Initial Planning Target Volume Research Articles

Validation of a Monte Carlo Framework for Out-of-Field Dose Calculations in Proton Therapy.

Proton therapy enables to deliver highly conformed dose distributions owing to the characteristic Bragg peak and the finite range of protons. However, during proton therapy, secondary neutrons are created, which can travel long distances and deposit dose in out-of-field volumes. This out-of-field absorbed dose needs to be considered for radiation-induced secondary cancers, which are particularly relevant in the case of pediatric treatments. Unfortunately, no method exists in clinics for the computation of the out-of-field dose distributions in proton therapy. To help overcome this limitation, a computational tool has been developed based on the Monte Carlo code TOPAS. The purpose of this work is to evaluate the accuracy of this tool in comparison to experimental data obtained from an anthropomorphic phantom irradiation. An anthropomorphic phantom of a 5-year-old child (ATOM, CIRS) was irradiated for a brain tumor treatment in an IBA Proteus Plus facility using a pencil beam dedicated nozzle. The treatment consisted of three pencil beam scanning fields employing a lucite range shifter. Proton energies ranged from 100 to 165 MeV. A median dose of 50.4 Gy(RBE) with 1.8 Gy(RBE) per fraction was prescribed to the initial planning target volume (PTV), which was located in the cerebellum. Thermoluminescent detectors (TLDs), namely, Li-7-enriched LiF : Mg, Ti (MTS-7) type, were used to detect gamma radiation, which is produced by nuclear reactions, and secondary as well as recoil protons created out-of-field by secondary neutrons. Li-6-enriched LiF : Mg,Cu,P (MCP-6) was combined with Li-7-enriched MCP-7 to measure thermal neutrons. TLDs were calibrated in Co-60 and reported on absorbed dose in water per target dose (μGy/Gy) as well as thermal neutron dose equivalent per target dose (μSv/Gy). Additionally, bubble detectors for personal neutron dosimetry (BD-PND) were used for measuring neutrons (>50 keV), which were calibrated in a Cf-252 neutron beam to report on neutron dose equivalent dose data. The Monte Carlo code TOPAS (version 3.6) was run using a phase-space file containing 1010 histories reaching an average standard statistical uncertainty of less than 0.2% (coverage factor k = 1) on all voxels scoring more than 50% of the maximum dose. The primary beam was modeled following a Fermi–Eyges description of the spot envelope fitted to measurements. For the Monte Carlo simulation, the chemical composition of the tissues represented in ATOM was employed. The dose was tallied as dose-to-water, and data were normalized to the target dose (physical dose) to report on absorbed doses per target dose (mSv/Gy) or neutron dose equivalent per target dose (μSv/Gy), while also an estimate of the total organ dose was provided for a target dose of 50.4 Gy(RBE). Out-of-field doses showed absorbed doses that were 5 to 6 orders of magnitude lower than the target dose. The discrepancy between TLD data and the corresponding scored values in the Monte Carlo calculations involving proton and gamma contributions was on average 18%. The comparison between the neutron equivalent doses between the Monte Carlo simulation and the measured neutron doses was on average 8%. Organ dose calculations revealed the highest dose for the thyroid, which was 120 mSv, while other organ doses ranged from 18 mSv in the lungs to 0.6 mSv in the testes. The proposed computational method for routine calculation of the out-of-the-field dose in proton therapy produces results that are compatible with the experimental data and allow to calculate out-of-field organ doses during proton therapy.

A prospective comparison of adaptive and fixed boost plans in radiotherapy for glioblastoma

PurposeTo analyze the efficacy of adaptive radiotherapy (ART) for glioblastoma.MethodsSixty-one glioblastoma patients who received ART were prospectively evaluated. The initial clinical target volume (CTVinitial) was represented by T2 hyperintensity on postoperative MRIs (pre-RT MRI [MRIpre])plus 10 mm. The initial planning target volume (PTVinitial) was the CTVinitial plus a 5-mm margin. The PTVinitial received 40 Gy. An MRI and a second planning CT were performed during radiotherapy (MRImid). Two types of boost CTVs (the resection cavity and residual tumor on enhanced T1-weighted MRI plus 10 mm) were created based on the MRIpre and MRImid (CTVboost-pre and -mid). The boost PTV (PTVboost) was the CTVboost plus 5 mm. Two types of boost plans (fixed and adaptive boost plans in the first and second planning CT, respectively) of 20 Gy were created. The PTV based on the post-RT MRI (PTVboost-post) was created, and the dose-volume histograms of the PTVboost-post in the fixed and adaptive boost plans were compared. Additionally, the conformity indices (CIs) of the fixed and adaptive boost plans were compared.ResultsThe median V95 of the PTVboost-post of the fixed and adaptive boost plans (V95pre and V95mid) were 95.6% and 98.3%, respectively (P < 0.01). The median V95pre and V95mid of patients after gross total resection (GTR) were 97.4% and 98.8%, respectively (P = 0.41); in contrast, the median values of patients after non-GTR were 91.9% and 98.2%, respectively (P < 0.01). The median CIs of the fixed and adaptive boost plans in all patients were 1.45 and 1.47, respectively (P = 0.31). The median CIs of the fixed and adaptive boost plans in patients after GTR were 1.61 and 1.48, respectively (P = 0.01); in contrast, those in patients after non-GTR were 1.36 and 1.44, respectively (P = 0.13).ConclusionART for glioblastoma improved the target coverage and dose reduction for the normal brain. By analyzing the results according to the resection rate, we can expect a decrease in normal brain dose in patients with GTR and an increase in coverage in those with partial resection or biopsy.

Reducing target volume in definitive radiotherapy for human papillomavirus-associated tonsil cancer.

To evaluate the efficacy and safety of reducing target volume in definitive radiotherapy for HPV-associated tonsil cancer. A single-institution cohort of 90 patients with human papillomavirus (HPV)-associated tonsil cancer who received definitive radiotherapy with a 5-mm expansion from the gross tumor volume to clinical target volume between 2008 and 2019 were included. The overlapping volume of initial planning target volume and the recurrent tumor was calculated and categorized as one of three failure types: in-field: ≥95%; marginal-field: 50%-94%; and out-field: <50%. With a median follow-up of 59.4months, the 3-year and 5-year local control rates were 94.4% and 92.8%, respectively. A total of seven local failures were identified, of which 4 (4.4%) were in-field, 2 (2.2%) were marginal-field, and 1 (1.1%) was out-field. Grade 3 acute and late toxicities developed in 30 (33.3%) and 5 (5.6%) patients, respectively. Reducing target volume could be an alternative option for selected patients with HPV-associated tonsil cancer.

Planning target volume as a\xa0predictor of disease progression in inoperable stage III non-small cell lung cancer patients treated with chemoradiotherapy and concurrent and/or sequential immune checkpoint inhibition

SummaryBackground. The present study evaluates outcome after chemoradiotherapy (CRT) with concurrent and/or sequential Programmed Cell Death 1 (PD-1) or Ligand 1 (PD-L1) immune checkpoint inhibition (CPI) for inoperable stage III NSCLC patients depending on planning target volume (PTV). Method and patients. Prospective data of thirty-three consecutive patients with inoperable stage III NSCLC treated with CRT and sequential durvalumab (67%, 22 patients) or concurrent and sequential nivolumab (33%, 11 patients) were analyzed. Different PTV cut offs and PTV as a continuous variable were evaluated for their association with progression-free (PFS), local–regional progression-free (LRPFS), extracranial distant metastasis-free (eMFS) and brain-metastasis free-survival (BMFS). Results. All patients were treated with conventionally fractionated thoracic radiotherapy (TRT); 93% to a total dose of at least 60 Gy, 97% of patients received two cycles of concurrent platinum-based chemotherapy. Median follow-up for the entire cohort was 19.9 (range: 6.0–42.4) months; median overall survival (OS), LRFS, BMFS and eMFS were not reached. Median PFS was 22.8 (95% CI: 10.7–34.8) months. Patients with PTV ≥ 900ccm had a significantly shorter PFS (6.9 vs 22.8 months, p = 0.020) and eMFS (8.1 months vs. not reached, p = 0.003). Furthermore, patients with PTV ≥ 900ccm and stage IIIC disease (UICC-TNM Classification 8th Edition) achieved a very poor outcome with a median PFS and eMFS of 3.6 vs 22.8 months (p < 0.001) and 3.6 months vs. not reached (p = 0.001), respectively. PTV as a continuous variable also had a significant impact on eMFS (p = 0.048). However, no significant association of different PTV cut-offs or PTV as a continuous variable with LRPFS and BMFS could be shown. The multivariate analysis that was performed for PTV ≥ 900ccm and age (≥ 65 years), gender (male), histology (non-ACC) as well as T- and N-stage (T4, N3) as covariates also revealed PTV ≥ 900ccm as the only factor that had a significant correlation with PFS (HR: 5.383 (95% CI:1.263–22.942, p = 0.023)). Conclusion. In this prospective analysis of inoperable stage III NSCLC patients treated with definitive CRT combined with concurrent and/or sequential CPI, significantly shorter PFS and eMFS were observed in patients with initial PTV ≥ 900ccm.

Interfractional target changes in brain metastases during 13-fraction stereotactic radiotherapy

BackgroundThe risk for radiation necrosis is lower in fractionated stereotactic radiotherapy (SRT) than in conventional radiotherapy, and 13-fraction SRT is our method of choice for the treatment of brain metastases ≥ around 2 cm or patients who are expected to have a good prognosis. As 13-fraction SRT lasts for at least 17 days, adaptive radiotherapy based on contrast-enhanced mid-treatment magnetic resonance imaging (MRI) is often necessary for patients undergoing 13-fraction SRT. In this study, we retrospectively analyzed interfractional target changes in patients with brain metastases treated with 13-fraction SRT.MethodsOur analyses included data from 23 patients and 27 metastatic brain lesions treated with 13-fraction SRT with dynamic conformal arc therapy. The peripheral dose prescribed to the planning target volume (PTV) was 39–44.2 Gy in 13-fractions. The gross tumor volume (GTV) of the initial SRT plan (initial GTV), initial PTV, and modified GTV based on the mid-treatment MRI scan (mid-treatment GTV) were assessed.ResultsThe median initial GTV was 3.8 cm3 and the median time from SRT initiation to the mid-treatment MRI scan was 6 days. Compared to the initial GTV, the mid-treatment GTV increased by more than 20% in five lesions and decreased by more than 20% in five lesions. Interfractional GTV volume changes of more than 20% were not significantly associated with primary disease or the presence of cystic components/necrosis. The mid-treatment GTV did not overlap perfectly with the initial PTV in more than half of the lesions.ConclusionsCompared to the initial GTV, the mid-treatment GTV changed by more than 20% in almost one-third of lesions treated with 13-fraction SRT. As SRT usually generates a steep dose gradient as well as increasing the maximum dose of PTV compared to conventional radiotherapy, assessment of the volume and locational target changes and adaptive radiotherapy should be considered as the number of fractions increases.

Management of local recurrences and regional failure in early stage non-small cell lung cancer after stereotactic body radiation therapy.

Stereotactic body radiation therapy (SBRT) is a very effective way to treat early stage non-small cell lung cancer (NSCLC) and small oligometastatic lung lesions with consistently high rates of local control, but both local and regional/distant recurrences still occur. The management of recurrences remains unsettled and may entail repeat SBRT, conventionally fractionated external beam RT (EF-EBRT), chemotherapy or surgery. Most patients with local recurrences [within the initial planning target volume (PTV)] can be salvaged successfully with good cancer specific survival. Nonetheless, proximity of the initial SBRT delivery to organs at risk (ribs, blood vessels, airways) may make retreatment more difficult. With attention to detail and careful patient selection, both surgery and reirradiation can be performed safely and effectively. Strategies for management of regional (nodal) recurrences may require conventional therapies tailored to the patterns of failure. The role of immunotherapy in salvage has not been elucidated as yet. We review here data on the available literature concerning salvage of SBRT lung patients.

Repeat stereotactic body radiation therapy (SBRT) for salvage of isolated local recurrence after definitive lung SBRT

PurposeOptimal management of isolated local recurrences after stereotactic body radiation therapy (SBRT) for early non-small cell lung cancer (NSCLC) is unknown and literature describing repeat SBRT for in-field recurrences after initial SBRT are sparse. We investigate the safety and efficacy of salvage SBRT for isolated local failures after initial SBRT for NSCLC. Methods/MaterialsPatients receiving SBRT for isolated local recurrence after initial SBRT for early NSCLC were identified using a prospective registry. Both courses were 3–5 fractions with a biologically effective dose (BED10) of ≥100 Gy. Local failure was defined as within 1 cm of the initial planning target volume (PTV) or an overlap of the ≥25% isodose lines of the first and second treatments. Failures >1 cm beyond the PTV and without ≥25% overlap, or with additional recurrence sites were excluded. Kaplan-Meier analysis was used to estimate survival. ResultsA total 21 patients receiving salvage SBRT from 2008 to 2017 were identified. Median interval from initial SBRT to salvage SBRT was 23 months (7–52). Six patients (29%) had central tumors. Median follow-up time from salvage SBRT was 24 months (3–60). Median overall survival after salvage was 39 months. After reirradiation, two-year primary tumor control was 81%, regional nodal control was 89%, distant control was 75% and overall survival was 68%. Grade 2 pneumonitis occurred in 2 patients (10%) and grade 2 chest wall toxicity in 4 patients (19%). No grade 3+ toxicity was observed. ConclusionsSalvage SBRT for isolated local failures after initial SBRT appears safe, with low treatment-related toxicity and encouraging rates of tumor control.

Adaptive radiation therapy for cervical esophageal cancer: dosimetric and volumetric analysis.

Cervical esophageal cancer (CEC) patients may suffer from significant anatomical changes due to tumor shrinkage or weight loss during radiotherapy. The aim of the study is to evaluate the volumetric and dosimetric changes in the target and critical volumes of CEC patients by using adaptive radiotherapy (ART) technique. Seven CEC patients treated in helical tomotherapy (HT) unit was analyzed. All patients had a replanning CT simulation at 3rd (CT2) and 5th (CT3) weeks in addition to the initial CT (CT1). Volumetric and dosimetric changes of target and organs at risk (OAR) were evaluated. The average weight loss of the patients was 9.03%. The major changes of the planning target volume (PTV), PTV boost, right and left parotid volumes were 4.74%; 15.93%; 26.82% and 26.64%, respectively. Using ART software was evaluated with first planning values (CT1) and pre-CT2-CT3 verification values. The correlation was decrease of the D95 and increase of the Dmax was statistically significant. When evaluated the varying values of the new CTs, there was no significant change between the initial PTV and adapted PTV's. But a significant decrease was observed at the summation plan for left and right parotids (P<0.05). The mean dose reductions of left and right parotid were 2.48 and 2.49 Gy, respectively. Our results showed that using ART technique was beneficial to ensure adequate doses to the target volumes and safe doses to the OARs for the patients who need replanning during RT in uncommon CEC patients.

Incorporating the rotational setup uncertainty into the planning target volume margin expansion for the single isocenter for multiple targets technique

PurposeThe single isocenter for multiple targets (SIMT) technique has become a popular treatment approach for multiple brain metastases. However, the rotational error that is introduced is usually not considered in planning target volume (PTV) expansion. We have developed a statistical model that takes into account both translational and rotational uncertainties. In this study, we incorporated the rotational error into PTV margin expansion for the clinical use of the SIMT technique. Methods and materialsIn the statistical model, both translational and rotational errors are assumed to follow the 3-dimensional, independent, normal distribution with a zero mean and standard deviations of σS and σR, where σR = 0.01424σD (rotational uncertainty in degree)×dI ⇔ T (distance in mm from isocenter to target). Based on this model, we derived in this study the additional PTV margin, ∆M, that is required to maintain the same coverage probability when the rotational uncertainty is present as a function of MS (initial PTV margin), σD, and dI ⇔ T. The maximum allowable dI ⇔ T, C and σD, C were also calculated as a function of user-specified ∆Mc/MS, the fraction of MS below which the extra PTV margins can be ignored. ResultsCombined PTV margin, ME, and additional PTV margin, ∆M, were plotted for commonly encountered clinical parameters including dI ⇔ T, MS, or σD. Unlike other reported margin recipes, ∆M is not a linear function of any of these 3 parameters. In addition, the rate of increase for ∆M is quite slow for small dI ⇔ T and becomes more significant for larger dI ⇔ T. Cutoff values dI ⇔ T, C and σD, C were also plotted for various ∆Mc/MS, which can be used to determine if an additional PTV margin is needed for the SIMT technique. ConclusionsThe presented data provide a convenient way for clinics to determine the appropriate PTV margin for the SIMT technique.

Treatment outcome for locally advanced non-small-cell lung cancer using TomoDirect plan and its characteristics compared to the TomoHelical plan.

IntroductionTomoDirect (TD) is an intensity‐modulated radiotherapy system that uses a fixed gantry angle instead of the rotational beam delivery used in the TomoHelical (TH) system. This study was performed (1) to evaluate the treatment outcome of the TD plan for locally advanced non‐small‐cell lung cancer (NSCLC) and (2) to compare the characteristics of TD plans with those of TH plans.MethodsTwenty‐one patients with NSCLC were treated using the TD system. The prescribed dose was 40 Gy/20 Fx for the initial planning target volume (PTV), which included the gross tumour volume (GTV) and lymph node regions. A boost plan of 20 Gy/10 Fx was then applied, focusing on the GTV. For the planning study, matched TH plans of 40 Gy for the initial PTV were created for each patient, to meet the same dosimetric constraints specified in the TD plans.ResultsThe 2‐year overall survival, progression‐free survival and local control rates were 47%, 45% and 74% respectively. Grade 2 treatment‐related pneumonitis occurred in three (14%) patients. The planning study comparing TD and TH showed that dose distribution to GTV and PTV were not significantly different. The lung V5 Gy was lower in the TD plans than TH plans (46.4 ± 5.4 vs. 52.3 ± 8.5), while the V20 Gy was higher (26.2 ± 4 vs. 24 ± 4.3). The TD plans had a significantly shorter treatment time than TH plans (4.5 ± 1.3 min vs. 9.8 ± 1.5 min).ConclusionsTD is a clinically acceptable treatment option for NSCSL. The quality of the TD and TH plans are comparable.

Passive proton therapy vs. IMRT planning study with focal boost for prostate cancer.

BackgroundExploiting biologic imaging, studies have been performed to boost dose to gross intraprostatic tumor volumes (GTV) while reducing dose elsewhere in the prostate. Interest in proton beams has increased due to superior normal-tissue sparing they afford. Our goal was to dosimetrically compare 3D conformal proton boost plans with intensity-modulated radiation therapy (IMRT) plans with respect to target coverage and avoiding organs at risk.MethodsTreatment planning computer tomography scans of ten patients were selected. For each patient, two hypothetical but realistic GTVs each with a fixed volume were contoured in different anatomical locations of the prostate. IMRT and proton beam plans were created with a prescribed dose of 50.4 Gy to the initial planning target volume (PTV) including the PTV of the seminal vesicles (PSV), 70.2 Gy to the PTV of the prostate (PPS), and 90 Gy to the PTV of the gross tumor volumes (PGTVs). For proton plans, uncertainties of range and patient setup were accounted for; apertures were adjusted until the dose-volume coverage of PTVs matched that of the IMRT plan. For both plans, prescribed PTV doses were made identical to allow for comparing normal-tissue doses.ResultsProtons delivered more homogeneous but less conformal doses to PGTVs than IMRT did and comparable doses to PSV and PPS. Volumes of bladder and rectum receiving doses higher than 65 Gy were similar for both plans. However, volumes receiving less than 65 Gy were significantly reduced, i.e., protons reduced integral dose by 45.6 % and 26.5 % for rectum and bladder, respectively. This volume-sparing was also seen in femoral heads and penile bulb.ConclusionsProtons delivered comparable doses to targets in dose homogeneity and conformity and spared normal tissues from intermediate-to-low doses better than IMRT did. Further improvement of dose sparing and changes in homogeneity and conformity may be achieved by reducing proton range uncertainties and from implementing intensity modulation.

Patterns of failure for glioblastoma multiforme following limited-margin radiation and concurrent temozolomide.

BackgroundTo analyze patterns of failure in patients with glioblastoma multiforme (GBM) treated with limited-margin radiation therapy and concurrent temozolomide. We hypothesize that patients treated with margins in accordance with Adult Brain Tumor Consortium guidelines (ABTC) will demonstrate patterns of failure consistent with previous series of patients treated with 2–3 cm margins.MethodsA retrospective review was performed of patients treated at the University of Alabama at Birmingham for GBM between 2000 and 2011. Ninety-five patients with biopsy-proven disease and documented disease progression after treatment were analyzed. The initial planning target volume includes the T1-enhancing tumor and surrounding edema plus a 1 cm margin. The boost planning target volume includes the T1-enhancing tumor plus a 1 cm margin. The tumors were classified as in-field, marginal, or distant if greater than 80%, 20-80%, or less than 20% of the recurrent volume fell within the 95% isodose line, respectively.ResultsThe median progression-free survival from the time of diagnosis to documented failure was 8 months (range 3–46). Of the 95 documented recurrences, 77 patients (81%) had an in-field component of treatment failure, 6 (6%) had a marginal component, and 27 (28%) had a distant component. Sixty-three patients (66%) demonstrated in-field only recurrence.ConclusionsThe low rate of marginal recurrence suggests that wider margins would have little impact on the pattern of failure, validating the use of limited margins in accordance ABTC guidelines.

Adaptive radiotherapy in lung cancer: dosimetric benefits and clinical outcome

Anatomical changes during radiotherapy (RT) might introduce discrepancies between planned and delivered doses. This study evaluates the need for adaptive treatment in lung cancer RT. 15 patients with non-small-cell lung cancer, undergoing radical RT with or without concurrent chemotherapy, consecutively underwent planning CT scans at baseline and after 44-46 Gy. Target volumes were delineated on both scans. Phase I delivered 44-46 Gy to the initial planning target volume (PTV). Two Phase II plans for 16-20 Gy were developed on initial and mid-treatment scans, the treatment being delivered with the mid-treatment plan. The second CT structure set was fused with the initial scan data set using dose wash. Volumetric and dosimetric changes in target volumes and critical structures were assessed. There was significant reduction in primary gross tumour volume (34.00%; p = 0.02) and PTV (34.70%; p < 0.01) in the second scan. In Plan 2, delivering the same dose to the initial PTV would have resulted in a significantly higher dose to the lung PTV (V20, 52.18%; V5, 21.76%; mean, 23.93%), contralateral lung (mean, 29.43%), heart (V10, 81.47%; V5, 56.62%; mean, 35.21%) and spinal cord (maximum dose, 37.53%). Treatment replanning can account for anatomical changes during RT and thereby enable better normal tissue sparing, while allowing radical target doses with the possibility of maximizing local control. This study supports the sparse dosimetric data regarding the quantitative tumour volume reduction, re-emphasizing the need for adaptive replanning for minimizing normal tissue toxicity without compromising local control, and adds to the existing body of literature.

High-dose, conventionally fractionated thoracic reirradiation for lung tumors

BackgroundLoco-regional recurrences and second primary lung tumors are not uncommon after high-dose thoracic radiotherapy. The availability of improved radiotherapy techniques increases options for reirradiation. We describe a single-institutional experience with high-dose conventional thoracic reirradiation for both loco-regional recurrences and new primary tumors. MethodsRetrospective chart review of patients undergoing reirradiation between February 2004 and February 2013. ResultsOf 24 patients identified, 54% had a loco-regional recurrence, and 46% a new primary tumor. The majority (63%) had stage III NSCLC at both initial and second treatment; median interval between treatments was 51 months (5–189), median follow-up after reirradiation was 19.3 months (95% CI: 2.8–35.9). Median overall survival (OS) after reirradiation was 13.5 months, with 1-year survival 51%. Median event-free survival (EFS) was 8.4 months. Median time between reirradiation and local progression (n=8) or distant progression (n=8) was 6.7 and 11.8 months, respectively. Three patients died with possible grade 5 bleeding. Other toxicities were uncommon. Planning target volume (PTV) at reirradiation was the most important prognostic factor; PTV <300 versus ≥300cc was significantly associated with median OS (17.4 vs 8.2 months, p=0.03) and EFS (14.1 vs 5.5 months, p=0.03). Magnitude of overlap between the initial and subsequent PTVs, and between dose distributions, did not influence survival. ConclusionThoracic reirradiation with high dose conventional radiotherapy appears to deliver a meaningful survival benefit in low volume new primary or recurrent lung cancer. Further studies are needed to confirm these findings, and to establish reliable normal tissue tolerance doses for reirradiation.

Dosimetric Advantages and Superior Treatment Delivery Efficiency of RapidArc over Conventional Intensity-modulated Radiotherapy in High-risk Prostate Cancer Involving Seminal Vesicles and Pelvic Nodes

AimsTo compare the dosimetry and treatment delivery efficiency of RapidArc with conventional intensity-modulated radiotherapy (IMRT) in the treatment of high-risk prostate cancer. Materials and methodsFifteen patients with high-risk localised prostate cancer were studied. Sequential treatment was used. The initial planning target volume (PTV-L) included the prostate, seminal vesicles and pelvic lymphatics, whereas the prostate boost PTV (PTV-P) included the prostate and seminal vesicles only. The total prescription dose was 76 Gy (44 Gy to PTV-L, 32 Gy to PTV-P; 2 Gy/fraction). Two separate planning techniques were generated for each patient: seven static-field IMRT versus two-arc RapidArc. Dose–volume parameters for the organs at risk, conformity index and homogeneity index for the PTVs, the calculated monitor units and treatment delivery time for both techniques were compared. ResultsRapidArc gave more conformal plans than IMRT for both PTVs. RapidArc gave a higher homogeneity index to the PTV-P and a similar homogeneity index to the PTV-L. The two techniques gave similar dosimetric results for the rectum, bladder and femoral heads. The mean dose (Dmean) and the maximum dose (Dmax) of the bowel space were reduced by 3.06 and 2.83%, respectively, with RapidArc. The V20 Gy, V30 Gy and V40 Gy for healthy tissues were reduced by 7.77, 14.25 and 17.55%, respectively, with RapidArc. The calculated treatment delivery time and monitor units were reduced by 74.09%/60.93% and 68.32%/48.06% for the PTV-L/PTV-P, respectively, with RapidArc. ConclusionRapidArc is better than conventional IMRT in terms of dosimetry and delivery efficiency for high-risk prostate cancer.

Proton therapy may allow for comprehensive elective nodal coverage for patients receiving neoadjuvant radiotherapy for localized pancreatic head cancers.

Neoadjuvant radiotherapy has the potential to improve local disease control for patients with localized pancreatic cancers. Concern about an increased risk of surgical complications due to small bowel and gastric exposure, however, has limited enthusiasm for this approach. Dosimetric studies have demonstrated the potential for proton therapy to reduce intestinal exposure compared with X-ray-based therapy. We sought to determine if neoadjuvant proton therapy allowed for field expansions to cover high-risk nodal stations in addition to the primary tumor. Twelve consecutive patients with nonmetastatic cancers of the pancreatic head underwent proton-based planning for neoadjuvant radiotherapy. Gross tumor volume was contoured using diagnostic computed tomography (CT) scans with oral and intravenous contrast. Four-dimensional planning scans were utilized to define an internal clinical target volume (ICTV). Five-mm planning target volume (PTV) expansions on the ICTV were generated to establish an initial PTV (PTV1). A second PTV was created using the initial PTV but was expanded to include the high-risk nodal targets as defined by the RTOG contouring atlas (PTV2). Optimized proton plans were generated for both PTVs for each patient. All PTVs received a dose of 50.4 cobalt gray equivalent (CGE). Normal-tissue exposures to the small bowel space, stomach, right kidney, left kidney and liver were recorded. Point spinal cord dose was limited to 45 CGE. Median PTV1 volume was 308.75 cm(3) (range, 133.33-495.61 cm(3)). Median PTV2 volume was 541.75 cm(3) (range, 399.44-691.14 cm(3)). In spite of the substantial enlargement of the PTV when high-risk lymph nodes were included in the treatment volume, normal-tissue exposures (stomach, bowel space, liver, and kidneys) were only minimally increased relative to the exposures seen when only the gross tumor target was treated. Proton therapy appears to allow for field expansions to cover high-risk lymph nodes without significantly increasing critical normal-tissue exposure in the neoadjuvant setting.

SU‐E‐T‐684: A Comprehensive Dosimetric Study of Pancreatic Cancer Treatment Using Three Dimensional (3D) Conformal Radiation Therapy, Intensity‐Modulated Radiation Therapy (IMRT), Volumetric Modulated Radiation Therapy (VMAT), Passive Scattering and Modulated Scanning Proton Therapy (PT)

Purpose: This study is to evaluate different radiation therapy modalities in pancreas cancer treatment and to explore the potential role of organs‐at‐risk (OARs) sparing using proton therapy (PT). Methods: Seven consecutive pancreatic cancer patients who had been previously treated with passive‐scattering PT were identified. The clinical target volume (CTV) include the pancreatic tumor bed as well as the adjacent high risk nodal areas. Treatment plans were generated using three‐field and four‐field 3DCRT, five‐field IMRT, two‐arc VMAT, two‐field passive‐scattering and modulated‐scanning PT. All plans delivered 50.4Gy to the initial planning target volume (PTV). 98% of PTV is covered by 95% of the prescription dose and 98% of CTV received 98% prescription dose. Posterior and right posterior oblique proton beams were used to minimize the range uncertainty and improve PT robustness. Pencil beam scanning (PBS) fields with single field uniform dose technique was used for modulated‐scanning PT. Results: All proton plans significantly reduced patient's body integrated dose. Both modulated‐scanning and passive‐scattering PT offer lower doses to the left kidney (mean and V18Gy) and bowel (mean and V20Gy). Modulated‐scanning PT reduced average stomach's mean dose to 168.2 cGy compare to 3‐field 3DCRT (1618.9 cGy P=0.0059), 4‐field 3DCRT (1565.3 cGy P=0.0062) IMRT (1003.47 cGy P=0.0162) and VMAT (1213.4 cGy P=0.0163), and average right kidney's mean dose to 765.7 cGy compared to 3‐field 3DCRT (2205.6 cGy P=0.0013), 4‐field 3DCRT(1825.9 cGy P=0.0009), IMRT(1515.5 cGy P=0.0028) and VMAT (1470.6 cGy P=0.0013). Moreover, modulated‐scanning PT offer lower bowel V20Gy(15.07%) compared to the passive‐scattering PT(28.18% P=0.006). However, IMRT and VMAT offer better target conformity compared to passive‐scattering PT (Passive‐scattering Conformity Index 80% =2.10±0.4, vs IMRT CI80=1.59 ±0.10 P=0.007, vs VMAT CI80=1.44 ±0.15 P=0.0015)Conclusion: The dosimetric advantage of modulated‐scanning PT points to the possibility of treating tumor bed and comprehensive nodal areas while providing a more tolerable treatment course.

A Clinical Study of Shrinking Field Radiation Therapy Based on 18F-FDG PET/CT for Stage III Non-Small Cell Lung Cancer

The aim is to investigate the feasibility of shrinking field technique after 40 Gy for stage III non-small cell lung cancer (NSCLC) during radiation therapy. Eighty-seven consecutive patients treated with intensity-modulated radiation therapy or three-dimensional conformal radiation therapy were enrolled in this study. (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) scanning was performed prior to treatment and repeated after 40 Gy, and the delineation of target volume was based on fused images of PET and CT. After 40 Gy of conventional fractionated radiotherapy to the initial planning target volume (PTV), a boost of 19.6-39.2 Gy was delivered to the shrunken PTV through late course accelerated hyperfractionated radiotherapy, and the median total dose was 66.0 Gy (range, 59.6-79.2 Gy). Gross tumor volume (GTV) and PTV regressions were recorded, and prescription doses with or without shrinking field were calculated. Local recurrence patterns were investigated through follow-up. The tumor volumes regressed in 84 (96.6%) patients and increased in 3 (3.4%) patients after 40 Gy. The mean GTV and PTV reduction was 38% (range, -13-95%) and 30% (range, -5-95%). Mean total prescription dose escalated from 62.0 Gy to 68.5 Gy through shrinking field technique. The median follow-up was 17 months, ranging from 5 to 46 months, and the 1- and 2-year overall survival rates in our study were 74.7% and 34.6%. The response rate was 79.5%, and radiation toxicity was acceptable. Tumor progression occurred in 67.8% (59/87) patients. Numbers of patients who had outfield, infield and both infield and outfield recurrences were 3 (3.4%), 26 (29.5%), and 3 (3.4%), respectively. In conclusion, significant tumor regression was observed after 40 Gy, and radiation dose escalated after shrinking field with acceptable toxicity and outfield relapse. Shrinking field radiotherapy based on (18)F-FDG PET/CT after 40 Gy was safe and feasible for stage III NSCLC.

Radiotherapy with volumetric modulated arc therapy for hepatocellular carcinoma patients ineligible for surgery or ablative treatments

The aim of this article is to report the dosimetric and clinical findings in the treatment of primary hepatocellular carcinoma (HCC) with volumetric modulated arc therapy (VMAT, RapidArc). A total of 138patients were investigated. Dose prescription ranged from 45-66Gy. Most patients (88.4 %) presented AJCC stage III or IV and 83 % were N0-M0. All were classified as Barcelona Clinic Liver Cancer (BCLC) stage A-C. All patients were treated using 10MV photons with single or multiple, coplanar or non-coplanar arcs, and cone-down technique in case of early response of tumors. The patients' median age was 66years (range 27-87years), 83 % were treated with 60Gy (12 % at 45Gy, 6 % at 66Gy), 62 % with cone-down, 98 % with multiple arcs. The mean initial planning target volume (PTV) was 777 ± 632cm(3); the mean final PTV (after the cone-down) was 583 ± 548cm(3). High target coverage was achieved. The final PTV was V98% > 98 %. Kidneys received on average 5 and 8Gy (left and right), while the maximum dose to the spinal cord was 22Gy; mean doses to esophagus and stomach were 23Gy and 15Gy, respectively. The average volume of healthy liver receiving more than 30Gy was 294 ± 145cm(3). Overall survival at 12months was 45 %; median survival was 10.3months (95 % confidence interval 7.2-13.3months). Actuarial local control at 6months was 95 % and 93.7 % at 12months. The median follow-up was 9months and a maximum of 28months. This study showed from the dosimetric point of view the feasibility and technical appropriateness of RapidArc for the treatment of HCC. Clinical results were positive and might suggest, with appropriate care, to consider RapidArc as an additional therapeutic opportunity for these patients.

Feasibility of Shrinking Field Radiation Therapy through 18F-FDG PET/CT after 40 Gy for Stage III Non-Small Cell Lung Cancers

To explore the feasibility of shrinking field technique after 40 Gy radiation through 18F-FDG PET/ CT during treatment for patients with stage III non-small cell lung cancer (NSCLC). In 66 consecutive patients with local-advanced NSCLC, 18F-FDG PET/CT scanning was performed prior to treatment and repeated after 40 Gy. Conventionally fractionated IMRT or CRT plans to a median total dose of 66 Gy (range, 60-78 Gy) were generated. The target volumes were delineated in composite images of CT and PET. Plan 1 was designed for 40 Gy to the initial planning target volume (PTV) with a subsequent 20-28 Gy-boost to the shrunken PTV. Plan 2 was delivering the same dose to the initial PTV without shrinking field. Accumulated doses of normal tissues were calculated using deformable image registration during the treatment course. The median GTV and PTV reduction were 35% and 30% after 40 Gy treatment. Target volume reduction was correlated with chemotherapy and sex. In plan 2, delivering the same dose to the initial PTV could have only been achieved in 10 (15.2%) patients. Significant differences (p<0.05) were observed regarding doses to the lung, spinal cord, esophagus and heart. Radiotherapy adaptive to tumor shrinkage determined by repeated 18F-FDG PET/CT after 40 Gy during treatment course might be feasible to spare more normal tissues, and has the potential to allow dose escalation and increased local control.