Comparing two strategies of dynamic intensity modulated radiation therapy (dIMRT) with 3-dimensional conformal radiation therapy (3DCRT) in the hypofractionated treatment of high-risk prostate cancer

Dosimetric evaluation study of IMRT and VMAT techniques for prostate cancer based on different multileaf collimator designs

The hypofractionated radiotherapy modality was established to reduce treatment durations and enhance therapeutic efficiency, as compared to conventional fractionation treatment. However, this modality is challenging because of rigid dosimetric constraints. This study aimed to assess the impact of multi-leaf collimator (MLC) widths (10 mm and 5 mm) on plan quality during the treatment of prostate cancer. Additionally, this study aimed to investigate the impact of the MLC mode of energy on the Agility flattening filter (FF), MLC Agility-free flattening filter (FFF), and MLCi2 for patients receiving hypofractionated radiotherapy. Two radiotherapy techniques; Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Radiotherapy (VMAT), were used in this research. In the present study, computed tomography simulations of ten patients (six plans per patient) with localized prostate adenocarcinoma were analyzed. Various dosimetric parameters were assessed, including monitor units, treatment delivery times, conformity, and homogeneity indices. To evaluate the plan quality, dose-volume histograms (DVHs) were estimated for each technique. The results demonstrated that the determined dosimetric parameters of planning target volume (PTV)p (such as D mean, conformity, and homogeneity index) showed greater improvement with MLC Agility FF and MLC Agility FFF than with MLCi2. Additionally, the treatment delivery time was reduced in the MLC Agility FF (by 31%) and MLC Agility FFF (by 10.8%) groups compared to the MLCi2 group. It is concluded that for both the VMAT and IMRT techniques, the smaller width (5 mm) MLCs revealed better planning target volume coverage, improved the dosimetric parameters for PTV, reduced the treatment time, and met the constraints for OARs. It is therefore recommended to use 5 mm MLCs for hypofractionated prostate cancer treatment due to better target coverage and better protection of OARs.

Evaluating Proton Dose and Associated Range Uncertainty Using Daily Cone-Beam CT

Purpose

This study aimed to quantitatively evaluate the range uncertainties that arise from daily cone-beam CT (CBCT) images for proton dose calculation compared to CT using a measurement-based technique.

Methods

For head and thorax phantoms, wedge-shaped intensity-modulated proton therapy (IMPT) treatment plans were created such that the gradient of the wedge intersected and was measured with a 2D ion chamber array. The measured 2D dose distributions were compared with 2D dose planes extracted from the dose distributions using the IMPT plan calculated on CT and CBCT. Treatment plans of a thymoma cancer patient treated with breath-hold (BH) IMPT were recalculated on 28 CBCTs and 9 CTs, and the resulting dose distributions were compared.

Results

The range uncertainties for the head phantom were determined to be 1.2% with CBCT, compared to 0.5% for CT, whereas the range uncertainties for the thorax phantom were 2.1% with CBCT, compared to 0.8% for CT. The doses calculated on CBCT and CT were similar with similar anatomy changes. For the thymoma patient, the primary source of anatomy change was the BH uncertainty, which could be up to 8 mm in the superior-inferior (SI) direction.

Conclusion

We developed a measurement-based range uncertainty evaluation method with high sensitivity and used it to validate the accuracy of CBCT-based range and dose calculation. Our study demonstrated that the CBCT-based dose calculation could be used for daily dose validation in selected proton patients.

Oral health-related quality of life (OHRQoL) in cardiovascular patients referring to Fatima Zahra Hospital in Sari, Iran

Background

Cardiovascular Disease (CVD) is one of the leading causes of mortality and morbidity and significantly impacts the health-related quality of life. Oral infections have been linked to cardiovascular diseases such as thrombosis, cardiac infarction, stroke, and peripheral vascular disease. This study aims to evaluate the effects of oral health on the quality of life in cardiovascular patients.

Methods

The oral health-related quality of life was measured using the OHIP-14 questionnaire. Demographic information, questions regarding smoke consumption, wearing removable prostheses, nine questions regarding xerostomia, and the existence of other systemic diseases were asked from 240 participants with cardiovascular diseases. The DMFT index was clinically examined in each patient. Also, the Plaque, Gingival, and Sulcular Bleeding Indices were measured on the Ramfjord teeth. Data analysis was conducted using SPSS version 16. The independent t test, Mann–Whitney test, the variance analysis, and the Kruskal–Wallis test were used to compare variables in the present study. Also, regression models were used to eliminate the effect of confounding variables.

Results

Gender variables, removable prosthesis, xerostomia, DMFT, and SBI were the main determinants of quality of life in CVD patients. The mean ADD-OHIP14 of participants in the study was calculated at 21.34 ± 17.40, and the SC-OHIP14 was 6.11 ± 5.07. The mean OHRQoL was higher in females than in males, and this difference was statistically significant. OHRQoL was significantly lower in patients wearing a removable prosthesis than in those without one. The relationship between age and xerostomia was significant in this study, and patients with xerostomia had a lower quality of life than those without xerostomia. Also, the mean DMFT index in subjects with xerostomia was 23.69 ± 7.76, which was statistically significant compared to those without xerostomia.

Conclusion

Cardiovascular patients experienced a decreased OHRQoL. Prevention or treatment of these problems seems to justify improving the quality of life in these patients.

Real-time intrafraction motion monitoring in external beam radiotherapy

Radiotherapy (RT) aims to deliver a spatially conformal dose of radiation to tumours while maximizing the dose sparing to healthy tissues. However, the internal patient anatomy is constantly moving due to respiratory, cardiac, gastrointestinal and urinary activity. The long term goal of the RT community to 'see what we treat, as we treat' and to act on this information instantaneously has resulted in rapid technological innovation. Specialized treatment machines, such as robotic or gimbal-steered linear accelerators (linac) with in-room imaging suites, have been developed specifically for real-time treatment adaptation. Additional equipment, such as stereoscopic kilovoltage (kV) imaging, ultrasound transducers and electromagnetic transponders, has been developed for intrafraction motion monitoring on conventional linacs. Magnetic resonance imaging (MRI) has been integrated with cobalt treatment units and more recently with linacs. In addition to hardware innovation, software development has played a substantial role in the development of motion monitoring methods based on respiratory motion surrogates and planar kV or Megavoltage (MV) imaging that is available on standard equipped linacs. In this paper, we review and compare the different intrafraction motion monitoring methods proposed in the literature and demonstrated in real-time on clinical data as well as their possible future developments. We then discuss general considerations on validation and quality assurance for clinical implementation. Besides photon RT, particle therapy is increasingly used to treat moving targets. However, transferring motion monitoring technologies from linacs to particle beam lines presents substantial challenges. Lessons learned from the implementation of real-time intrafraction monitoring for photon RT will be used as a basis to discuss the implementation of these methods for particle RT.

The effect of body contouring on the dose distribution delivered with volumetric-modulated arc therapy technique

The purpose of the study was to investigate the dosimetric effect defining the body structure with various Hounsfield unit (HU) threshold values on the dose distributions of volumetric‐modulated arc therapy (VMAT) plans. Twenty patients with prostate cancer and twenty patients with head and neck (H&N) cancer were retrospectively selected. For each patient, the body structure was redefined with HU threshold values of −180(Body180), −350(Body350), −700(Body700), and −980(Body980). For each patient, dose‐volumetric parameters with those body structures were calculated using identical VMAT plans. The differences in dose‐volumetric parameters due to the varied HU threshold values were calculated. For the prostate boost target volume, the maximum dose, mean dose, D95%, and D5% with Body180 were higher than those with Body980 by approximately 0.7% (p<0.001). For H&N target volumes, the changes in D95% of the targets receiving 67.5 Gy, 54 Gy, and 48 Gy between Body180 and Body980 were −1.2%, −0.9%, and −1.2%, respectively (p<0.001). The differences were larger for H&N VMAT plans than for prostate VMAT plans due to the inclusion of an immobilization device in the irradiated region in H&N cases. To apply all attenuating materials to dose calculation, the body structure would be defined with −980 HU. Otherwise, systematic error of about 1%, resulting in underdosage of the target volume, can occur.

PACS number: 87.55.ne

Acute toxicity of hypofractionated intensity-modulated radiotherapy for prostate cancer

BACKGROUND

Dose-escalated hypofractionated radiotherapy (hfrt) using intensity-modulated radiotherapy (imrt), with inclusion of the pelvic lymph nodes (plns), plus androgen suppression therapy (ast) in high-risk prostate cancer patients should improve patient outcomes, but acute toxicity could limit its feasibility.

METHODS

Our single-centre phase ii prospective study enrolled 40 high-risk prostate cancer patients. All patients received hfrt using imrt with daily mega-voltage computed tomography imaging guidance, with 95% of planning target volumes (ptv68 and ptv50) receiving 68 Gy and 50 Gy (respectively) in 25 daily fractions. The boost volume was targeted to the involved plns and the prostate (minus the urethra plus 3 mm and minus 3 mm from adjacent rectal wall) and totalled up to 75 Gy in 25 fractions. Acute toxicity scores were recorded weekly during and 3 months after radiotherapy (rt) administration.

RESULTS

For the 37 patients who completed rt and the 3-month follow-up, median age was 65.5 years (range: 50-76 years). Disease was organ-confined (T1c-T2c) in 23 patients (62.1%), and node-positive in 5 patients (13.5%). All patients received long-term ast. Maximum acute genitourinary (gu) and gastrointestinal (gi) toxicity peaked at grade 2 in 6 of 36 evaluated patients (16.6%) and in 4 of 31 evaluated patients (12.9%) respectively. Diarrhea and urinary frequency were the chief complaints. Dose-volume parameters demonstrated no correlation with toxicity. The ptv treatment objectives were met in 36 of the 37 patients.

CONCLUSIONS

This hfrt dose-escalation trial in high-risk prostate cancer has demonstrated the feasibility of administering 75 Gy in 25 fractions with minimal acute gi and gu toxicities. Further follow-up will report late toxicities and outcomes.

Comparison of the light charged particles on scatter radiation dose in thyroid hadron therapy

BACKGROUND

Hadron therapy is a novel technique of cancer radiation therapy which employs charged particles beams, (1)H and light ions in particular. Due to their physical and radiobiological properties, they allow one to obtain a more conformal treatment, sparing better the healthy tissues located in proximity of the tumor and allowing a higher control of the disease. Objective : As it is well known, these light particles can interact with nuclei in the tissue, and produce the different secondary particles such as neutron and photon. These particles can damage specially the critical organs behind of thyroid gland.

METHODS

In this research, we simulated neck geometry by MCNPX code and calculated the light particles dose at distance of 2.14 cm in thyroid gland, for different particles beam: (1)H, (2)H, (3)He, and (4)He. Thyroid treatment is important because the spine and vertebrae is situated right behind to the thyroid gland on the posterior side.

RESULTS

The results show that (2)H has the most total flux for photon and neutron, 1.944E-3 and 1.7666E-2, respectively. Whereas (1)H and (3)He have best conditions, 8.88609E-4 and 1.35431E-3 for photon, 4.90506E-4 and 4.34057E-3 for neutron, respectively. The same calculation has obtained for energy depositions for these particles.

CONCLUSION

In this research, we investigated that which of these light particles can deliver the maximum dose to the normal tissues and the minimum dose to the tumor. By comparing these results for the mentioned light particles, we find out (1)H and (3)He is the best therapy choices for thyroid glands whereas (2)H is the worst.

Whole-pelvic nodal radiation therapy in the context of hypofractionation for high-risk prostate cancer patients: a step forward

Given the low α/β ratio of prostate cancer, prostate hypofractionation has been tested through numerous clinical studies. There is a growing body of literature suggesting that with high conformal radiation therapy and even with more sophisticated radiation techniques, such as high-dose-rate brachytherapy or image-guided intensity modulated radiation therapy, morbidity associated with shortening overall treatment time with higher doses per fraction remains low when compared with protracted conventional radiation therapy to the prostate only. In high-risk prostate cancer patients, there is accumulating evidence that either dose escalation to the prostate or hypofractionation may improve outcome. Nevertheless, selected patients who have a high risk of lymph node involvement may benefit from whole-pelvic radiation therapy (WPRT). Although combining WPRT with hypofractionated prostate radiation therapy is feasible, it remains investigational. By combining modern advances in radiation oncology (high-dose-rate prostate brachytherapy, intensity modulated radiation therapy with an improved image guidance for soft-tissue sparing), it is hypothesized that WPRT could take advantage of recent results from hypofractionation trials. Moreover, the results from hypofractionation trials raise questions as to whether hypofractionation to pelvic lymph nodes with a high risk of occult involvement might improve the outcomes in WPRT. Although investigational, this review discusses the challenging idea of WPRT in the context of hypofractionation for patients with high-risk prostate cancer.

Empirical estimation of beam-on time for prostate cancer patients treated on Tomotherapy

BACKGROUND AND AIM

This study proposed a method to estimate the beam-on time for prostate cancer patients treated on Tomotherapy when FW (field width), PF (pitch factor), modulation factor (MF) and treatment length (TL) were given.

MATERIAL AND METHODS

THE STUDY WAS DIVIDED INTO TWO PARTS: building and verifying the model. To build a model, 160 treatment plans were created for 10 patients. The plans differed in combination of FW, PF and MF. For all plans a graph of beam-on time as a function of TL was created and a linear trend function was fitted. Equation for each trend line was determined and used in a correlation model. Finally, 62 plans verified the treatment time computation model - the real execution time was compared with our estimation and irradiation time calculated based on the equation provided by the manufacturer.

RESULTS

A linear trend function was drawn and the coefficient of determination R (2) and the Pearson correlation coefficient r were calculated for each of the 8 trend lines corresponding to the adequate treatment plan. An equation to correct the model was determined to estimate more accurately the beam-on time for different MFs. From 62 verification treatment plans, only 5 disagreed by more than 60 s with the real time from the HT software. Whereas, for the equation provided by the manufacturer the discrepancy was observed in 16 cases.

CONCLUSIONS

Our study showed that the model can well predict the treatment time for a given TL, MF, FW and it can be used in clinical practice.

Providing a fast conversion of total dose to biological effective dose (BED) for hybrid seed brachytherapy

Optimization of permanent seed implant brachytherapy plans for treatment of prostate cancer should be based on biological effective dose (BED) distributions, since dose does not accurately represent biological effects between different types of sources. Currently, biological optimization for these plans is not feasible due to the amount of time necessary to calculate the BED distribution. This study provides a fast calculation method, based on the total dose, to calculate the BED distribution. Distributions of various numbers of hybrid seeds were used to calculate total dose distributions, as well as BED distributions. Hybrid seeds are a mixture of different isotopes (in this study ¹²⁵I and ¹⁰³Pd). Three ratios of hybrid seeds were investigated: 25/75, 50/50, and 75/25. The total dose and BED value from each voxel were coupled together to produce graphs of total dose vs. BED. Equations were then derived from these graphs. The study investigated four types of tissue: bladder, rectum, prostate, and other normal tissue. Equations were derived from the total dose – BED correspondence. Accuracy of conversion from total dose to BED was within 2 Gy; however, accuracy of conversion was found to be better for high total dose regions as compared to lower dose regions. The method introduced in this paper allows one to perform fast conversion of total dose to BED for brachytherapy using hybrid seeds, which makes the BED‐based plan optimization practical. The method defined here can be extended to other ratios, as well as other tissues that are affected by permanent seed implant brachytherapy (i.e., breast).

PACS number: 87.55.de

Hypofractionated helical tomotherapy using 2.5-2.6 Gy daily fractions for localized prostate cancer

BACKGROUND

The purpose of this study is to evaluate the tolerability of hypofractionated helical tomotherapy (HT) in the treatment of localized prostate cancer.

MATERIALS AND METHODS

We evaluated 48 patients with primary adenocarcinoma of the prostate (cT1-T3N0M0) who were treated with hypofractionated HT from August 2008 through July 2011. Hypofractionated regimens included: 68.04 Gy at 2.52 Gy/fraction, 70 Gy at 2.5 Gy/fraction, and 70.2 Gy at 2.6 Gy/fraction. Genitourinary (GU) and gastrointestinal (GI) toxicity was scored using the Radiation Therapy Oncology Group scoring system.

RESULTS

Thirty-two patients were treated with 68.04 Gy, 5 patients with 70 Gy, and 11 with 70.2 Gy. The median age at diagnosis was 69 years (range 49-87) and the median follow-up 11 months (range 7-40). Grade 2 acute GI toxicity occurred in 9 patients (19 %). No grade 3 or higher acute GI toxicity was observed. Grade 2 and 3 acute GU toxicities occurred in 19 and 6 % of patients, respectively. The incidence of late grade 2 GI and GU toxicity was 4 and 2 %, respectively. No grade 3 or higher late toxicities were observed. Multivariate analysis showed that patients treated at 2.6 Gy/fraction or those who received a total radiation dose ≥70 Gy had higher rates of grade ≥2 acute GU toxicity (P = 0.004 and P = 0.048, respectively).

CONCLUSION

Hypofractionated HT in the treatment of localized prostate cancer is well tolerated with no grade 3 or higher early or late GI and GU toxicities. Further research is needed to assess definitive late toxicity and tumor control.

Detection and correction for EPID and gantry sag during arc delivery using cine EPID imaging

PURPOSE

Electronic portal imaging devices (EPIDs) have been studied and used for pretreatment and in-vivo dosimetry applications for many years. The application of EPIDs for dosimetry in arc treatments requires accurate characterization of the mechanical sag of the EPID and gantry during rotation. Several studies have investigated the effects of gravity on the sag of these systems but each have limitations. In this study, an easy experiment setup and accurate algorithm have been introduced to characterize and correct for the effect of EPID and gantry sag during arc delivery.

METHODS

Three metallic ball bearings were used as markers in the beam: two of them fixed to the gantry head and the third positioned at the isocenter. EPID images were acquired during a 360° gantry rotation in cine imaging mode. The markers were tracked in EPID images and a robust in-house developed MATLAB code was used to analyse the images and find the EPID sag in three directions as well as the EPID + gantry sag by comparison to the reference gantry zero image. The algorithm results were then tested against independent methods. The method was applied to compare the effect in clockwise and counter clockwise gantry rotations and different source-to-detector distances (SDDs). The results were monitored for one linear accelerator over a course of 15 months and six other linear-accelerators from two treatment centers were also investigated using this method. The generalized shift patterns were derived from the data and used in an image registration algorithm to correct for the effect of the mechanical sag in the system. The Gamma evaluation (3%, 3 mm) technique was used to investigate the improvement in alignment of cine EPID images of a fixed field, by comparing both individual images and the sum of images in a series with the reference gantry zero image.

RESULTS

The mechanical sag during gantry rotation was dependent on the gantry angle and was larger in the in-plane direction, although the patterns were not identical for various linear-accelerators. The reproducibility of measurements was within 0.2 mm over a period of 15 months. The direction of gantry rotation and SDD did not affect the results by more than 0.3 mm. Results of independent tests agreed with the algorithm within the accuracy of the measurement tools. When comparing summed images, the percentage of points with Gamma index <1 increased from 85.4% to 94.1% after correcting for the EPID sag, and to 99.3% after correction for gantry + EPID sag.

CONCLUSIONS

The measurement method and algorithms introduced in this study use cine-images, are highly accurate, simple, fast, and reproducible. It tests all gantry angles and provides a suitable automatic analysis and correction tool to improve EPID dosimetry and perform comprehensive linac QA for arc treatments.

Optimization of treatment planning parameters used in tomotherapy for prostate cancer patients

BACKGROUND AND PURPOSE

Tomotherapy treatment planning depends on parameters that are not used conventionally such as: field width (FW), pitch factor (PF) and modulation factor (MF). The aim of this study is to analyze the relationship between these parameters and their influence on the quality of treatment plans and beam-on time.

MATERIAL AND METHODS

Ten prostate cancer patients were included in the study. For each patient, two cases of irradiation were considered depending on the target volume: PTV1 included the prostate gland, seminal vesicles, pelvic lymph nodes and a 1 cm margin, whereas PTV2 included only the prostate gland with a 1 cm margin. For each patient and each case of irradiation (PTV1 and PTV2) 8 treatment plans were created - all consisted of a different combination of planning parameters (FW = 1.05, 2.5, 5 cm; PF = 0.107, 0.215, 0.43; MF = 1.5, 2.5, 3.5). Default values used in this study were FW = 2.5 cm, PF = 0.215 and MF = 2.5. Hence, for plans with different FWs, parameters of PF and MF were 0.215 and 2.5, respectively; for different PFs, FW and MF were 2.5 and 2.5, respectively; finally for different MFs, FW and PF were 2.5 and 0.215, respectively. The reference plan was optimized for FW = 1.05 cm, PF = 0.107 and MF = 3.5, which was assumed to result in the best dose distribution and the longest treatment time. As a result, 160 plans were created. Each plan was analyzed for dose distribution and execution time.

RESULTS AND CONCLUSION

: Treatment plans with FW of 5 cm resulted in the shortest execution time compromising the dose distribution. Moreover, the dose fall off in the longitudinal direction was not sharp. FW of 1.05 cm and PF of 0.107 were not recommended for routine prostate plans due to long execution time, which was 3 times longer than for plans with FW = 5 cm. There was no substantial decrease of irradiation time when PF was increased from 0.215 to 0.43 for both cases (PTV1 and PTV2); however, the dose distribution was slightly compromised. Finally, decreasing MF from 2.5 to 1.5 was useless because it did not change the beam-on time; however, it did remarkably decrease the dose distribution. Nevertheless, increasing MF up to 3.5 could be considered. The lowest EUD for the rectum and intestines, could be observed for PF = 0.107. For the other plans the differences were rather small (the EUD was almost the same). By reducing PF from 0.43 to 0.107 or FW from 5 to 1.05 the EUD for bladder (in PTV1 case) decreased by 3.13% and 2.60%. When PTV2 was a target volume, the EUD for bladder decreased by 4.54% and 3.43% when FW was changed from 5 to 1.05 and MF from 1.5 to 3.5, respectively. For optimal balance between beam-on time and dose distribution in OARs for routine patients, the authors would suggest to use: FW = 2.5, PF = 0.215 and MF = 2.5.

Calculating prescription doses for new sources by biologically effective dose matching

PURPOSE

In current clinical practice, single isotopes, such as (125)I or (103)Pd, are used as single sources in prostate seed implants. A mixture of two radionuclides in the seeds has been proposed for prostate cancer treatment. This study investigates a method for determining the prescription dose for these new seeds using the biological effective dose (BED).

METHODS

Ten prostate cancer cases previously treated using single radionuclide seeds were selected for this study. The BED distribution for these cases was calculated. Plans using other radionuclides were then calculated based on this BED distribution. Prescription values could then be obtained for the calculated plans. The method was verified by calculating the prescription dose for (103)Pd and (125)I and comparing to clinical values. The method was then applied to a hybrid seed that consisted of a mixture of (125)I and (103)Pd radionuclides, which deliver equal dose to 1cm from the source in water (50/50D@1 cm). A prescription BED value was also calculated.

RESULTS

A prescription BED of 110 Gy was found to correlate to a prescription dose of 145, 120, and 137 Gy for (125)I, (103)Pd, and 50/50D@1 cm hybrid seeds, respectively.

CONCLUSION

The method introduced in this article allows one to calculate the prescription dose for new and novel sources in brachytherapy. The method was verified by calculating a prescription dose for (125)I and (103)Pd radionuclides that coincides with values used clinically.

Implementing RapidArc into clinical routine: a comprehensive program from machine QA to TPS validation and patient QA

PURPOSE

With the increased commercial availability of intensity modulated arc therapy (IMAT) comes the need for comprehensive QA programs, covering the different aspects of this newly available technology. This manuscript proposes such a program for the RapidArc (RA) (Varian Medical Systems, Palo Alto) IMAT solution.

METHODS

The program was developed and tested out for a Millennium120 MLC on iX Clinacs and a HighDefinition MLC on a Novalis TX, using a variety of measurement equipment including Gafchromic film, 2D ion chamber arrays (Seven29 and StarCheck, PTW, Freiburg, Germany) with inclinometer and Octavius phantom, the Delta4 systam (ScandiDos, Uppsala, Sweden) and the portal imager (EPID). First, a number of complementary machine QA tests were developed to monitor the correct interplay between the accelerating/decelerating gantry, the variable dose rate and the MLC position, straining the delivery to the maximum allowed limits. Second, a systematic approach to the validation of the dose calculation for RA was adopted, starting with static gantry and RA specific static MLC shapes and gradually moving to dynamic gantry, dynamic MLC shapes. RA plans were then optimized on a series of artificial structures created within the homogeneous Octavius phantom and within a heterogeneous lung phantom. These served the double purpose of testing the behavior of the optimization algorithm (PRO) as well as the precision of the forward dose calculation. Finally, patient QA on a series of clinical cases was performed with different methods. In addition to the well established in-phantom QA, we evaluated the portal dosimetry solution within the Varian approach.

RESULTS

For routine machine QA, the "Snooker Cue" test on the EPID proved to be the most sensitive to overall problem detection. It is also the most practical one. The "Twinkle" and "Sunrise" tests were useful to obtain well differentiated information on the individual treatment delivery components. The AAA8.9 dose calculations showed excellent agreement with all corresponding measurements, except in areas where the 2.5 mm fixed fluence resolution was insufficient to accurately model the tongue and groove effect or the dose through nearly closed opposing leafs. Such cases benefited from the increased fluence resolution in AAA10.0. In the clinical RA fields, these effects were smeared out spatially and the impact of the fluence resolution was considerably less pronounced. The RA plans on the artificial structure sets demonstrated some interesting characteristics of the PRO8.9 optimizer, such as a sometimes unexpected dependence on the collimator rotation and a suboptimal coverage of targets within lung tissue. Although the portal dosimetry was successfully validated, we are reluctant to use it as a sole means of patient QA as long as no gantry angle information is embedded.

CONCLUSIONS

The all-in validation program allows a systematic approach in monitoring the different levels of RA treatments. With the systematic approach comes a better understanding of both the capabilities and the limits of the used solution. The program can be useful for implementation, but also for the validation of major upgrades.

Assessing the role of volumetric modulated arc therapy (VMAT) relative to IMRT and helical tomotherapy in the management of localized, locally advanced, and post-operative prostate cancer

PURPOSE

To quantify differences in treatment delivery efficiency and dosimetry between step-and-shoot intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and helical tomotherapy (HT) for prostate treatment.

METHODS AND MATERIALS

Twenty-five prostate cancer patients were selected retrospectively for this planning study. Treatment plans were generated for: prostate alone (n = 5), prostate + seminal vesicles (n = 5), prostate + seminal vesicles + pelvic lymph nodes (n = 5), prostate bed (n = 5), and prostate bed + pelvic lymph nodes (n = 5). Target coverage, dose homogeneity, integral dose, monitor units (MU), and sparing of organs at risk (OAR) were compared across techniques. Time required to deliver each plan was measured.

RESULTS

The dosimetric quality of IMRT, VMAT, and HT plans were comparable for target coverage (planning target volume V95%, clinical target volume V100% all >98.7%) and sparing of organs at risk (OAR) for all treatment groups. Although HT resulted in a slightly higher integral dose and mean doses to the OAR, it yielded a lower maximum dose to all OAR examined. VMAT resulted in reductions in treatment times over IMRT (mean = 75%) and HT (mean = 70%). VMAT required 15-38% fewer monitor units than IMRT over all treatment volumes, with the reduction per fraction ranging from 100-423 MU from the smallest to largest volumes.

CONCLUSIONS

VMAT improves efficiency of delivery for equivalent dosimetric quality as IMRT and HT across various prostate cancer treatment volumes in the intact and postoperative settings.

Does Helical Tomotherapy Improve Dose Conformity and Normal Tissue Sparing Compared to Conventional IMRT? A Dosimetric Comparison in High Risk Prostate Cancer

The study was designed to compare Helical Tomotherapy (HT) based IMRT and conventional sliding window (SW IMRT) in patients with high risk prostate cancer. Complementary plans with HT and SWIMRT were compared using DVH parameters. The PTV Prostate was prescribed 74 Gy in 37 fractions and the nodal PTV received 55 Gy in 37 fractions by simultaneous integrated boost. Conformity Index, Homogeneity Index and dose-volume parameters were compared. The conformity index (CI) of HT (0.77, SD = 0.54) plans tended to be better (p = 0.069) compared to SWIMRT (0.70, SD = 0.01) for prostate PTV. CI for nodal PTV was similar. Helical tomotherapy plans were more homogeneous, with homogeneity index (HI) of 0.04 compared to 0.06 in SWIMRT (p = 0.018) for PTV prostate and HI of 0.06 and 0.15 (p = 0.025) for PTV nodes respectively. Median dose to bladder (p = 0.025) and rectum (p = 0.012) were less with HT. However, HT delivered a higher D10Gy and D1Gy to rectum and bladder overlap volumes as a consequence of achieving better homogeneity. Femoral heads were better spared with HT plans (p = 0.012). HT improves dose homogeneity, target coverage and conformity as compared to SWIMRT, with overall improvement in critical organ sparing.

Choline PET based dose-painting in prostate cancer--modelling of dose effects

BACKGROUND

Several randomized trials have documented the value of radiation dose escalation in patients with prostate cancer, especially in patients with intermediate risk profile. Up to now dose escalation is usually applied to the whole prostate. IMRT and related techniques currently allow for dose escalation in sub-volumes of the organ. However, the sensitivity of the imaging modality and the fact that small islands of cancer are often dispersed within the whole organ may limit these approaches with regard to a clear clinical benefit. In order to assess potential effects of a dose escalation in certain sub-volumes based on choline PET imaging a mathematical dose-response model was developed.

METHODS

Based on different assumptions for alpha/beta, gamma 50, sensitivity and specificity of choline PET, the influence of the whole prostate and simultaneous integrated boost (SIB) dose on tumor control probability (TCP) was calculated. Based on the given heterogeneity of all potential variables certain representative permutations of the parameters were chosen and, subsequently, the influence on TCP was assessed.

RESULTS

Using schedules with 74 Gy within the whole prostate and a SIB dose of 90 Gy the TCP increase ranged from 23.1% (high detection rate of choline PET, low whole prostate dose, high gamma 50/ASTRO definition for tumor control) to 1.4% TCP gain (low sensitivity of PET, high whole prostate dose, CN + 2 definition for tumor control) or even 0% in selected cases. The corresponding initial TCP values without integrated boost ranged from 67.3% to 100%. According to a large data set of intermediate-risk prostate cancer patients the resulting TCP gains ranged from 22.2% to 10.1% (ASTRO definition) or from 13.2% to 6.0% (CN + 2 definition).

DISCUSSION

Although a simplified mathematical model was employed, the presented model allows for an estimation in how far given schedules are relevant for clinical practice. However, the benefit of a SIB based on choline PET seems less than intuitively expected. Only under the assumption of high detection rates and low initial TCP values the TCP gain has been shown to be relevant.

CONCLUSIONS

Based on the employed assumptions, specific dose escalation to choline PET positive areas within the prostate may increase the local control rates. Due to the lack of exact PET sensitivity and prostate alpha/beta parameter, no firm conclusions can be made. Small variations may completely abrogate the clinical benefit of a SIB based on choline PET imaging.