Intensity-modulated Radiotherapy For Cervical Cancer Research Articles

Dosimetric Analysis of Limiting Pelvic Bone Dose in Intensity-modulated Radiotherapy for Cervical Cancer

Numerous studies have indicated the significant importance of pelvic dose in the radiotherapy process for cervical cancer patients. However, research on the actual pelvic bone dose in the treatment of cervical cancer patients using different techniques is currently relatively limited. In this study, we selected 50 postoperative cervical cancer patients. For each patient, three treatment plans with pelvic dose constraints were designed: sIMRT, VMAT, and HT. Statistical analysis was conducted on the target area and organ at risk parameters of the three groups of plans. The results indicate that all three treatment plans meet the clinical requirements. Regarding organs at risk, compared to the sIMRT and VMAT groups, the HT group showed a reduction of 11.85% and 11.07%, respectively, in V40 of bladder. Additionally, compared to the sIMRT and HT groups, the VMAT group exhibited a reduction of 14.94% and 9.53%, respectively, in V10 of pelvic bone. Furthermore, compared to the sIMRT and HT groups, the VMAT group showed a reduction of 10.76% and 6.75%, respectively, in V20 of pelvic bone, and these differences were also statistically significant (t = 21.630, t = –16.621, P < 0.05). In summary, individualized treatment design can be conducted in clinical practice based on the specific conditions of patients.

Clinical study of acute toxicity of pelvic bone marrow-sparing intensity-modulated radiotherapy for cervical cancer.

To compare the dose volume of the target area and the toxicity of pelvic bone marrow-sparing intensity-modulated radiotherapy (PBMS-IMRT) with routine IMRT in patients undergoing radiochemotherapy for cervical cancer. Forty patients with indications for adjuvant radiochemotherapy after cervical cancer surgery were selected and randomly divided into IMRT (n = 20) and PBMS-IMRT (n = 20) groups to observe and record the toxicity and its severity in the blood, gastrointestinal tract, and genitourinary system. There was no significant difference in the target area conformity index (CI) or homogeneity index (HI) between the two groups (p > 0.05). The pelvic bone V10-V50 in the PBMS-IMRT group were lower than those in the IMRT group (p < 0.05), and there was lower hematological toxicity (p < 0.05) and fewer delays or interruptions in chemotherapy and/or radiotherapy (p < 0.05) in the PBMS-IMRT group. The toxicity to the gastrointestinal and genitourinary systems in the two groups was not significantly different (p > 0.05). PBMS-IMRT significantly reduced the dose volume of the pelvic bone marrow, thereby reducing the incidence of bone marrow suppression. However, it had no significant impact on the gastrointestinal or genitourinary systems.

Fractional dose verification of intensity-modulated radiotherapy for cervical cancer based on exit fluences and Log files

To investigate the feasibility of fractional dose verification (DV) using the exit fluence (Flux) and log file (Log) of intensity-modulated radiotherapy (IMRT) for cervical cancer. Fluxes and Logs were collected from an Alderson radiotherapy (ART) phantom and 17 cervical cancer patients, respectively. Fluxes were measured with an electronic portal imaging device for 2D-DV using γ index and dose difference (DD). Logs were retrieved from the Aria server and used to reconstruct the 3D dose by combining the planned CT data for 3D-DV using γ index. The ART position was changed from 0.1 cm to 1 cm with a step size of 0.2 cm and from 1 cm to 3 cm with a step size of 1 cm to test the accuracy of 2D-DV. The correlations between the phantom's DV results and its positioning errors (PEs) were analyzed, as were those between the patients' DV results and their treatment fractions (TFs). For 2D-DV, the γ value of each field with 3%/3 mm criteria in the ART phantom was more than 95% when a PE was ≤5 mm. The same PE introduced using DD3% caused the passed rates to fall below the 95% tolerance. Both γ and DD showed negative correlations with PEs (R ∈ [–0.997, −0.765], P < 0.05). In 82.35% of patients, gamma values with 3%/3 mm criteria exceeded 86% in all TFs, and were greater than 93% in 98.38% of TFs. For the other patients, the γ values ranged from 38 to 100% due to significant reductions of their bladder volume and target. It displayed negative correlations with the TFs (R∈ [–0.903, −0.824], P < 0.05). For 3D-DV, no significant relationship was found between the γ values with 1%/1 mm criteria and the ART PEs or the TFs of all patients (P < 0.05). The daily DV method using the Flux and Log could be used to detect the positioning errors, as well as anatomical changes.

Dosimetric impacts of cone-beam computed tomography (CBCT)-based anatomic changes in intensity-modulated radiotherapy for cervical cancer.

To evaluate the effects of dose to tumors and organs at risk (OARs) on inter-fractional anatomic changes. We evaluated nine patients with cervical cancer treated with intensity-modulated radiotherapy (IMRT) (45 Gy in 25 fractions) using kV cone-beam computed tomography (CBCT) image guidance once or twice a week before treatment. For each patient, the original plan on the computed tomography (CT) image was copied to merged images, and then the fractional doses were calculated. Subsequently, deformable accumulated doses were obtained by summing the fractional absolute doses into a single dose in MIM Maestro software. The volume changes in the target and OARs were compared between the original CT and merged CBCT images, and the differences in the fractional and accumulated doses were also evaluated. Sixty-nine merged CBCT images were obtained and analyzed in this study. For the target areas, the volume changes in the clinical target volume (CTV) and planning target volume (PTV) reached -18.05% and -24.11% at most, respectively. The fractional D2% of the CTV and PTV was generally higher than the original plans, and the accumulated deviations were 2.27%±0.82% (P<0.01) and 2.42%±1.28% (P<0.01), respectively. The fractional D98% of the PTV was underdosed up to 18.28% for 78% of patients, and the accumulated deviations were -2.06% to -17.29% (P<0.05). For the OARs, the bladder volume changes were the most dramatic, reducing up to 93.60%. The fractional Dmean and D2cc of the bladder were generally higher than the original plans, and there were significant differences in their accumulated values (P<0.05). There was no obvious trend of rectal volume change with -69.65% to 74.20%. The rectum Dmean and D2cc of the accumulated were not significantly different from the planned dose (P>0.05). For patients with cervical cancer, the changes in bladder and rectal volume were greater than in the target volume. Although the volume changes in the bladder and rectum had no significant effect on D98% of the CTV and PTV, they had a significant effect on their own D2cc and the D2% of the CTV and PTV. More attention should be paid to the volume changes in the bladder and rectum in clinical work.

Preliminary Results on In-Vivo Dose Measurement of Intensity-Modulated Radiotherapy for Cervical Cancer

To investigate the relationship between the results of in-vivo dose (IVD) measurement and setup errors based on Alderson radiotherapy (ART) phantom, and to monitor the IVD changes of intensity-modulated radiotherapy (IMRT) for cervical cancer patients. Electronic portal imaging device (EPID) images and logfile data were collected from ART phantom and 12 patients with cervical cancer, which were used for two-dimensional (2D) IVD verification [evaluation indexes: Gamma analysis (γ) and percent dose difference (DD)] and three-dimensional (3D) IVD verification (evaluation indexes: γ), respectively. The positioning errors with ranges of 0.1∼1 cm and 1∼3cm in the step size of 0.2 cm and 1 cm were artificially introduced in ART phantom. The correlations between IVD results of phantom and its setup errors were analyzed, and the correlations between IVD results of the patients and their treatment fractions were evaluated. The 26 groups of EPID images and corresponding logfiles data from ART phantom and 206 groups from the patients were obtained respectively. The setup errors of ART phantom were not correlated with the corresponding 3D IVD γ1%/1mm (P > 0.05). The 2D IVD averages of ART phantom (γ3%/3mm,mean, γ2%/2mm, mean, γ1%/1mm,mean, DD3%,mean) showed strongly negative correlations with the setup errors (R∈[–0.997, –0.765], P < 0.05). The treatment fractions of all patients were not correlated with their 3D IVD γ1%/1mm (P > 0.05). For 2D IVD verification, DD3%,mean of all patients was negatively correlated with the treatment fractions (R∈[–0.953, –0.499], P < 0.05), among which, γ3%/3mm, mean of 9 patients was more than 89% in all treatment fractions, and γ3%/3mm, mean of the 9 patients was more than 93% for 98.57% treatment fractions. For other 3 patients, γ3%/3mm, mean showed strongly negative correlations with the treatment fractions (R∈[–0.903, –0.824], P < 0.05), with the range of 38% and 100%. Their CBCT images showed that the bladder volume decreased significantly (the relative changes: 82.08%, 84.41% and 73.59%, respectively) and the target retracted significantly (the relative changes: 38.12%, 59.79% and 24.46%, respectively). Conducting IVD verification could monitor the mechanical stability of accelerator and the changes of IVD in patients, and also evaluate the positional deviation of tumors and surrounding organs with IGRT technology, which could improve the safety and quality assurance of radiotherapy for cervical cancer patients and provide guidance for patients with adaptive radiotherapy.

Evaluation of plan quality and robustness of IMPT and helical IMRT for cervical cancer

BackgroundBoth plan quality and robustness were investigated through comparing some dosimetric metrics between intensity modulated proton therapy (IMPT) and helical tomotherapy based intensity modulated radiotherapy (IMRT) for cervical cancer.MethodsBoth a spot-scanning robust (SRO) IMPT plan and a helical tomotherapy robust (TRO) IMRT plan were generated for each of 18 patients. In order to evaluate the quality of nominal plans without dose perturbations, planning scores (PS) on clinical target volume (CTV) and five organs at risk (OARs) based on clinical experience, and normal tissue complication probabilities (NTCP) of rectum and sigmoid were calculated based on Lyman-Kutcher-Burman (LKB) model. Dose volume histogram bands width (DVHBW) were calculated in 28 perturbed scenarios to evaluate plan robustness.ResultsCompared with TRO, the average scores of SRO nominal plans were higher in target metrics [V46.8Gy, V50Gy, Conformity and Homogeneity](16.5 vs. 15.1), and in OARs metrics (60.9 vs. 53.3), including bladder [V35,V45, Dmean,D2cc], rectum [V40,V45,D2cc,Dmax], bowel [V35,V40,V45, Dmax], sigmoid [V40,Dmax] and femoral heads [V30,Dmax]. Meanwhile, NTCP calculation showed that the toxicities of rectum and sigmoid in SRO were lower than those in TRO (rectum: 2.8% vs. 4.8%, p < 0.05; sigmoid: 5.2% vs. 5.7%, p < 0.05). DVHBW in target coverage for the SRO plan was smaller than that for the TRO plan (0.6% vs. 2.1%), which means that the SRO plan generated a more robust plan in target.ConclusionBetter CTV coverage and OAR Sparing were obtained in SRO nominal plan. Based on NTCP calculation, SRO was expected to allow a small reduction in rectal toxicity. Furthermore, SRO generated a more robust plan in CTV target coverage.

Recurrence pattern and influencing factors of intensity-modulated radiotherapy for cervical cancer

With the rapid development of precise radiotherapy technology, the use of intensity-modulated radiation therapy (IMRT) in gynecological malignant tumor has been gradually increased. IMRT could result in a good local control rate as well as superior clinical outcome in patients with cervical cancer after radical radiotherapy. The recurrence pattern of radiotherapy includes in-field recurrence, out-of-field and combined failure. The recurrence pattern of radical IMRT for cervical cancer is mainly out-of-field recurrence. Out-of-field recurrence may be related to inadequate imaging evaluation before treatment. In-field recurrence may be related to insufficient radiation dose in target area and differences of tumor sensitivity.

Study on the significance of consistency of preoperative and postoperative bladder filling in patients with cervical cancer for target area and organ at risk in IMRT

Objective Bladder filling in patients with cervical cancer before and after operation during intensity-modulated radiotherapy (IMRT) was controlled by using bladder volume measurement instrument (BVI 9400). The displacement errors of the target area and the changes of the irradiation dose and the morphology of the filling bladder were compared. The significance of consistency of preoperative and postoperative bladder filling in IMRT for cervical cancer was investigated. Methods Forty-five patients with cervical cancer treated with radiotherapy in our hospital in 2018 were recruited and divided into A, B and C groups (n=15). In group A, patients did not undergo surgery, patients in group B received radical resection of cervical cancer (bladder volume measurement (BVI 9400) was utilized to monitor the bladder urine volume in both A and B groups before treatment). In group C, patients who self-controlled urination without monitoring bladder urine volume before treatment were randomly selected. All patients in three groups underwent KV-CBCT scan before treatment for online registration analysis. The displacement errors in the x-(left and right), y-(head and foot), z-axis directions (ventral and dorsal), PTV coverage volume percentage(V100) and percentage difference (ΔV100) of the prescription dose were calculated. Results The average displacement errors in the x-, y-, z-axis directions were as follows: 1.67 mm, 1.55 mm and 1.67 mm in group A, 1.43 mm, 1.58 mm and 1.84 mm in group B, and 2.27 mm, 2.30 mm and 2.08 mm in group C, respectively. In group A, the V100 was calculated as 96.96% and ΔV100 was 1.17%. In group B, V100 was 95.9% and ΔV100 was 1.29%. In group C, V100 was 94.02% and ΔV100 was 2.17%. Conclusions Controlling the consistency of bladder filling can reduce the effect of inconsistency of bladder filling upon the displacement errors to certain extent, which can guarantee the accuracy of the target location and the irradiation dose of the target, protect the bladder, small intestine and rectum, and alleviate the radiation-induced response of cervical cancer patients. Key words: Bladder filling status; Planning target volume; Cervical neoplasm/intensity-modulated radiotherapy

Clinical outcome of extended-field irradiation vs. pelvic irradiation using intensity-modulated radiotherapy for cervical cancer.

The aim of the present study was to evaluate the distinctions in survival and toxicity between patients with cervical cancer with common iliac node or para-aortic node involvement, who were treated with extended-field intensity-modulated radiotherapy (EF-IMRT) and patients with or without lower involved pelvic nodes, who were treated with pelvic IMRT. A total of 55 patients treated with EF-IMRT and 52 patients treated with pelvic IMRT at the Sun Yat-Sen University Cancer Center (Guangzhou, China) were retrospectively analyzed. Patients treated with EF-IMRT had the highest level of lymph node involvement to the para-aortic or common iliac nodes, while patients treated with pelvic IMRT had no para-aortic or common iliac nodes involved (P<0.001). The median follow-up time was 29.5 months. The 3-year overall survival (OS) rates of EF-IMRT and pelvic IMRT were 79.4 and 82.3% (P=0.45), respectively, and the 3-year disease-free survival (DFS) rates of EF-IMRT and pelvic IMRT were 61.0 and 73.7% (P=0.55), respectively. Cox's regression analysis revealed that EF irradiation was a protective prognostic factor for OS and DFS. A total of 16 patients in the EF-IMRT group and 13 patients in the pelvic IMRT group experienced treatment failure (P=0.67), with the patterns of failure being the same for the two groups (P=0.88). The cumulative incidence of grade 3 and 4 acute toxicities in the EF-IMRT group was 34.5%, in comparison with 19.2% in the pelvic group (P=0.048). The results of the present study suggest that patients with cervical cancer with grossly involved common iliac or para-aortic nodes should be electively subjected to EF irradiation to improve the survival and alter patterns of recurrence. Notably, EF irradiation delivered via IMRT exhibits an increased toxicity incidence, however, this remains within an acceptable range.

Preliminary application and discussion of independent 3D dose calculation in intensity-modulated radiotherapy for cervical cancer

Objective To assess the feasibility for the automated treatment planning verification system Mobius3D (M3D) to perform an independent 3D dose calculation in intensity-modulated radiotherapy (IMRT) for cervical cancer. Methods Twenty patients with cervical cancer were randomly selected. With treatment planning systems (Pinnacle, Version 9.2; Eclipse, Version 13.5), all IMRT plans were divided into 7 fields to meet the dosimetric goals. The optimized plans were exported to the M3D server. The percentage differences in the volume of region of interest (ROI) and the dose calculation of target volume and organ at risk (OAR) were evaluated for the two treatment planning systems, and theγ passing rate was used to assess the accuracy of M3D calculation. Results The difference in the volume of ROI for Pinnacle 9.2 to M3D was less than that for Eclipse 13.5 to M3D, with maximum differences of 0.22%±0.69% and 3.5%±1.89% for Pinnacle 9.2 and Eclipse 13.5, respectively. The differences in the dose calculation of target volume and OAR for the two treatment planning systems to M3D were within ±1%. After recalculating by M3D, the dose difference between Pinnacle 9.2 and M3D was smaller than that between Eclipse 13.5 and M3D, but the mean differences were all within ±3%. The γ passing rates for target volume and OAR were more than 95% on average. Conclusions The method of utilizing the automated treatment planning verification system to validate the accuracy of plans is convenient. It can be used as a secondary check tool to improve accuracy in IMRT dose calculation. Key words: Intensity-modulated radiotherapy; Dose calculation; Quality assurance

Influence of sub-field area on dose distribution in intensity-modulated radiotherapy for cervical cancer

Objective To investigate the optimization of therapeutic regimen through the adjustment of the minimum sub-field area in intensity-modulated radiotherapy (IMRT) for cervical cancer, under the premise of no influence on the dose to target volume or organs at risk. Methods A total of 12 patients with pathologically confirmed cervical cancer were enrolled, and the prescribed dose to the planning target volume (PTV) was 50 Gy in 25 fractions. The Pinnacle 8.0m treatment planning system was used for all patients, and 16 IMRT plans were developed for each patient, with the application of 9 evenly distributed fixed incidence directions (0°, 40°, 80°, 120°, 160°, 200°, 240°, 280°, and 320°), a minimum sub-field number of 80, and a minimum sub-field hop count (MU) of 5 MU.The range of sub-field area was 2-81 cm2.Direct machine parameter optimization was used for inverse-planned optimization calculation, and all the plans met the requirements of the clinical prescribed dose. The dose-volume histogram was used to evaluate the dose distribution in target volume and organs at risk. Results With the sub-field area increasing from 2 cm2 to 81 cm2, the total hop count of IMRT plan was reduced from (1 405±170) MU to (490±47) MU (P=0.000), and when the sub-field area increased above 6 cm×6 cm, the total hop count was reduced significantly (P=0.000). In the IMRT plan with a minimum sub-field area of 2-49 cm2, there was no significant difference in dose between the target volume and the organs at risk (P>0.05). The dose to the rectum, the bladder, and both femoral heads showed no significant differences across the IMRT plans with different minimum sub-field areas (P>0.05). Conclusions When the Pinnacle 8.0m treatment planning system is used to develop IMRT plans for cervical cancer, the requirements for clinical dose can still be met with a minimum sub-field area reaching 7 cm×7 cm, and there are significant reductions in sub-field hop count and total hop count. Key words: Cervix neoplasms/intensity-modulated radiotherapy; Inverse planning optimization; Area of segment field

Early changes of volume and spatial location in target and normal tissues caused by IMRT for cervical cancer.

To investigate the early changes of volume and spatial location in target and normal tissues caused by intensity-modulated radiotherapy (IMRT) for cervical cancer. Forty patients with cervical cancer were included in this study and treated by IMRT. Computed tomography (CT) was performed before radiotherapy and when the patient had received 27 Gy in 15 fractions. After image registration, the volume of interest (VOI) for the targets and organs at risk was delineated by clinicians on the CT images. Changes of volume, spatial location and Dice similarity were calculated for all VOIs. There were significant changes in gross tumor volume (GTV) in the primary tumor (GTV-T) with t = 8.304 (p&lt;0.01) and visible pelvic lymph nodes (GTV-N) with t = 4.996 (p&lt;0.01) caused by IMRT. The mean volume differences for GTV-T and GTV-N were 38.64% ± 19.50% (range 3.16%-86.49%) and 42.49% ± 25.68% (range 2.79%-87.42%), respectively. Among the organs at risk, the bladder had the greatest volume change with 55.13% ± 33.40% (range 3.25%-116.01%). The Dice similarity for GTV-T and GTV-N was 0.50 ± 0.18 (range 0.10-0.85) and 0.31 ± 0.20 (range 0.00-0.71), respectively. The rectum had the least Dice similarity among the normal tissues, with a mean value of 0.57 ± 0.14 (range 0.18-0.76). There were significant changes in volume and spatial location of the target and normal tissues after 27 Gy IMRT. In order to maintain the radiation dose to the targets and minimize the radiation to normal tissues, it is necessary to modify the radiotherapy planning.

A study of changes in volume and location of target areas and organs at risk in intensity-modulated radiotherapy for cervical cancer

Objective To investigate the changes in volume and spatial location of target areas and normal tissues before and during intensity-modulated radiotherapy(IMRT)for cervical cancer by quantitative means. Methods Forty patients with cervical cancer who were treated with IMRT were enrolled as subjects. Computed tomography(CT)was performed before IMRT and during IMRT when a dose of 27 Gy(15 fractions)was reached. Clinicians delineated the target areas and organs at risk in the two groups of CT images. The target areas and organs at risk in one group of images were mapped to the other group of CT image by image registration using the Pinnacle treatment planning system. Volume changes in target areas and organs at risk were analyzed, and changes in the spatial location were evaluated by volume difference method and Dice similarity method. Comparison was made by paired t-test. Results There were significant differences in gross target volumes of primary tumor lesions(GTV-T)and pelvic metastatic lymph nodes(GTV-N)before and during IMRT(P= 0.000; P= 0.000). According to the evaluation by volume difference method, the average rate of change in GTV-T was(38.64±19. 50)% with a range between 3. 16% and 86. 49%, while the average rate of change in GTV-N was(42.49± 25. 68)% with a range between 2. 79% and 87. 42%. In the organs at risk, the bladder had the maximum rate of volume change, the average of which was(55.13±33. 40)% with a range between 3. 25% and 116. 01%. According to the evaluation by Dice similarity method, the average Dice similarity coefficient for GTV-T was 0.50± 0. 18 with a range between 0. 10 and 0. 85, while the average Dice similarity coefficient for GTV-N was 0.31±0. 20 with a range between 0.00 and 0.71. The rectum had the minimum Dice coefficient in the organs at risk, the average of which was 0.57± 0. 14 with a range between 0. 18 and 0. 76. Conclusions For patients with cervical cancer to receive IMRT, since there are substantial changes in volume and spatial location of target areas and normal tissues before and during treatment, it is quite necessary to modify the treatment regimen in time in order to provide adequate doses for target areas and avoid overdose for organs at risk. Key words: Cervical neoplasms/intensity-modulated radiotherapy; DICE parameter; Volume change rate

SU-E-T-618: Dosimetric Comparison of Manual and Beam Angle Optimization of Gantry Angles in IMRT for Cervical Cancer

Purpose: To evaluate the dosimetric characteristics of intensity-modulated radiotherapy (IMRT) treatment plan with beam angle optimization. Methods: Ten post-operation patients with cervical cancer were included in this analysis. Two IMRT plans using seven beams were designed in each patient. A standard coplanar equi-space beam angles were used in the first plan (plan 1), whereas the selection of beam angle was optimized by beam angle optimization algorithm in Varian Eclipse treatment planning system for the same number of beams in the second plan (plan 2). Two plans were designed for each patient with the same dose-volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and total MU were compared. Results: For conformity and homogeneity in PTV, no statistically differences were observed in the two plans. For the mean dose in bladder, plan 2 were significantly lower than plan 1(p<0.05). No statistically significant differences were observed between two plans for the mean doses in rectum, left and right femur heads. Compared with plan1, the average monitor units reduced 16% in plan 2. Conclusion: The IMRT plan based on beam angle optimization for cervical cancer could reduce the dose delivered to bladder and also reduce MU. Therefore there were some dosimetric advantages in the IMRT plan with beam angle optimization for cervical cancer.

A Systematic Review of Organ Motion and Image-guided Strategies in External Beam Radiotherapy for Cervical Cancer

Advanced radiotherapy techniques, such as intensity-modulated radiotherapy (IMRT), may significantly benefit cervical cancer patients, in terms of reducing late toxicity and potentiating dose escalation. Given the steep dose gradients around the planning target volume (PTV) with IMRT planning, internal movement of organs during treatment may cause geographical miss of the target and unnecessary organs at risk (OAR) inclusion into high dose regions. It is therefore important to consider the extent and patterns of organ motion and to investigate potential image-guided radiotherapy (IGRT) solutions before implementing IMRT for cervical cancer. A systematic literature search was carried out using Medline, Embase, Cochrane Library, Web of Science, Cinahl and Pubmed. Database-appropriate search strategies were developed based upon terms for uterine neoplasms, IGRT, organ motion and target volume. In total, 448 studies were identified and screened to find 39 relevant studies, 12 of which were abstracts. These studies show that within the target volume for cervical cancer radiotherapy, uterine motion is greater than cervical. Uterine motion is predominantly influenced by bladder filling, cervical motion by rectal filling. Organ motion patterns are patient specific, with some having very little (5 mm) and others having much larger shifts (40 mm) of the target volume. Population-based clinical target volume (CTV)–PTV margins would be large (up to 4 cm around the uterus), resulting in unnecessary OAR inclusion within the PTV, reducing the benefits of IMRT. Potential solutions include anisotropic margins with increased margins in the anteroposterior and superoinferior directions, or greater PTV margins around the uterine fundus than the cervix. As pelvic organ motion seems to be patient specific, individualised PTV margins and adaptive IGRT strategies have also been recommended to ensure target volume coverage while increasing OAR sparing. Although these strategies are promising, they need significant validation before they can be adopted into clinical practice.

Dosimetric comparison of different multileaf collimator leaves in treatment planning of intensity-modulated radiotherapy for cervical cancer

To study the effect of multileaf collimator (MLC) leaf widths (standard MLC [sMLC] width of 10mm and micro-MLC [mMLC] width of 4mm) on intensity-modulated radiotherapy (IMRT) for cervical cancer. Between January 2010 and August 2010, a retrospective analysis was conducted on 12 patients with cervical cancer. The treatment plans for all patients were generated with the same machine setup parameters and optimization methods in a treatment planning system (TPS) based on 2 commercial Elekta MLC devices. The dose distribution for the planning tumor volume (PTV), the dose sparing for organs at risk (OARs), the monitor units (MUs), and the number of IMRT segments were evaluated. For the delivery efficiency, the MUs were significantly higher in the sMLC-IMRT plan than in the mMLC-IMRT plan (802 ± 56.9 vs 702 ± 56.7; p < 0.05). The number of segments in the plans were 58.75 ± 1.8 and 59 ± 1.04 (p > 0.05). For the planning quality, the conformity index (CI) between the 2 paired IMRT plans with the mMLC and the sMLC did not differ significantly (average: 0.817 ± 0.024 vs 0.810 ± 0.028; p > 0.05). The differences of the homogeneity index (HI) between the 2 paired plans were statistically significant (average: 1.122 ± 0.010 vs 1.132 ± 0.014; p < 0.01). For OARs, the rectum, bladder, small intestine, and bony pelvis were evaluated in terms of V10, V20, V30, and V40, percentage of contoured OAR volumes receiving 10, 20, 30, and 40Gy, respectively, and the mean dose (Dmean) received. The IMRT plans with the mMLC protected the OARs better than the plans with the sMLC. There were significant differences (p < 0.05) in evaluated parameters between the 2 paired IMRT plans, except for V30 and V40 of the rectum and V10, V20, V40, and Dmean of the bladder. IMRT plans with the mMLC showed advantages over the plans with the sMLC in dose homogeneity for targets, dose sparing of OARs, and fewer MUs in cervical cancer.

Pelvic Radiotherapy for Cancer of the Cervix: Is What You Plan Actually What You Deliver?

Whole pelvic intensity-modulated radiotherapy (IMRT) is increasingly being used to treat cervix cancer and other gynecologic tumors. However, tumor and normal organ movement during treatment can substantially detract from the benefits of this approach. This study explored the effect of internal anatomic changes on the dose delivered to the tumor and organs at risk using a strategy integrating deformable soft-tissue modeling with simulated dose accumulation. Twenty patients with cervix cancer underwent baseline and weekly pelvic magnetic resonance imaging during treatment. Interfraction organ motion and delivered (accumulated) dose was modeled for three treatment scenarios: four-field box, large-margin whole pelvic IMRT (20-mm planning target volume, but 10 mm inferiorly) and small-margin IMRT (5-mm planning target volume). Individually, the planned dose was not the same as the simulated delivered dose; however, when taken as a group, this was not statistically significant for the four-field box and large-margin IMRT plans. The small-margin IMRT plans yielded adequate target coverage in most patients; however, significant target underdosing occurred in 1 patient who displayed excessive, unpredictable internal target movement. The delivered doses to the organs at risk were significantly reduced with the small-margin plan, although substantial variability was present among the patients. Simulated dose accumulation might provide a more accurate depiction of the target and organ at risk coverage during fractionated whole pelvic IMRT for cervical cancer. The adequacy of primary tumor coverage using 5-mm planning target volume margins is contingent on the use of daily image-guided setup.

Conformal and Intensity-modulated Radiotherapy for Cervical Cancer

Three-dimensional radiotherapy planning techniques, including conformal radiotherapy and intensity-modulated radiotherapy, have potential for improving outcomes in cervical cancer. Accurate target volume definition is essential in order to maximise normal tissue sparing while minimising the risk of a geographical miss. This reduction in toxicity provides the option of dose escalation, particularly with simultaneous integrated boost intensity-modulated radiotherapy. The evidence for the current use and potential applications of these techniques in the treatment of cervical cancer are discussed.

907 ORAL Dose escalation with simultaneous integrated boost intensity-modulated radiotherapy for cervical cancer – impact of interfractional organ motion

Because of biologic, medical, and sometimes logistic reasons, patients may be treated with 3D conformal therapy or intensity-modulated radiation therapy (IMRT) for the initial treatment volume (PTV1) followed by a sequential IMRT boost dose delivered to the boost volume (PTV2). In some patients, both PTV1 and PTV2 may be simultaneously treated by IMRT (simultaneous integrated boost technique). The purpose of this work was to assess the sequential and simultaneous integrated boost IMRT delivery techniques on target coverage and normal-tissue sparing.Fifteen patients with head-and-neck (H&N), lung, and prostate cancer were selected for this comparative study. Each site included 5 patients. In all patients, the target consisted of PTV1 and PTV2. The prescription doses to PTV1 and PTV2 were 46 Gy and 66 Gy (H&N cases), 45 Gy and 66.6 Gy (lung cases), 50 Gy and 78 Gy (prostate cases), respectively. The critical structures included the following: spinal cord, parotid glands, and brainstem (H&N structures); spinal cord, esophagus, lungs, and heart (lung structures); and bladder, rectum, femurs (prostate structures). For all cases, three IMRT plans were created: (1) 3D conformal therapy to PTV1 followed by sequential IMRT boost to PTV2 (sequential-IMRT1), (2) IMRT to PTV1 followed by sequential IMRT boost to PTV2 (sequential-IMRT2), and (3) Simultaneous integrated IMRT boost to both PTV1 and PTV2 (SIB-IMRT). The treatment plans were compared in terms of their dose–volume histograms, target volume covered by 100% of the prescription dose (D100%), and maximum and mean structure doses (Dmax and Dmean).H&N cases: SIB-IMRT produced better sparing of both parotids than sequential-IMRT1, although sequential-IMRT2 also provided adequate parotid sparing. On average, the mean cord dose for sequential-IMRT1 was 29 Gy. The mean cord dose was reduced to ∼20 Gy with both sequential-IMRT2 and SIB-IMRT. Prostate cases: The volume of rectum receiving 70 Gy or more (V>70 Gy) was reduced to 18.6 Gy with SIB-IMRT from 22.2 Gy with sequential-IMRT2. SIB-IMRT reduced the mean doses to both bladder and rectum by ∼10% and ∼7%, respectively, as compared to sequential-IMRT2. The mean left and right femur doses with SIB-IMRT were ∼32% lower than obtained with sequential-IMRT1. Lung cases: The mean heart dose was reduced by ∼33% with SIB-IMRT as compared to sequential-IMRT1. The mean esophagus dose was also reduced by ∼10% using SIB-IMRT as compared to sequential-IMRT1. The percentage of the lung volume receiving 20 Gy (V20 Gy) was reduced to 26% by SIB-IMRT from 30.6% with sequential-IMRT1.For equal PTV coverage, both sequential-IMRT techniques demonstrated moderately improved sparing of the critical structures. SIB-IMRT, however, markedly reduced doses to the critical structures for most of the cases considered in this study. The conformality of the SIB-IMRT plans was also much superior to that obtained with both sequential-IMRT techniques. The improved conformality gained with SIB-IMRT may suggest that the dose to nontarget tissues will be lower.

Early Clinical Outcome With Concurrent Chemotherapy and Extended-Field, Intensity-Modulated Radiotherapy for Cervical Cancer

To assess the early clinical outcomes with concurrent cisplatin and extended-field intensity-modulated radiotherapy (EF-IMRT) for carcinoma of the cervix. Thirty-six patients with Stage IB2-IVA cervical cancer treated with EF-IMRT were evaluated. The pelvic lymph nodes were involved in 19 patients, and of these 19 patients, 10 also had para-aortic nodal disease. The treatment volume included the cervix, uterus, parametria, presacral space, upper vagina, and pelvic, common iliac, and para-aortic nodes to the superior border of L1. Patients were assessed for acute toxicities according to the National Cancer Institute Common Toxicity Criteria for Adverse Events, version 3.0. All late toxicities were scored with the Radiation Therapy Oncology Group late toxicity score. All patients completed the prescribed course of EF-IMRT. All but 2 patients received brachytherapy. Median length of treatment was 53 days. The median follow-up was 18 months. Acute Grade > or = 3 gastrointestinal, genitourinary, and myelotoxicity were seen in 1, 1, and 10 patients, respectively. Thirty-four patients had complete response to treatment. Of these 34 patients, 11 developed recurrences. The first site of recurrence was in-field in 2 patients (pelvis in 1, pelvis and para-aortic in 1) and distant in 9 patients. The 2-year actuarial locoregional control, disease-free survival, overall survival, and Grade > or = 3 toxicity rates for the entire cohort were 80%, 51%, 65%, and 10%, respectively. Extended-field IMRT with concurrent chemotherapy was tolerated well, with acceptable acute and early late toxicities. The locoregional control rate was good, with distant metastases being the predominant mode of failure. We are continuing to accrue a larger number of patients and longer follow-up data to further extend our initial observations with this approach.