IMRT

Dose escalation in radiation therapy has led to increased control rates with some clinical trial evidence that rectal toxicity may be reduced when using intensity-modulated radiotherapy (IMRT) over 3D conformal radiotherapy (3DCRT) for dose-escalated prostate radiotherapy. However, IMRT for prostate patients is not yet standard in many Australian radiation oncology centres. This study investigates dosimetric changes that can be observed between IMRT and 3DCRT in prostate radiotherapy. Fifteen patients were selected for analysis. Two target definitions were investigated – prostate-only and prostate plus seminal vesicles (p + SVs). A five-field 3DCRT and seven field IMRT plan were created for each patient and target definition. The planning target volume coverage was matched for both plans. Doses to the rectum, bladder and femoral heads were compared using dose volume histograms. The rectal normal tissue complication probabilities (NTCPs) were calculated and compared for the 3DCRT and IMRT plans. The delivery efficiency was investigated. The IMRT plans resulted in reductions in the V25, V50, V60, V70 and V75 Gy values for both the prostate-only and p + SVs targets. Rectal NTCP was reduced with IMRT for three different sets of model parameters. The reductions in rectal dose and NTCP were much larger for the p + SVs target. Delivery of IMRT plans was less efficient than for 3DCRT plans. IMRT resulted in superior plans based on dosimetric and biological endpoints. The dosimetric gains with IMRT were greater for the more complex p + SVs target. The gains made came at the cost of decreased delivery efficiency.

Purpose: To investigate the interplay effect of intrafractional motion when using Enhanced Dynamic Wedge (EDW) and Intensity Modulated Radiotherapy (IMRT) with gated delivery. Methods: EDW of angles 30, 45 & 60 (field size 10x10sq.cm) and sliding window IMRT bench-mark fluences were delivered using 6MV beams from a Varian CL2100CD with millennium 120 MLC at 100, 400 and 600MU/min dose-rates for static and gated operation using RPM. The IMRT MatriXX system and 0.6cc ionization chamber were placed at 5cm depth on the Quasar motion platform to measure 2D fluence and point doses. The motion platform was programmed for breathing frequencies 0.125, 0.17 and 0.25Hz with the jaw/MLC movement in the same direction. During the gated mode, duty cycles were 25%, 50%, 75% and 100% (un-gated). The 2D fluence comparison and variation in point dose of gated operation with static measurement for various breathing frequencies, duty cycles and dose rates was performed and fluence comparisons analyzed using gamma criteria of 3%/3mm. Results: Fluence and point-dose deviations of EDW and IMRT increased with increasing duty cycle and breathing frequency. The gamma evaluation of the 25% duty cycle was found to be closest to the static measurements and the point dose deviation was <2%, while for larger duty cycles, the deviations were upto 15% which increased with increasing EDW angles, although with no apparent relationship with the dose rate. At lower dose rates, more number of pixels passed the gamma evaluation criteria. The deviations for 100% duty cycle with breathing frequency of 0.25Hz and dose rate of 100MU/min were -5.7%, -8.9% and -15.8% for 30, 45 and 60 EDW angles respectively. Conclusions: The interplay effect demonstrates considerable error in the delivery of dynamic intensity modulated treatments, which is reduced by appropriate gating.

Background

Since December 2009 a new VMAT planning system tool is available in Oncentra(R) MasterPlan v3.3 (Nucletron B.V.). The purpose of this study was to work out standard parameters for the optimization of prostate cancer.

Methods

For ten patients with localized prostate cancer plans for simultaneous integrated boost were optimized, varying systematically the number of arcs, collimator angle, the maximum delivery time, and the gantry spacing. Homogeneity in clinical target volume, minimum dose in planning target volume, median dose in the organs at risk, maximum dose in the posterior part of the rectum, and number of monitor units were evaluated using student's test for statistical analysis. Measurements were performed with a 2D-array, taking the delivery time, and compared to the calculation by the gamma method.

Results

Plans with collimator 45degrees were superior to plans with collimator 0degrees. Single arc resulted in higher minimum dose in the planning target volume, but also higher dose values to the organs at risk, requiring less monitor units per fraction dose than dual arc. Single arc needs a higher value (per arc) for the maximum delivery time parameter than dual arc, but as only one arc is needed, the measured delivery time was shorter and stayed below 2.5 min versus 3 to 5 min. Balancing plan quality, dosimetric results and calculation time, a gantry spacing of 4degrees led to optimal results.

Conclusion

A set of parameters has been found which can be used as standard for volumetric modulated arc therapy planning of prostate cancer.

Purpose: IMRT (intensity-modulated radiotherapy) verification techniques are reviewed together with investigations demonstrating the intrinsic verification problems. Material and Methods: Different IMRT verification procedures for either class solutions or individual patients are demonstrated. Among the latter are techniques like fluence or three-dimensional (3-D) dose distribution verification within a transfer phantom. Different radiographic films and absolute dose probes are investigated for their suitability. Finally, Monte Carlo techniques (XVMC/VEF) are used for error detection and IMRT verification. Results: During introduction of clinical IMRT for head and neck (H&N) tumors, we concurrently applied fluence, relative, and absolute dose measurement. While fluence and relative dose are in rather good agreement with calculations, absolute dose is always low when compared to the TPS (TMS 6.1A, Nucletron B.V.) by 5–7%. This deviation seems to depend not on the number of segments, but can strongly depend on MLC misalignment. Further investigations have revealed the importance of a detailed commissioning of the TPS down to the small-field range using diamond or diode probes and its detailed verification. In addition, simple tests have shown that dose calculation approximations in the IMRT option of TMS are one major source of the dose deviation. XVMC/VEF does not use such approximations. Conclusion: The procedure starts with a detailed TPS commissioning and verification process. Different verification methods are recommended during clinical IMRT implementation phase, in order to locate sources of error. Later on, a minimal program could consist of a fluence or relative dose verification procedure with few films and absolute dose measurement, followed by an intensive MLC quality assurance (QA). Inverse Monte Carlo systems, like IMCO++/IKO or Hyperion, seem to be able to reduce the effort. Ziel: Neben einem Überblick über Verifikationstechniken der IMRT (intensitätsmodulierten Radiotherapie) werden Untersuchungen zu intrinsischen Verifikationsproblemen dargestellt. Material und Methodik: Verschiedene Verifikationsmethoden für Klassenlösungen sowie für individuelle Patientenpläne werden demonstriert, wie etwa Fluenz- und dreidimensionale Dosisverteilungen in einem Ersatzphantom. Dazu werden verschiedene Radiographiefilme und Absolutdosissonden auf ihre Eignung untersucht. Monte-Carlo-Techniken (XVMC/VEF) werden zur Fehleranalyse eingesetzt und auf ihre Tauglichkeit zur Verifikation untersucht. Ergebnisse: Bei der klinischen Einführung der IMRT bei Kopf-Hals-Tumoren wurden parallel Fluenz-, relativ- und absolutdosimetrische Verfahren zur Verifikation angewandt. Während die Fluenz- und Dosisverteilungen gut mit den Berechnungen übereinstimmen, sind die Absolutdosen systematisch um 5–7% niedriger als die mit dem TPS (TMS 6.1A) berechneten. Die Abweichung scheint nicht von der Gesamtzahl der Segmente des Plans abzuhängen, kann aber relativ stark von einer geringen Abweichung der MLC-Leaves vom Sollwert abhängen. Weitere Untersuchungen zeigen auf, wie wichtig eine detaillierte TPS-Kommissionierung bis in den Bereich kleiner Feldgrößen mit umfangreichen Verifikationen und einfachen Tests ist. Damit konnte ein wichtiger Beitrag zum Dosisfehler, nämlich zusätzliche Näherungen bei der Dosisberechnung von IMRT-Plänen, verantwortlich gemacht werden. XVMC/VEF verwendet keine derartigen Näherungen. Schlussfolgerung: Die Prozedur beginnt mit einer detaillierten TPS-Kommisionierung und Verifikation. Während der klinischen Einführungsphase sollten unterschiedliche Verifikationsverfahren eingesetzt werden, um etwaige Fehler aufzuspüren. Später kann ein Minimalprogramm verwendet werden, das entweder aus Fluenz- oder Relativdosismessungen in Verbindung mit einer Absolutdosisbestimmung besteht. Unabhängig davon sollte eine intensive Qualitätssicherung (QS) des MLCs erfolgen. Inverse Monte- Carlo-Systeme wie IMCO++/IKO oder Hyperion sind vermutlich geeignet, den Aufwand beträchtlich zu reduzieren.

"Image-guided intensity-modulated radiotherapy for patients with locally advanced gastric cancer: a clinical feasibility study.
Badakhshi H, Gruen A, Graf R, Boehmer D, Budach V.
Source: Gastric Cancer. 2013 Oct 11.
Department for Radiation Oncology, Charité School of Medicine and University Hospital Berlin, Augustenburger Platz 1, 13353, Berlin, Germany, Harun.Badakhshi@charite.de.
Abstract
BACKGROUND:
The aim of this study was to determine the medical and technical feasibility of intensity-modulated radiotherapy (IMRT) in high-risk nonmetastatic gastric cancer stage II and III after primary gastrectomy and D2 lymphadenectomy.
METHODS AND MATERIALS:
A prospective nonrandomized phase II trial was performed on 25 consecutive patients with gastric cancer with high risk (T3-4, N1-3, G2-3, R0-1). The dose delivered was 45 Gy (1.80 Gy per fraction) in IMRT technique. Concurrent 5-fluorouracil-based chemotherapy at 225 mg/m2 was administered as a continuous intravenous infusion. Primary endpoints were acute gastrointestinal toxicity (CTC 4.0) and technical feasibility of IMRT in regard to dose planning and radiation delivery.
RESULTS:
Early acute events were defined as clinical and chemical adverse effects of IMRT and concurrent chemotherapy during treatment. By definition, 90 days after the end of IMRT has been evaluated as acute-phase toxicity. No patient had grade 4 or higher acute adverse events. Clinical grade 3 toxicity occurred in two patients (8 %) with diarrhea and in one case (4 %) with nausea. Hematological changes with grade 3 occurred in three cases (12 %) with hemoglobin decrease, in five cases (25 %) as leukopenia, and in one case (4 %) with thrombocytopenia. The mean dose for liver was 16 Gy and the percentage volume exceeding 30 Gy (V30) was 21 %. Mean dose for right and left kidney was 9 and 13 Gy, respectively, and V20 was 9 % and 13 %, respectively. Heart received a median dose of 15 Gy and V40 was 17 %. The mean dose to the bowel was 11 Gy and V40 was 6 %. Spinal cord had at maximum 33 Gy in median. Specifics of dose distribution, including the coverage, for the target region were as follows: minimum was 33 Gy, maximum 48.6 Gy, and mean dose 44.6 Gy. The prescribed dose (45 Gy) covered 99 % and 95 % of planning target volume (OTV) in 66 % and 92 % of cases, respectively. Median PTV was 15.77 ml (range, 805-3,604 ml).
CONCLUSIONS:
The data support the practical feasibility of IMRT in adjuvant treatment in high-risk gastric cancer in the postoperative setting as a proof of principle. Acute toxicity has been tolerable."

Purpose: To investigate the dosimetric effect of the Leaf Motion Calculator (LMC) parameters using sliding window technique in head and neck IMRT. Materials and Methods: Two head and neck IMRT patients (T1/T2,N0) were selected for this study. The actual fluence of the IMRT plans were calculated by varying the LMC parameters which includes, dose rates from 100 to 600 MU/min, MLC limiting leaf speed (0.5 to 3.0 cm/sec) and minimum dynamic leaf gap (0.05 to 0.2cm) from the same optimal fluence. The doses to OAR, total monitor unit (MU), low and high dose volumes were analyzed. Results: The doses to OAR, low and high dose volume (10%, 50% & 95% of isodose) increases with increase in dose rate and decreases with increase in limiting leaf speed. The total MU also increases with increase in dose rate and decreases with increase in leaf speed. When the dose rate increases from 300 MU/min to 600MU/min, the total MU significantly increase by 12% at a limiting leaf speed of 2.5cm/sec. There was no significant difference in doses to OAR, total MU, low and high dose volumes for minimum dynamic leaf gap between 0.05 to 0.10 cm. Conclusion: OAR sparing is observed with lower dose rate and higher leaf speed. There is no significant difference in PTV coverage and high dose volumes with dose rate as well as limited leaf speed. However, in the low dose volumes significant difference was observed for leaf speed less than 1.5cm/sec.

Purpose: Glioblastoma Multiforme (GBM) is the most common malignant brain tumor and frequently recurs in the same location after radiotherapy. Intensive treatment targeting localized lesion is required to improve GBM outcome, but dose escalation using conventional methods is limited by healthy tissue tolerance. Helical Tomotherapy (HT) Dose Painting (DP) treatments were simulated to safely deliver high doses in the recurrent regions. Materials and methods: Apparent Diffusion Coefficient (ADC) data from five recurrent GBM were retrospectively considered for planning. Hypo-fractionated (25À50 Gy, 5 fractions) voxel-based prescriptions were opportunely converted to personalized structured-based dose maps to create DP plans with a commercial Treatment Planning System. Optimized plans were generated and analyzed in terms of plan conformity to dose prescription (Q 0.90–1.10), tolerance of the healthy tissues (D MAX), and dosimetry accuracy of the deliverable plans (c-index). Results: Only three of the five cases could receive a safe retreatment without violating the maximum critical organs dose constraints. The conformity of the simulated plans was between 40.9% and 79.9% (Q 0.90–1.10), their delivery time was in the range of 38.3–63.6 min, while the dosimetry showed c-index of 82.4–92.4%. Conclusions: This study proved the ability of our method to simulate personalized, deliverable and dosi-metrically accurate DPBN plans. HT hypo-fractionated treatments guided by ADC maps can be realized and applied to deliver high doses in the GBM recurrent regions, although there are some critical issues related to low Q 0.90–1.10 values, to exceeding of healthy-tissue dose constraints for some patients and long delivery times.

Background and Purpose: Treatment planning for malignant pleural mesothelioma (MPM) is a challenging task due to the relatively large size of the target and the need to spare critical organs that overlap with or are within the target volume. We aimed to develop a knowledge-based-model (KBM) using RapidPlan for patients with two intact lungs.
Materials and Methods: Data from 57 patients treated with volumetric modulated arc therapy (VMAT) were chosen for training the dose estimation model at a single dose level. The prescription dose was 50.4 Gy in 1.8 Gy fractions. The model was validated on 23 new patients by comparing the clinical plan (CP) to the RapidPlan (RP). Time taken to plan the RP was compared to that for CP.
Results: For similar target coverage and plan inhomogeneity, RP significantly improved the sparing of the contralateral lung, heart, stomach, esophagus and ipsilateral kidney. On average, the contralateral lung V5Gy and V10Gy were reduced by 13.9% (p<0.001) and 7.9% (p<0.001) respectively. The mean heart dose was reduced by 5 Gy (p<0.001) and V30 Gy by 9.1% (p<0.001). Mean dose to the stomach and esophagus were both reduced by 5 Gy (p<0.001) and the ipsilateral kidney V18 Gy by 4.1% (p<0.001). Mean total lung dose was reduced by 0.8 Gy with RP which enabled an increase in prescription dose by 1 fraction Absolute volume of ipsilateral lung was adequately spared by both techniques, while sparing of all other organs namely the cord, liver and bowel was not compromised with RP. Time taken with RP was 20 minutes, 45 seconds versus at least 4 hours for an experienced treatment planner.
Conclusion: The RP model for MPM showed improved sparing of critical organs with a reduced treatment planning time and increased prescription dose.

We compared 3D conformal planning, static field intensity modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) to investigate the suitable treatment plan and delivery method for a right-sided reconstructed chest wall and nodal case. The dose prescribed for the reconstructed chest wall and regional nodes was 50.4 Gy. Plans were compared for target coverage and doses of the lungs, heart, contralateral breast, and healthy tissue. All plans achieved acceptable coverage of the target and IMNs. The best right lung sparing achieved with 3D was a V20 Gy of 31.09%. Compared to it, VMAT reduced the same by 10.85% and improved the CI and HI over 3D by 18.75% and 2%, respectively. The ipsilateral lung V5 Gy to V20 Gy decreased with VMAT over IMRT by as high as 17.1%. The contralateral lung V5 Gy was also lowered with VMAT compared to IMRT by 16.22%. The MU and treatment beams were lowered with VMAT over IMRT by 30% and 10, respectively, decreasing the treatment time by >50%. VMAT was the treatment plan and delivery method of choice for this case due to a combination of improved lung sparing and reduced treatment time without compromising target coverage.

Patient-specific verification of intensity-modulated radiation therapy (IMRT) plans can be done by dosimetric measurements or by independent dose or monitor unit calculations. The aim of this study was the clinical evaluation of IMRT verification based on a fast Monte Carlo (MC) program with regard to possible benefits compared to commonly used film dosimetry.25 head-and-neck IMRT plans were recalculated by a pencil beam based treatment planning system (TPS) using an appropriate quality assurance (QA) phantom. All plans were verified both by film and diode dosimetry and compared to MC simulations. The irradiated films, the results of diode measurements and the computed dose distributions were evaluated, and the data were compared on the basis of gamma maps and dose-difference histograms.Average deviations in the high-dose region between diode measurements and point dose calculations performed with the TPS and MC program were 0.7 ± 2.7% and 1.2 ± 3.1%, respectively. For film measurements, the mean gamma values with 3% dose difference and 3 mm distance-to-agreement were 0.74 ± 0.28 (TPS as reference) with dose deviations up to 10%. Corresponding values were significantly reduced to 0.34 ± 0.09 for MC dose calculation. The total time needed for both verification procedures is comparable, however, by far less labor intensive in the case of MC simulations.The presented study showed that independent dose calculation verification of IMRT plans with a fast MC program has the potential to eclipse film dosimetry more and more in the near future. Thus, the linac-specific QA part will necessarily become more important. In combination with MC simulations and due to the simple set-up, point-dose measurements for dosimetric plausibility checks are recommended at least in the IMRT introduction phase.Die patientenbezogene Verifikation bei intensitätsmodulierter Strahlentherapie (IMRT) kann sowohl durch dosimetrische Messungen als auch durch unabhängige Dosis- oder Monitoreinheitenberechnung erfolgen. Ziel dieser Studie war die klinische Evaluation der IMRT-Verifikation auf Grundlage eines schnellen Monte-Carlo- (MC-) Programms im Hinblick auf mögliche Vorteile verglichen mit der noch immer häufig eingesetzten Filmdosimetrie.25 Kopf-Hals-IMRT-Pläne wurden mit einem Bestrahlungsplanungssystem (BPS) mit Pencil-Beam-Algorithmus unter Verwendung eines geeigneten Phantoms zur Qualitätssicherung (QS) neu berechnet. Alle Bestrahlungspläne wurden sowohl mittels Film- als auch Diodendosimetrie verifiziert und mit MC-Simulationen verglichen. Die bestrahlten Filme, die Ergebnisse der Diodenmessungen und die berechneten Dosisverteilungen wurden ausgewertet, und die Daten beruhend auf Gamma-Karten und Dosis-Differenz-Histogrammen analysiert.Im Schnitt wichen Diodenmessungen und Punktdosisberechnungen durch das BPS bzw. MC-Programm in der Hochdosisregion um 0, 7 ± 2, 7% bzw. 1, 2 ± 3, 1% voneinander ab. Für die Filmdosimetrie betrug der mittlere Gamma-Index bei einem Gamma-Kriterium von 3% Dosisdifferenz und 3 mm räumlichem Abstand 0, 74 ± 0, 28 (BPS als Referenz) mit Dosisabweichungen bis zu 10%. Die entsprechenden Werte waren maßgeblich reduziert auf 0, 34 ± 0, 09 für die MC-Dosisberechnung. Die Gesamtzeit beider Verifikationsmethoden ist zwar vergleichbar, allerdings weitaus weniger arbeitsaufwändig im Fall von MC-Simulationen.Die vorgestellte Studie ergab, dass die unabhängige Dosisberechnung von IMRT-Plänen mit einem schnellen MC-Programm das Potenzial besitzt, die Filmdosimetrie immer mehr in den Hintergrund zu drängen. Die maschinenbezogene QS wird daher zwangsläufig an Bedeutung gewinnen. Zusammen mit MC-Simulationen und aufgrund des einfachen Vorgehens werden Punktdosismessungen für dosimetrische Plausibilitätskontrollen zumindest in der Einführungsphase der IMRT empfohlen.

This paper presents the preclinical evaluation of a novel immobilization system for patients undergoing external beam radiation treatment of head and neck tumors. An immobilization mask is manufactured directly from a 3-D model, built using the CT data routinely acquired for treatment planning so there is no need to take plaster of Paris moulds. Research suggests that many patients find the mould room visit distressing and so rapid prototyping could potentially improve the overall patient experience. Evaluation of a computer model of the immobilization system using an anthropomorphic phantom shows that &gt;99% of vertices are within a tolerance of ±0.2 mm. Hausdorff distance was used to analyze CT slices obtained by rescanning the phantom with a printed mask in position. These results show that for &gt;80% of the slices the median “worse-case” tolerance is approximately 4 mm. These measurements suggest that printed masks can achieve similar levels of immobilization to those of syste...

The purpose of this study was to evaluate the dosimetric effect of the leaf width of a multileaf collimator (MLC) in intensity modulated radiotherapy (IMRT) delivery techniques for small- and large-volume targets. We retrospectively selected previously treated 5 intracranial and 5 head-neck patients for this study to represent small- (range, 18.37-72.75 cc; mean, 42.99 cc) and large-volume (range, 312.31-472.84 cc; mean, 361.14 cc) targets. A 6-MV photon beam data was configured for Brianlab m3 (3 mm), Varian Millennium 120 (5 mm) and Millennium 80 (10 mm) MLCs in the Eclipse treatment-planning system. Sliding window and step-shoot IMRT plans were generated for intracranial patients using all the above-mentioned MLCs; but due to the field size limitation of Brainlab MLC, we used only 5-mm and 10-mm MLCs in the head-and-neck patients. Target conformity, dose to the critical organs and dose to normal tissues were recorded and evaluated. Although the 3-mm MLC resulted in better target conformity (mean difference of 7.7% over 5-mm MLC and 12.7% over 10-mm MLC) over other MLCs for small-volume targets, it increased the total monitor units of the plans. No appreciable differences in terms of target conformity, organ at risk and normal-tissue sparing were observed between the 5-mm and 10-mm MLCs for large-volume targets. The effect of MLC leaf width was not quantifiably different in sliding window and step and shoot techniques. In addition, we observed that there was no additional benefit to the sliding-window (SW) technique when compared to the step-shoot (SS) technique as a result of reduction of MLC leaf width.

Objective: Postmastectomy radiation therapy (PMRT) to the chest wall and regional nodal irradiation (RNI) in women with node-positive breast cancer is known to reduce locoregional recurrence and distant metastases, as well as improve overall survival. Standard 3-dimensional (3D) conformal techniques may not be able to provide a clinically optimal plan for treatment, especially when coverage to the internal mammary nodes is required. Although advanced delivery techniques such as volumetric-modulated arc therapy (VMAT) can be used to better spare the heart and lungs, there is an increase in low dose exposure to normal tissue compared with 3D conformal planning. In a situation where 3D conformal planning provides an acceptable dose distribution for the majority of critical organs, it may not be justifiable to use VMAT to reduce dose to a few organs, while increasing low-dose exposure to the entire patient. In such cases, a combination of VMAT and 3D can be suitable to generate a clinic...

This paper presents the preclinical evaluation of a novel immobilization system for patients undergoing external beam radiation treatment of head and neck tumors. An immobilization mask is manufactured directly from a 3-D model, built using the CT data routinely acquired for treatment planning so there is no need to take plaster of Paris moulds. Research suggests that many patients find the mould room visit distressing and so rapid prototyping could potentially improve the overall patient experience. Evaluation of a computer model of the immobilization system using an anthropomorphic phantom shows that &gt;99% of vertices are within a tolerance of ±0.2 mm. Hausdorff distance was used to analyze CT slices obtained by rescanning the phantom with a printed mask in position. These results show that for &gt;80% of the slices the median “worse-case” tolerance is approximately 4 mm. These measurements suggest that printed masks can achieve similar levels of immobilization to those of syste...

Objective: Postmastectomy radiation therapy (PMRT) to the chest wall and regional nodal irradiation (RNI) in women with node-positive breast cancer is known to reduce locoregional recurrence and distant metastases, as well as improve overall survival. Standard 3-dimensional (3D) conformal techniques may not be able to provide a clinically optimal plan for treatment, especially when coverage to the internal mammary nodes is required. Although advanced delivery techniques such as volumet-ric-modulated arc therapy (VMAT) can be used to better spare the heart and lungs, there is an increase in low dose exposure to normal tissue compared with 3D conformal planning. In a situation where 3D conformal planning provides an acceptable dose distribution for the majority of critical organs, it may not be justifiable to use VMAT to reduce dose to a few organs, while increasing low-dose exposure to the entire patient. In such cases, a combination of VMAT and 3D can be suitable to generate a clinically acceptable dose distribution without an unnecessary increase in low dose exposure. In this report we describe a left-and a right-sided case, which have benefited from this approach. Methods and Materials: The left-sided case was of a 59-year-old woman with stage IIIC cancer who had undergone a bilateral mastectomy requiring PMRT to the chest wall along with RNI. The right-sided case was of a 51-year-old woman with stage IIIC cancer who had undergone a lumpectomy requiring whole-breast radiation (WBI) with RNI. Computed tomography (CT) scans were acquired from the chin to the upper abdomen during free breathing at 3-mm slice spacing with the patient positioned on an angle board and head turned to the contralateral side. Contouring of the target volume was done as per Radiation Therapy Oncology Group (RTOG) guidelines. Three plans were done for each case, the first using 3D conformal planning with the partially wide tangents (PWT) technique, the second using volumetric-modulated arc therapy (VMAT) alone, and finally using a combination of 3D and VMAT. A dosimetric comparison of the plans was performed in each case. Results: For both the left-and the right-sided cases, the PTV D95, V95 as well as the IMN D95 were comparable among all the plans; however, the hotspot in terms of the PTV D05 was found to be lower for the VMAT and the combined plan. The homogeneity index (HI) and the conformity index (CI) were best with the combined plan. For both the left-and the right-sided cases, the heart was well spared with the PWT technique. The MHD was the highest with VMAT as were the volumes covered by lower doses, namely 15 Gy and 5 Gy. However, combining VMAT and PWT did not compromise the V15 Gy and V5 Gy compared with PWT. The ipsilateral lung V20 Gy was the highest (≥ 45%) with PWT technique yielding a clinically unacceptable plan in both cases. The combination of VMAT and PWT not only maintained the ipsilateral lung V20 Gy ≤ 30%, but also kept the V5 Gy comparable to or lower than the corresponding PWT plan. The trend in the result for the total lung was similar to that of the ipsilateral lung. The contralateral breast was best spared with PWT; however, the combination plan did not compromise dose to the contralateral breast compared with the former technique. Conclusions: Combination of VMAT and 3D was not only able to preserve the mean dose to the heart, but was able to also reduce the ipsilateral lung V20 Gy without increasing low dose to all of the organs compared to using VMAT alone.

Purpose or Objective
To report acute hematological toxicity (HT) and dose
volume correlates in patients receiving postoperative
bowel sparing intensity-modulated radiotherapy (IMRT)
and cisplatin within a Phase III trial for late bowel toxicity
reduction in patients with cervical cancer.
Material and Methods
Clinical database of Phase III trial (NCT01279135) that
randomizes patients to IMRT (Tomotherapy) and 3DCRT
was searched to select patient strata that received IMRT
(50 Gy/25#/5 wks) and concurrent cisplatin (40 mg/m2)
from Jan, 2011 to Jun, 2016. The IMRT planning aimed at
restricting V15 and V40 Small Bowel to ≤ 200 and 100 cc
respectively. No prospective bone marrow (BM)
constraints were applied. The data base was reviewed to
determine worst grade of HT toxicity. IMRT planning scans
were dearchived and pelvic BM was delineated in 2 sets;
whole bone (WB), and freehand (FH) inner cavity of bone
from top of L3 vertebra to ischial tuberosity. Various BM
sub-volumes namely whole pelvis + lumbar (WPL), lumbar vertebra, sacrum, ilium, ischium, femoral head and neck, whole pelvis (WP), lower pelvis(LP) were contoured and dose volume histograms (DVH) parameters (V5, V10, V20, V30, and V40) were obtained. Receiver operating characteristic (ROC) curve identified DVH thresholds that predicted for grade≥ II HT toxicity with highest specificity.
All data was dichotomized across these cut-offs.
Univariate and multivariate analysis was performed with
SPSS, version 20.
Results
Of the 94 patients randomized to IMRT arm, 74 received
concurrent cisplatin (median cycles=4). Grades I-V HT was seen in 55.5%, 32.5%, 5%, 0% and 0% patients, respectively demonstrating low incidence of HT during bowel sparing IMRT. Leukopenia, neutropenia, anemia, and thrombocytopenia ≥ grade II was observed in 24.3%, 5.3%, 17.6%, and 0%, respectively. None of the HT resulted in treatment break. On comparing BM delineation techniques the FH sub volumes were 25%-47% of WB sub-volumes. The mean V5, V10, V20, V30, and V40 for WP FH and WB were 99%, 93%, 77%, 60%, and 36%; and 99%, 94%, 80%, 60%, and 36%, respectively suggesting unintended desirable BM
sparing. On univariate analysis WPL FH V30 > 55% (p=0.04)
predicted for overall grade ≥ II HT, WP V10 >95% (p= 0.04) for grade ≥ II leucopenia and ilium V20 > 90% (p=0.04) for hemoglobin toxicity. On multivariate analysis, only WP FH V10 >95% (p value 0.04, OR 3.3 (1-11.5) was statistically significant for grade ≥ II leucopenia.
Conclusion
The IMRT arm of NCT01279135 (PARCER study) that
employed strict bowel constraints also had unintentional
dosimetrically desirable BM sparing. This was associated with low absolute rates of HT. Within the setting of bowel sparing IMRT WP FH V10 should be restricted to ≤95% for simultaneous bowel and BM sparing. However as none of the other dosimetric variables predicted for HT, WB marrow contours could serve as a resource sparing strategy while planning pelvic IMRT.

Purpose: The main purpose of this study is to perform the dosimetric comparison between Intensity modulated radiation therapy (IMRT) and Volumetric modulated arc therapy (VMAT) for the prostate cancer by using dose-volume histograms (DVH). Methods: IMRT plan and VMAT plan were generated using 7 fields and 2 arcs, respectively, for the total dose of 76 Gy. Planning target volume (PTV) was evaluated for the maximum dose, mean dose, minimum dose, and conformity index. Rectum and bladder were evaluated for V70Gy, V50Gy, and V30Gy. The number of MUs between IMRT and VMAT plan was evaluated too. Results: The PTV dose evaluation showed that VMAT plan produced values closer to the prescription dose than did IMRT plan. The conformity index was also slightly better in VMAT plan (1.15) than in IMRT plan (1.17). The relative volume of bladder receiving radiation was always lower in VMAT plan for all parameters. However, IMRT was better than VMAT at V70Gy and V30Gy, whereas VMAT was better at V50Gy. The MUs were higher in IMRT plan (812) when compared to the one in VMAT plan (560). Conclusion: Both the VMAT and IMRT produced clinically acceptable treatment plan for the prostate cancer. Based on the single case in this study, VMAT produced slightly favorable dosimetric results.