A treatment planning comparison between a novel rotating gamma system and robotic linear accelerator based intracranial stereotactic radiosurgery/radiotherapy.

To compare the dosimetric parameters of a novel rotating gamma ray system (RGS) with well-established CyberKnife system (CK) for treating malignant brain lesions. RGS has a treatment head of 16 cobalt-60 sources focused to the isocenter, which can rotate 360° on the ring gantry and swing 35° in the superior direction. We compared several dosimetric parameters in 10 patients undergoing brain stereotactic radiosurgery including plan normalization, number of beams and nodes for CK and shots for RGS, collimators used, estimated treatment time, D 2 cm and conformity index (CI) among two modalities. The median plan normalization for RGS was 56.7% versus 68.5% (p = 0.002) for CK plans. The median number of shots from RGS was 7.5 whereas the median number of beams and nodes for CK was 79.5 and 46. The median collimator's diameter used was 3.5 mm for RGS as compared to 5 mm for CK (p = 0.26). Mean D 2 cm was 5.57 Gy for CyberKnife whereas it was 3.11 Gy for RGS (p = 0.99). For RGS plans, the median CI was 1.4 compared to 1.3 for the CK treatment plans (p = 0.98). The average minimum and maximum doses to optic chiasm were 21 and 93 cGy for RGS as compared to 32 and 209 cGy for CK whereas these were 0.5 and 364 cGy by RGS and 18 and 399 cGy by CK to brainstem. The mean V12 Gy for brain predicting for radionecrosis with RGS was 3.75 cm3 as compared to 4.09 cm3 with the CK (p = 0.41). The dosimetric parameters of a novel RGS with a ring type gantry are comparable with CyberKnife, allowing its use for intracranial lesions and is worth exploring in a clinical setting.

Weekly paclitaxel with concurrent radiotherapy followed by adjuvant chemotherapy in locally advanced nasopharyngeal carcinoma.

PURPOSE: To evaluate the efficacy and toxicity of weekly paclitaxel with concurrent radiotherapy followed by adjuvant chemotherapy (AC) in patients with locally advanced nasopharyngeal carcinoma (NPC). METHODS AND MATERIALS: Between 2004 and 2007, 54 patients with locally advanced NPC were included in this protocol. PATIENT CHARACTERISTICS: median age 48; 69% male; 52% World Health Organization (WHO) III; 50% stage III, 50% stage IV. The patients underwent a course of definitive conventional radiotherapy (70 Gy in 7 weeks with 2 Gy/fraction), with concurrent weekly paclitaxel 35 mg/m(2) from the first to the sixth week of radiation. AC was started 4 weeks after the end of the radiotherapy (RT), paclitaxel 135 mg/m(2) on day 1 and cisplatin 30 mg/m(2) on days 1-3 were administered every 4 weeks for two cycles. RESULTS: Median follow-up was 32 months. Eighty-five percentage of complete response and 15% partial response were achieved at the time of one month after AC. The 3-year actuarial rate of local regional control was 86%; distant metastases-free survival, progression-free survival and overall survival at 3 years were 81%, 69% and 76%, respectively. Forty-nine (91%) patients completed six courses of concurrent chemotherapy with weekly paclitaxel, and 4 (7%) patients delayed at the second cycle of AC. No patient developed severe acute toxicities. CONCLUSIONS: Weekly paclitaxel with concurrent RT followed by AC is a potentially effective and toxicity tolerable method for locally advanced NPC. Further studies are needed to identify the optimal dose of weekly paclitaxel in this strategy.

Breast intensity-modulated radiation therapy reduces time spent with acute dermatitis for women of all breast sizes during radiation.

PURPOSE: To study the time spent with radiation-induced dermatitis during a course of radiation therapy for breast cancer in women treated with conventional or intensity-modulated radiation therapy (IMRT). METHODS AND MATERIALS: The study population consisted of 804 consecutive women with early-stage breast cancer treated with breast-conserving surgery and radiation from 2001 to 2006. All patients were treated with whole-breast radiation followed by a boost to the tumor bed. Whole-breast radiation consisted of conventional wedged photon tangents (n = 405) earlier in the study period and mostly of photon IMRT (n = 399) in later years. All patients had acute dermatitis graded each week of treatment. RESULTS: The breakdown of the cases of maximum acute dermatitis by grade was as follows: 3%, Grade 0; 34%, Grade 1; 61%, Grade 2; and 2%, Grade 3. The breakdown of cases of maximum toxicity by technique was as follows: 48%, Grade 0/1, and 52%, Grade 2/3, for IMRT; and 25%, Grade 0/1, and 75%, Grade 2/3, for conventional radiation therapy (p < 0.0001). The IMRT patients spent 82% of weeks during treatment with Grade 0/1 dermatitis and 18% with Grade 2/3 dermatitis, compared with 29% and 71% of patients, respectively, treated with conventional radiation (p < 0.0001). Furthermore, the time spent with Grade 2/3 toxicity was decreased in IMRT patients with small (p = 0.0015), medium (p < 0.0001), and large (p < 0.0001) breasts. CONCLUSIONS: Breast IMRT is associated with a significant decrease both in the time spent during treatment with Grade 2/3 dermatitis and in the maximum severity of dermatitis compared with that associated with conventional radiation, regardless of breast size.

Dosimetric comparison of stereotactic body radiotherapy using 4D CT and multiphase CT images for treatment planning of lung cancer: evaluation of the impact on daily dose coverage.

PURPOSE: To investigate the dosimetric impact of using 4D CT and multiphase (helical) CT images for treatment planning target definition and the daily target coverage in hypofractionated stereotactic body radiotherapy (SBRT) of lung cancer. MATERIALS AND METHODS: For 10 consecutive patients treated with SBRT, a set of 4D CT images and three sets of multiphase helical CT scans, taken during free-breathing, end-inspiration and end-expiration breath-hold, were obtained. Three separate planning target volumes (PTVs) were created from these image sets. A PTV(4D) was created from the maximum intensity projection (MIP) reconstructed 4D images by adding a 3mm margin to the internal target volume (ITV). A PTV(3CT) was created by generating ITV from gross target volumes (GTVs) contoured from the three multiphase images. Finally, a third conventional PTV (denoted PTV(conv)) was created by adding 5mm in the axial direction and 10mm in the longitudinal direction to the GTV (in this work, GTV=CTV=clinical target volume) generated from free-breathing helical CT scans. Treatment planning was performed based on PTV(4D) (denoted as Plan-1), and the plan was adopted for PTV(3CT) and PTV(conv) to form Plan-2 and Plan-3, respectively, by superimposing "Plan-1" onto the helical free-breathing CT data set using modified beam apertures that conformed to either PTV(3CT) or PTV(conv). We first studied the impact of PTV design on treatment planning by evaluating the dosimetry of the three PTVs under the three plans, respectively. Then we examined the effect of the PTV designs on the daily target coverage by utilizing pre-treatment localization CT (CT-on-rails) images for daily GTV contouring and dose recalculation. The changes in the dose parameters of D(95) and D(99) (the dose received by 95% and 99% of the target volume, respectively), and the V(p) (the volume receiving the prescription dose) of the daily GTVs were compared under the three plans before and after setup error correction. RESULTS: For all 10 patients, we found that the PTV(4D) consistently resulted in the smallest volumes compared with the other PTV's (p=0.005). In general, the plans generated based PTV(3CT) could provide reasonably good coverage for PTV(4D), while the reverse can only achieve 90% of the planned values for PTV(3CT). The coverage of both PTV(4D) and PTV(3CT) in Plan-3 generally reserves the original planned values in terms of D(95), D(99), and V(p,) with the average ratios of 0.996, 0.977, and 0.977, respectively, for PTV(3CT), and 1.025, 1.025, and 1.0, respectively, for PTV(4D). However, it increased the dose significantly to normal lung tissue. Additionally, the plans generated using the PTV(4D) presented an equivalent daily target coverage compared to the plans generated using the PTV(3CT) (p=0.953) and PTV(conv) (p=0.773) after setup error correction. Consequently, this minimized the dose to the surrounding normal lung. CONCLUSION: Compared to the conventional approach using helical images for target definition, 4D CT and multiphase 3D CT have the advantage to provide patient-specific tumor motion information, based on which such designed PTVs could ensure daily target coverage. 4D CT-based treatment planning further reduces the amount of normal lung being irradiated while still providing a good target coverage when image guidance is used.

Monte Carlo determination of radiation-induced cancer risks for prostate patients undergoing intensity- modulated radiation therapy.

The application of intensity-modulated radiation therapy (IMRT) has enabled the delivery of high doses to the target volume while sparing the surrounding normal tissues. The drawbacks of intensity modulation, as implemented using a computer controlled multileaf collimator (MLC), are the larger number of monitor units (MUs) and longer beam-on time as compared with conventional radiotherapy. Additionally, IMRT uses more beam directions--typically 5-- 9 for prostate treatment--to achieve highly conformal dose and normal-tissue sparing. In the present work, we study radiation-induced cancer risks attributable to IMRT delivery using MLC for prostate patients. Whole-body computed tomography scans were used in our study to calculate (according to report no. 116 from the National Council on Radiation Protection and Measurements) the effective dose equivalent received by individual organs. We used EGS4 and MCSIM to compute the dose for IMRT and three-dimensional conformal radiotherapy. The effects of collimator rotation, distance from the treatment field, and scatter and leakage contribution to the whole-body dose were investigated. We calculated the whole-body dose equivalent to estimate the increase in the risk of secondary malignancies. Our results showed an overall doubling in the risk of secondary malignancies from the application of IMRT as compared with conventional radiotherapy. This increase in the risk of secondary malignancies is not necessarily related to a relative increase in MUs. The whole-body dose equivalent was also affected by collimator rotation, field size, and the energy of the photon beam. Smaller field sizes of low energy photon beams (that is, 6 MV) with the MLC axis along the lateral axis of the patient resulted in the lowest whole-body dose. Our results can be used to evaluate the risk of secondary malignancies for prostate IMRT patients.

Benefit of three-dimensional image-guided stereotactic localization in the hypofractionated treatment of lung cancer.

PURPOSE: The aim of this study was to investigate the benefit of image-guided stereotactic localization in the hypofractionated treatment for medically inoperable non-small-cell lung cancer. METHODS AND MATERIALS: A stereotactic body localizer (SBL) system was used for patient immobilization, reliable image registration among multiphase computed tomography (CT) scanning, and image-guided stereotactic localization. Three sets of CT scans were taken (free breathing, and breath holding at the end-tidal inspiration and expiration, respectively) to contrast target motion. Target delineation was performed on all 3 sets of images and the combination of the targets forms an internal target volume (ITV). In this retrospective study of treatment dose verification, we performed image fusion between the simulation CT scan and each pretreatment CT scan to obtain the same target and critical structure information. The same treatment plans were reloaded onto each pretreatment CT scan with their respective stereotactic coordinate system. The changes in dose distributions were assessed by dose-volume histograms of the planning target volume (PTV) and the critical structures before and after isocenter corrections which were prompted by image-guided stereotactic localization. We compared D95, D99, and V95 for the PTV and internal target volume, and V20 and V30 for the ipsilateral lung. RESULTS: Our retrospective study for 10 patients with 40 dose reconstructions showed that the average D95, D99, and V95 of the PTVs are 92.1%, 88.1%, and 95.8% of the planned values before isocenter corrections. With the corrections, all of these values are improved to 100% of the planned values. CONCLUSIONS: Three-dimensional image guidance is crucial for stereotactic radiotherapy of lung tumors.

Dosimetric advantage and clinical implication of a micro-multileaf collimator in the treatment of prostate with intensity-modulated radiotherapy.

This paper investigates the dosimetric benefits of a micro-multileaf (4-mm leaf width) collimator (mMLC) for intensity-modulated radiation therapy (IMRT) treatment planning of the prostate cancer and its potential application for dose escalation and hypofractionation. We compared treatment plans for IMRT delivery using 2 different multileaf collimator (MLC) leaf widths (4 vs. 10 mm) for 10 patients with prostate cancer. Treatment planning was performed on the XknifeRT2 treatment planning system. All beams and optimization parameters were identical for the mMLC and MLC plans. All of the plans were normalized to ensure that 95% of the planning target volume (PTV) received 100% of the prescribed dose (74 Gy). The differences in dose distribution between the 2 groups of plans using the mMLC and the MLC were assessed by dose-volume histogram (DVH) analysis of the target and critical organs. Significant reductions in the volume of rectum receiving medium to higher doses were achieved using the mMLC. The average decrease in the volume of the rectum receiving 40, 50, and 60 Gy using the mMLC plans was 40.2%, 33.4%, and 17.7%, respectively, with p-values less than 0.0001 for V40 and V50 and 0.012 for V60. The mean dose reductions for D17 and D35 for the rectum were 20.0% (p < 0.0001) and 18.3% (p < 0.0002), respectively, when compared to those with the MLC plans. There were consistent reductions in all dose indices studied for the bladder. The target dose inhomogeneity was improved in the mMLC plans by an average of 32%. In the high-dose range, there was no significant difference in the dose deposited in the "hottest" 1 cc of the rectum between the 2 MLC plans for all cases (p > 0.78). Because of the reduction of rectal volume receiving medium to higher doses, dose to the prostate target can be escalated by about 20 Gy to over 74 Gy, while keeping the rectal dose (either denoted by D17 or D35) the same as those with the use of the MLC. The maximum achievable dose, derived when the rectum is allowed to reach the tolerance level, was found to be in the range of 113-172 Gy (using the tolerance value of D17). We conclude that the use of the mMLC for IMRT of the prostate may facilitate dose hypofractionation due to its dosimetric advantage in significantly improving the DVH parameters of the prostate and critical organs. When used for conventional fractionation scheme, mMLC for IMRT of the prostate may reduce the toxicity to the critical organs.