D. Deshpande

A treatment planning study comparing volumetric arc modulation with RapidArc and fixed field IMRT for cervix uteri radiotherapy

PURPOSE A treatment planning study was performed to evaluate the performance of the novel volumetric modulated single arc radiotherapy on cervix uteri cancer patients. Conventional fixed field IMRT was used as benchmark. METHODS AND MATERIALS CT datasets of eight patients were included in the study. Plans were optimised with the aim to assess organs at risk and healthy tissue sparing while enforcing highly conformal target coverage. Planning objectives for PTV were: maximum significant dose lower than 52.5 Gy and minimum significant dose higher than 47.5 Gy. For organs at risk, the median and maximum doses were constrained to be lower than 30 (rectum), 35 (bladder) and 25 Gy (small bowel) and 47.5 Gy; additional objectives were set on various volume thresholds. Plans were evaluated on parameters derived from dose volume histograms and on NTCP estimates. Peripheral doses at 5, 10 and 15 cm from the PTV surface were recorded to assess the low-level dose bath. The MU and delivery time were scored to measure expected treatment efficiency. RESULTS Both RapidArc and IMRT resulted in equivalent target coverage but RapidArc had an improved homogeneity (D(5%)-D(95%) = 3.5 +/- 0.6 Gy for RapidArc and 4.3 +/- 0.8 Gy for IMRT) and conformity index (CI(90%) = 1.30 +/- 0.06 for RapidArc and 1.41 +/- 0.15 for IMRT). On rectum the mean dose was reduced by about 6 Gy (10 Gy for the rectum fraction not included in the PTV). Similar trends were observed for the various dose levels with reductions ranging from approximately 3 to 14.4 Gy. For the bladder, RapidArc allowed a reduction of mean dose ranging from approximately 4 to 6Gy and a reduction from approximately 3 to 9 Gy w.r.t. IMRT. Similar trends but with smaller absolute differences were observed for the small bowel and left and right femur. NTCP calculations on bladder and rectum confirmed the DVH data with a potential relative reduction ranging from 30 to 70% from IMRT to RapidArc. The healthy tissue was significantly less irradiated in the medium to high dose regions (from 20 to 30 Gy) and the integral dose reduction with RapidArc was about 12% compared to IMRT. Concerning peripheral dose, the relative difference between IMRT and RapidArc was of 9 +/- 2%, 43 +/- 11% and 36 +/- 5% at 5, 10 and 15 cm from the PTV surface, respectively. The MU/Gy from RapidArc was 245 +/- 17 corresponding to an expected average beam on time of 73 +/- 10 s per fractions of 2 Gy. IMRT plans presented higher values with an average of MU/Gy = 479 +/- 63. CONCLUSION RapidArc was investigated for cervix uteri cancer showing significant improvements in organs at risk and healthy tissue sparing with uncompromised target coverage leading to better conformal avoidance of treatments w.r.t. conventional IMRT. This, in combination with the confirmed short delivery time, can lead to clinically significant advances in the management of this highly aggressive cancer type. Clinical protocols are now advised to evaluate prospectively the potential benefit observed at the planning level.

Volumetric modulated arc radiotherapy for carcinomas of the oro-pharynx, hypo-pharynx and larynx: A treatment planning comparison with fixed field IMRT

PURPOSE A planning study was performed to evaluate the performance of volumetric modulated arc radiotherapy on head and neck cancer patients. Conventional fixed field IMRT was used as a benchmark. METHODS AND MATERIALS CT datasets of 29 patients with squamous cell carcinoma of the oro-pharynx, hypo-pharynx and larynx were included. Plans for fixed beam IMRT, single (RA1) and double (RA2) modulated arcs with the RapidArc technique were optimised. Dose prescription was set to 66 Gy to the primary tumour (at 2.2 Gy/fraction), 60 Gy to intermediate-risk nodes and 54 Gy to low-risk nodal levels. The planning objectives for PTV were minimum dose >95%, and maximum dose <107%. Maximum dose to spinal cord was limited to 46 Gy, maximum to brain stem to 50 Gy. For parotids, mean dose <26 Gy (or median <30 Gy) was assumed as the objective. The MU and delivery time were scored to measure expected treatment efficiency. RESULTS Target coverage and homogeneity results improved with RA2 plans compared to both RA1 and IMRT. All the techniques fulfilled the objectives on maximum dose, while small deviations were observed on minimum dose for PTV. The conformity index (CI(95%)) was 1.7+/-0.2 for all the three techniques. RA2 allowed a reduction of D(2%) to spinal cord of approximately 3 Gy compared to IMRT (RA1 D(2%) increased it of approximately 1 Gy). On brain stem, D(2%) was reduced from 12 Gy (RA1 vs. IMRT) to 13.5 Gy (RA2 vs. IMRT). The mean dose to ipsi-lateral parotids was reduced from 40 Gy (IMRT) to 36.2 Gy (RA1) and 34.4 Gy (RA2). The mean dose to the contra-lateral gland ranged from 32.6 Gy (IMRT) to 30.9 Gy (RA1) and 28.2 Gy (RA2). CONCLUSION RapidArc was investigated for head and neck cancer. RA1 and RA2 showed some improvements in organs at risk and healthy tissue sparing, while only RA2 offered improved target coverage with respect to conventional IMRT.

Primary carcinoma of the vagina: Tata Memorial Hospital experience

PURPOSE Carcinoma of the vagina is a rare gynecological malignancy comprising approximately 2% of all the gynecological malignancies. We have analyzed the treatment outcome of the patients treated at the Tata Memorial Hospital from January 1984 to December 1993. METHODS AND MATERIALS In this 10-year period, 134 patients of primary vaginal cancers were registered at our hospital. Of these, 75 patients received complete treatment and are analyzed. RESULTS Disease-free survival (DFS) for the whole group is 50%, and overall survival (OAS) is 60%. Most locoregional recurrences and distant failures are noted in the 2 years following treatment. DFS at 5 years is as follows: Stage I (5 patients), Stage IIA (37 patients), Stage IIB (15 patients), Stage III (14 patients), and Stage IV (4 patients); are 40%, 55%, 60%, 50%, and 25%, respectively. The DFS for patients with complete response (42 patients) to external radiation at 5 years is 68%, with partial response (25 patients) is 35%, and with poor or no response (6 patients) is 18% (p = 0.0000). We observed that brachytherapy was an important part of the treatment, and patients who received brachytherapy (59 patients), either with a vaginal intracavitary applicator (30 patients) or interstitial implant (29 patients) had a DFS of 53% and 56%, respectively, while 15 patients who received external radiation alone had a DFS of 30%. Patients receiving brachytherapy within 4 weeks of external radiation had a DFS of 60% as compared to 30% when the interval was more than 4 weeks. CONCLUSION The factors indicating prognosis are: site and extent of involvement, presence of lymph nodes at presentation, technique of brachytherapy, and interval between external radiation and brachytherapy.

Radiation Therapy with Implanted Cardiac Pacemaker Devices: a Clinical and Dosimetric Analysis of Patients and Proposed Precautions

AIMS To report the radiation planning dosimetric aspects and clinical outcomes of patients with implanted cardiac pacemakers. MATERIALS AND METHODS Between 2005 and 2009, eight patients with in situ cardiac pacemakers of varied primary site were treated at our hospital. All patients underwent computed tomography-based treatment planning. The target volumes, organs at risk and pacemaker device were all contoured. A treatment plan optimally covering the target area and maximally sparing the pacemaker was generated. All patients were evaluated at baseline, during radiotherapy and after radiotherapy conclusion by a cardiologist as well as pacemaker company personnel. RESULTS The median age at presentation was 67 (range 53-77) years. There were three men with head and neck primaries, two men with lung primaries and three women with breast primaries. The prescribed dose ranged from 45 to 70 Gy in 25-35 fractions with a daily dose of 1.8-2.0 Gy. Four patients had the pacemaker implanted on the same side as the radiotherapy target. The dose ranges for the minimum, mean and maximum doses to the pacemaker were 0.06-2.0, 0.07-20.6 and 0.14-60.0 Gy, respectively. Radiation therapy was safely delivered in all patients without any untoward effects. At 5 months of median follow-up, all patients were well with no malfunction of the pacemaker. CONCLUSION A series of eight patients with in situ pacemakers treated with radiotherapy is reported. Radiotherapy can be safely delivered in patients with implanted cardiac pacemakers. However, it mandates a cautious approach in planning and treatment delivery to ensure the least possible dose to the pacemaker. Close liaison with the cardiologist and a pacemaker clinic before, during and after the course of treatment is essential to ensure patient safety.

Dosimetric evaluation of rectum and bladder using image-based CT planning and orthogonal radiographs with ICRU 38 recommendations in intracavitary brachytherapy

The purpose is to compare CT-based dosimetry with International Commission on Radiation Units and Measurements (ICRU 38) bladder and rectum reference points in patients of carcinoma of uterine cervix treated with intracavitary brachytherapy (ICA). Twenty-two consecutive patients were evaluated. Orthogonal radiographs and CT images were acquired and transferred to PLATO planning system. Bladder and rectal reference points were identified according to ICRU 38 recommendations. Dosimetry was carried out based on Manchester system. Patient treatment was done using 192Iridium high dose rate (HDR) remote after-loading machine based on the conventional radiograph-based dosimetry. ICRU rectal and bladder point doses from the radiograph plans were compared with D2, dose received by 2 cm3 of the organ receiving maximum dose from CT plan. V2, volume of organ receiving dose more than the ICRU reference point, was evaluated. The mean (±standard deviation) volume of rectum and bladder was 60 (±28) cm3 and 138 (±41) cm3 respectively. The mean reference volume in radiograph and CT plan was 105 (±7) cm3 and 107 (±7) cm3 respectively. It was found that 6 (±4) cm3 of rectum and 16 (±10) cm3 of bladder received dose more than the prescription dose. V2 of rectum and bladder was 7 (±1.7) cm3 and 20.8 (±6) cm3 respectively. Mean D2 of rectum and bladder was found to be 1.11 (±0.2) and 1.56 (±0.6) times the mean ICRU reference points respectively. This dosimteric study suggests that comparison of orthogonal X-ray-based and CT-based HDR ICA planning is feasible. ICRU rectal point dose correlates well with maximum rectal dose, while ICRU bladder point underestimates the maximum bladder dose.

Intraoperative high-dose-rate 192Ir radical implant in early breast cancer: A quality assurance and dosimetry study

PURPOSE To evaluate the variability in catheter length, geometry, and dosimetric parameters of radical intraoperative high-dose-rate breasts implant during 7-11 days. METHODS AND MATERIALS Simulator X-rays, CT scans, and dosimetric studies were repeated on alternate days in 14 consecutive patients treated with radical intraoperative two- or three-plane nylon catheter high-dose-rate implant (34 Gy in 10 fractions within 5 days). RESULTS Significant variation was found in catheter length, but no major change was noted in implant geometry, homogeneity, or inhomogeneity indexes. A variation in length of >5 mm in one or more catheters was seen in all patients and >10 mm in 11 patients at any time during the implant. Of the 171 catheters in 14 patients, 100 (58%) and 38 (22%) showed a variation of >5 mm or >10 mm, respectively. The variation of >10 mm was reduced from 32% of catheters in the first 5 patients to 17% in the subsequent 9 patients (p = 0.028). Rigid catheter fixation might reduce length variation but may cause skin necrosis if the expanding cavity indents the skin for a long period against the fixation device. A dose homogeneity index of 0.90 (range 0.85-0.92) and dose nonuniformity ratio of 0.20 (range 0.12-0.25) were satisfactory. CONCLUSION The catheter fixation and exit catheter length should be measured daily and if the implant is in situ for more than a few days, orthogonal X-rays and, if indicated, dosimetry should be repeated at least once.

Use of peripheral dose data from uniform dynamic multileaf collimation fields to estimate out-of-field organ dose in patients treated employing sliding window intensity-modulated radiotherapy

Peripheral doses (PD) from uniform dynamic multileaf collimation (DMLC) fields were measured for 6 MV x-rays on a Varian linear accelerator using a 0.6 cc ionization chamber inserted at 5 cm depth into a 35 x 35 x 105 cm3 plastic water phantom. PD measurements were also carried out under identical conditions for seven patients treated for head and neck and cervical cancer employing sliding window intensity-modulated radiotherapy (IMRT). The measured PD from these patient-specific intensity-modulated beams (IMBs) were compared with the corresponding data from uniform DMLC fields having similar jaws setting. The measured PD per monitor unit (PD/MU) decreases almost exponentially with out-of-field distance for all uniform DMLC and static fields. For the same strip field width of 1.2 cm, uniform DMLC fields with a larger size of 14 x 22 cm2 deliver an average of 3.51 (SD = 0.51) times higher PD/MU at all out-of-field distances compared to 6 x 6 cm2. Similar to uniform DMLC fields, PD/MU measured from different patient-specific IMBs was found to decrease almost exponentially with out-of-field distance and increase with increase in field dimension. PD per MU from uniform DMLC fields and patient-specific IMBs having similar jaws setting shows good agreement (+/-7%) except at the most proximal distance, where a variation of more than 10% (maximum 15%) was observed. Our study shows that PD data generated from uniform DMLC fields can be used as baseline data to estimate out-of-field critical organ or whole-body dose in patients treated employing sliding window IMRT if an appropriate correction factor for field dimension is applied. The whole-body dose information can be used to estimate the possible increase in risk of fatal secondary malignancy in patients treated employing sliding window IMRT.

Dosimetric comparison of inverse optimization with geometric optimization in combination with graphical optimization for HDR prostate implants

The purpose of this study is to compare geometric optimization (GO) with anatomy based inverse optimization (ABIO). Five patients of carcinoma prostate treated with HDR interstitial brachytherapy had been studied. Post implant CT scans of 5 mm slice thickness were obtained; target volume and other critical structures rectum, bladder and urethra were drawn by the clinician. Plans were obtained with geometric optimization and anatomy based inversed optimization. Anatomy based inverse planning implemented currently in PLATO BPS version 14.2, is based on geometric and dose point optimization and designed to account for the critical structures. Graphical optimization (GrO) is used to fine-tune the distribution ie to reduce the dose to critical structures and to improve the target coverage in both geometric optimization and anatomy based inverse optimization plans. DVH of target, rectum, bladder and urethra were evaluated and compared, dose homogeneity index and conformity index were also evaluated for all the plans. The mean target coverage was 93.9±7%, 90.3±4%, 82±13%, 91.6±3 for different optimization techniques GO, GO_gr, ABIO and ABIO_gr respectively. The target coverage in ABIO is not clinically acceptable. Maximum dose, dose to 2% of the volume of urethra D2%,U was 137±12%, 123.2±2%, 111.5±9, 122.7±4 for GO, GO_gr, ABIO and ABIO_gr respectively. The mean conformity index values were 0.71, 0.76, 0.65, 0.82 for GO, GO_gr, ABIO, ABIO_gr respectively. ABIO_gr has a good conformity over all other optimization techniques. However the difference is not very significant between GO and GO_gr. The mean values of DHI are 0.81, 0.77, 0.65 and 0.75 for GO, GO_gr, ABIO and ABIO_gr respectively. Geometric optimization is highly homogenous compared to all other optimization techniques. To conclude, target coverage in ABIO is not clinically acceptable. However ABIO followed by graphical optimization is much superior in sparing of critical structures and conformity compared to geometrical optimization. Target coverage is marginally better in GO compared to ABIO_gr. Homogeneity is superior in GO compared to ABIO_gr. However ABIO_gr plans were clinically acceptable with respect to homogeneity. Further, dose escalation to the target is possible with ABIO, without exceeding the tolerance dose to urethra. Clinical correlation of genitourinary toxicity has to be studied.

Performance evaluation of a dedicated computed tomography scanner used for virtual simulation using in-house fabricated CT phantoms

Comprehensive tests on single slice CT scanner was carried out using in-house fabricated phantoms/test tools following AAPM recommended methods to independently validate the auto-performance test (APT) results. Test results of all the electromechanical parameters were found within the specified limits. Radiation and sensitivity profile widths were within ± 0.05 cm of the set slice thickness. Effective energy corresponding to nominal kVp of 80, 110 and 130 were 49.99, 55.08 and 59.48 keV, respectively. Percentage noise obtained by APT was 1.32% while the independently measured value was 0.38%. Observed contrast resolutions by independent method at 0.78% and 12% contrast difference were 4 mm and 1.25 mm (= 4 lp/cm) respectively. However, high contrast resolution (limiting spatial resolution) by APT at 50, 10 and 2% MTF levels were 9, 12.5 and 14.1 lp/cm respectively. Difference in calculated and measured CT numbers of water, air, teflon, acrylic, polystyrene and polypropylene were in the range of 0 to 24 HU, while this difference was 46 and 94 HU in case of nylon and bakelite respectively. The contrast scale determined using CT linearity phantom was 1.998×10−4 cm−1/CT number. CT dose index (CTDI) and weighted CTDI (CTDIw) measured at different kVp for standard head and body phantoms were smaller than manufacturer-specified and system-calculated values and were found within the manufacturer-specified limit of ± 20%. Measured CTDIs on surface (head: 3.6 cGy and body: 2.6 cGy) and at the center (3.3 cGy, head; and 1.2 cGy, body) were comparable to reported values of other similar CT scanners and were also within the industry-quoted CTDI range. Comprehensive QA and independent validation of APT results are necessary to obtain baseline data for CT virtual simulation.

Commissioning and Comprehensive Quality Assurance of Commercial 3D Treatment Planning System Using IAEA Technical Report Series - 430

The purpose of this work is to report the results of commissioning and to establish a quality assurance (QA) program for commercial 3D treatment planning system (TPS) based on IAEA Technical Report Series 430. Eclipse™ v 7.3.10, (Varian Medical Systems, Palo Alto, CA, USA) TPS was commissioned for a Clinac 6EX (Varian Medical Systems, Palo Alto, CA, USA) linear accelerator. CT images of a phantom with various known in-homogeneities were acquired. The images were transferred to TPS and tested for various parameters related to patient data acquisition, anatomical modeling, plan evaluation and dose calculation. Dosimetric parameters including open, asymmetric and wedged shaped fields, oblique incidence, buildup region behavior and SSD dependence were evaluated. Representative clinical cases were tested for MU calculation and point doses. The maximum variation between the measured and the known CT numbers was 20 ± 11.7 HU (1 SD). The results of all non-dosimetric tests were found within tolerance, however expansion at the sharp corners was found distorted. The accuracy of the DVH calculations depends on the grid size. TPS calculations of all the dosimetric parameters were in good agreement with the measured values, however for asymmetric open and wedged fields, few points were found out of tolerance. Smaller grid size calculation showed better agreement of dose calculation in the build-up region. Independent tests for MU calculation showed a variation within ±2% (relative to planning system), meanwhile variation of 3.0% was observed when the central axis was blocked. The test results were in agreement with the tolerance specified by IAEA TRS 430. A subset of the commissioning tests has been identified as a baseline data for an ongoing QA program.