Comparison of treatment plans using intensity-modulated radiotherapy and three-dimensional conformal radiotherapy for paranasal sinus carcinoma

PURPOSE: To compare intensity-modulated radiotherapy (IMRT) treatment planning with three-dimensional conformal radiotherapy (3D-CRT) planning for paranasal sinus carcinoma. MATERIALS AND METHODS: Treatment plans using traditional 3-field technique, 3D-CRT planning, and inverse planning IMRT were developed for a case of paranasal sinus cancer requiring adjuvant radiotherapy. Plans were compared with respect to dose conformality, dose-volume histograms, doses to critical normal tissues, and ease of treatment delivery. RESULTS: The inverse-planned IMRT technique was more conformal around the tumor target volume than conventional techniques. The dose-volume histograms demonstrated significantly better critical normal-tissue sparing with the IMRT plans, while able to deliver a minimum dose of 60 Gy to the clinical tumor volume and 70 Gy to the gross tumor volume. Acute toxicities in our analysis were minimal. CONCLUSIONS: IMRT planning provided improved tumor target coverage when compared to 3D-CRT treatment planning. There was significant sparing of optic structures and other normal tissues, including the brainstem. Inverse planning IMRT provided the best treatment for all paranasal sinus carcinomas, but required stringent immobilization criteria. Further studies are needed to establish the true clinical advantage of this modality.     

A dosimetric comparison of non-coplanar IMRT versus Helical Tomotherapy for nasal cavity and paranasal sinus cancer.

PURPOSES: To determine if there are clinically significant differences between the dosimetry of sinus tumors delivered by non-coplanar LINAC-based IMRT techniques and Helical Tomotherapy (HT). HT is capable of delivering highly conformal and uniform target dosimetry. However, HT lacks non-coplanar capability, which is commonly used for linear accelerator-based IMRT for nasal cavity and paranasal sinus tumors. METHODS AND MATERIALS: We selected 10 patients with representative early and advanced nasal cavity and paranasal sinus malignancies treated with a preoperative dose of 50 Gy/25 fractions without coverage of the cervical lymphatics for dosimetric comparison. Each plan was independently optimized using either Corvus inverse treatment planning system, commissioned for a Varian 2300 CD linear accelerator with 1cm multileaf collimator (MLC) leaves, or the HT inverse treatment planning system. A non-coplanar seven field technique was used in all Corvus plans with five mid-sagittal fields and two anterior oblique fields as described by Claus et al. [F. Claus, W. De Gersem, C. De Wagter, et al., An implementation strategy for IMRT of ethmoid sinus cancer and bilateral sparing of the optic pathways, Int J Radiat Oncol Biol Phys 51 (2001) 318-331], whereas only coplanar beamlets were used in HT planning. Dose plans were compared using DVHs, the minimum PTV dose to 1cm3 of the PTV, a uniformity index of planned treatment volume (PTV), and a comprehensive quality index (CQI) based on the maximum dose to optical structures, parotids and the brainstem which were deemed as the most critical adjacent structures. RESULTS: Both planning systems showed comparable PTV dose coverage, but HT had significantly higher uniformity (p<0.01) inside the PTV. The CQI for all organs at risk were equivalent except ipsilateral lenses and eyes, which received statistically lower dose from HT plans (p<0.01). CONCLUSIONS: Overall HT provided equivalent or slightly better normal structure avoidance with a more uniform PTV dose for nasal cavity and paranasal sinus cancer treatment than non-coplanar LINAC-based IMRT. The disadvantage of coplanar geometry in HT is apparently counterbalanced by the larger number of fields.     

Simplified intensity-modulated radiotherapy using pre-defined segments to reduce cardiac complications in left-sided breast cancer

BACKGROUND AND PURPOSE: Left-sided breast cancer patients pose a difficult clinical challenge when significant heart and contralateral breast irradiation are present, particularly with tangential uniform beams. The aims of the study are: (1) to design and evaluate a simplified intensity-modulated radiotherapy (IMRT) (SI) solution using pre-defined segments, (2) to compare the SI technique with a conformal (CN) and a full fluence IMRT (FI) approach using two sets of beam orientations, clinical (-C) and optimal (-O), and (3) to quantify the benefits of treatment technique and beam orientation. PATIENTS AND METHODS: Nine left-sided breast cancer patients with a maximum heart distance of at least 2.0 cm were planned using three different techniques and two different beam orientations. All three techniques were planned using clinical orientations (i.e. CN-C, FI-C and SI-C). Two techniques were planned using more optimal orientations (i.e. FI-O and SI-O). Dose-volume histograms and radiobiologic modelling are used for plan evaluation. RESULTS: The average mean planning target volume (PTV) doses are 91.6+/-4.5, 98.4+/-6.3, 102.0+/-8.7, 100.0+/-5.9 and 103.9+/-8.3% for the CN-C, FI-C, SI-C, FI-O and SI-O plans, respectively. The average normal tissue complication probabilities for late excess cardiac mortality are 2.1+/-0.6, 0.2+/-0.1, 0.2+/-0.1, 0.1+/-0.0 and 0.1+/-0.0%, respectively. For a given beam orientation, FI plans are the best and CN plans are the worst. The dose distributions for the SI-C and FI-C plans are almost identical with significant heart sparing but at a cost of some target underdosage. The dose distributions are better conformed around the PTV with more optimal beam orientations, resulting in better sparing of adjacent organs at risk. FI-C plans are inferior to SI-O plans. CONCLUSIONS: For clinical uniform two-beam orientations, significant heart sparing is possible with the addition of intensity modulation but at the expense of worsening target coverage. Simplified IMRT can, for all intents, be substituted for full IMRT with clinical beam orientations. Applying more optimal non-uniform beam orientations improves PTV coverage while maintaining significant heart sparing but increases the PTV dose heterogeneity.     

A practical approach to assess clinical planning tradeoffs in the design of individualized IMRT treatment plans

Background and purpose

To investigate the tradeoffs between organ at risk sparing and tumour coverage for IMRT treatment of lung tumours, and to develop a tool for clinical use to graphically represent these tradeoffs.

Material and methods

For 5 patients with inoperable non-small cell lung cancer (NSCLC) different IMRT plans were generated using a standard TPS. The plans were automatically generated for a range of IMRT settings (weights and dose levels of the objective functions) and were systematically evaluated, focusing on the tradeoffs between organ at risk (OAR) dose and target coverage. A method to analyze and visualize planning tradeoffs was developed and evaluated.

Results

Lung and oesophagus were identified as the critical organs at risk for NSCLC, the sparing of which strongly influences PTV coverage. Systematically analyzing the tradeoffs between these organs revealed that the sparing of these organs was approximately linearly related to PTV coverage parameters. Using this property, a tool was developed to graphically present the tradeoffs between the sparing of these organs at risk and the PTV coverage. The tool is an effective method to visualize the tradeoffs.

Conclusions

A tool was developed to assist IMRT plan design and selection. The clear presentation of the tradeoffs between OAR dose and coverage facilitates the optimization process and offers additional information to the clinician for a patient specific choice of the optimal IMRT plan.     

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

PURPOSE: A 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 MATERIALS: CT 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. RESULTS: P-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 approximately 9 Gy, V(5 Gy) approximately 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). CONCLUSION: For 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.     

Irradiation of paranasal sinus tumors, a delineation and dose comparison study.

PURPOSE: To determine the influence of observer variation and treatment planner variation on the dose delivered to the target and normal structures when irradiating paranasal sinus carcinomas. PATIENTS AND METHODS: Nine patients with paranasal sinus tumors underwent debulking surgery and subsequent radiation therapy. Two observers from two different institutions delineated the clinical target volumes (CTVs) for the elective and the boost volumes. These volumes were expanded in three dimensions with a 5-mm margin. At both institutions, a three-dimensional conformal treatment plan of 46 Gy to the elective volumes, plus 20 Gy to the boost target volumes, was designed. The delineated volumes and treatment plans were compared. RESULTS: The mean volume ratio between institutions of the elective CTVs was 0.9 (standard error = 0.05). The differences were located mainly at the bottom of the nasal cavity and at the frontal border of the target areas. The differences in boost CTVs were large; the mean volume ratio was 2.6 (standard error = 0.58). After expansion of the CTV, the mean distance between the planning target volume (PTV) and the chiasm differed by 0.5 cm between the two institutions. Cases with smaller distances between the PTV and the chiasm had more underdosage to the PTV. This effect was less pronounced for institution A (1 vol.%/cm) than for institution B (10 vol.%/cm) treatment plans, which were less conformal. When the treatment plan was designed for the PTV of institution B, 23 volume % of the PTV of institution A received <95% of the prescribed dose. If the treatment plan was designed for the (on average larger) PTV of institution A, the underdosed volume of PTV at institution B was 17%. The relative underdosage to the "other" PTV was larger when the original treatment plan was more conformal. CONCLUSION: In the irradiation of paranasal sinus cancer, both the treatment planner and the observer have a significant influence on the dose to the target and organs at risk. Both effects are similar in magnitude. The observer effect increases with more conformal treatment plans. Minimizing the observer variation is important for adequate irradiation of paranasal sinus cancer.     

Single arc volumetric modulated arc therapy for complex brain gliomas: is there an advantage as compared to intensity modulated radiotherapy or by adding a partial arc?

The objective of this study was to determine if volumetric modulated arc therapy (VMAT) offers advantages over intensity modulated radiotherapy (IMRT) for complex brain gliomas and evaluate the role of an additional partial arc. Twelve patients with glioma involving critical organs at risk (OAR) were selected [six low grade brainstem glioma (BG) and six glioblastoma (GB) cases]. BGs were prescribed 54 Gy/30 fractions (frx), and GB treated to 50 Gy/30 frx to a lower dose PTV (PTV50) with a simultaneous integrated boost delivering a total dose of 60 Gy/30?frx to a higher dose PTV (PTV60). VMAT was planned with a single arc (VMAT1) and with an additional coplanar partial arc spanning 90° (VMAT2). We observed VMATI improving the PTV equivalent uniform dose (EUD) for BG cases (p=0.027), improving the V95 for the PTV50 in GB cases (p=0.026) and resulting in more conformal GB plans (p=0.008) as compare to IMRT. However, for the GB PTV60, IMRT achieved favorable V95 over VMAT1 and VMAT2 (0.0046 and 0.008, respectively). The GB total integral dose (ID) was significantly lower with VMAT1 and VMAT2 (p=0.049 and p=0.006, respectively). Both VMAT1 and VMAT2 reduced the ID, however, only at the 5 Gy threshold for BG cases (p=0.011 and 0.005, respectively). VMAT achieved a lower spinal cord maximum dose and EUD for BG cases and higher optic nerve doses, otherwise no significant differences were observed. VMAT1 yielded the fastest treatment times and least MU. We conclude that VMAT offers faster treatment delivery for complex brain tumors while maintaining similar dosimetric qualities to IMRT. Selective dosimetric advantages in terms of spinal cord sparing and lowering the ID are observed favoring the use of an additional coplanar partial arc.     

Does inverse‐planned intensity‐modulated radiation therapy have a role in the treatment of patients with left‐sided breast cancer?

Introduction: The purpose of the study was to determine if multi‐field inverse‐planned intensity‐modulated radiation therapy (IMRT) improves on the sparing of organs at risk (heart, lungs and contralateral breast) when compared with field‐in‐field forward‐planned RT (FiF). Methods: The planning CT scans of 10 women with left‐sided breast cancer previously treated with whole‐breast RT on an inclined breast board with both arms supported above the head were retrieved. The whole breast planning target volume (PTV) was defined by clinical mark‐up and contoured on all relevant CT slices as were the organs at risk. For each patient, three plans were generated using FiF, five‐ and nine‐field inverse‐planned IMRT, all to a total dose of 50 Gy to the whole breast. Mean and maximum doses to the organs at risk and the homogeneity index (HI) of the whole‐breast PTV were compared. Results: The mean heart dose for the FiF plans was 2.63 Gy compared with 4.04 Gy for the five‐field and 4.30 Gy for the nine‐field IMRT plans, with no significant differences in the HI of the whole‐breast PTV in all plans. The FiF plans resulted in a mean contralateral breast dose of 0.58 Gy compared with 0.70 and 2.08 Gy for the five‐ and nine‐field IMRT plans, respectively. Conclusions: FiF resulted in a lower mean heart and contralateral breast dose with comparable HI of the whole‐breast PTV in comparison with inverse‐planned IMRT using five or nine fields.     

Dose Planning Study of Target Volume Coverage with Intensity-Modulated Radiotherapy for Nasopharyngeal Carcinoma: Penang General Hospital Experience

Background: To compare the dosimetric coverage of target volumes and organs at risk in the radicaltreatment of nasopharyngeal carcinoma (NPC) between intensity-modulated radiotherapy (IMRT) and threedimensionalconformal radiotherapy (3DCRT). Materials and Methods: Data from 10 consecutive patientstreated with IMRT from June-October 2011 in Penang General Hospital were collected retrospectively foranalysis. For each patient, dose volume histograms were generated for both the IMRT and 3DCRT plans usinga total dose of 70Gy. Comparison of the plans was accomplished by comparing the target volume coverage (5measures) and sparing of organs at risk (17 organs) for each patient using both IMRT and 3DCRT. The meansof each comparison target volume coverage measures and organs at risk measures were obtained and testedfor statistical significance using the paired Student t-test. Results: All 5 measures for target volume coverageshowed marked dosimetric superiority of IMRT over 3DCRT. V70 and V66.5 for PTV70 showed an absoluteimprovement of 39.3% and 24.1% respectively. V59.4 and V56.4 for PTV59.4 showed advantages of 18.4% and16.4%. Moreover, the mean PTV70 dose revealed a 5.1 Gy higher dose with IMRT. Only 4 out of 17 organsat risk showed statistically significant difference in their means which were clinically meaningful between theIMRT and 3DCRT techniques. IMRT was superior in sparing the spinal cord (less 5.8Gy), V30 of right parotid(less 14.3%) and V30 of the left parotid (less 13.1%). The V55 of the left cochlea was lower with 3DCRT (less44.3%). Conclusions: IMRT is superior to 3DCRT due to its dosimetric advantage in target volume coveragewhile delivering acceptable doses to organs at risk. A total dose of 70Gy with IMRT should be considered as astandard of care for radical treatment of NPC.     

Intensity-modulated radiotherapy improves target coverage, spinal cord sparing and allows dose escalation in patients with locally advanced cancer of the larynx.

BACKGROUND AND PURPOSE: An investigation has been carried out into the potential of intensity-modulated radiotherapy (IMRT) to improve the coverage of the targets and the sparing of the spinal cord (SC) in radiotherapy treatment of the larynx and bilateral cervical lymph nodes, in patients with advanced larynx cancer. PATIENTS AND METHODS: Conventional radiotherapy (CRT) and IMRT plans were produced for six patients to treat the larynx (PTV1) and lymph nodes (PTV2) to 50 Gy (phase 1). A second plan was created to treat the PTV1 to 65 Gy and PTV2 to 50 Gy (phases 1 and 2). The potential to escalate the dose to both the larynx (to 67 Gy) and the nodes (to 56 Gy) was investigated for the IMRT plans. RESULTS: The phase 1 treatment gave average minimum doses (dose received by 99% volume) of 38.1 (+/-8.2) and 48.5 (+/-0.2)Gy for PTV1, treated by CRT and IMRT, respectively, and 35.9 (+/-2.9) and 46.2 (+/-1.8)Gy for PTV2. For the two phase treatment the average minimum doses to PTV1 were 51.6 (+/-8.2) (CRT) and 62.1 (+/-0.7)Gy (IMRT) (p=0.028) and for PTV2 were 36.2 (+/-2.9) (CRT) and 46.8 (+/-0.5)Gy (IMRT) (P=0.0004). The average maximum doses (dose received by 1% volume) to the SC were 42.5 (+/-1.9) (CRT) and 37.9 (+/-1.4)Gy (IMRT) (P=0.01). For the dose escalated IMRT plans the minimum dose to PTV1 was 64.6 (+/-0.5) and 50.8 (+/-1.8)Gy to PTV2. The average SC maximum was 41.5 (+/-1.6)Gy. CONCLUSIONS: IMRT offers improved target homogeneity and reduces irradiation of the SC. This sparing of normal tissue structures is sufficient that significant dose escalation of both the larynx and lymph nodes may be possible.     

乳腺癌保乳术后调强放疗与常规放疗的剂量学比较

 目的　探讨早期乳腺癌保乳术后全乳适形调强放射治疗（IMRT）的剂量学优势。方法　选择10例接受保乳手术的Tis~2N0M0早期乳腺癌病例,其中左侧乳腺癌6例,右侧乳腺癌4例,应用三维治疗计划系统（3D-TPS）为每位患者设计两种全乳放射治疗计划,即切线野常规计划与IMRT计划,处方剂量均为50 Gy／25次。用剂量体积直方图（DVH）来比较两种计划中计划靶体积（PTV）、危及器官（OARS）的剂量学差异。结果　靶区覆盖率在两种计划中相似,分别为97.83 %、97.61 %,与常规计划相比IMRT计划的PTV接受＜95 %处方剂量与＞103 %处方剂量的体积百分比之和（IHI） 从25.42 %减少到2.71 %,PTV接受至少105 %处方剂量照射的体积百分比（V105 %）从25.79 %减少到1.08 %,IMRT计划改善IHI和减少V105 %的平均值,在PTV较大的患者中更明显。左侧乳腺癌患者心脏的平均剂量（Dmean）从6.72 Gy减少到4.95 Gy、心脏接受30 Gy照射的体积百分比（V30）从7.23 %减少到1.04 %。所有患者同侧肺的Dmean从9.19 Gy减少到7.65 Gy、至少接受20 Gy 照射的体积百分比（V20）从22.34 %减少到20.18 %。对侧乳腺Dmean从5.12 Gy减少到3.52 Gy,对侧肺Dmean从2.76 Gy减少到1.79 Gy。右侧患者肝脏Dmean从7.23 Gy减少到1.04 Gy。结论　全乳IMRT的剂量学优势主要是在保证靶区覆盖率的前提下,显著改善了靶区剂量分布的均匀性,并在一定程度上降低OARS的受照剂量与容积,乳房体积大的病例可以通过IMRT获得更好的剂量学结果。     

Multiple fields may offer better esophagus sparing without increased probability of lung toxicity in optimized IMRT of lung tumors

PURPOSE: To evaluate whether increasing numbers of intensity-modulated radiation therapy (IMRT) fields enhance lung-tumor dose without additional predicted toxicity for difficult planning geometries. METHODS AND MATERIALS: Data from 8 previous three dimensional conformal radiation therapy (3D-CRT) patients with tumors located in various regions of each lung, but with planning target volumes (PTVs) overlapping part of the esophagus, were used as input. Four optimized-beamlet IMRT plans (1 plan that used the 3D-CRT beam arrangement and 3 plans with 3, 5, or 7 axial, but predominantly one-sided, fields) were compared. For IMRT, the equivalent uniform dose (EUD) in the whole PTV was optimized simultaneously with that in a reduced PTV exclusive of the esophagus. Normal-tissue complication probability-based costlets were used for the esophagus, heart, and lung. RESULTS: Overall, IMRT plans (optimized by use of EUD to judiciously allow relaxed PTV dose homogeneity) result in better minimum PTV isodose surface coverage and better average EUD values than does conformal planning; dose generally increases with the number of fields. Even 7-field plans do not significantly alter normal-lung mean-dose values or lung volumes that receive more than 13, 20, or 30 Gy. CONCLUSION: Optimized many-field IMRT plans can lead to escalated lung-tumor dose in the special case of esophagus overlapping PTV, without unacceptable alteration in the dose distribution to normal lung.