Intensity modulated radiotherapy for sinonasal malignancies with a focus on optic pathway preservation
© Chi et al.; licensee BioMed Central Ltd. 2013
Received: 1 October 2012
Accepted: 31 December 2012
Published: 7 January 2013
To assess if intensity-modulated radiotherapy (IMRT) can possibly lead to improved local control and lower incidence of vision impairment/blindness in comparison to non-IMRT techniques when treating sinonasal malignancies; what is the most optimal dose constraints for the optic pathway; and the impact of different IMRT strategies on optic pathway sparing in this setting.
Methods and materials
A literature search in the PubMed databases was conducted in July, 2012.
Clinical studies on IMRT and 2D/3D (2 dimensional/3 dimensional) RT for sinonasal malignancies suggest improved local control and lower incidence of severe vision impairment with IMRT in comparison to non-IMRT techniques. As observed in the non-IMRT studies, blindness due to disease progression may occur despite a lack of severe toxicity possibly due to the difficulty of controlling locally very advanced disease with a dose ≤ 70 Gy. Concurrent chemotherapy’s influence on the the risk of severe optic toxicity after radiotherapy is unclear. A maximum dose of ≤ 54 Gy with conventional fractionation to the optic pathway may decrease the risk of blindness. Increased magnitude of intensity modulation through increasing the number of segments, beams, and using a combination of coplanar and non-coplanar arrangements may help increase dose conformality and optic pathway sparing when IMRT is used.
IMRT optimized with appropriate strategies may be the treatment of choice for the most optimal local control and optic pathway sparing when treating sinonasal malignancy.
Being less than 1% of all cancer, sinonasal malignancies frequently present in the locally advanced stage [1, 2]. This poses a therapeutic challenge in the treatment planning and delivery of definitive or adjuvant radiotherapy due to the proximity of the primary tumors to critical normal structures, such as the optic nerves (ON) and chiasm (OC). Severe vision impairment and blindness are often encountered after therapeutic doses were delivered in the pre-IMRT era [3–19]. This was most commonly observed in the era of conventional radiotherapy (2D), when doses to the target volume and adjacent critical structures could not be well defined [3–9, 14–19]. Due to the lack of the ability to deliver a highly conformal radiation dose, the clinical outcome in the 2 D era is also poor [3–9]. As an ideal approach to deliver a meaningful dose to the primary tumor or the postoperative tumor bed, and optimally preserve the optic pathway, which is often immediately adjacent to the planning target volume (PTV), intensity modulated radiotherapy (IMRT) has been utilized with excellent short term results [20, 21]. Since the adaptation of IMRT into clinical practice, the clinical outcome of IMRT for sinonasal malignancies have been reported by many institutions with improved visual preservation [22–26]. However, there was no consensus on the dose limits for optimal visual preservation. Thus, we conduct this review to analyze if the incidence of vision impairment and blindness after IMRT is less frequent in comparison to conventional/three dimensional conformal radiotherapy (3D-CRT) when treating sinonasal malignancies and local tumor control follow IMRT when compared with non-IMRT techniques; the relationship of vision impairment and radiation dose to the optic pathway in this setting; and how various strategies of IMRT delivery may influence optic structure sparing.
Methods and materials
This systematic review of literature was to investigate the clinical outcome and the incidence of vision impairment and blindness relative to the doses to the optic pathway after 2D RT, 3D-CRT, and IMRT for sinonasal malignancies in order to demonstrate if IMRT can potentially lower the incidence of vision impairment without any compromise of tumor control. In addition, we will explore the potential advantages & disadvantages of various IMRT delivery strategies for optic pathway sparing in this setting. A search based on PubMed electronic databases was conducted in July, 2012 to select studies outlining the following: clinical outcome of radiotherapy for sinonasal or paranasal malignancies; vision impairment and blindness after radiotherapy. The following terms were explored and used for each database search: sinonasal malignancies, paranasal sinus tumors, nasal cavity & ethmoid sinus tumors, vision impairment, optic neuropathy, optic retinopathy, blindness, radiotherapy, IMRT. For clinical reports, only the most complete and most recently published full length study reporting the clinical outcome and treatment related toxicity after 2D/3D RT, IMRT, or any combination of them for predominantly carcinomas from the sinonasal complex has been selected from any one institution. Two separate studies from one single institution were selected only if they described the outcome after RT delivered with two different techniques, or when one is reporting the outcome for exclusively one RT delivery approach and another is a comparison study of clinical outcome after RT delivered with various techniques. Studies describing the technical aspects of RT delivery were selected as long as the same investigation was not duplicated by the same group of authors. Conventional fractionation of 1.8 to 2 Gy per day is assumed unless otherwise indicated in this study.
Fifteen studies published between 1983 and 2009 [3–17], describing the clinical outcome and optic toxicity in detail after 2D or 3D RT; 2 studies published between 2008 & 2009 [18, 19], reporting the clinical outcome & optic toxicity profile after RT delivered with a combination of 2D/3D RT & IMRT; 5 studies published between 2006 and 2012 [22–26], reporting the clinical outcome & optic toxicity after exclusively IMRT; and 3 studies published between 2007 and 2012 comparing the clinical outcome & incidence of optic toxicity after IMRT and non-IMRT techniques [27–29] were selected for the clinical portion of this review. Twelve studies describing the technical aspects of IMRT for paranasal malignancies were also selected for exploration of what would be the best approach to optimize optic pathway sparing [30–41].
Local control & optic toxicity when IMRT is not used, or used in only a portion of patients
Optic toxicity after 2D RT for sinonasal malignancies
Median follow up (mo)
Dose to the optic pathway
54 Gy/27 frxǂ (40–70 Gy)
54 & 60 Gy*
64–70 Gy/32–35 frx ± brachytherapy to 82 Gy¶
62%; 16/19 recurrences are stage III or IV
16% optic retinopathy & neuropathy
2% unilateral blindness
Retina: 58.3 Gy/29 frxǂ.
8.2% ipsilateral blindness due to optic neuropathy; bilateral blindness due to chiasm injury at 10 yrs:
ON: 61.6 Gy/30 frxǂ;
Retinopathy: 20% when 50–60 Gy received;
50–60 Gy: 8%;
OC: 57.1 Gy/30 frxǂ
Optic neuropathy: 2.3% when optic nerve received 44–60 Gy (56 Gy); 34% when optic nerve received 61–78 Gy at 10 yrs
61–76 Gy: 24%.
45-55 Gy/15–16 frx
9.9% unilateral blindness, 2.0% bilateral blindness.
50-70 Gy/25–35 frx
42-72 Gy, 2 Gy daily or bid delivered with Co-60 or electrons
13.6% (3/22) blindness (60 Gy/30 frx and 52 Gy/26 bid frx)
34-86 Gy, various fractionation
6.7% (after 65 Gy received)
6.7% who received > 68 Gy
Optic toxicity after 3D RT for sinonasal malignancies
Median follow up (mo)
Dose to the optic pathway
65 Gy/26 frx or 70 Gy/35 frx
42.1% grade 3 or 4 optic toxicity at 2 years (CTCAE v.3); severe optic toxicity is 56% in patients with orbital invasion
60-68 Gy/30–34 frx
2 due to disease progression, 1 due to cataract
5 yr LC:
-Ipsilateral: 5.7-46.1 Gy
-Contralateral: 3.8-25.6 Gy
OC: 11.3-36.2 Gy
Definitive: 63.5 Gy¶
1 patient 3 years after RT due to vascular glaucoma
Postoperative: 61.8 - 63.1 Gy¶
-Ipsilateral 48.1 Gy¶
-Contralateral 22.0 Gy¶
OC: 43.5 Gy¶
Definitive: 68.4 Gyǂ;
1 retinal artery occlusion and 1 optic neuropathy after 68.4 Gy delivered.
Postoperative: 55.8 -67.8 Gyǂ
Optic toxicity after combined techniques for sinonasal malignancies
Median follow up (mo)
Dose to the optic pathway
66 Gy/33 frxǂ
27.9%; 33.3% patients with orbital invasion experienced severe optic toxicity
5 yr LC:
RON: 73.8 Gy2ǂ*
OC: 70 Gy2ǂ*
64 Gy/32 frxǂ
1 case of unilateral blindness after both optic nerves received a maximum dose of 61 Gy
14% LENT SOMA grade 3–4 opthalmologic toxicity at 5 years (2D 15%, 3D 4%)
2.4% unilateral blindness
50-70 Gy, 1.8-2 Gy/frx; 60 Gy/30 frx for 3D CRT
ON/OC dose was limited to 54 Gy
3 due to disease progression
Definitive 61.7 Gy¶
1 IMRT successfully spared optic nerves and chiasm with mean doses of 33.9 Gy & 38.9 Gy to those two structures
Optic neuropathy in 2 pts (1.9%) & optic retinopathy in 1 pt (0.9%); all led to blindness
Postoperative 60.9 Gy¶
Preoperative 55.7 Gy¶
Mostly 1.8-2 Gy/frx
2D/3D: 69%, IMRT 31%
70 Gy/35 frxǂ
1 case of Optic neuropathy, 77 Gy to ON
1 due to optic neuropathy 7 years after IMRT
Preoperative: 55 Gyǂ
5 yr LC: 63%
Postoperative: 64.8 Gyǂ
Definitive: 70 Gyǂ
Pre or post operative:
As shown in several studies, the incidence of vision impairment appears to correlate with the radiation dose received by the optic pathway [5, 9, 11–16]. The incidence of vision impairment appeared to be low when the optic pathway has received less than 60 Gy. As shown by Jiang et al. the 10 year incidence of optic neuropathy was 2.3% when the optic nerve (ON) received 44–60 Gy, which increased to 34% when the dose to the optic nerve was 61–78 Gy . Optic chiasm injury, which led to bilateral blindness, increased from 8% to 24% when the OC dose increased from 50–60 Gy to 61–76 Gy . In other studies, severe vision impairment/blindness was also more commonly found when radiation dose to the optic apparatus exceeded 60 Gy [9, 13–15]. However, only 1 case of radiation related blindness was reported when the ON/OC dose was limited to < 54 Gy [11, 12, 16]. Among all seventeen studies, a low incidence of blindness due to disease progression was observed in two studies that reported outcome after 3D RT alone and 2D/3D RT [11, 16]. Both studies did not report any treatment related vision impairment.
Chemotherapy was combined with RT (2.6%–100% of the patients in each study, mostly < 50%) predominantly in a sequential fashion in multiple studies [3, 5–7, 10–12, 14–18]. In these studies, the effect of chemotherapy on RT-related vision impairment has not been well described other than the fact concurrent chemo-radiation as reported by Homma et al. has been associated with a high incidence of severe optic toxicity .
Local control & optic toxicity after IMRT
Optic toxicity after IMRT for sinonasal malignancies
Median follow up (mo)
Dose to the optic pathway
Madani CTCAE v2
70 Gy/35 frx
ON/OC constraint: V60 <5%.
Actual Dose to 2% vol¶:
Late:1.4% Grade 3 visual impairment related to IMRT in non-previously treated pts; 2.7% grade 3 impairment due to tumor invasion in both non-previously irradiated & re-irradiated pts
Ipsilateral 58.4 Gy; Contralateral 51.3 Gy
OC: 47.4 Gy
PTV 60 Gy/30 frx, bst CTV 66 Gy/33 frxǂ
81% at 2 yrs
ON/OC constraint: 54 Gy.
RON: 37.9 Gyǂ
LON: 37.4 Gyǂ
OC: 25.3 Gyǂ
GTV 70 Gy/33 frx, CTV 58 Gy/33 frxǂ
ON/OC constraints: D1% 54 Gy (ON), 45 Gy (OC).
OC: 52.3 Gy¶;
Ipsilateral 59.1 Gy¶
Contralateral 45.2 Gy¶
PTV1 70 Gy
ON/OC constraint: < 54 Gy.
No RTOG grade 3–4 toxicity
PTV2 60 Gy
PTV3 54 Gy
All in 33 frx
ipsilateral 53 Gyǂ
contralateral 41 Gyǂ
OC 50 Gyǂ
Wiegner CTCAE v3
High risk PTV 66 Gy/33 frx, 74.4 Gy, 1.2 Gy bid in 5 pts; SRS/SRT bst in 4 pts: 8 Gy x 1 frx or 5 Gy x 2 frx
ON/OC constraint: 45 Gy, 63 Gy if treated with bid schedule.
1 grade 3 optic neuropathy related to herpes zoster infection, 1 grade 3 corneal ulcer
Optic sparing, IMRT vs. non-IMRT
Dose to optic structures
60-66 Gy/30–33 frx for both IMRT and 3D-CRT
LC: 76% vs. 67% at 2 yrs favoring IMRT (p = 0.06);
ON/OC constraint: ≤ 60 Gy for IMRT.
No vision impairment after IMRT
DFS: 72% vs. 60% at 2 yrs favoring IMRT (p = 0.02)
15.8% radiation induced retinopathy after 3D CRT.
OS: 89% vs. 73% at 2 yrs favoring IMRT (p = 0.07)
IMRT(70%): 60–74 Gy
LC: 80% for IMRT & 64% for 3D CRT (p = 0.2)
Dmaxǂ (IMRT vs. 3DCRT) when 70 Gy/35 frx was prescribed:
Ocular toxicity: 32% after 3DCRT, 5% after IMRT (p < 0.0001)
3DCRT(30%): 60–70 Gy
OC 47 Gy vs. 54 Gy
Blindness: 1 after IMRT, 3 after 3DCRT
Organ preservation 88% vs. 65% favoring IMRT (p = 0.01)
-Ipsilateral 50 Gy vs. 56 Gy
-Contralateral 42 Gy vs. 48 Gy
2D 50–74 Gy
≥ RTOG grade 3 visual toxicity
3D 50–73 Gy
IMRT 66–72 Gy
Blindness is only observed after 2D RT only (5.1% of pts treated with 2D RT)
Among IMRT-only studies, 16% & 56% of the patients in studies by Hoppe et al. & Wieger et al. respectively, have received chemotherapy as well [25, 26]. In the IMRT vs. non-IMRT studies, 35.4% and 15% of the patients reported by Al-Mamgami et al. & Chen et al. received chemotherapy [28, 29]. No clear effect of chemotherapy on vision impairment after RT was observed in these studies.
Technique of IMRT delivery for the treatment of sinonasal malignancy
Techniques of IMRT delivery ± comparison with 2D/3D techniques
ON/OC dose constraints
IMRT vs. 2D/3D RT
64 Gy/32 frx
Contra-lateral ON Dmax ≤ 60 Gy
On average, IMRT decreased the Dmax to the contralateral ON when compared with 2D & 3D RT(56.4 Gy vs. 65.7 Gy & 64.2 Gy), and minimized volume receiving <95% prescribed dose (8.5% vs. 15.1% & 14.7%)
Static IMRT vs. 3D CRT
70 Gy/35 frx
Dmax ≤ 60 Gy
IMRT improved PTV coverage by the dose prescribed in general (93.0 ± 2.2% vs. 89.0 ± 4.8%, p = 0.005), no benefit in OAR sparing.
Modulator IMRT vs. 3D CRT
60-66 Gy/30–33 frx
Dmax ≤ 54 Gy
35% minimal transmission IMRT decreased Dmax to the ON/OC (p < 0.05), and is comparable to static IMRT in ON/OC sparing
15 beam IMRT; Sequential tomotherapy (MIMic); 5-field 3D CRT; 3-field 2D RT
Minimal dose of 60 Gy to CTV & 70 Gy to GTV
Dmax ≤ 54 Gy
IMRT achieved better GTV coverage & sparing of OC when compared to 2D & 3D RT
Passive scanning PT; IMRT; 3D CRT; 2D RT
60-70 Gy to the PTV
≤ 50 Gy to ON/OC
Not significantly different, 3D CRT & IMRT achieved better OAR sparing than 2D RT. PT decreased OAR mean dose by > 60% when compared to 3D CRT & IMRT.
6-7 beam coplanar IMRT; 3 field; 4 field
70.2 Gy/39 frx to PTV
IMRT did not demonstrate any clear advantage over conventional 4 field plans.
4-11 beam IMRT, 5/9 beam setups were coplanar
70 Gy/35 frx
≤ 60 Gy
Increased beam & segment number and non-coplanar setup may lead to improved PTV dose coverage and improved OAR sparing in selected cases.
9 beam coplanar IMRT; 5 beam non-coplanar/coplanar IMRT
63 Gy/35 frx to PTV
Dmax < 50 Gy
Target dose better, mean dose to both ON & Dmax to the contralateral ON was significantly lower with the 5 beam approach.
5 beam coplanar IMRT; 5 beam non-coplanar IMRT
Dmax < 55 Gy
No obvious difference in OAR sparing & target dose coverage was found
7 beam non-coplanar IMRT vs. HT
50 Gy/25 frx
Comparable PTV dose coverage & OAR sparing, although better sparing of ipsilateral eye & lens
9-11 beam coplanar IMRT vs. HT
70 Gy/35 frx
Dmax: 54 Gy
HT reduced Dmax to OC, ipsilateral ON & retina; improved target dose homogeneity
9 beam coplanar IMRT vs. 3D CRT
70 Gy/35 frx
Dmax ≤ 60 Gy
Clinical decision to spare the contralateral ON only can lead to improved PTV dose coverage and improved TCP when compared to bilateral ON sparing IMRT and 3D CRT.
At last, the importance of incorporating clinical decision into the IMRT optimization process was demonstrated by Tsien et al.. In their study to deliver 70 Gy, the decision to spare only the contralateral optic pathway led to noticeably improved PTV coverage when compared to 3D CRT, which may result in better tumor control when compared to 3D CRT, and IMRT plans which were optimized to spare bilateral optic pathways.
To our best knowledge, this is the first systematic review that investigates the clinical outcome and the level of optic pathway sparing after IMRT in comparison to 2D/3D RT for sinonasal malignancies. As described above, worse local control and high incidence of severe optic toxicity are mostly found after 2D RT (Tables 1, 2, 3 and 4). Improved local control and lower incidence of severe vision impairment was found after 3D CRT and IMRT, with IMRT being associated with the better local control and lower incidence of severe vision impairment in general (Tables 2, 4 and 5). As shown by Dirix et al. statistically significantly improved 2-year DFS and noticeably better toxicity profile was found following IMRT when compared with patients who were previous treated to the same doses with 3D CRT . Although not statistically significant, improved local control in two other studies which compared IMRT and 3D and/or 2D RT were also seen, while one of them also demonstrated statistically significant improvement in optic organ preservation with IMRT over 3D CRT [28, 29]. Further improvement in treatment outcome may lay in combining IMRT with newer class of systemic agents as those found in the treatment of other malignancies [42–45].
A few cases of blindness due to disease progression were reported in two studies [11, 16]. No severe treatment related vision impairment was reported while a local control of approximately 60% was achieved in both studies. This may be due to the difficulty of controlling locally very advanced disease. These studies included 38.7% and 56.67% of T4 disease, yet none had patients receiving more than 70 Gy [11, 16]. The local control rate after definitive RT delivered with mostly non-IMRT techniques [11, 14, 18, 19] has been poor in general, especially for T4b disease even when a dose of 70 Gy was given . Thus, a higher dose than previously used may need to be used when treating very locally advanced disease, with sacrificing the ipsilateral optic pathway being considered. On the other hand, superior conformal avoidance of the optic structures with IMRT may improve the outcome of definitive RT for sinonasal malignancies. This is evidenced by Wiegner et al. who observed a local control of only 60% after definitive IMRT delivering the conventionally accepted dose in a cohort of patients among whom 76% had T4 disease .
A high incidence of severe optic toxicity was observed following concurrent intra-arterial chemotherapy and 3D RT as shown by Homma et al. despite the excellent local control of 83% achieved in their study . Thus, concurrent chemotherapy, such as intra-arterial cisplatin in this study, may potentially be a contributing factor to severe optic toxicity after radiotherapy for sinonasal malignancies. Such high rate of optic toxicity was not observed in other studies including patients who also received chemotherapy. Therefore, whether the addition of chemotherapy worsens optic toxicity following RT for sinonasal malignancies is unclear at this time.
IMRT can be challenging at times as no clear consensus exist on how to set the dose constraints for the optic structures (ON/OC). As previous described, a lower incidence of severe vision impairment has been reported in 2D/3D studies when the radiation dose to the optic pathway was kept to ≤ 60 Gy [3–19]. This finding was again evidenced in the IMRT studies. As an illustration, Madani et al. reported only 1.4% severe optic toxicity when < 5% of the optic pathway received more than 60 Gy . The best chance of vision preservation and the avoidance of severe vision impairment appear to be associated with keeping the maximal radiation dose to the optic pathway to approximately 54 Gy or less [3–26]. This is also corroborated by the QUANTEC report on the radiation dose volume effect on the optic pathway . However, it may be difficult to obtain if the tumor is close to the optic apparatus. Other confounding factors such as the volume of the optic apparatus receiving high radiation dose, the influence of chemotherapy and chronic conditions, such as, diabetes mellitus, warrants further investigation in the future . Altered fractionation has not been shown to be associated with worse optic toxicity profiles when compared with other studies in which conventional fractionation is used [5, 6, 8, 9, 25]. This is especially true when the fractional dose was only slightly above 2 Gy [5, 25]. pt]?>Thus, the dose volume effects of altered fractionation schedules with > 2 Gy per fraction will need to be further characterized in the future since many studies were conducted in the pre-3D era when dose to different structures cannot be accurately estimated.
Only small studies on a limited number of patients have conducted to compare IMRT with non-IMRT techniques, and various IMRT strategies [30–41]. Thus, no clear demonstration of the superiority of IMRT over 2D/3D techniques can be made based on these dosimetric studies. However, increased magnitude of intensity modulation through increasing the number of segments, beams, and using a combination of coplanar and non-coplanar arrangements may help increase dose conformality and optic pathway sparing when IMRT is used to treat sinonasal malignancies. This is suggested in studies which demonstrated HT’s superiority over linac-based coplanar IMRT in target dose homogeneity and optic structure sparing; but comparable optic pathway sparing when HT and non-coplanar IMRT were compared [39, 40]. HT’s delivers image guided IMRT with intensity modulation through 51 equally spaced angles . One important component of IMRT optimization to treat sinonasal malignancies is the incorporation of clinical decision into the optimization process. As shown by Tsien et al. decision to spare the contralateral ON only may lead to improved IMRT plan quality and potentially better tumor control in certain cases .
Dose conformality to the target volume and conformal avoidance of the organs at risk achieved through IMRT may provide better local control and less optic toxicity compared to conventional radiotherapy technique. A dose of 54 Gy or less delivered with conventional fractionation to the optic apparatus may provide optimal visual preservation if the tumor is not close to these critical structures. Further prospective studies with long-term follow-up should be conducted to assess how best to preserve vision and improve local control.
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