Volumetric modulated arc therapy versus conventional intensity modulated radiation therapy for stereotactic spine radiotherapy: A planning study and early clinical data

Background and purpose

Outcomes for selected patients with spinal metastases may be improved by dose escalation using stereotactic body radiation therapy (SBRT). As target geometry is complex, we compared SBRT plans using volumetric modulated arc radiotherapy (RapidArc®, RA) and conventional intensity-modulated radiotherapy (IMRT).

Materials and methods

RA and IMRT plans to deliver a fraction of 16 Gy to at least 90% of planning target volume (PTV) were compared for PTV coverage, normal organ sparing and estimated delivery times. Group 1 consisted of PTVs to only vertebral body (n = 3), while group 2 had PTVs encompassing the entire vertebra (n = 4). Finally, RA delivery parameters in four patients were assessed.

Results

Both techniques delivered 16 Gy to a mean of 95% and 85% of the PTV in groups 1 and 2, respectively. Spinal cord sparing was comparable; mean V_{10-partial cord} for RA and IMRT in group 1 was 3.6%, and was 9.4% versus 11.5%, respectively, in group 2. Estimated mean treatment times for RA with 2-3 arcs and IMRT were comparable. Clinical RA beam-on times ranged from 11 to 15.4 min.

Conclusions

Both RA and conventional IMRT plans deliver high quality vertebral SBRT, but plan quality was poorer when the PTV consisted of the entire vertebra.     

Endorectal balloon reduces anorectal doses in post-prostatectomy intensity-modulated radiotherapy

Background and purpose

To investigate the effect of an endorectal balloon (ERB) on anal wall (Awall) and rectal wall (Rwall) doses in high-dose post-prostatectomy intensity-modulated radiotherapy (IMRT).

Materials and methods

For 20 patients, referred for salvage IMRT after prostatectomy for prostate cancer, two planning CT-scans were performed: one with and one without an air-filled ERB. A planning target volume (PTV) was defined, using international guidelines. Furthermore, the Awall and Rwall were delineated. In both the scans, IMRT plans were generated with a prescribed dose of 70 Gy. The mean dose (D_mean), maximum dose, minimum dose, and volumes exposed to doses ranging from ?20 to ?70 Gy (V₂₀-V₇₀) to the Awall and Rwall were calculated. Finally, inner Rwall surface areas exposed to doses ranging from ?20 to ?70 Gy (A₂₀-A₇₀) were calculated. Dose-parameters were compared between plans with and without ERB.

Results

All Awall parameters, except V₇₀, were significantly reduced by the ERB with an overall D_mean reduction of 6 Gy. Absolute reductions in dose-volume parameters varied from 5% to 11%. Significantly reduced Rwall V₃₀, V₄₀, and A₄₀ were observed with ERB, irrespective of the target volume size.

Conclusion

ERB application significantly reduces Awall and to a lesser degree Rwall doses in high-dose post-prostatectomy IMRT.     

Dosimetric effect of setup motion and target volume margin reduction in pediatric ependymoma

Purpose

Quantify the dosimetric effect of inter- and intrafractional motion on intensity-modulated radiation therapy (IMRT) and three-dimensional (3D) planning via changes in the generalized equivalent uniform dose (gEUD), predicted tumor control probability (TCP) and normal tissue complication probability (NTCP) for pediatric ependymoma.

Methods and materials

Twenty patients treated between 1998 and 2002 with a 3D plan (CTV = 1 cm, PTV = 5 mm) were selected. Two IMRT plans were created for the 1 cm CTV (PTV = 5 mm and PTV = 0 mm), and a third IMRT plan for a 5 mm CTV (PTV = 0 mm).Direct simulation with inter- and intrafractional motion was performed for 3D and IMRT plans based on daily pre and post-treatment cone beam CT information obtained from 20 well-matched patients (age, supine/prone, use of GA) on a localization protocol. Calculated TCP, NTCP, Conformity Index (CI), and predictive IQ were compared.

Results

IMRT improved the calculated TCP by 2.8 ± 2.8 vs. 3D (p < 0.001). Inter- and intrafractional motion results in a TCP loss of 0.4 ± 0.7 (p = 0.02) and 0.0 ± 0.1 (p = 0.14) for the IMRT plan with PTV = 0 mm. Mean NTCP for 3D and IMRT with PTV = 5 mm, PTV = 0 mm, and CTV = 5 mm for the cochlea was: 66.6, 29.4, 8.7. Mean NTCP change due to motion was <5%. CI was 0.70 ± 0.06 for IMRT and 0.5 ± 0.10 for 3D. Predictive IQ was 10.0 ± 10.3 points higher for IMRT vs. 3D.

Conclusions

IMRT improves calculated TCP vs. 3D. Daily localization can allow for a safe reduction in the PTV margin, while maintaining target coverage; reducing the CTV margin can further reduce NTCP and may reduce future side-effects.     

Is ad-hoc plan adaptation based on 2-Step IMRT feasible?

Background

The ability of a geometry-based method to expeditiously adapt a “2-Step” step and shoot IMRT plan was explored. Both changes of the geometry of target and organ at risk have to be balanced. A retrospective prostate planning study was performed to investigate the relative benefits of beam segment adaptation to the changes in target and organ at risk coverage.

Methods

Four patients with six planning cases with extraordinarily large deformations of rectum and prostate were chosen for the study. A 9-field IMRT plan (A) using 2-Step IMRT segments was planned on an initial CT study. The plan had to fulfil all the requirements of a conventional high-quality step and shoot IMRT plan. To adapt to changes of the anatomy in a further CT data set, three approaches were considered: the original plan with optimized isocentre position (B), a newly optimized plan (C) and the original plan, adapted using the 2-Step IMRT optimization rules (D). DVH parameters were utilized for quantification of plan quality: D₉₉ for the CTV and the central planning target volume (PTV), D₉₅ for an outer PTV, V₉₅, V₈₀ and V₅₀ for rectum and bladder.

Results

The adapted plan (D) achieved almost the same target coverage as the newly optimized plan (C). Target coverage for plan B was poor and for the organs at risk, the rectum V₈₀ was slightly increased. The volume with more than 95% of the target dose (V₉₅) was 1.5 ± 1.5 cm³ for the newly optimized plan (C), compared to 2.2 ± 1.3 cm³ for the original plan (A) and 7.2 ± 4.8 cm³ (B) on the first and the second CT, respectively. The adapted plan resulted in 4.3 ± 2.1 cm³ (D), an intermediate dose load to the rectum. All other parameters were comparable for the newly optimized and the adapted plan.

Conclusions

The first results for adaptation of interfractional changes using the 2-Step IMRT algorithm are encouraging. The plans were superior to plans with optimized isocentre position and only marginally inferior to a newly optimized plan.     

Comparison of intensity-modulated radiotherapy, adaptive radiotherapy, proton radiotherapy, and adaptive proton radiotherapy for treatment of locally advanced head and neck cancer

Background and purpose

Various radiotherapy planning methods for locally advanced squamous cell carcinoma of the head and neck (SCCHN) have been proposed to decrease normal tissue toxicity. We compare IMRT, adaptive IMRT, proton therapy (IMPT), and adaptive IMPT for SCCHN.

Materials and methods

Initial and re-simulation CT images from 10 consecutive patients with SCCHN were used to quantify dosimetric differences between photon and proton therapy. Contouring was performed on both CTs, and plans (n = 40 plans) and dose-volume histograms were generated.

Results

The mean GTV volume decreased 53.4% with re-simulation. All plans provided comparable PTV coverage. Compared with IMRT, adaptive IMRT significantly reduced the maximum dose to the mandible (p = 0.020) and mean doses to the contralateral parotid gland (p = 0.049) and larynx (p = 0.049). Compared with IMRT and adaptive IMRT, IMPT significantly lowered the maximum doses to the spinal cord (p < 0.002 for both) and brainstem (p < 0.002 for both) and mean doses to the larynx (p < 0.002 for both) and ipsilateral (p = 0.004 IMRT, p = 0.050 adaptive) and contralateral (p < 0.002 IMRT, p = 0.010 adaptive) parotid glands. Adaptive IMPT significantly reduced doses to all critical structures compared with IMRT and adaptive IMRT and several critical structures compared with non-adaptive IMPT.

Conclusions

Although adaptive IMRT reduced dose to several normal structures compared with standard IMRT, non-adaptive proton therapy had a more favorable dosimetric profile than IMRT or adaptive IMRT and may obviate the need for adaptive planning. Protons allowed significant sparing of the spinal cord, parotid glands, larynx, and brainstem and should be considered for SCCHN to decrease normal tissue toxicity while still providing optimal tumor coverage.     

A quality control model that uses PTV-rectal distances to predict the lowest achievable rectum dose,improves IMRT planning for patients with prostate cancer

Background and purpose

To predict the lowest achievable rectum D35 for quality assurance of IMRT plans of prostate cancer patients.

Materials and methods

For each of 24 patients from a database of 47 previously treated patients, the anatomy was compared to the anatomies of the other 46 to predict the minimal achievable rectum D35. The 24 patients were then replanned to obtain maximally reduced rectum D35. Next, the newly derived plans were added to the database to replace the original clinical plans, and new predictions of the lowest achievable rectum D35 were made.

Results

After replanning, the rectum D35 reduced by 9.3 Gy ± 6.1 (average ± 1 SD; p < 0.001) compared to the original plan. The first predictions of the rectum D35 were 4.8 Gy ± 4.2 (average ± 1 SD; p < 0.001) too high when evaluated with the new plans. After updating the database, the replanned and newly predicted rectum D35 agreed within 0.1 Gy ± 2.8 (average ± 1 SD; p = 0.89). The doses to the bladder, anus and femoral heads did not increase compared to the original plans.

Conclusions

For individual prostate patients, the lowest achievable rectum D35 in IMRT planning can be accurately predicted from dose distributions of previously treated patients by quantitative comparison of patient anatomies. These predictions can be used to quantitatively assess the quality of IMRT plans.     

A study of middle ear function in the treatment of nasopharyngeal carcinoma with IMRT technique

Purpose

This study evaluates the difference in damage to middle ear function with CRT and IMRT techniques in the treatment of nasopharyngeal carcinoma (NPC). We explore the isthmus of the Eustachian tube (ET) as the key anatomic site for the prevention of radiation-induced otitis media with effusion.

Methods and materials

Eighty-two patients with NPC were divided into two groups: 40 patients treated with CRT and 42 patients treated with IMRT. The difference between dosage over the middle ear cavity and the isthmus of the ET was evaluated in both CRT group and IMRT group. All patients underwent hearing tests including pure tone audiometry and impedance audiometry before and after RT.

Results

The dosage difference to the middle ear cavity and isthmus between these two groups was statistically significant (p < 0.05). The difference in hearing test results between these two groups was also statistically significant (p < 0.05). If we limited the dose to the middle ear cavity under 34 Gy and the dose to the isthmus under 53 Gy with IMRT, we may decrease radiation-induced OME even with the larger 2.25 Gy fraction size.

Conclusions

IMRT may have better protected the middle ear function compared with the CRT technique, even with larger fraction sizes than for the conventional CRT technique.     

Dosimetric effect of target expansion and setup uncertainty during radiation therapy in pediatric craniopharyngioma

Purpose

Investigate the effect of tumor change and setup uncertainties on target coverage for pediatric craniopharyngioma during RT.

Methods and materials

Fifteen pediatric patients with craniopharyngioma (mean 5.1 years) were included in this study. MRI was performed before and a median of six times during RT to monitor changes in the tumor volume. IMRT plans were created and compared to the CRT plan used for treatment. The role of adaptive therapy based on GTV changes was investigated. Dosimetric effects of interfraction and intrafraction motion were examined.

Results

The mean of the maximal change in the GTV was 28.5% [−20.7% to 82.0%]. For the standard margin IMRT plans, the mean D₉₅ of the base plan on the base target was 53.6 Gy [53.1-54.1]. The mean D₉₅ of the base plans on the adaptive targets was 52.1 Gy [47.9-54.1]. The D₉₅ for the adaptive plan on the adaptive target was 53.8 Gy [53.4-54.3]. A linear regression equation of y=-0.12x , r² = 0.70, was found for the percent change in D₉₅ of the PTV (y) vs. the percent change in the GTV (x). Inter and intrafraction motion did not affect the target coverage for standard and reduced margin plans.

Conclusions

The GTV of pediatric craniopharyngioma patients change size during therapy and adaptive planning is critical for conformal plans; therefore early and regular surveillance imaging is required.     

Inclusion of clinical risk factors into NTCP modelling of late rectal toxicity after high dose radiotherapy for prostate cancer

Background and purpose

To fit an NTCP model including clinical risk factors to late rectal toxicities after radiotherapy for prostate cancer.

Methods and materials

Data of 669 patients were considered. The probability of late toxicity within 36 months (bleeding and incontinence) was fitted with the original and a modified Logit-EUD model, including clinical factors by fitting a subset specific TD₅₀s: the ratio of TD₅₀s with and without including the clinical variable was the dose-modifying factor (D_mod).

Results

Abdominal surgery (surg) was a risk factor for G2-G3 bleeding, reflecting in a TD₅₀ = 82.7 Gy and 88.4 Gy for patients with and without surg (D_mod = 0.94; 0.90 for G3 bleeding); acute toxicity was also an important risk factor for G2-G3 bleeding (D_mod = 0.93). Concerning incontinence, surg and previous diseases of the colon were the clinical co-factors. D_mod(surg) and D_mod(colon) were 0.50 and 0.42, respectively for chronic incontinence and 0.73 and 0.64, respectively for mean incontinence score ?1. Best-fit n values were 0.03-0.05 and 1 for bleeding and incontinence, respectively. The inclusion of clinical factors always improved the predictive value of the models.

Conclusions

The inclusion of predisposing clinical factors improves NTCP estimation; the assessment of other clinical and genetic factors will be useful to reduce parameter uncertainties.     

A treatment planning study comparing helical tomotherapy with intensity-modulated radiotherapy for the treatment of anal cancer

Purpose

A planning study to compare helical tomotherapy (HT) and intensity-modulated radiotherapy (IMRT) for the treatment of anal canal cancer.

Materials and methods

Sixteen (8 males and 8 females) patients with anal cancer previously treated radically were identified. HT and IMRT plans were generated and dosimetric comparisons of the plans were performed. The planning goals were to deliver 54 Gy to the tumor (PTV_54Gy) and 48 Gy to the nodes at risk (PTV_Node) in 30 fractions.

Results

PTVs: HT plans were more homogeneous for both men and women. Male patients: HT vs. IMRT: D_max: 55.87 ± 0.58 vs. 59.17 ± 3.24 (p = 0.036); D_min: 52.91 ± 0.36 vs. 44.09 ± 6.84 (p = 0.012); female patients: HT vs. IMRT: D_max: 56.14 ± 0.71 vs. 59.47 ± 0.81 (p = 0.012); D_min: 52.36 ± 0.87 vs. 50.97 ± 1.42 (p = 0.028). OARs: In general, HT plans delivered a lower dose to the peritoneal cavity, external genitalia and the bladder and IMRT plans resulted in greater sparing of the pelvic bones (iliac crest/femur) for both men and women. Iliac crest/femur: the difference was significant only for the mean V10 Gy of iliac crest in women (p ? 0.012). External genitalia: HT plans achieved better sparing in women compared to men (p ? 0.046). For men, the mean doses were 18.96 ± 3.17 and 15.72 ± 3.21 for the HT and IMRT plan, respectively (p ? 0.017). Skin: both techniques achieved comparable sparing of the non-target skin (p = NS).

Conclusions

HT and IMRT techniques achieved comparable target dose coverage and organ sparing, whereas HT plans were more homogeneous for both men and women.     

Single Arc Volumetric Modulated Arc Therapy of head and neck cancer

Background

The quality of Volumetric Modulated Arc Therapy (VMAT) plans is highly dependent on the performance of the optimization algorithm used. Recently new algorithms have become available which are capable of generating VMAT plans for Elekta accelerators. The VMAT algorithm in Pinnacle³® is named SmartArc and its capability to generate treatment plans for head and neck cancer was tested.

Methods

Twenty-five patients with oropharyngeal or hypopharyngeal carcinoma, previously treated with IMRT by means of Pinnacle³® and Elekta accelerators, were replanned with single arc VMAT. The VMAT planning objectives were to achieve clinical target coverage and sparing of the organs at risk (OAR). Comparison with the original clinically used IMRT was made by evaluating (1) dose-volume histograms (DVHs) for PTVs, (2) DVHs for OARs, (3) delivery time and monitor units (MU), and (4) treatment accuracy.

Results

Equivalent or superior target coverage and sparing of OARs were achieved with VMAT compared to IMRT. Volumes in the healthy tissues receiving between 17.3 Gy and 49.4 Gy were significantly reduced and the conformity (CI_95%) of the elective PTV was improved from 1.7 with IMRT to 1.6 with VMAT. Compared to step-and-shoot IMRT, VMAT reduced the number of MUs by 8.5% to 460 ± 63 MUs per fraction, and delivered on an Elekta Synergy accelerator, the treatment time was on average reduced by 35% to 241 ± 16 s. In Delta4® measurements of the VMAT treatments, 99.6 ± 0.5% of the detector points passed a 3 mm and 3% gamma criterion, identical to the results of IMRT.

Conclusions

The target coverages obtained in the IMRT and VMAT plans were found to be very similar. SmartArc generated single arc VMAT plans with equivalent or better target coverage and sparing of OARs compared to IMRT, while both delivery time and MUs were decreased. Very good dose accuracy results were obtained delivering the plans on an Elekta accelerator.     

A methodology for incorporating functional bone marrow sparing in IMRT planning for pelvic radiation therapy

Background and purpose

The purpose of this study was to design a radiation therapy treatment planning approach that would spare hematopoietically active bone marrow using [¹⁸F]FLT PET imaging.

Materials and methods

We have developed an IMRT planning methodology to incorporate functional PET imaging using [¹⁸F]FLT scans. Plans were generated for two simulated cervical cancer patients, where pelvic active bone marrow regions were incorporated as avoidance regions based on the ranges: SUV4 ? 4; 4 > SUV3 ? 3; and 3 > SUV2 ? 2. Dose objectives were set to reduce bone marrow volume that received 10 (V₁₀) and 20 (V₂₀) Gy.

Results

Active bone marrow regions identified by [¹⁸F]FLT with an SUV ? 2, SUV ? 3, and SUV ? 4 represented an average of 43.0%, 15.3%, and 5.8%, respectively of the total osseous pelvis for the two cases studied. Improved dose-volume histograms for all identified bone marrow SUV volumes and decreases in V₁₀, and V₂₀ were achieved without clinically significant changes to PTV or OAR doses.

Conclusions

Incorporation of [¹⁸F]FLT PET in IMRT planning provides a methodology to reduce radiation dose to active bone marrow without compromising PTV or OAR dose objectives in pelvic malignancies.     

Stereotactic radiotherapy for peripheral lung tumors: A comparison of volumetric modulated arc therapy with 3 other delivery techniques

Purpose

Volumetric modulated arc therapy (RapidArc) allows for fast delivery of stereotactic body radiotherapy (SBRT) delivery in stage I lung tumors. We compared dose distributions and delivery times between RapidArc and common delivery techniques in small tumors.

Methods

In 18 patients who completed RapidArc SBRT for tumors measuring <70 cm³, new treatment plans were generated using non-coplanar 3D conformal fields (conf-SBRT) and dynamic conformal arc radiotherapy (DCA). For 9 patients with tumors adjacent to the chest wall, co-planar intensity-modulated radiotherapy (IMRT) plans were also generated. PTV dose coverage, organs at risk (OAR) doses and treatment delivery times were assessed.

Results

RapidArc plans achieved a superior conformity index (CI) and lower V_45Gy to chest wall (p < 0.05) compared to all other techniques. RapidArc led to a small increase in V_5Gy to contralateral lung compared to conf-SBRT (4.4 ± 4% versus 1.2 ± 1.8%, p = 0.011). For other OAR, RapidArc and conf-SBRT plans were comparable, and both were superior to DCA plans. Delivery of a 7.5 Gy-fraction required 3.9 min (RapidArc), 11.6 min (conf-SBRT), and 12 min (IMRT).

Conclusions

In stage I lung tumors measuring <70 cm³, RapidArc plans achieved both the highest dose conformity and shortest delivery times.     

Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer

Introduction

Volumetric modulated arc therapy (VMAT), a complex treatment strategy for intensity-modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares VMAT against established IMRT and 3D-conformal radiation therapy (3D-CRT) delivery techniques.

Methods

Based on CT datasets of 9 patients treated for prostate cancer step-and-shoot IMRT, serial tomotherapy (MIMiC), 3D-CRT and VMAT were compared with regard to plan quality and treatment efficiency. Two VMAT approaches (one rotation (VMAT1x) and one rotation plus a second 200° rotation (VMAT2x)) were calculated for the plan comparison. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D_95% (dose encompassing 95% of the target volume). For plan efficiency evaluation, treatment time and number of monitor units (MU) were considered.

Results

For MIMiC/IMRT_MLC/VMAT2x/VMAT1x/3D-CRT, mean CI was 1.5/1.23/1.45/1.51/1.46 and HI was 1.19/1.1/1.09/1.11/1.04. For a prescribed dose of 76 Gy, mean doses to organs-at-risk (OAR) were 50.69 Gy/53.99 Gy/60.29 Gy/61.59 Gy/66.33 Gy for the anterior half of the rectum and 31.85 Gy/34.89 Gy/38.75 Gy/38.57 Gy/55.43 Gy for the posterior rectum. Volumes of non-target normal tissue receiving ?70% of prescribed dose (53 Gy) were 337 ml/284 ml/482 ml/505 ml/414 ml, for ? 50% (38 Gy) 869 ml/933 ml/1155 ml/1231 ml/1993 ml and for ? 30% (23 Gy) 2819 ml/3414 ml/3340 ml/3438 ml /3061 ml. D_95% was 69.79 Gy/70.51 Gy/71,7 Gy/71.59 Gy/73.42 Gy. Mean treatment time was 12 min/6 min/3.7 min/1.8 min/2.5 min.

Conclusion

All approaches yield treatment plans of improved quality when compared to 3D-conformal treatments, with serial tomotherapy providing best OAR sparing and VMAT being the most efficient treatment option in our comparison. Plans which were calculated with 3D-CRT provided good target coverage but resulted in higher dose to the rectum.     

Dose escalation in prostate cancer using intensity modulated neutron radiotherapy

Background and purpose

Initial promising results of 3D conformal neutron radiotherapy (3D-CNRT) were subsequently limited by high normal tissue toxicities. It is now possible to deliver intensity modulated neutron radiotherapy (IMNRT). The present work compares photon IMRT, 3D-CNRT and IMNRT for three prostate patients to quantify the benefits of IMNRT.

Materials and methods

We compare updated 3D-CNRT plans, IMNRT plans, and conventional IMRT plans by translating neutron DVHs into effective photon DVHs using the dose dependent radiobiological effectiveness (RBE) for each structure. RBE curves are parameterized for a range of normal tissue and prostate tumor values. Generalized equivalent uniform dose (gEUD) and gEUD in 2 Gy fractions (gEUD₂) is calculated for each structure, plan, and parameterization. Rectal sparing and dose to prostate-GTV are compared for 3D-CNRT, IMNRT, and IMRT as a function of normal tissue and prostate RBE.

Results

The closer the RBE values of prostate tumor and normal tissue, the greater the advantage of IMNRT over 3D-CNRT. The rectal sparing achieved using IMNRT ranged from ∼5% to 13% depending upon the choice of RBE for rectum and the α/β value of prostate tumor. IMNRT may provide a theoretical dose advantage over photon IMRT if the α/β value of prostate is 1.5 and the RBEs of prostate and rectum differ by more than 5%. For higher values of prostate α/β any advantages of IMNRT over IMRT could require that the RBEs of prostate and rectum differ by as much as 20%.

Conclusions

IMNRT provides a clear normal tissue sparing advantage over 3D-CNRT. The advantage increases when the RBEs of the target structure and the normal tissue are similar. This RBE translation method could help identify clinical sites where the dose sparing advantages of IMNRT would allow for the exploitation of the radiobiological advantages of high-LET neutron radiotherapy.     

Optimising stereotactic body radiotherapy for non-small cell lung cancer with volumetric intensity-modulated arc therapy--a planning study

Aims

The potential advantages of stereotactic body radiotherapy (SBRT) for early stage non-small cell lung cancer (NSCLC) over conventional fractionated radiotherapy include a higher biological effective dose, a reduction in accelerated repopulation, greater patient convenience and reduced demand on radiotherapy resources. Before introducing SBRT in our department, a review of planning and delivery was undertaken, starting with an assessment of optimum beam number and arrangement.

Materials and methods

Radiotherapy planning computed tomography scans for five patients previously treated for T1 peripheral NSCLC were selected. In each the contoured tumour had planning target volume (PTV) margins of 1 cm in all directions. Forward-planned three-field coplanar and non-coplanar plans and a seven-field coplanar plan were produced and optimised. In-house inverse-planning software (AutoBeam) was used to generate three-, five-, seven- and nine-field coplanar and non-coplanar plans and two volumetric intensity-modulated arc therapy (VMAT) plans. The resulting V₂₀, V₁₁, PTV₉₀, PTV₉₅ and mean lung dose were compared.

Results

Analysis of variance showed non-coplanar plans to have lower V₁₁ and higher PTV₉₀ and PTV₉₅ than coplanar plans. VMAT showed equivalent V₂₀ and target coverage when compared with the best non-coplanar plans, but with a faster delivery time (2 min 8 s versus 12 min 40 s).

Conclusions

Inverse-planned five-field non-coplanar plans and VMAT improve target coverage while minimising the higher dose to normal lung tissue for SBRT of NSCLC compared with coplanar beam arrangements. VMAT is preferable because of significantly shorter treatment delivery times.