New inverse planning technology for image-guided cervical cancer brachytherapy: Description and evaluation within a clinical frame

Purpose

To test the feasibility of a new inverse planning technology based on the Hybrid Inverse treatment Planning and Optimisation (HIPO) algorithm for image-guided cervical cancer brachytherapy in comparison to conventional manual optimisation as applied in recent clinical practice based on long-term intracavitary cervical cancer brachytherapy experience.

Materials and methods

The clinically applied treatment plans of 10 tandem/ring (T/R) and 10 cases with additional needles (T/R + N) planned with PLATO v14.3 were included. Standard loading patterns were manually optimised to reach an optimal coverage with 7 Gy per fraction to the High Risk CTV and to fulfil dose constraints for organs at risk. For each of these patients an inverse plan was retrospectively created with Oncentra GYN v0.9.14. Anatomy based automatic source activation was based on the topography of target and organs. The HIPO algorithm included individual gradient and modification restrictions for the T/R and needle dwell times to preserve the spatial high-dose distribution as known from the long-term clinical experience in the standard cervical cancer brachytherapy and with manual planning.

Results

HIPO could achieve a better target coverage (V100) for all T/R and 7 T/R + N patients. Changes in the shape of the overdose volume (V200/400) were limited. The D_2cc per fraction for bladder, rectum and sigmoid colon was on average lower by 0.2 Gy, 0.4 Gy, 0.2 Gy, respectively, for T/R patients and 0.6 Gy, 0.3 Gy, 0.3 Gy for T/R + N patients (a decrease from 4.5 to 4 Gy per fraction means a total dose reduction of 5 Gy EQD2 for a 4-fraction schedule). In general the dwell times in the additional needles were lower compared to manual planning. The sparing factors were always better for HIPO plans. Additionally, in 7 T/R and 7 T/R + N patients all three D_0.1cc, D_1cc and D_2cc for vagina wall were lower and a smaller area of vagina was covered by the reference dose in HIPO plans. Overall loading times in the tandem, the ring and the needles, as well as dose distribution, were largely preserved with adaptations performed due to specific topographical variations, in particular in lateral and caudal directions.

Conclusions

Inverse planning based on the HIPO algorithm can produce treatment plans for cervical cancer brachytherapy which are comparable to plans based on manual optimisation as applied in clinical practice. It is essential to take into account the spatial dose distribution in addition to the DVH-based constraints. The proposed inverse planning concept is feasible for improving the therapeutic ratio and limiting substantial high-dose regions around needles.     

Postmastectomy intensity modulated radiation therapy following immediate expander-implant reconstruction

Background/purpose

To evaluate radiation plans of patients undergoing mastectomy with immediate expander-implant reconstruction followed by postmastectomy radiation therapy (PMRT).

Materials/methods

We identified 41 patients from June 2004 to May 2007 who underwent mastectomy, immediate expander-implant reconstruction, and PMRT with intensity-modulated radiation therapy. We assessed chest wall (CW) coverage and volume of heart and lung irradiated.

Results

In 73% of patients, all CW borders were adequately covered, and in 22%, all but 1 border were adequately covered. The total lung V₂₀ was <20% in 39/41 patients. The mean lung V₂₀ was 13% (range, 3-23%), and the mean heart D_mean was 2.81 Gy (range, 0.53-9.60 Gy). In patients with left-sided lesions without internal mammary nodes (IMNs) treatment (n = 22), the mean lung V₂₀ was 12.6% and the mean heart D_mean was 3.90 Gy, and in the patient with IMN treatment, the lung V₂₀ was 18% and heart D_mean was 8.04 Gy. For right-sided lesions without IMN treatment (n = 12), the mean lung V₂₀ was 12.4% and the mean heart D_mean was 0.90 Gy, and in patients with IMN treatment (n = 6), these numbers were 17.8% and 1.76 Gy. At a median follow-up of 29 months, the 30-month actuarial local control was 97%.

Conclusions

In women undergoing immediate expander-implant reconstruction, PMRT can achieve excellent local control with acceptable heart and lung doses. These results can be achieved even when the IMN are being treated, although doses to the heart and lungs will be higher.     

Correlation of dose-volume parameters, endoscopic and clinical rectal side effects in cervix cancer patients treated with definitive radiotherapy including MRI-based brachytherapy

Purpose

Correlation of dosimetric parameters for MRI-based 3D treatment planning with rectoscopic findings and clinical rectal side effects.

Methods and materials

Rectosigmoidoscopy and rectal morbidity assessment were performed on 35 cervical cancer patients treated with external beam radiotherapy (EBRT) and HDR-intracavitary brachytherapy (ICB). The total doses, normalised to 2 Gy fractions (EQD2, α/β = 3 Gy), in 0.1, 1.0 and 2.0 cm³ (D_0.1cc, D_1cc, D_2cc) of rectum were determined by summation of EBRT and ICB plans. Correlation analysis between clinical symptoms (LENT/SOMA) and rectoscopic changes (Vienna Rectoscopy Score, VRS) was performed. For dose-response analyses, the logit model was applied.

Results

Mean follow-up was 18 months. LENT/SOMA score was 1 in 4 patients, 2 in 8 patients, 4 in 1 patient. Telangiectasia was found in 26 patients (74%), five of them had ulceration corresponding to the 0.1 cm³ volume (anterior wall). Mean values D_0.1cc, D_1cc, and D_2cc were 81 ± 13, 70 ± 9 and 66 ± 8 Gy, respectively. The ED50 values for VRS ? 3 and for LENT/SOMA ? 2 significantly increased with decreasing volumes. D_2cc was higher in patients with VRS ? 3 compared to VRS < 3 (72 ± 6 vs 62 ± 7 Gy; p < 0.001) and in symptomatic vs asymptomatic patients (72 ± 6 vs 63±8 Gy; p < 0.001). VRS correlated with the LENT/SOMA score.

Conclusions

Rectosigmoidoscopy is sensitive in detecting mucosal changes, independent of clinical symptoms. The localization of these changes corresponds to the high dose volumes as defined by imaging. The development of mucosal and clinical changes in the rectum follows a clear dose-effect and volume-effect. DVH parameters could be established.     

Decline of dose coverage between intraoperative planning and post implant dosimetry for I-125 permanent prostate brachytherapy: Comparison between loose and stranded seed implants

Background and purpose

In permanent prostate brachytherapy the dose distributions 4 weeks post implant differ from the intraoperative dose distributions. The purpose of this study is to compare intraoperative planning and post implant dosimetry for loose and stranded seed implants.

Materials and methods

This study investigates prostate dose coverage in 389 patients with stage T1 or T2 prostate cancer treated in the years 2005, 2006 and 2007. The patients received either a loose seed or a stranded seed implant. All patients had US-based intraoperative planning and CT/MRI-based post implant dosimetry after 4 weeks.

Results

Intraoperative and post implant D₉₀ values amounted 183 ± 13 Gy (mean ± standard deviation) and 161 ± 30 Gy, respectively. Decline of D₉₀ values (mean and 95% confidence interval) between intraoperative planning and post implant dosimetry for RAPID strand (n = 67), Intersource strand (n = 136) and loose selectSeeds (n = 186) implants amounted to −40 (−45 to −34) Gy, −25 (−28 to −21) Gy and −15 (−18 to −21) Gy, respectively.

Conclusions

The patients treated in the period 2005-2007 with stranded or loose seed implants had on average adequate D₉₀ values of 161 ± 30 Gy. Post implant D₉₀ values were 22 ± 27 Gy lower compared to intraoperative planning. Decline of dose coverage between intraoperative planning and post implant dosimetry was significantly larger for the stranded seed implants.     

The effect of alternative biological modelling parameters (α/β and half time of repair T1/2) on reported EQD2 values in the treatment of advanced cervical cancer

Purpose

To evaluate the effect of different α/β and half-time of repair T_½ on the assessment of clinical treatment plans for patients with cervical cancer.

Materials and methods

We used EBRT and BT treatment plans of five patients, planned with MRI guided BT. We computed 3D EQD2 dose distributions of combined EBRT and BT treatments and calculated D90 of high-risk clinical target volume (HR-CTV) and D_2cc for bladder and rectum, and the ratio D_2cc(bladder)/D90(HR-CTV). BT was modelled as PDR (two applications of 32 × 60 cGy) and HDR (two applications of 2 × 7 Gy). We assumed a low, standard and high value for the biological parameters: HR-CTV α/β = 5/10/15 Gy and T_½ = 0.5/1.5/2.5 h; OAR α/β = 2/3/4 Gy; T_½ = 0.5/1.5/4.5 h.

Results

The chosen variation in modelling parameters had a much larger effect on PDR treatments than on HDR treatments, especially for OAR, thus creating larger uncertainties. The relative mean range of the ratio D_2cc(bladder)/D90(HR-CTV) is 72% for PDR and 25% for HDR. Out of the 125 modelled combinations 48 PDR plans and 23 HDR plans comply with clinical objectives.

Conclusion

For HDR brachytherapy, only α/β has a significant impact on reported EQD2 values, whereas for PDR both α/β and T_1/2 are important.Generally, the ratio D_2cc(bladder)/D90(HR-CTV) is more favourable for PDR, even considering the larger uncertainties in EQD2.     

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.     

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.     

Dose-effect relationship for local control of cervical cancer by magnetic resonance image-guided brachytherapy

Background and purpose

To analyse dose-response relationships for local control of cervical cancer after MR image-guided brachytherapy (IGBT) based on dose-volume histogram parameters.

Methods and materials

The analysis includes 141 patients with cervix cancer (stages IB-IVA) treated with 45-50.4 Gy EBRT ± cisplatin plus 4 × 7 Gy IGBT. Gross tumour volume (GTV), high risk clinical target volume (HR CTV) and intermediate risk CTV (IR CTV) were delineated and DVH parameters (D90, D100) were assessed. Doses were converted to the equivalent dose in 2 Gy (EQD2) using linear-quadratic model (α/β = 10 Gy). Groups of patients were formed according to tumour size at diagnosis (GTV_D) of 2-5 cm (group 1) or >5 cm (2), with subgroups of the latter for HR CTV size at first IGBT 2-5 cm (2a) or >5 cm (2b). Dose-response dependence for local recurrence was evaluated by logit analysis.

Results

Eighteen local recurrences in the true pelvis were observed. Dose-response analyses revealed a significant effect of HR CTV D100 (p = 0.02) and D90 (p = 0.005). The ED50-values for tumour control were 33 ± 15 Gy (D100) and 45 ± 19 Gy (D90). ED90-values were 67 Gy (95% confidence interval [50;104]) and 86 Gy [77;113], respectively.

Conclusions

A significant dependence of local control on D100 and D90 for HR CTV was found. Tumour control rates of >90% can be expected at doses >67 Gy and 86 Gy, respectively.     

Dosimetric predictor identification for radiation-induced liver disease after hypofractionated conformal radiotherapy for primary liver carcinoma patients with Child-Pugh Grade A cirrhosis

Purpose

Radiation-induced liver disease (RILD) is the most severe complication in liver cancer treatment. The aim of this study was to identify dosimetric predictors for RILD in primary liver carcinoma (PLC) patients with Child-Pugh Grade A cirrhosis after hypofractionated conformal radiotherapy (CRT).

Methods and materials

A total of 114 eligible patients (mean age 45 years old) were enrolled and treated. The mean gross tumor volume (GTV) was (378.3 ± 308.1) cm³. A median dose of 53 Gy was delivered to the PLC by hypofractionated CRT (three fractions/week) with a median fraction size of 4.6 Gy (range: 4-6 Gy).

Results

Patients were followed up for 1-79 months (median 19 months) after the completion of irradiation. RILD was diagnosed in nine (7.9%) patients. Univariate analyses revealed that GTV and the percentage of normal liver volume receiving more than 5-40 Gy irradiations (V_5-40) were related to the risk of developing RILD. Multivariate analyses demonstrated that only GTV and V₂₀ were independent predictors. Using V₂₀ as the predictor for RILD, the accuracy, sensitivity, and specificity was 76.3%, 88.9%, and 75.2%, respectively.

Conclusions

Our data suggest that V₂₀ is the unique significant dosimetric predictor for RILD risks in PLC patients with Child-Pugh Grade A cirrhosis after hypofractionated CRT.     

Does atlas-based autosegmentation of neck levels require subsequent manual contour editing to avoid risk of severe target underdosage? A dosimetric analysis

Background and purpose

To investigate the dosimetric impact of not editing auto-contours of the elective neck and organs at risk (OAR), generated with atlas-based autosegmentation (ABAS) (Elekta software) for head and neck cancer patients.

Materials and methods

For nine patients ABAS auto-contours and auto-contours edited by two observers were available. Based on the non-edited auto-contours clinically acceptable IMRT plans were constructed (designated ‘ABAS plans’). These plans were then evaluated for the two edited structure sets, by quantifying the percentage of the neck-PTV receiving more than 95% of the prescribed dose (V₉₅) and the near-minimum dose (D₉₉) in the neck PTV. Dice coefficients and mean contour distances were calculated to quantify the similarity of ABAS auto-contours with the structure sets edited by observer 1 and observer 2. To study the dosimetric importance of editing OAR auto-contours a new IMRT plan was generated for each patient-observer combination, based on the observer’s edited CTV and the non-edited salivary gland auto-contours. For each plan mean doses for the non-edited glands were compared with doses for the same glands edited by the observer.

Results

For both observers, edited neck CTVs were larger than ABAS auto-contours (p ? 0.04), by a mean of 8.7%. When evaluating ABAS plans on the PTVs of the edited structure sets, V₉₅ reduced by 7.2% ± 5.4% (1 SD) (p < 0.03). The mean reduction in D₉₉ was 14.2 Gy (range 1-54 Gy). Even for Dice coefficients >0.8 and mean contour distances <1 mm, reductions in D₉₉ up to 11 Gy were observed. For treatment plans based on observer PTVs and non-edited auto-contoured salivary glands, the mean doses in the edited glands differed by only −0.6 Gy ± 1.0 Gy (p = 0.06).

Conclusions

Editing of auto-contoured neck CTVs generated by ABAS is required to avoid large underdosages in target volumes. Often used similarity measures for evaluation of auto-contouring algorithms, such as dice coefficients, do not predict well for expected PTV underdose. Editing of salivary glands is less important as mean doses achieved for non-edited glands predict well for edited structures.     

Dose escalation in the radiotherapy of non-small-cell lung cancer with aperture-based intensity modulation and photon beam energy optimization for non-preselected patients

Purpose

To verify the potential of aperture-based intensity-modulated radiotherapy (AB-IMRT) to realize dose escalation plans for non-preselected non-small-cell lung cancer (NSCLC) patients, using photon beam energy optimization.

Methods and materials

Seven cases of NSCLC were retrospectively studied. Clinical reference plans were made at 60 Gy by an experienced dosimetrist. Dose escalation was applied to PTV2, a subvolume within the main PTV1. Escalation plans were optimized by considering beam angles (table and gantry), energy (6 and 23 MV) and weights, for an increasing dose to the PTV2, starting from 66 Gy and keeping 30 fractions.

Results

In five cases, doses over 78 Gy could be achieved before exceeding organs at risk (OARs) standard tolerance. Peripheral overdosages, as well as lung and spinal cord tolerance doses, limited escalation. Means ± SD V_95% parameters were (97.3 ± 0.9)% for PTV1s and (96.7 ± 2.2)% for PTV2s. Doses to OARs were also maintained at acceptable levels. Optimized plans made use of both low- and high-energy beams and had a similar number of monitor units compared to the 60 Gy clinical plans.

Conclusions

The AB-IMRT system can successfully realize dose escalation for a sizeable number of cases. Plans produced contained few large segments, and are applicable to a wide range of tumor volumes and locations.     

Dosimetric comparison of liver tumour radiotherapy in all respiratory phases and in one phase using 4DCT

Purpose

Delineation of target volume could be performed on all respiratory phases and radiation is delivered during free breathing cycle, or on the basis of one respiratory phase and deliver gated treatment choosing a specific phase for irradiation. We performed the comparison of both techniques in terms of target and normal tissue dose distributions.

Materials and methods

We analysed 26 metastatic liver tumours using 4DCT to characterize tumour motion and to create treatment volumes: GITV4D was based on all 8 respiratory phases and GTVGAT was based on one specific phase. A 5 mm automatic expansion was added to the GTVs to create PTVs. Two treatment plans were prepared to the total dose of 36 Gy in 3 fractions and dose-volume distributions were analysed for the target and organs at risk. Target motion along the superior-inferior direction was greatest with the mean of 1.1 cm ± 0.3, and in the lateral the mean was 0.7 cm ± 0.3.

Results

GTV and PTV volumes were larger in the 4D than in the GAT, mean 30.7 vs. 19.3 cm³, and 66.7 vs. 45.1 cm³. We achieved similar dose coverage in PTV4D, for the 4D plan, and PTVGAT for the GAT plan, but a decrease in the average minimum dose to 17.8 Gy and the average mean dose to 35.3 Gy was found in PTV4D in the GAT plan. Radiotherapy delivered using GAT resulted in lower liver doses than using 4D with reduction of mean volume receiving 5 Gy by 6.5% ± 5, V_15Gy by 4.5% ± 3.4, V_21Gy by 3.4% ± 2.8 and reduction of mean kidney volume receiving 5 Gy by 9.1% ± 7.9, V_15Gy by 4.1% ± 6.4, V_21Gy by 3.2% ± 5.6. We also found correlations between PTV volume reduction with GAT, GTV motion and doses to normal tissues.

Conclusions

Gated radiotherapy could potentially allow a reduction in PTV volumes from those delineated on all respiratory phases, maintaining acceptable target coverage. Smaller target volumes improve doses distribution in normal tissue especially in the liver and kidney, but also spinal cord and intestine. A significant correlation has been found between dose and volume reduction in the OARs and both GTV motion and PTV volume reduction.     

Adaptive functional image-guided IMRT in pharyngo-laryngeal squamous cell carcinoma: Is the gain in dose distribution worth the effort?

Background and purpose

The planning process in radiotherapy (RT) typically involves the acquisition of a unique set of CT images - and eventually of functional images - which is used for delineation of target volumes (TV) and organs at risk (OAR) and for dose calculation. Restricting the delineation and dose calculation solely on pre-treatment images is an oversimplification as it is only a snapshot of the patient’s anatomy. The objectives of the present study were (1) to assess the consequences of anatomic modification in dose distribution for both TVs and OARs; (2) to assess the potential benefit of adaptive strategies using Helical Tomotherapy (HT); and (3) to compare CT-based and FDG-PET-based adaptive planning strategies.

Materials and methods

Ten patients with H&N SCC were imaged before and during concomitant chemo-RT using CT and FDG-PET acquisition after a mean dose of 14.2, 24.5, 35.0 and 44.9 Gy. Simultaneous integrated boost IMRT planning was performed using HT. We compared (1) the planned dose distribution, (2) the delivered dose distributions that took into account impact of anatomical modifications on dose distribution, (3) the adaptive dose distributions after replanning to take into account the anatomic modifications and the anatomic or functional GTV shrinkage.

Results

There was an increase between the planned and the delivered high dose volumes, which correlated with the slope of the GTV shrinkage. The adaptive high dose volumes were significantly smaller than the delivered ones. The difference between the adaptive and the delivered high dose volume also correlated with the slope of the GTV shrinkage. For both parotid glands combined, the delivered D_mean showed a statistical trend for an increase of 4.4% compared to the planned D_mean. For the ipsilateral parotid glands, there was a correlation between the D_mean gain and the slope of the GTV shrinkage when an adaptive planning was used. For the oral cavity, the adaptive D_mean was 10% smaller than the delivered ones. For the PRV around the spinal cord, there was an increase of about 4.5% between the delivered and the planned D_2%. The adaptive planning translated into a decrease in D_2% of 7.2%. The differences between the delivered and planned D_2% and between the adaptive and the delivered D_2% were correlated with the slope of the GTV shrinkage. For the CTV_proph and PTV_proph coverage, adaptive strategy induced a better dose conformation. No significant difference was observed in the various figures of merit between PET-based plan and CT-based isodose distributions.

Conclusions

The dose distribution that is actually delivered to patients significantly differs from what was planned because of anatomic modifications. Adaptive multi-modality IMRT is feasible in H&N tumors and could compensate and improve dose distribution. Some useful surrogate criteria or “flags” are, however, needed to identify patients who might benefit from an adaptive strategy. The optimal adaptive strategy still needs to be defined and prospective studies will have to be conducted to address the safety and the clinical impact of such approaches on patient outcome.     

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.     

Volumetric modulated arc therapy and breath-hold in image-guided locoregional left-sided breast irradiation

Purpose

To investigate the effects of using volumetric modulated arc therapy (VMAT) and/or voluntary moderate deep inspiration breath-hold (vmDIBH) in the radiation therapy (RT) of left-sided breast cancer including the regional lymph nodes.

Materials and methods

For 13 patients, four treatment combinations were compared; 3D-conformal RT (i.e., forward IMRT) in free-breathing 3D-CRT(FB), 3D-CRT(vmDIBH), 2 partial arcs VMAT(FB), and VMAT(vmDIBH). Prescribed dose was 42.56 Gy in 16 fractions. For 10 additional patients, 3D-CRT and VMAT in vmDIBH only were also compared.

Results

Dose conformity, PTV coverage, ipsilateral and total lung doses were significantly better for VMAT plans compared to 3D-CRT. Mean heart dose (D_mean,heart) reduction in 3D-CRT(vmDIBH) was between 0.9 and 8.6 Gy, depending on initial D_mean,heart (in 3D-CRT(FB) plans). VMAT(vmDIBH) reduced the D_mean,heart further when D_mean,heart was still >3.2 Gy in 3D-CRT(vmDIBH). Mean contralateral breast dose was higher for VMAT plans (2.7 Gy) compared to 3DCRT plans (0.7 Gy).

Conclusions

VMAT and 3D-CRT(vmDIBH) significantly reduced heart dose for patients treated with locoregional RT of left-sided breast cancer. When D_mean,heart exceeded 3.2 Gy in 3D-CRT(vmDIBH) plans, VMAT(vmDIBH) resulted in a cumulative heart dose reduction. VMAT also provided better target coverage and reduced ipsilateral lung dose, at the expense of a small increase in the dose to the contralateral breast.     

Electron arc therapy for bilateral chest wall irradiation: treatment planning and dosimetric study

Aims

The treatment of patients with synchronous bilateral breast cancer is a challenge. We present a report of dosimetric data of patients with bilateral chest walls as the target treated with electron arc therapy.

Materials and methods

Ten consecutive patients who had undergone electron arc therapy to the bilateral chest wall for breast cancer were analysed. After positioning and immobilisation, patients underwent computed tomography scans from the neck to the upper abdomen. Electron arc plans were generated using the PLATO RTS (V1.8.2 Nucletron) treatment planning system. Electron energy was chosen depending upon the depth and thickness of the planning target volume (PTV). For all patients, the arc angle ranged between 80 and 280° (start angle 80°, stop angle 280°). The homogeneity index, coverage index and doses to organs at risk were evaluated. The patient-specific output factor and thermoluminescence dosimetry (TLD) measurements were carried out for all patients. The total planned dose to the PTV was 50 Gy/25 fractions/5 weeks.

Results

The mean PTV (± standard deviation) was 568.9 (±116) cm³. The mean PTV coverage was 89 (±5.8)% of the prescribed dose. For the right lung, the mean values of D₁ and D₁₀ were 46 (±7.6) and 30 (±9) Gy, respectively. For the left lung, the mean values of D₁ and D₁₀ were 45 (±7) and 27 (±8) Gy, respectively. For the heart, the mean values of D₁, D₅ and D₁₀ were 21 (±15), 13.5 (±12) and 9 (±9) Gy, respectively. The mean values of TLD at various pre-specified locations on the chest wall surface were 1.84, 1.82, 1.82, 1.89 and 1.78 Gy, respectively

Conclusion

The electron arc technique for treating the bilateral chest wall is a feasible and pragmatic technique. This technique has the twin advantages of adequate coverage of the target volume and sparing of adjacent normal structures. However, compared with other techniques, it needs a firm quality assurance protocol for dosimetry and treatment delivery.