Integrated-boost IMRT or 3-D-CRT using FET-PET based auto-contoured target volume delineation for glioblastoma multiforme - a dosimetric comparison

Purpose

A study was performed comparing dosimetric characteristics of volumetric modulated arcs (RapidArc, RA) and fixed field intensity modulated therapy (IMRT) on patients with bilateral breast carcinoma.

Materials and methods

Plans for IMRT and RA, were optimised for 10 patients prescribing 50 Gy to the breast (PTVII, 2.0 Gy/fraction) and 60 Gy to the tumour bed (PTVI, 2.4 Gy/fraction). Objectives were: for PTVs V_90%>95%, D_max<107%; Mean lung dose MLD<15 Gy, V_{20 Gy}<22%; heart involvement was to be minimised. The MU and delivery time measured treatment efficiency. Pre-treatment dosimetry was performed using EPID and a 2D-array based methods.

Results

For PTVII minus PTVI, V_90% was 97.8 ± 3.4% for RA and 94.0 ± 3.5% for IMRT (findings are reported as mean ± 1 standard deviation); D_5%-D_95% (homogeneity) was 7.3 ± 1.4 Gy (RA) and 11.0 ± 1.1 Gy (IMRT). Conformity index (V_95%/V_PTVII) was 1.10 ± 0.06 (RA) and 1.14 ± 0.09 (IMRT). MLD was <9.5 Gy for all cases on each lung, V_{20 Gy} was 9.7 ± 1.3% (RA) and 12.8 ± 2.5% (IMRT) on left lung, similar for right lung. Mean dose to heart was 6.0 ± 2.7 Gy (RA) and 7.4 ± 2.5 Gy (IMRT). MU resulted in 796 ± 121 (RA) and 1398 ± 301 (IMRT); the average measured treatment time was 3.0 ± 0.1 minutes (RA) and 11.5 ± 2.0 (IMRT). From pre-treatment dosimetry, % of field area with γ <1 resulted 98.8 ± 1.3% and 99.1 ± 1.5% for RA and IMRT respectively with EPID and 99.1 ± 1.8% and 99.5 ± 1.3% with 2D-array (ΔD = 3% and DTA = 3 mm).

Conclusion

RapidArc showed dosimetric improvements with respect to IMRT, delivery parameters confirmed its logistical advantages, pre-treatment dosimetry proved its reliability.     

Comparaison entre arcthérapie volumétrique modulée et tomothérapie pour le cancer du col utérin,avec irradiation lomboaortique

PurposeIntensity-modulated radiotherapy (IMRT) has proven its dosimetric superiority over conformational radiotherapy for cervix cancers in terms of digestive toxicity. Volumetric modulated arctherapy (VMAT) has shown its dosimetric interest when compared to IMRT with static beams. The purpose of our study was to compare conformational radiotherapy, VMAT and tomotherapy for cervical cancers with para-aortic lymph nodes irradiation.Patients and methodsThe dosimetric data from ten patients were compared between the three techniques, with collection of the dose received by the planning target volume, kidneys, bowel, rectum, bladder, bone marrow and spinal cord, as well as the complete dose.ResultsThere was a significant difference in favour of VMAT and tomotherapy when compared with conformational radiotherapy for the organs at risk: intestines (V_20 Gy, V_30 Gy and V_45 Gy), rectum (V_30 Gy and V_45 Gy), bladder (V_30 Gy and V_45 Gy) and kidneys (V_12 Gy, D_average, V_20 Gy). Volumes receiving 20, 30 and 45 Gy were significantly higher in conformational radiotherapy than in VMAT and tomotherapy. There was a significant difference in favour of tomotherapy when compared with VMAT for V_12 Gy in kidneys and V_45 Gy in the bladder.ConclusionThis study confirms the interest of VMAT and tomotherapy for pelvic and para-aortic lymph nodes irradiation of cervix cancer when compared with conformational radiotherapy. There was little difference between VMAT and tomotherapy, except for kidney sparing, which was better with tomotherapy and thus may be interesting for patients receiving nephrotoxic chemotherapy.     

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 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.     

Improving bladder cancer treatment with radiotherapy using separate intensity modulated radiotherapy plans for boost and elective fields

The aim of this study is to investigate to what extent IMRT can decrease the dose to the organs at risk in bladder cancer treatment compared with conformal treatment while making separate treatment plans for the elective field and the boost. Special attention is paid to sparing small intestines. Twenty patients who were treated with the field-in-field technique (FiF) were re-planned with intensity modulated radiotherapy (IMRT) using five and seven beams, respectively. Separate treatment plans were made for the elective field (including the pelvic lymph nodes) and the boost, which enables position correction for bone and tumour separately. The prescribed dose was 40 Gy to the elective field and 55 or 60 Gy to the planning target volume (PTV). For bladder and rectum, V_45Gy and V_55Gy were compared, and for small intestines, V_25Gy and V_40Gy. The dose distribution with IMRT conformed better to the shape of the target. There was no significant difference between the techniques in dose to the healthy bladder. The median V_40Gy of the small intestines decreased from 114 to 66 cc (P = 0.001) with five beam IMRT, and to 55 cc (P = 0.001) with seven beam IMRT compared with FiF. V_45Gy for rectum decreased from 34.2% to 17.5% (P = 0.004) for both five and seven beam plans, while V_55Gy for rectum remained the same. With IMRT, a statistically significant dose decrease to the small intestines can be achieved while covering both tumour and elective PTV adequately.     

Evaluation of treatment plan quality of IMRT and VMAT with and without flattening filter using Pareto optimal fronts

Purpose

To investigate the differences in treatment plan quality of IMRT and VMAT with and without flattening filter using Pareto optimal fronts, for two treatment sites of different anatomic complexity.

Materials and Methods

Pareto optimal fronts (POFs) were generated for six prostate and head-and-neck cancer patients by stepwise reduction of the constraint (during the optimization process) of the primary organ-at-risk (OAR). 9-static field IMRT and 360°-single-arc VMAT plans with flattening filter (FF) and without flattening filter (FFF) were compared. The volume receiving 5 Gy or more (V_5Gy) was used to estimate the low dose exposure. Furthermore, the number of monitor units (MUs) and measurements of the delivery time (T) were used to assess the efficiency of the treatment plans.

Results

A significant increase in MUs was found when using FFF-beams while the treatment plan quality was at least equivalent to the FF-beams. T was decreased by 18% for prostate for IMRT with FFF-beams and by 4% for head-and-neck cases, but increased by 22% and 16% for VMAT. A reduction of up to 5% of V_5Gy was found for IMRT prostate cases with FFF-beams.

Conclusions

The evaluation of the POFs showed an at least comparable treatment plan quality of FFF-beams compared to FF-beams for both treatment sites and modalities. For smaller targets the advantageous characteristics of FFF-beams could be better exploited.     

Dual arc volumetric-modulated arc radiotherapy (VMAT) of nasopharyngeal carcinomas: a simultaneous integrated boost treatment plan comparison with intensity-modulated radiotherapies and single arc VMAT

AimsTo compare the performance of volumetric-modulated arc radiotherapy (VMAT) by dual arc with fixed beam intensity-modulated radiotherapies (IMRTs) and single arc VMAT on nasopharyngeal carcinomas (NPC).Materials and methodsTwenty NPC cases were re-planned using the planning system of the Pinnacle^3®SmartArc (SA) module to compare the performance of the following four techniques: seven-field (7F) and 18-field (18F) fixed beam IMRT, and single (SA₁) and dual arc VMAT (SA₂). The plan was delivered on an Elekta Synergy? Linac equipped with an 80-leaf 1 cm multileaf collimator. Three dose levels of planning target volumes (PTVs) with 70/59.4/54.0 Gy in 33 fractions were prescribed and delivered as a simultaneous integrated boost. The conformity index and homogeneity index of the PTVs, the comprehensive quality index (CQI), the normal tissue complication probability for the organs at risk (OARs), and the planning time, delivery efficiency and accuracy were analysed.ResultsA significantly inferior conformity index at the three dose levels of PTV and homogeneity index of PTV₇₀ were observed in SA₁ compared with the other techniques. Comparable conformity index and homogeneity index of the PTV were observed among 7F/18F IMRT and SA₂. Based on the CQI of the 11 OARs, the most efficient dose reduction was observed in 18F IMRT followed in order by SA₂, 7F IMRT and SA₁. The planning time was on average 13.2/24.9/40.1/42.8 min for 7F/18F IMRT/SA₁/SA₂, respectively. With regards to the delivery efficiency compared with 7F IMRT, a 51 and 41% reduction in delivery time was achieved by SA₁ and SA₂, respectively. All techniques presented a high quality assurance pass rate (>98%) of the Γ_3mm,3% criterion.ConclusionIn NPC cases, SA₂ gave superior results in terms of PTV coverage and OAR sparing compared with SA₁ and approached the performance achieved by 18F IMRT, but without sacrificing the delivery efficiency.     

A treatment planning study using non-coplanar static fields and coplanar arcs for whole breast radiotherapy of patients with concave geometry

PurposeA treatment planning study was performed to evaluate the performance of new radiotherapy techniques based on non-coplanar multiple fields or on dynamic conformal arcs for early stage breast treatments.Methods and materialsCT datasets of 7 different patients that were deemed unsuitable for tangential beam treatment due to a large volume of lung in the treatment fields were used as input for the study. Standard tangential field plans and inversely modulated IMRT plans were used as benchmark to evaluate performances of conformal plans with 3 non-coplanar fields (3F-NC), with 2 short dynamic conformal arcs (2-Arc) or hybrid plans with one static conformal field and one dynamic conformal arc (P-Arc). All plans were designed to achieve the higher target coverage and minimum ipsilateral lung involvement depending on the planning technique with a key objective to avoid involvement of the contralateral breast. The following planning objectives were selected. For PTV: D_1% (maximum significant dose) lower than 110% and D_99% (minimum significant dose) higher than 90%. For the ipsilateral lung a mean dose lower than 15 Gy and/or a volume receiving more than 20 Gy lower than 22%. For contralateral breast, all techniques but IMRT were set to have no beam impinging this organ at risk, while for IMRT plans were further designed to keep the mean dose lower than 5 Gy and to minimise the volume receiving a dose higher than 70% of the prescribed dose.ResultsP-Arc resulted to be on average a better technique, as it provides a PTV dose distribution highly conformal (Conformity index 1.45), homogeneous (D_5% − D_95% = 15.6%), with adequate coverage (V_90% = 96.4%) and a limited involvement of the ipsilateral lung (MLD ∼ 9 Gy, V_5Gy ∼ 36%, NTCP < 2%) when compared to four other treatment techniques. 3F-NC presented similar but slightly worse performances on target: Conformity index 1.57, D_5% − D_95% = 18.1%, V_90% = 95.7%). 3F-NC on ipsilateral lung resulted as the P-Arc. The tangential approach, the 2-Arc or the IMRT techniques, resulted to be inferior to the previous in either conformality (tangentials), ipsilateral lung sparing (tangentials, 2-Arc and IMRT) and in contralateral or healthy tissue involvement (IMRT).ConclusionFor early stage breast cancer when high sparing of lung tissues is required and no involvement of contralateral breast is allowed, the P-Arc or the 3F-NC techniques might be recommended in terms of dosimetric expectations.     

Comparison of dosimetric parameters and acute toxicity of intensity-modulated and three-dimensional radiotherapy in patients with cervix carcinoma: A randomized prospective study

PurposeThe use of intensity-modulated radiotherapy (IMRT) to treat cervix carcinoma has increased, however prospective randomized trials are still lacking.AimTo compare the dosimetric parameters and associated acute toxicity in patients with cervix carcinoma treated with three-dimensional (3D) conformal radiotherapy and IMRT.Patients and methodsForty patients were randomized in two arms each consisting of 20 patients. Patients in both arms received concurrent chemoradiation (cisplatin 40 mg/m² weekly; 50 Gy/25 fractions). Patients were treated with 3D conformal radiotherapy in one arm and with IMRT in another arm. After external beam radiotherapy, all patients received brachytherapy (21 Gy/3 fractions at weekly interval). For dosimetric comparison, both kinds of the plans were done for all the patients. All patients were assessed throughout and until 90 days after completion of treatment for acute gastrointestinal, genitourinary and hematologic toxicities.ResultsBoth plans achieved adequate planning target volume coverage, while mean conformity index was found significantly better in IMRT plans (P-value = 0.001). D₃₅ (dose to 35% volume) and D₅₀ for bladder was reduced by 14.62 and 32.57% and for rectum by 23.82 and 43.68% in IMRT. For IMRT, V₄₅ (volume receiving 45 Gy) of bowel were found significantly lesser (P-value = 0.0001), non-tumour integral dose was found significantly higher (P-value = 0.0240) and V₂₀ of bone marrow was found significantly reduced (P-value = 0.019) in comparison to that in 3D conformal radiotherapy. Significant reduction of grade 2 or more (20 vs 45%; P-value = 0.058) and grade ≥ 3 (5 vs 15%, P-value = 0.004) acute genitourinary toxicity and grade 2 or more (20 vs 45%, P-value = 0.003) and grade 3 or more (5 vs. 20%, P-value = 0.004) acute gastrointestinal toxicity while no significant difference for grade 2 and 3 or more haematological toxicity was noted in patients treated with IMRT compared to 3D conformal radiotherapy.ConclusionIMRT provide a good alternative for treatment of cervix carcinoma with lower acute gastrointestinal and acute genitourinary toxicity with similar target coverage compared to 3D conformal radiotherapy.     

Radionecrosis after repeated courses of radiotherapy under stereotactic conditions for brain metastases: Analysis of clinical and dosimetric data from a retrospective cohort of 184 patients

PurposeBetween 10 and 40% of patients with cancer will develop one or more brain metastases (BMs). Stereotactic radiotherapy (SRT) is part of the therapeutic arsenal for the treatment of de novo or recurrent BM. Its main interest is to delay whole brain radiation therapy (WBRT), which may cause cognitive toxicity. However, SRT is not exempt from long-term toxicity, and the most widely known SRT is radionecrosis (RN). The objective of this study was to analyze the occurrence of RN per BM and per patient.Material and methodsBetween 2010 and 2020, data from 184 patients treated for 915 BMs by two to six SRT sessions for local or distant brain recurrence without previous or intercurrent WBRT were retrospectively reviewed. RN was examined on trimestral follow-up MRI and potentially confirmed by surgery or nuclear medicine. For each BM and SRT session plan, summation V_12Gy, V_14Gy, V_21Gy and V_23Gy isodoses were collected. Volumes of intersections were created between the 12 Gy isodose at the first SRT and the 18 Gy isodose of the following SRT (V_18-12Gy).ResultsAt the end of follow-up, 23.0% of patients presented RN, and 6.3% of BM presented RN. Median follow-up of BM was 13.3 months (95%CI 18.3–20.8). The median interval between BM irradiation and RN was 8.7 months (95% CI 9.2–14.7). Six-, 12- and 24-month RN-free survival rates per BM were 75%, 54% and 29%, respectively. The median RN-free survival per patient was 15.3 months (95% CI 13.6–18.1). In multivariate analysis, the occurrence of RN per BM was statistically associated with local reirradiation (P < 0.001) and the number of SRTs (P < 0.001). In univariate analysis, the occurrence of RN per patient was statistically associated with the sum of all V_18-12Gy (P = 0.02). No statistical association was found in multivariate analysis. A sum of all V_{18-12 Gy} of less than 1.5 ml was associated with a 14.6% risk of RN, compared with 35.6% when the sum of all V_{18-12 Gy} was superior to 1.5 ml. The sum of all V_18-12Gy larger than 1.5 ml was associated with a 74% specificity and 53% sensitivity of RN (P < 0.001).ConclusionBased on these results, a small number of BMs show RN during repeated SRT for local or distant recurrent BMs. Local reirradiation was the most predictive factor of brain RN. A V_{18-12 Gy} larger than 7.6 ml in the case of local reirradiation or larger than 1.5 ml in proximity reirradiation were prognostic factors of RN. The more BM patients need radiation therapy, and the longer they survive after irradiation, the higher their individual risk of developing RN.     

Skull Base Meningioma — Comparison of Intensity-modulated Radiotherapy Planning Techniques using the Moduleaf Micro-multileaf Collimator and Helical Tomotherapy

AimsTherapeutic radiotherapy to lesions of the skull base is limited by complex target shapes and their proximity to organs at risk. Intensity-modulated radiotherapy (IMRT) using helical tomotherapy may result in improved dose distributions and safer dose escalation. The aim of this study was to compare plan efficacy and efficiency using, linac-based micro-multileaf collimator (mMLC) IMRT and helical tomotherapy.Materials and methodsFive cases of skull base meningioma, previously treated with three-dimensional conformal radiotherapy (50 Gy/30 fractions) were identified. They were re-planned to a dose of 60 Gy/30 fractions using IMRT with Moduleaf mMLC (2.5 mm) and helical tomotherapy. Plan efficacy was compared using measures of PTV₆₀ coverage (D_min, D_max, V_90%, V_95% and V_100%). Plan efficiency was assessed by comparing estimated beam-on times.ResultsThe critical structure dose was limited to below predetermined tolerance levels in all cases, with similar doses obtained between techniques. The average PTV₆₀ D_max, D_min, D_med, D_mean, V_90%, V_95% and V_100% across the five cases achieved were as follows: mMLC IMRT: 64.9 Gy, 40.1 Gy, 60 Gy, 59.6 Gy, 95.4%, 88.8% and 69.2%, respectively; helical tomotherapy: 67.2 Gy, 50.3 Gy, 60 Gy, 59.9 Gy, 95.8%, 83.5% and 51.9%, respectively. The average treatment time per fraction was 18.4 min for IMRT with mMLC and 6.7 min for helical tomotherapy.DiscussionThis study shows that safe dose escalation to a dose of 60 G y to skull base lesions can be achieved; using either mMLC- or helical tomotherapy-based IMRT. A plan comparison between the two solutions is difficult, but they seem to be similar in efficacy with any small differences being difficult to interpret and of questionable clinical significance. Helical tomotherapy has the advantage of a significantly decreased beam-on time.     

膀胱不同充盈状态下RapidArc与IMRT对早期宫颈癌靶区剂量的影响

  目的  比较不同放疗技术及膀胱充盈状态对宫颈癌术后放疗靶区剂量的分布及正常组织受照体积的影响,探讨宫颈癌术后放疗的理想模式。   方法  选择10例宫颈癌术后患者,分别进行膀胱充盈状态及排空状态下模拟CT扫描,处方剂量50 Gy,分别制定双弧快速旋转调强计划（RapidArc）及7野调强适形计划（IMRT）。计划的实施均为Varian公司的TrueBeam直线加速器。利用每个计划的剂量一体积直方图（DVH）进行数据分析。   结果  膀胱充盈状态下IMRT及RapidArc的靶区均匀性指数分别为1.05及1.04（P>0.05）,膀胱排空状态下IMRT及RapidArc的靶区均匀性指数均为1.04（P>0.05）。膀胱充盈状态下,IMRT及Rapi. dArc的靶区适形度指数分别为0.71及0.73（P>0.05）。膀胱排空状态下,IMRT及RapidArc的靶区适形度指数分别为0.71及0.73（P>0.05）。小肠及膀胱接受30 Gy及40 Gy剂量的体积,膀胱充盈状态下优于膀胱排空状态,两种技术间无显著性差异。直肠及膀胱接受30 Gy剂量的体积IMRT优于RapidArc。RapidArc在治疗时间及机器跳数上明显优于IMRT。   结论   7f-IMRT及双弧RapidArc在靶区适形度及均匀性方面无显著性差异;无论何种技术,膀胱充盈状态对小肠及膀胱的保护均优于膀胱排空状态;IMRT在直肠及膀胱的保护方面均优于RapidArc,RapidArc在机器跳数及治疗时间上优于IMRT。