumley C, et al. (2009) Volumetric modulated arc therapy and conventional intensity-modulated radiotherapy for simul- taneous maximal intraprostatic boost: a planning compar- ison study. Clin Oncol 21: 401–407 .
  36. Crijns W, Budiharto T, Defraene G, Verstraete J, Depuydt T, et al. (2010) IMRT-based optimization approaches for volumetric modulated single arc radio- therapy planning. Radiother Oncol 95: 149–152 .
  37. Guckenberger M, Richter A, Krieger T, Wilbert J, Baier K, et al. (2009) Is a single arc sufficient in volumetric- modulated arc therapy (VMAT) for complex-shaped target volumes? Radiother Oncol 93: 259–265 .
  38. Fontenot JD, King ML, Johnson SA, Wood CG, Price MJ, et al. (2011) Single-arc volumetric-modulated arc therapy can provide dose distributions equivalent to fixed-beam intensity-modulated radiation therapy for prostatic irradiation with seminal vesicle and/or lymph node involvement. Br J Radiol 85: 231-236 .
  39. Davidson MT, Blake SJ, Batchelar DL, Cheung P, Mah K (2011) Assessing the role of volumetric modulated arc therapy (VMAT) relative to IMRT and helical tomotherapy in the management of localized, locally advanced, and post-operative prostate cancer. Int J Radiat Oncol Biol Phys 80: 1550-1558 .
  40. Aznar MC, Petersen PM, Logadottir A, Lindberg H, Korreman SS, et al. (2010) Rotational radiotherapy for prostate cancer in clinical practice. Radiother Oncol 97: 480-484 .
  41. Morales-Paliza MA, Coffey CW, Ding GX (2010) Evaluation of the dynamic conformal arc therapy in comparison to intensity-modulated radiation therapy in prostate, brain, head-and-neck and spine tumors. J Appl Clin Med Phys 12: 3197 .
  42. Jouyaux F, De Crevoisier R, Manens JP, Bellec J, Cazoulat G, et al. (2010) High dose for prostate irradiation with image guided radiotherapy: contribution of intensity modulation arctherapy. Cancer Radiother 14: 679-689 .
  43.  Sale C, Moloney P (2011) Dose comparisons for conformal, IMRT and VMAT prostate plans. J Med Imaging RadiatOncol 55: 611-621 .
  44. Fogarty GB, Ng D, Liu G, Haydu LE, Bhandari N (2011) Volumetric modulated arc therapy is superior to conventional intensity modulated radiotherapy--a comparison among prostate cancer patients treated in an Australian centre. Radiat Oncol 6: 108 .
  45. Leszczy?ski W, Slosarek K, Szlag M (2012) Comparison of dose distribution in IMRT and RapidArc technique in prostate radiotherapy. Rep Pract Oncol Radiother 17: 347-351 .
  46. Sze HC, Lee MC, Hung WM, Yau TK, Lee AW (2012) RapidArc radiotherapy planning for prostate cancer: single-arc and double-arc techniques vs. intensity-modulated radiotherapy. Med Dosim 37: 87-91 .
  47. Ishii K, Ogino R, Okada W, Nakahara R, Kawamorita R, et al. (2013) A dosimetric comparison of RapidArc and IMRT with hypofractionated simultaneous integrated boost to the prostate for treatment of prostate cancer. Br J Radiol 86: 20130199 .
  48. Elith CA, Dempsey SE, Warren-Forward HM (2013) A retrospective planning analysis comparing intensity modulated radiation therapy (IMRT) to volumetric modulated arc therapy (VMAT) using two optimization algorithms for the treatment of early-stage prostate cancer. J Med Radiat Sci 60: 84-92 .
  49. Poon DM, Kam M, Leung CM, Chau R, Wong S, et al. (2013) Dosimetric advantages and superior treatment delivery efficiency of RapidArc over conventional intensity-modulated radiotherapy in high-risk prostate cancer involving seminal vesicles and pelvic nodes. Clin Oncol (R Coll Radiol) 25: 706-712 .
  50. Kinhikar RA, Pawar AB, Mahantshetty U, Murthy V, Dheshpande DD, et al. (2014) Rapid Arc, helical tomotherapy, sliding window intensity modulated radiotherapy and three dimensional conformal radiation for localized prostate cancer: A dosimetric comparison. J Can Res Ther 10: 575-582 .
  51. Peters S, Schiefer H, Plasswilm L (2014) A treatment planning study comparing Elekta VMAT and fixed field IMRT using the varian treatment planning system eclipse. Radiat Oncol 9: 153 .
  52. Riou O, Regnault de la Mothe P, Azria D, Aillères N, Dubois JB, et al. (2013) Simultaneous integrated boost plan comparison of volumetric-modulated arc therapy and sliding window intensity-modulated radiotherapy for whole pelvis irradiation of locally advanced prostate cancer. J Appl Clin Med Phys 14: 4094 .
  53. Alvarez Moret J, Koelbl O, Bogner L (2009) Quasi-IMAT technique and secondary cancer risk in prostate cancer. StrahlentherOnkol 185: 248-253 .
  54. Murthy V, Gupta T, Kadam A, Ghosh-Laskar S, Budrukkar A, et al. (2009) Time trial: a prospective comparative study of the time-resource burden for three-dimensional conformal radiotherapy and intensity-modulated radiotherapy in head and neck cancers. J Cancer Res Ther 5: 107-112 .
  55. Miles EA, Clark CH, Urbano MTG, Bidmead M, Dearnaley DP, et al. (2005) The impact of introducing intensity modulated radiotherapy into routine clinical practice. RadiotherapyOncol 77: 241-246 .
  56. Xia P, Fu KK, Wong GW, Akazawa C, Verhey LJ (2000) Comparison of treatment plans involving intensity-modulated radiotherapy for nasopharyngeal carcinoma. Int J Radiat Oncol Biol Phys 48: 329-337 .
  57. Hoogeman MS, Nuyttens JJ, Levendag PC, Heijmen BJM (2008) Time dependence of intrafraction patient motion assessed by repeat stereoscopic imaging. Int J Radiat Oncol Biol Phys 70: 609-618 .
  58. Wang JZ, Li XA, D'Souza WD, Stewart RD (2003) Impact of prolonged fraction delivery times on tumor control: a note of caution for intensity-modulated radiation therapy (IMRT). Int J Radiat Oncol Biol Phys 57: 543-552 .
  59. Fowler JF, Welsh JS, Howard SP (2004) Loss of biological effect in prolonged fraction delivery. Int J Radiat Oncol Biol Phys 59: 242-249 .
  60. Reynders T, Tournel K, De Coninck P, Heymann S, Vinh-Hung V, et al. (2009) Dosimetric assessment of static and helical tomotherapy in the clinical implementation of breast cancer treatments. Radiotherapy Oncol 93: 71-79 .
  61. Sterzing F, Schubert K, Sroka-Perez G, Kalz J, Debus J, et al. (2008) Helical tomotherapy. Experiences of the first 150 patients in Heidelberg. Strahlenther Onkol 184: 8-14 .
  62. Cozzarini C, Fiorino C, Di Muzio N, Alongi F, Broggi S, et al. (2007) Significant reduction of acute toxicity following pelvic irradiation with helical tomotherapy in patients with localized prostate cancer. Radiotherapy Oncol 84: 164-170 .
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