Median Planning Target Volume Research Articles

Accelerated partial breast irradiation using proton beams: Initial dosimetric experience

The unique dosimetric features of proton radiotherapy make it an attractive modality for normal tissue sparing. We present our initial experience with protons for three-dimensional, conformal, external-beam accelerated partial breast irradiation (3D-CPBI). From March 2004 to June 2005, 25 patients with tumors < or =2 cm and negative axillary nodes were treated with proton 3D-CPBI. The prescribed dose was 32 Cobalt Gray Equivalents (CGE) in 4 CGE fractions given twice daily. One to three fields were used to provide adequate planning target volume (PTV) coverage and dose homogeneity. Excellent PTV coverage and dose homogeneity were obtained in all patients with one to three proton beams. The median PTV receiving 95% of the prescribed dose was 100%. Dose inhomogeneity exceeded 10% in only 1 patient (4%). The median volume of nontarget breast tissue receiving 50% of the prescribed dose was 23%. Median volumes of ipsilateral lung receiving 20 CGE, 10 CGE, and 5 CGE were 0%, 1%, and 2%, respectively. The contralateral lung and heart received essentially no radiation dose. Cost analysis suggests that proton 3D-CPBI is only modestly more expensive (25%) than traditional whole-breast irradiation (WBI). Proton 3D-CPBI is technically feasible, providing both excellent PTV coverage and normal tissue sparing. It markedly reduces the volume of nontarget breast tissue irradiated compared with photon-based 3D-CPBI, addressing a principle disadvantage of external-beam approaches to PBI. As proton therapy becomes more widely available, it may prove an attractive tool for 3D-CPBI.

Dosimetric comparison of intensity-modulated, conformal, and four-field pelvic radiotherapy boost plans for gynecologic cancer: a retrospective planning study

PurposeTo evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiotherapy (CRT) or 4-field box boost (4FB) in women with gynecologic malignancies who are unsuitable for brachytherapy for technical or medical reasons.MethodsDosimetric and toxicity information was analyzed for 12 patients with cervical (8), endometrial (2) or vaginal (2) cancer previously treated with external beam pelvic radiotherapy and a CRT boost. Optimized IMRT boost treatment plans were then developed for each of the 12 patients and compared to CRT and 4FB plans. The plans were compared in terms of dose conformality and critical normal tissue avoidance.ResultsThe median planning target volume (PTV) was 151 cm3 (range 58–512 cm3). The median overlap of the contoured rectum with the PTV was 15 (1–56) %, and 11 (4–35) % for the bladder. Two of the 12 patients, both with large PTVs and large overlap of the contoured rectum and PTV, developed grade 3 rectal bleeding. The dose conformity was significantly improved with IMRT over CRT and 4FB (p ≤ 0.001 for both). IMRT also yielded an overall improvement in the rectal and bladder dose-volume distributions relative to CRT and 4FB. The volume of rectum that received the highest doses (>66% of the prescription) was reduced by 22% (p < 0.001) with IMRT relative to 4FB, and the bladder volume was reduced by 19% (p < 0.001). This was at the expense of an increase in the volume of these organs receiving doses in the lowest range (<33%).ConclusionThese results indicate that IMRT can improve target coverage and reduce dose to critical structures in gynecologic patients receiving an external beam radiotherapy boost. This dosimetric advantage will be integrated with other patient and treatment-specific factors, particularly internal tumor movement during fractionated radiotherapy, in the context of a future image-guided radiation therapy study.

Dose to the intracranial arteries in stereotactic and intensity-modulated radiotherapy for skull base tumors

To examine retrospectively the maximum dose to the large skull base/intracranial arteries in fractionated stereotactic radiotherapy (FSRT) and intensity-modulated radiotherapy (IMRT), because of the potential risk of perfusion disturbances. Overall, 56 patients with tumors adjacent to at least one major artery were analyzed. Our strategy was to perform FSRT with these criteria: 1.8 Gy per fraction, planning target volume (PTV) enclosed by the 95% isodose, maximum dose 107%. Dose limits were applied to established organs at risk, but not the vessels. If FSRT planning failed to meet any of these criteria, IMRT was planned with the same objectives. In 31 patients (median PTV, 23 cm3), the FSRT plan fulfilled all criteria. No artery received a dose > or =105%. Twenty-five patients (median PTV, 39 cm3) needed IMRT planning. In 11 of 25 patients (median PTV, 85 cm3), no plan satisfying all our criteria could be calculated. Only in this group, moderately increased maximum vessel doses were observed (106-110%, n = 7, median PTV, 121 cm3). The median PTV dose gradient was 29% (significantly different from the 14 patients with satisfactory IMRT plans). Three of the four patients in this group had paranasal sinus tumors. The doses to the major arteries should be calculated in IMRT planning for critical tumor locations if a dose gradient >13% within the PTV can not be avoided because the PTV is large or includes air cavities.

Precision radiotherapy for hemangiopericytomas of the central nervous system

Radiotherapy (RT) plays a major role in the management of hemangiopericytomas (HAP). The present analysis evaluates the role of precision RT in the management of HAP of the central nervous system (CNS) and represents one of the largest series of HAP treated with RT that can be found in the literature. Of 37 consecutive patients with histologically confirmed HAP who were treated at the institution between 1984 and 2004, the majority, 25 tumors, was localized within the skull base (n = 25) and 4 tumors were localized at the spine. In 25 patients, high-precision RT was delivered as fractionated stereotactic RT or intensity modulated RT. Median age at primary diagnosis was 40.5 years (range, 10-77 yrs). After primary diagnosis, surgical resection was performed in 23 patients. A median total dose of 54 Gy was delivered in a fractionation of 5 x 1.8-2 Gy per week. The median planning target volume was 58.2 mL (range, 10-412 mL). The median follow-up time was 34 months (range, 3-166 mos). Radiotherapy was well tolerated by all patients. Seventeen patients of this series remain alive. Overall survival rates at 5 and 10 years are 100% and 64%, respectively. Actuarial survival rates after RT were 85% and 69% at 3 and 5 years, respectively. Progression-free survival after RT 80% and 61% at 3 and 5 years, respectively. High-precision RT is an effective and safe treatment modality for patients with HAP of the CNS and the spine and achieves highly acceptable tumor control, while sparing normal tissue.

Precision radiotherapy in the treatment of haemangiopericytomas of the central nervous system

1545 Background: Haemangiopericytomas (HAP) are rare tumors, that arise from pericytes, the contractile cells surrounding capillaries, also referred to as the pericytes of Zimmermann. Intracranial HAP have been classified as “angioblastic” members of the meningioma family. They have a high tendency to recur locally and they are associated with a high risk to metastasize. Radiotherapy (RT) plays a major control in the management of HAP. The present analysis evaluates the role of high precision RT in the management HAP of the CNS. Methods: Thirty-seven consecutive patients with histologically diagnosed HAP were treated at our institution between 1984 and 2004. The majority of the tumors was localized within the skull (n=25), and 2 tumors were localized at that spine. Out of these 37 patients, we selected 25 patients with tumors of the CNS and the spine for analysis which were treated with high precision radiotherapy delivered as Fractionated Stereotactic RT (FSRT) or Intensity Modulated Radiotherapy (IMRT). Median age at primary diagnosis was 40.5 years (range 10–77 years). After primary diagnosis, surgical resection was performed in 23 patients. Median time between primary diagnosis and RT was 20 months (range 1–382 months). For treatment planning, patients were immobilized by an individual precision head mask or a whole body fixation system made of Scotch Cast. Target delineation and treatment planning were performed in a stereotactic setup. A median total dose of 56.4 Gy was delivered in a fractionation of 5 x 1.8–2 Gy per week, with a median Planning Target Volume (PTV) of 58.2 ml. Median follow-up time was 34 months (range 3–166 months). Results: Seventeen patients out of 25 of this series remain alive. Overall survival rates at 5 and 10 years were 100% and 64%, respectively. Actuarial survival rates after RT were 85% and 69% at 3 and 5 years, respectively. Progression-free survival rates after RT were 80% and 61% at 3 and 5 years, respectively. No severe late toxicities could be observed. Conclusions: High precision radiotherapy is an effective and safe treatment modality for patients with HAP of the CNS with highly acceptable tumor control while sparing normal tissue. No significant financial relationships to disclose.

Hypofractionated stereotactic re-irradiation: treatment option in recurrent malignant glioma.

BackgroundHypofractionated stereotactic radiotherapy (HFSRT) is one salvage treatment option in previously irradiated patients with recurrent malignant glioma. We analyzed the results of HFSRT and prognostic factors in a single-institution series.MethodsBetween 1997 and 2003, 19 patients with recurrent malignant glioma (14 glioblastoma on most recent histology, 5 anaplastic astrocytoma) were treated with HFSRT. The median interval from post-operative radiotherapy to HFSRT was 19 (range 3–116) months, the median daily single dose 5 (4–10) Gy, the median total dose 30 (20–30) Gy and the median planning target volume 15 (4–70) ml.ResultsThe median overall survival (OS) was 9.3 (1.9-77.6+) months from the time of HFSRT, 15.4 months for grade III and 7.9 months for grade IV tumors (p = 0.029, log-rank test). Two patients were alive at 34.6 and 77.6 months. OS was longer after a total dose of 30 Gy (11.1 months) than after total doses of <30 Gy (7.4 months; p = 0.051). Of five (26%) reoperations, none was performed for presumed or histologically predominant radiation necrosis. Median time to tumor progression after HFSRT on imaging was 4.9 months (1.3 to 37.3) months.ConclusionHFSRT with conservative total doses of no more than 30 Gy is safe and leads to similar OS times as more aggressive treatment schemes. In individual patients, HFSRT in combination with other salvage treatment modalities, was associated with long-term survival.

Multifractionated image-guided and stereotactic intensity-modulated radiotherapy of paraspinal tumors: A preliminary report

The use of image-guided and stereotactic intensity-modulated radiotherapy (IMRT) techniques have made the delivery of high-dose radiation to lesions within close proximity to the spinal cord feasible. This report presents clinical and physical data regarding the use of IMRT coupled with noninvasive body frames (stereotactic and image-guided) for multifractionated radiotherapy. The Memorial Sloan-Kettering Cancer Center (Memorial) stereotactic body frame (MSBF) and Memorial body cradle (MBC) have been developed as noninvasive immobilizing devices for paraspinal IMRT using stereotactic (MSBF) and image-guided (MBC) techniques. Patients were either previously irradiated or prescribed doses beyond spinal cord tolerance (54 Gy in standard fractionation) and had unresectable gross disease involving the spinal canal. The planning target volume (PTV) was the gross tumor volume with a 1 cm margin. The PTV was not allowed to include the spinal cord contour. All treatment planning was performed using software developed within the institution. Isocenter verification was performed with an in-room computed tomography scan (MSBF) or electronic portal imaging devices, or both. Patients were followed up with serial magnetic resonance imaging every 3-4 months, and no patients were lost to follow-up. Kaplan-Meier statistics were used for analysis of clinical data. Both the MSBF and MBC were able to provide setup accuracy within 2 mm. With a median follow-up of 11 months, 35 patients (14 primary and 21 secondary malignancies) underwent treatment. The median dose previously received was 3000 cGy in 10 fractions. The median dose prescribed for these patients was 2000 cGy/5 fractions (2000-3000 cGy), which provided a median PTV V100 of 88%. In previously unirradiated patients, the median prescribed dose was 7000 cGy (5940-7000 cGy) with a median PTV V100 of 90%. The median Dmax to the cord was 34% and 68% for previously irradiated and never irradiated patients, respectively. More than 90% of patients experienced palliation from pain, weakness, or paresthesia; 75% and 81% of secondary and primary lesions, respectively, exhibited local control at the time of last follow-up. No cases of radiation-induced myelopathy or radiculopathy have thus far been encountered. Precision stereotactic and image-guided paraspinal IMRT allows the delivery of high doses of radiation in multiple fractions to tumors within close proximity to the spinal cord while respecting cord tolerance. Although preliminary, the clinical results are encouraging.

Influence of Calculation Algorithm on Dose Distribution in Irradiation of Non-Small Cell Lung Cancer (NSCLC)

The influence of two different calculation algorithms (“pencil beam” [PB] versus “collapsed cone” [CC]) on dose distribution, as well as the dose-volume histograms (DVHs) of the planning target volume (PTV) and the organs at risk was analyzed for irradiation of lung cancer. Between 10/2001 and 02/2002 three-dimensional treatment planning was done in ten patients with lung cancer (Helax, TMS®, V.6.01). The PTV, the ipsilateral lung (IL) and the contralateral lung (CL) were defined in each axial CT slice (slice thickness 1 cm). Dose distributions for three-dimensional multiple-field technique were calculated using a PB and a CC algorithm, respectively. Normalization was in accordance with ICRU 50. The DVHs were analyzed relating the minimum, maximum, median and mean dose to the volumes of interest (VOI). Median PTV amounted to 774 cm3. Minimum dose within the PTV was 67.4% for CC and 75.6% for PB algorithm (p = 0.04). Using the CC algorithm, only 76.5% of the PTV was included by the 95% isodose, whereas 90.1% was included when the PB algorithm (p = 0.01) was used. Median volume of IL amounted to 1 953 cm3. Mean dose to IL was 43.0% for CC and 44.0% for PB algorithm (p = 0.02). Median volume of IL within the 80% isodose was 19.6% for CC and 24.1% for PB algorithm (p < 0.01). Median volume of CL amounted to 1 847 cm3. Mean dose to CL was 17.4% for CC and 18.1% for PB algorithm (p < 0.01). Volume of CL within the 80% isodose was 3.3% for CC and 4.1% for PB algorithm (p = 0.03). The CC and PB calculation algorithms result in different dose distributions in case of lung tumors. Particularly the minimum dose to the PTV, which may be relevant for tumor control, is significantly lower for CC. Since it is generally accepted that the CC algorithm describes secondary particle transport more exactly than PB models, the use of the latter should be critically evaluated in the treatment planning of lung cancer.

Clinical implementation of intensity-modulated arc therapy (IMAT) for rectal cancer

Purpose In rectal cancer, combined radiotherapy and chemotherapy, either pre- or postoperatively, is an accepted treatment. Late small bowel (SB) toxicity is a feared side effect and limits radiation-dose escalation in a volume-dependent way. A planning strategy for intensity- modulated arc therapy (IMAT) was developed, and IMAT was clinically implemented with the aim to reduce the volume of SB irradiated at high doses and thus reduce SB toxicity. We report on the treatment plans of the first 7 patients, on the comparison of IMAT with conventional 3D planning (3D), and on the feasibility of IMAT delivery. Methods and materials Seven patients, who were referred to our department for preoperative ( n = 4) or postoperative ( n = 3) radiotherapy for rectal cancer, gave written consent for IMAT treatment. All patients had a planning CT in prone position. The delineation of the clinical target volume was done after fusion of CT and MRI, with the help of a radiologist. For the IMAT plan, arcs were generated using an anatomy-based segmentation tool. The optimization of the arcs was done by weight optimization (WO) and leaf position optimization (LPO), both of which were adapted for IMAT purposes. The 3D plans used one posterior and two lateral wedged beams, of which the outlines were shaped to the beam's-eye view projection of the planning target volume (PTV). Beam WO was done by constrained matrix inversion. For dose–volume histogram analysis, all plans were normalized to 45 Gy as median PTV dose. Polymer gel dosimetry (PGD) on a humanoid phantom was used for the validation of the total chain (planning to delivery). IMAT treatments were delivered by an Elekta Sl i Plus linear accelerator using prototype software with the same interlock class as in clinical mode. Results The IMAT plan resulted in 3 to 6 arcs, with a mean delivery time of 6.3 min and a mean of 456 monitor units (MU) for a 180 cGy fraction. The minimal dose in the PTV was not significantly different between 3D and IMAT plans. Inhomogeneity was highest for the IMAT plans (14.1%) and lowest for the 3D plans (9.9%). Mean dose to the SB was significantly lower for the IMAT plans (12.4 Gy) than for the 3D plans (17.0 Gy). The volume of SB receiving less than any dose level was lower for the IMAT plans than for 3D plans. Integral dose was lower in the IMAT plans than for the 3D plans (respectively 244 J and 262 J to deliver 45 Gy). Differences between the PGD measured dose and the calculated dose were as small for IMAT as for 3D treatments. Conclusion IMAT plans are deliverable within a 5–10-minute time slot, and result in a lower dose to the SB than 3D plans, without creating significant underdosages in the PTV. PGD showed that IMAT delivery is as accurate as 3D delivery.

Accelerated partial-breast irradiation using 3D Conformal External Beam Radiotherapy for patients with early-stage breast cancer: Preliminary results of an ongoing Phase I trial

To investigate the feasibility and side effects of using 3D Conformal External Beam Radiotherapy (3D-CRT) to give accelerated partial breast irradiation (APBI)following tumor excision in patients with early-stage breast cancer. From August 2003 to February 2004, 24 patients have been enrolled on a Phase I, IRB approved study (with an accrual goal of 100 patients). Data analysis was performed on the first 22 patients who have completed therapy. Eligibility criteria include: infiltrating ductal carcinoma (or special subtype) of 2 cm or less; negative sentinel node or axillary dissection; margin width 2 mm or greater; no lymphovascular invasion; and no extensive intraductal component. The gross target volume (GTV) consisted of the lumpectomy cavity. The planning target volume (PTV) consisted of the GTV plus a 15–20 mm margin which included 5mm for breathing motion and treatment setup uncertainties. This figure was estimated based on pilot study measurements, but is being measured formally in a companion study. The prescribed dose (PD) was 32 Gy in 8 fractions b.i.d. separated by 6 hours; dose inhomogeneity across the PTV was to be less than 10%. The treatment was delivered in 4 consecutive days for 21 patients and within a week in one patient. Patients were treated in the supine position with 3 beams (17 patients) or 4 beams (5 patients) using a Varian 2100C machine. Mixed photons-electron fields were used in 21 patients and photons only in 1 patient. Cosmesis and skin reaction were assessed by the patient and the treating physician at the start of treatment, after 3–4 weeks and after 6–8 weeks, and then every 6 months. Follow-up ranged from 1–6 months All patients consented to the study. The average tumor size was 0.86 cm (SD, 0.5 cm), and the median was 0.9 cm. Fourteen patients had left and 8 right-sided breast cancers. Two patients received adjuvant chemotherapy and 10 started hormonal therapy after APBI. The mean and median GTV was 42.9 cc and 34.0 cc, respectively (range, 6–196 cc). The mean and median PTV was 178.1 cc and 151 cc, respectively (range, 78–568 cc). The median percentage of the whole breast designated as PTV was 23% (range 11%-41%). The mean doses received by 20% (V20), 10% (V10) and 5% (V5) of the ipsilateral lung volume were 2.3 Gy, 4.5 Gy and 6.7 Gy, respectively. The mean V20, V10 and V5 doses of the heart in patients with left breast tumors were 1.5 Gy, 2.2 Gy and 3.2 Gy, respectively. The mean and median doses received by 50% of the non-target breast tissue (whole breast minus PTV) were 6.7 Gy and 4.0 Gy, respectively. No skin changes greater than Grade 1 erythema were noted during or at the end of treatment. At the initial follow-up visit, 9/22 patients (41%) experienced mild erythema, 2/22 (9%) had moderate erythema, and none had moist desquamation. Cosmetic results were rated by the patient and treating physician as good or excellent in all cases. This initial report of an ongoing phase I trial using 3D-CRT APBI shows that such treatment is technically feasible with minimal acute toxicity. Doses to the lung and heart are significantly reduced compared with whole breast irradiation. Compared with interstitial approaches to APBI, 3 DCRT delivers more dose to non-target breast tissue, but the long-term biological consequences of this additional exposure is unknown. Completion of the trial and additional follow-up are needed to assess the long-term effects of this approach on normal-tissue sequelae and treatment efficacy

Escalated median dose for pituitary macroadenomas using intensity-modulated radiation therapy

Three-dimensional conformal radiotherapy (3D CRT) has become an established treatment for pituitary macroadenomas. This study is an investigation into the possible dosimetric advantages of intensity-modulated radiotherapy for such critically located tumors. Three consecutive patients with pituitary macroadenoma previously treated with 3D CRT were replanned with inverse-planned IMRT using Helax-TMS (V.6.0, Helax AB, Uppsala, Sweden. Fusion of computed tomography (CT) with postoperative magnetic resonance imaging (MRI) was performed within the planning system to define the gross tumor volume (GTV), planning target volume (PTV), and normal structures including the optic chiasm. Dose-volume histograms (DVHs) for the 3D CRT plans were then compared with those of the corresponding prospective IMRT plans. Both techniques maintained critical structure doses below tolerance levels while maintaining a minimum dose of 45 Gy to 100% of the PTV. While IMRT plans deliver consistently more heterogeneous dose distributions to the PTV, the median PTV dose is elevated in the IMRT plans compared with the 3D CRT plans. For critically located tumors like these pituitary macroadenomas, IMRT allows escalation of the median dose to the tumor without an accompanying loss in critical structure sparing or creating unacceptable cold spots within the PTV.

Fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT) for small acoustic neuromas

Eight patients with acoustic neuromas were treated using a novel method developed at our institution for delivering fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT). We present treatment parameters, dosimetry analysis, and preliminary clinical outcome. The method incorporates high-precision invasive fixation, obliquely-oriented tomotherapy arcs, and reduced dimension pencil beams. The delivered dose distributions for the 8 patients treated from April 1999 to May 2001 were assessed for dose conformality, homogeneity, and doses to organs at risk. Total doses prescribed were 54 Gy in daily doses of 1.8 Gy. Results show that the median planning target volume (gross tumor volume plus a safety margin of 2 mm) was 2.48 cm 3 (1.64 to 16.86 cm 3) and that the median conformality and homogeneity indices were 1.69 (1.56 to 2.16) and 1.12 (1.09 to 1.19), respectively. The respective average mean and maximum doses to the brain stem were 12.67 Gy and 53.86 Gy. The treatment parameters for the novel FS-IMRT method developed here document excellent dose conformality and normal tissue sparing. Preliminary short-term follow-up (mean 17, median 18.5 months) revealed a 100% local control and hearing preservation rate. No new persistent impairment of facial and trigeminal nerve was observed. Our current follow-up experience indicates a reasonable potential for achieving outcomes comparable to established stereotactic radiotherapy techniques.

Leaf position optimization for step-and-shoot IMRT

Purpose: To describe the theoretical basis, the algorithm, and implementation of a tool that optimizes segment shapes and weights for step-and-shoot intensity-modulated radiation therapy delivered by multileaf collimators. Methods and Materials: The tool, called SOWAT (Segment Outline and Weight Adapting Tool) is applied to a set of segments, segment weights, and corresponding dose distribution, computed by an external dose computation engine. SOWAT evaluates the effects of changing the position of each collimating leaf of each segment on an objective function, as follows. Changing a leaf position causes a change in the segment-specific dose matrix, which is calculated by a fast dose computation algorithm. A weighted sum of all segment-specific dose matrices provides the dose distribution and allows computation of the value of the objective function. Only leaf position changes that comply with the multileaf collimator constraints are evaluated. Leaf position changes that tend to decrease the value of the objective function are retained. After several possible positions have been evaluated for all collimating leaves of all segments, an external dose engine recomputes the dose distribution, based on the adapted leaf positions and weights. The plan is evaluated. If the plan is accepted, a segment sequencer is used to make the prescription files for the treatment machine. Otherwise, the user can restart SOWAT using the new set of segments, segment weights, and corresponding dose distribution. The implementation was illustrated using two example cases. The first example is a T1N0M0 supraglottic cancer case that was distributed as a multicenter planning exercise by investigators from Rotterdam, The Netherlands. The exercise involved a two-phase plan. Phase 1 involved the delivery of 46 Gy to a concave-shaped planning target volume (PTV) consisting of the primary tumor volume and the elective lymph nodal regions II–IV on both sides of the neck. Phase 2 involved a boost of 24 Gy to the primary tumor region only. SOWAT was applied to the Phase 1 plan. Parotid sparing was a planning goal. The second implementation example is an ethmoid sinus cancer case, planned with the intent of bilateral visus sparing. The median PTV prescription dose was 70 Gy with a maximum dose constraint to the optic pathway structures of 60 Gy. Results: The initial set of segments, segment weights, and corresponding dose distribution were obtained, respectively, by an anatomy-based segmentation tool, a segment weight optimization tool, and a differential scatter-air ratio dose computation algorithm as external dose engine. For the supraglottic case, this resulted in a plan that proved to be comparable to the plans obtained at the other institutes by forward or inverse planning techniques. After using SOWAT, the minimum PTV dose and PTV dose homogeneity increased; the maximum dose to the spinal cord decreased from 38 Gy to 32 Gy. The left parotid mean dose decreased from 22 Gy to 19 Gy and the right parotid mean dose from 20 to 18 Gy. For the ethmoid sinus case, the target homogeneity increased by leaf position optimization, together with a better sparing of the optical tracts. Conclusions: By using SOWAT, the plans improved with respect to all plan evaluation end points. Compliance with the multileaf collimator constraints is guaranteed. The treatment delivery time remains almost unchanged, because no additional segments are created.

Comparison of intensity-modulated tomotherapy with stereotactically guided conformal radiotherapy for brain tumors

Purpose: Intensity-modulated radiotherapy (IMRT) offers the potential to more closely conform dose distributions to the target, and spare organs at risk (OAR). Its clinical value is still being defined. The present study aims to compare IMRT with stereotactically guided conformal radiotherapy (SCRT) for patients with medium size convex-shaped brain tumors.Methods and Materials: Five patients planned with SCRT were replanned with the IMRT-tomotherapy method using the Peacock system (Nomos Corporation). The planning target volume (PTV) and relevant OAR were assessed, and compared relative to SCRT plans using dose statistics, dose–volume histograms (DVH), and the Radiation Therapy Oncology Group (RTOG) stereotactic radiosurgery criteria.Results: The median and mean PTV were 78 cm3 and 85 cm3 respectively (range 62–119 cm3). The differences in PTV doses for the whole group (Peacock–SCRT ±1 SD) were 2% ± 1.8 (minimum PTV), and 0.1% ± 1.9 (maximum PTV). The PTV homogeneity achieved by Peacock was 12.1% ± 1.7 compared to 13.9% ± 1.3 with SCRT. Using RTOG guidelines, Peacock plans provided acceptable PTV coverage for all 5/5 plans compared to minor coverage deviations in 4/5 SCRT plans; acceptable homogeneity index for both plans (Peacock = 1.1 vs. SCRT = 1.2); and comparable conformity index (1.4 each). As a consequence of the transaxial method of arc delivery, the optic nerves received mean and maximum doses that were 11.1 to 11.6%, and 10.3 to 15.2% higher respectively with Peacock plan. The maximum optic lens, and brainstem dose were 3.1 to 4.8% higher, and 0.6% lower respectively with Peacock plan. However, all doses remained below the tolerance threshold (5 Gy for lens, and 50 Gy for optic nerves) and were clinically acceptable.Conclusions: The Peacock method provided improved PTV coverage, albeit small, in this group of convex tumors. Although the OAR doses were higher using the Peacock plans, all doses remained within the clinically defined threshold and were clinically acceptable. Further improvements may be expected using other methods of IMRT planning that do not limit the treatment delivery to transaxial arcs. Each IMRT system needs to be individually assessed as the paradigm utilized may provide different outcomes.

Linear accelerator radiosurgery for recurrent malignant tumors of the skull base.

The efficacy of linear accelerator-based radiosurgery for patients who have preirradiated recurrent nasopharyngeal carcinomas and unresectable recurrent sarcomas invading the base of skull was assessed. Thirteen patients were treated: 8 patients had carcinomas arising from the nasopharynx (lymphoepithelioma, 4; squamous cell carcinoma, 2; adenoid-cystic, 2); 5 patients had sarcomas (rhabdomyosarcoma, 1; chordoma, 1; chondrosarcoma, 1; hemangiopericytoma, 2). All patients had had repeated tumor resections or irradiation, hindering any further conventional fractionated radiotherapy or surgery. Convergent-beam irradiation was performed with a modified linear accelerator (8-MeV photons). Because of irregular tumor configuration, multiple (up to seven) isocenters had to be used in 10 of 13 patients to match the target volume with the reference isodose (60%-80%). Each isocenter was irradiated with 6 to 10 arcs. The median planning target volume was 33 mL (4-128 mL) and the median dose was 15 Gy (9-24 Gy). Median survival time was 9 months in 8 patients who had recurrent nasopharyngeal carcinomas. Three patients who had complete or partial tumor remission survived 1.5 to 3.5 years. All of the sarcoma patients responded to radiosurgery. After a follow-up of 28 to 67 months, 4 of 5 patients are alive. This investigation demonstrates that radiosurgery is an effective tool in palliative treatment for patients who have recurrent, extensively pretreated nasopharyngeal cancer. Patients who have recurrent sarcomas of the base of skull may be treated for long-term palliation or even for cure.

O-21-306 - Orbital cavernous hemangiomas and lymphangiomas

To describe the results of conformal radiotherapy in advanced juvenile nasopharyngeal angiofibroma in a tertiary care institution.Retrospective chart review was conducted for 8 patients treated with conformal radiotherapy between 2006 and 2009. The median follow-up was 17 months. All patients had Stage IIIB disease with intracranial extension. Radiotherapy was considered as treatment because patients were deemed inoperable owing to extensive intracranial/intraorbital extension or proximity to optic nerve. All but 1 patient were treated with intensity-modulated radiotherapy using seven coplanar fields. Median (range) dose prescribed was 39.6 (30–46) Gy. Actuarial analysis of local control and descriptive analysis of toxicity profile was conducted.Despite the large and complex target volume (median planning target volume, 292 cm3), intensity-modulated radiotherapy achieved conformal dose distributions (median van't Reit index, 0.66). Significant sparing of the surrounding organs at risk was obtained. No significant Grade 3/4 toxicities were experienced during or after treatment. Actual local control at 2 years was 87.5%. One patient died 1 month after radiotherapy secondary to massive epistaxis. The remaining 7 patients had progressive resolution of disease and were symptom-free at last follow-up. Persistent rhinitis was the only significant toxicity, seen in 1 patient.Conformal radiotherapy results in good local control with minimal acute and late side effects in juvenile nasopharyngeal angiofibromas, even in the presence of advanced disease.