Radiosurgery for ventricular tachycardia (RAVENTA): interim analysis of a multicenter multiplatform feasibility trial

BACKGROUND

Single-session cardiac stereotactic radiation therapy (SBRT) has demonstrated promising results for patients with refractory ventricular tachycardia (VT). However, the full safety profile of this novel treatment remains unknown and very limited data from prospective clinical multicenter trials are available.

METHODS

The prospective multicenter multiplatform RAVENTA (radiosurgery for ventricular tachycardia) study assesses high-precision image-guided cardiac SBRT with 25 Gy delivered to the VT substrate determined by high-definition endocardial and/or epicardial electrophysiological mapping in patients with refractory VT ineligible for catheter ablation and an implanted cardioverter defibrillator (ICD). Primary endpoint is the feasibility of full-dose application and procedural safety (defined as an incidence of serious [grade ≥ 3] treatment-related complications ≤ 5% within 30 days after therapy). Secondary endpoints comprise VT burden, ICD interventions, treatment-related toxicity, and quality of life. We present the results of a protocol-defined interim analysis.

RESULTS

Between 10/2019 and 12/2021, a total of five patients were included at three university medical centers. In all cases, the treatment was carried out without complications. There were no serious potentially treatment-related adverse events and no deterioration of left ventricular ejection fraction upon echocardiography. Three patients had a decrease in VT episodes during follow-up. One patient underwent subsequent catheter ablation for a new VT with different morphology. One patient with local VT recurrence died 6 weeks after treatment in cardiogenic shock.

CONCLUSION

The interim analysis of the RAVENTA trial demonstrates early initial feasibility of this new treatment without serious complications within 30 days after treatment in five patients. Recruitment will continue as planned and the study has been expanded to further university medical centers.

TRIAL REGISTRATION NUMBER

NCT03867747 (clinicaltrials.gov). Registered March 8, 2019. Study start: October 1, 2019.

Multilayer intensity modulated contact interventional radiotherapy (brachytherapy): Stretching the therapeutic window in skin cancer

Interventional radiotherapy (IRT, brachytherapy) is a highly effective treatment method for non-melanoma skin cancer (NMSC). Traditionally, the maximum depth of NMSC lesions considered eligible for contact IRT was 5 mm; however, following several national surveys and recent recommendations, such cut-off, lesions thicker than 5 mm may be treated by contact IRT. The use of image guidance in defining the actual depth in treating NMSC to correctly identify clinical target volume (CTV) and prevent unnecessary toxicity is of paramount importance. The aim of the paper was to describe a multilayer arrangement of catheters to treat NMSC lesions thicker than 5 mm, thus proposing an example of dynamic intensity modulated IRT, using different catheter-to-skin distance of sources to reach the best CTV coverage and maximally reduce the excess of dose to the skin.

A step towards routine for stereotactic radioablation in refractory ventricular tachycardia – interim analysis on short term safety of the first prospective, multi-centre, multi-platform study RAVENTA

Background

Ventricular tachycardia (VT) is a potentially life-threatening heart rhythm disorder originating in heterogeneous conduction velocity in the ventricular myocardium, e.g. by scar formation in ischaemic or dilated cardiomyopathy. Current guideline-directed medical therapy comprises implantable cardioverter defibrillator (ICD), antiarrhythmic drugs, and endocardial/epicardial catheter ablation. There is a serious recurrence rate for example due to diffuse fibrosis, progress of disease, or insufficient ablation depth or volume.

In cases when Catheter ablation and antiarrhythmic medication failed to reduce VT burden, stereotactic body radiation therapy (SBRT) may become an additional treatment option. To date there have been several small retrospective case series and some single-centre prospective studies showing promising results.

Purpose

For the purpose of obtaining the authorization of a randomized trial, a feasibility study was designed. The primary objective is to demonstrate sufficient safety of cardiac SBRT for the non-invasive treatment of VT and whether the dose needed can be delivered while sparing sensitive surrounding structures (e.g. stomach, oesophagus, vena cava, coronary arteries, ICD). Secondarily, the effect on VT burden is reported.

Methods

The RAVENTA study (RAdiosurgery for VENtricular TAchycardias) is the first prospective, multicentre study on SBRT in patients suffering from refractory VTs worldwide. Patients were enrolled according to strict inclusion criteria. First, an electrophysiology study using a high definition mapping system was performed to identify the substrate (target region). In order to plan SBRT a planning computed tomography scan was obtained. Finally, a single dose of 25 Gy was administered to the target region. Neither sedation nor anaesthesia is necessary during SBRT.

Primary endpoint is feasibility defined as complete dose application and absence of severe (grade ≥3) treatment-related toxicity within 30 days of treatment. RAVENTA is powered to reject the hypothesis of 70% feasibility, if in fact feasibility is 95%. This is a pre-defined interim analysis with the aim of stopping early for futility.

Results

Between October 2019 and December 2021, the first 5 patients (characteristics shown in Table 1) could be enrolled and radiotherapy was delivered without major complications. Cardiac SBRT took on average 30 minutes. There was no treatment-related severe toxicity. Furthermore, we could not record any negative effect on functionality of the ICD: constant sensing amplitude and pacing capture threshold. In the short-term, patients showed a clear decrease in VT burden.

Conclusion

These preliminary data of the first multi-centre, multi-platform study on cardiac SBRT on refractory VT demonstrated sufficient short-term feasibility to continue the RAVENTA study. Meanwhile the study has been expanded to 6 centres in Germany.

Funding Acknowledgement

Type of funding sources: None.

Treatment Planning for Cardiac Radioablation: Multicenter Multiplatform Benchmarking for the XXX Trial

PURPOSE

Cardiac radioablation is a novel treatment option for patients with refractory ventricular tachycardia (VT) unsuitable for catheter ablation. The quality of treatment planning depends on dose specifications, platform capabilities, and experience of the treating staff. To harmonize the treatment planning, benchmarking of this process is necessary for multicenter clinical studies such as the XXX trial.

METHODS AND MATERIALS

Planning computed tomography data and consensus structures from three patients were sent to five academic centers for independent plan development using a variety of platforms and techniques with the XXX study protocol serving as guideline. Three-dimensional dose distributions and treatment plan details were collected and analyzed. In addition, an objective relative plan quality ranking system for VT treatments was established.

RESULTS

For each case, three coplanar volumetric modulated arc (VMAT) plans for C-arm linear accelerators (LINAC) and three non-coplanar treatment plans for robotic arm LINAC were generated. All plans were suitable for clinical applications with minor deviations from study guidelines in most centers. Eleven of 18 treatment plans showed maximal one minor deviation each for target and cardiac substructures. However, dose-volume histograms showed substantial differences: in one case, the PTV≥30Gy ranged from 0.0% to 79.9% and the RIVA V_14Gy ranged from 4.0% to 45.4%. Overall, the VMAT plans had steeper dose gradients in the high dose region, while the plans for the robotic arm LINAC had smaller low dose regions. Thereby, VMAT plans required only about half as many monitor units, resulting in shorter delivery times, possibly an important factor in treatment outcome.

CONCLUSIONS

Cardiac radioablation is feasible with robotic arm and C-arm LINAC systems with comparable plan quality. Although cross-center training and best practice guidelines have been provided, further recommendations, especially for cardiac substructures, and ranking of dose guidelines will be helpful to optimize cardiac radioablation outcomes.

Tumor-dose-rate variations during robotic radiosurgery of oligo and multiple brain metastases

Purpose

For step-and-shoot robotic stereotactic radiosurgery (SRS) the dose delivered over time, called local tumor-dose-rate (TDR), may strongly vary during treatment of multiple lesions. The authors sought to evaluate technical parameters influencing TDR and correlate TDR to clinical outcome.

Material and methods

A total of 23 patients with 162 oligo (1–3) and multiple (>3) brain metastases (OBM/MBM) treated in 33 SRS sessions were retrospectively analyzed. Median PTV were 0.11 cc (0.01–6.36 cc) and 0.50 cc (0.12–3.68 cc) for OBM and MBM, respectively. Prescription dose ranged from 16 to 20 Gy prescribed to the median 70% isodose line. The maximum dose-rate for planning target volume (PTV) percentage p in time span s during treatment (TDR_s,p) was calculated for various p and s based on treatment log files and in-house software.

Results

TDR_60min,98% was 0.30 Gy/min (0.23–0.87 Gy/min) for OBM and 0.22 Gy/min (0.12–0.63 Gy/min) for MBM, respectively, and increased by 0.03 Gy/min per prescribed Gy. TDR_60min,98% strongly correlated with treatment time (ρ = −0.717, p < 0.001), monitor units (MU) (ρ = −0.767, p < 0.001), number of beams (ρ = −0.755, p < 0.001) and beam directions (ρ = −0.685, p < 0.001) as well as lesions treated per collimator (ρ = −0.708, P < 0.001). Median overall survival (OS) was 20 months and 1‑ and 2‑year local control (LC) was 98.8% and 90.3%, respectively. LC did not correlate with any TDR, but tumor response (partial response [PR] or complete response [CR]) correlated with all TDR in univariate analysis (e.g., TDR_60min,98%: hazard ration [HR] = 0.974, confidence interval [CI] = 0.952–0.996, p = 0.019). In multivariate analysis only concomitant targeted therapy or immunotherapy and breast cancer tumor histology remained a significant factor for tumor response. Local grade ≥2 radiation-induced tissue reactions were noted in 26.3% (OBM) and 5.2% (MBM), respectively, mainly influenced by tumor volume (p < 0.001).

Conclusions

Large TDR variations are noted during MBM-SRS which mainly arise from prolonged treatment times. Clinically, low TDR corresponded with decreased local tumor responses, although the main influencing factor was concomitant medication.

Radiosurgery for ventricular tachycardia: preclinical and clinical evidence and study design for a German multi-center multi-platform feasibility trial (RAVENTA)

Background

Single-session high-dose stereotactic radiotherapy (radiosurgery) is a new treatment option for otherwise untreatable patients suffering from refractory ventricular tachycardia (VT). In the initial single-center case studies and feasibility trials, cardiac radiosurgery has led to significant reductions of VT burden with limited toxicities. However, the full safety profile remains largely unknown.

Methods/design

In this multi-center, multi-platform clinical feasibility trial which we plan is to assess the initial safety profile of radiosurgery for ventricular tachycardia (RAVENTA). High-precision image-guided single-session radiosurgery with 25 Gy will be delivered to the VT substrate determined by high-definition endocardial electrophysiological mapping. The primary endpoint is safety in terms of successful dose delivery without severe treatment-related side effects in the first 30 days after radiosurgery. Secondary endpoints are the assessment of VT burden, reduction of implantable cardioverter defibrillator (ICD) interventions [shock, anti-tachycardia pacing (ATP)], mid-term side effects and quality-of-life (QoL) in the first year after radiosurgery. The planned sample size is 20 patients with the goal of demonstrating safety and feasibility of cardiac radiosurgery in ≥ 70% of the patients. Quality assurance is provided by initial contouring and planning benchmark studies, joint multi-center treatment decisions, sequential patient safety evaluations, interim analyses, independent monitoring, and a dedicated data and safety monitoring board.

Discussion

RAVENTA will be the first study to provide the initial robust multi-center multi-platform prospective data on the therapeutic value of cardiac radiosurgery for ventricular tachycardia.

Trial registration number

NCT03867747 (clinicaltrials.gov). Registered March 8, 2019. The study was initiated on November 18th, 2019, and is currently recruiting patients.

Graphic abstract

Treatment planning for spinal radiosurgery : A competitive multiplatform benchmark challenge

PURPOSE

To investigate the quality of treatment plans of spinal radiosurgery derived from different planning and delivery systems. The comparisons include robotic delivery and intensity modulated arc therapy (IMAT) approaches. Multiple centers with equal systems were used to reduce a bias based on individual's planning abilities. The study used a series of three complex spine lesions to maximize the difference in plan quality among the various approaches.

METHODS

Internationally recognized experts in the field of treatment planning and spinal radiosurgery from 12 centers with various treatment planning systems participated. For a complex spinal lesion, the results were compared against a previously published benchmark plan derived for CyberKnife radiosurgery (CKRS) using circular cones only. For two additional cases, one with multiple small lesions infiltrating three vertebrae and a single vertebra lesion treated with integrated boost, the results were compared against a benchmark plan generated using a best practice guideline for CKRS. All plans were rated based on a previously established ranking system.

RESULTS

All 12 centers could reach equality (n = 4) or outperform (n = 8) the benchmark plan. For the multiple lesions and the single vertebra lesion plan only 5 and 3 of the 12 centers, respectively, reached equality or outperformed the best practice benchmark plan. However, the absolute differences in target and critical structure dosimetry were small and strongly planner-dependent rather than system-dependent. Overall, gantry-based IMAT with simple planning techniques (two coplanar arcs) produced faster treatments and significantly outperformed static gantry intensity modulated radiation therapy (IMRT) and multileaf collimator (MLC) or non-MLC CKRS treatment plan quality regardless of the system (mean rank out of 4 was 1.2 vs. 3.1, p = 0.002).

CONCLUSIONS

High plan quality for complex spinal radiosurgery was achieved among all systems and all participating centers in this planning challenge. This study concludes that simple IMAT techniques can generate significantly better plan quality compared to previous established CKRS benchmarks.

Usability and accuracy of high-resolution detectors for daily quality assurance for robotic radiosurgery

For daily CyberKnife QA a Winston-Lutz-Test (Automated-Quality-Assurance, AQA) is used to determine sub-millimeter deviations in beam delivery accuracy. This test is performed using gafchromic film, an extensive and user-dependent method requiring the use of disposables. We therefore analyzed the usability and accuracy of high-resolution detector arrays. We analyzed a liquid-filled ionization-chamber array (Octavius 1000SRS, PTW, Germany), which has a central resolution of 2.5mm. To test sufficient sensitivity, beam profiles with robot shifts of 0.1mm along the arrays' axes were measured. The detected deviation between the shifted and central profile were compared to the real robot's position. We then compared the results to the SRS-Profiler (SunNuclear, USA) with 4.0mm resolution and to the Nonius (QUART, Germany), a single-line diode detector with 2.8mm resolution. Finally, AQA variance and usability were analyzed performing a number of AQA tests over time, which required the use of specially designed fixtures for each array, and the results were compared to film. Concerning sensitivity, the 1000SRS detected the beam profile shifts with a maximum difference of 0.11mm (mean deviation = 0.03mm) compared to the actual robot shift. The Nonius and SRS-Profiler showed differences of up to 0.15mm and 0.69mm with mean deviation of 0.05mm and 0.18mm, respectively. Analyzing the variation of AQA results over time, the 1000SRS showed a comparable standard deviation to film (0.26mm vs. 0.18mm). The SRS-Profiler and the Nonius showed a standard deviation of 0.16mm and 0.24mm, respectively. The 1000SRS seems to provide equivalent accuracy and sensitivity to the gold standard film when performing daily AQA tests. Compared to other detectors in our study the sensitivity as well as the accuracy of the 1000SRS appears to be superior and more user-friendly. Furthermore, no significant modification of the standard AQA procedure is required when introducing 1000SRS for CyberKnife AQA.

Dosimetric Implications of Residual Tracking Errors During Robotic SBRT of Liver Metastases

PURPOSE

Although the metric precision of robotic stereotactic body radiation therapy in the presence of breathing motion is widely known, we investigated the dosimetric implications of breathing phase-related residual tracking errors.

METHODS AND MATERIALS

In 24 patients (28 liver metastases) treated with the CyberKnife, we recorded the residual correlation, prediction, and rotational tracking errors from 90 fractions and binned them into 10 breathing phases. The average breathing phase errors were used to shift and rotate the clinical tumor volume (CTV) and planning target volume (PTV) for each phase to calculate a pseudo 4-dimensional error dose distribution for comparison with the original planned dose distribution.

RESULTS

The median systematic directional correlation, prediction, and absolute aggregate rotation errors were 0.3 mm (range, 0.1-1.3 mm), 0.01 mm (range, 0.00-0.05 mm), and 1.5° (range, 0.4°-2.7°), respectively. Dosimetrically, 44%, 81%, and 92% of all voxels differed by less than 1%, 3%, and 5% of the planned local dose, respectively. The median coverage reduction for the PTV was 1.1% (range in coverage difference, -7.8% to +0.8%), significantly depending on correlation (P=.026) and rotational (P=.005) error. With a 3-mm PTV margin, the median coverage change for the CTV was 0.0% (range, -1.0% to +5.4%), not significantly depending on any investigated parameter. In 42% of patients, the 3-mm margin did not fully compensate for the residual tracking errors, resulting in a CTV coverage reduction of 0.1% to 1.0%.

CONCLUSIONS

For liver tumors treated with robotic stereotactic body radiation therapy, a safety margin of 3 mm is not always sufficient to cover all residual tracking errors. Dosimetrically, this translates into only small CTV coverage reductions.

Effective method of measuring the radioactivity of [ 131I]-capsule prior to radioiodine therapy with significant reduction of the radiation exposure to the medical staff

Radiation Protection in Radiology, Nuclear Medicine and Radio Oncology is of the utmost importance. Radioiodine therapy is a frequently used and effective method for the treatment of thyroid disease. Prior to each therapy the radioactivity of the [131I]-capsule must be determined to prevent misadministration. This leads to a significant radiation exposure to the staff. We describe an alternative method, allowing a considerable reduction of the radiation exposure. Two [131I]-capsules (A01 = 2818.5; A02 = 7355.0 MBq) were measured multiple times in their own delivery lead containers - that is to say, [131I]-capsules remain inside the containers during the measurements (shielded measurement) using a dose calibrator and a well-type and a thyroid uptake probe. The results of the shielded measurements were correlated linearly with the [131I]-capsules radioactivity to create calibration curves for the used devices. Additional radioactivity measurements of 50 [131I]-capsules of different radioactivities were done to validate the shielded measuring method. The personal skin dose rate (HP(0.07)) was determined using calibrated thermo luminescent dosimeters. The determination coefficients for the calibration curves were R2 > 0.9980 for all devices. The relative uncertainty of the shielded measurement was < 6.8%. At a distance of 10 cm from the unshielded capsule the HP(0.07) was 46.18 μSv/(GBq•s), and on the surface of the lead container containing the [131I]-capsule the HP(0.07) was 2.99 and 0.27 μSv/(GBq•s) for the two used container sizes. The calculated reduction of the effective dose by using the shielded measuring method was, depending on the used container size, 74.0% and 97.4%, compared to the measurement of the unshielded [131I]-capsule using a dose calibrator. The measured reduction of the effective radiation dose in the practice was 56.6% and 94.9 for size I and size II containers. The shielded [131I]-capsule measurement reduces the radiation exposure to the staff significantly and offers the same accuracy of the unshielded measurement in the same amount of time. In order to maintain the consistency of the measuring method, monthly tests have to be done by measuring a [131I]-capsule with known radioactivity.

Modelling second malignancy risks from low dose rate and high dose rate brachytherapy as monotherapy for localised prostate cancer

BACKGROUND AND PURPOSE

To estimate the risks of radiation-induced rectal and bladder cancers following low dose rate (LDR) and high dose rate (HDR) brachytherapy as monotherapy for localised prostate cancer and compare to external beam radiotherapy techniques.

MATERIALS AND METHODS

LDR and HDR brachytherapy monotherapy plans were generated for three prostate CT datasets. Second cancer risks were assessed using Schneider's concept of organ equivalent dose. LDR risks were assessed according to a mechanistic model and a bell-shaped model. HDR risks were assessed according to a bell-shaped model. Relative risks and excess absolute risks were estimated and compared to external beam techniques.

RESULTS

Excess absolute risks of second rectal or bladder cancer were low for both LDR (irrespective of the model used for calculation) and HDR techniques. Average excess absolute risks of rectal cancer for LDR brachytherapy according to the mechanistic model were 0.71 per 10,000 person-years (PY) and 0.84 per 10,000 PY respectively, and according to the bell-shaped model, were 0.47 and 0.78 per 10,000 PY respectively. For HDR, the average excess absolute risks for second rectal and bladder cancers were 0.74 and 1.62 per 10,000 PY respectively. The absolute differences between techniques were very low and clinically irrelevant. Compared to external beam prostate radiotherapy techniques, LDR and HDR brachytherapy resulted in the lowest risks of second rectal and bladder cancer.

CONCLUSIONS

This study shows both LDR and HDR brachytherapy monotherapy result in low estimated risks of radiation-induced rectal and bladder cancer. LDR resulted in lower bladder cancer risks than HDR, and lower or similar risks of rectal cancer. In absolute terms these differences between techniques were very small. Compared to external beam techniques, second rectal and bladder cancer risks were lowest for brachytherapy.

Inverse treatment planning for spinal robotic radiosurgery: an international multi-institutional benchmark trial

Stereotactic radiosurgery (SRS) is the accurate, conformal delivery of high‐dose radiation to well‐defined targets while minimizing normal structure doses via steep dose gradients. While inverse treatment planning (ITP) with computerized optimization algorithms are routine, many aspects of the planning process remain user‐dependent. We performed an international, multi‐institutional benchmark trial to study planning variability and to analyze preferable ITP practice for spinal robotic radiosurgery. 10 SRS treatment plans were generated for a complex‐shaped spinal metastasis with 21 Gy in 3 fractions and tight constraints for spinal cord (V14Gy<2 cc, V18Gy<0.1 cc) and target (coverage >95%). The resulting plans were rated on a scale from 1 to 4 (excellent‐poor) in five categories (constraint compliance, optimization goals, low‐dose regions, ITP complexity, and clinical acceptability) by a blinded review panel. Additionally, the plans were mathematically rated based on plan indices (critical structure and target doses, conformity, monitor units, normal tissue complication probability, and treatment time) and compared to the human rankings. The treatment plans and the reviewers' rankings varied substantially among the participating centers. The average mean overall rank was 2.4 (1.2‐4.0) and 8/10 plans were rated excellent in at least one category by at least one reviewer. The mathematical rankings agreed with the mean overall human rankings in 9/10 cases pointing toward the possibility for sole mathematical plan quality comparison. The final rankings revealed that a plan with a well‐balanced trade‐off among all planning objectives was preferred for treatment by most participants, reviewers, and the mathematical ranking system. Furthermore, this plan was generated with simple planning techniques. Our multi‐institutional planning study found wide variability in ITP approaches for spinal robotic radiosurgery. The participants', reviewers', and mathematical match on preferable treatment plans and ITP techniques indicate that agreement on treatment planning and plan quality can be reached for spinal robotic radiosurgery.

PACS number(s): 87.55.de

Air-kerma evaluation at the maze entrance of HDR brachytherapy facilities

In the absence of procedures for evaluating the design of brachytherapy (BT) facilities for radiation protection purposes, the methodology used for external beam radiotherapy facilities is often adapted. The purpose of this study is to adapt the NCRP 151 methodology for estimating the air-kerma rate at the door in BT facilities. Such methodology was checked against Monte Carlo (MC) techniques using the code Geant4. Five different facility designs were studied for (192)Ir and (60)Co HDR applications to account for several different bunker layouts.For the estimation of the lead thickness needed at the door, the use of transmission data for the real spectra at the door instead of the ones emitted by (192)Ir and (60)Co will reduce the lead thickness by a factor of five for (192)Ir and ten for (60)Co. This will significantly lighten the door and hence simplify construction and operating requirements for all bunkers.The adaptation proposed in this study to estimate the air-kerma rate at the door depends on the complexity of the maze: it provides good results for bunkers with a maze (i.e. similar to those used for linacs for which the NCRP 151 methodology was developed) but fails for less conventional designs. For those facilities, a specific Monte Carlo study is in order for reasons of safety and cost-effectiveness.

Second primary cancers after radiation for prostate cancer: a systematic review of the clinical data and impact of treatment technique

The development of a radiation induced second primary cancer (SPC) is one the most serious long term consequences of successful cancer treatment. This review aims to evaluate SPC in prostate cancer (PCa) patients treated with radiotherapy, and assess whether radiation technique influences SPC. A systematic review of the literature was performed to identify studies examining SPC in irradiated PCa patients. This identified 19 registry publications, 21 institutional series and 7 other studies. There is marked heterogeneity in published studies. An increased risk of radiation-induced SPC has been identified in several studies, particularly those with longer durations of follow-up. The risk of radiation-induced SPC appears small, in the range of 1 in 220 to 1 in 290 over all durations of follow-up, and may increase to 1 in 70 for patients followed up for more than 10 years, based on studies which include patients treated with older radiation techniques (i.e. non-conformal, large field). To date there are insufficient clinical data to draw firm conclusions about the impact of more modern techniques such as IMRT and brachytherapy on SPC risk, although limited evidence is encouraging. In conclusion, despite heterogeneity between studies, an increased risk of SPC following radiation for PCa has been identified in several studies, and this risk appears to increase over time. This must be borne in mind when considering which patients to irradiate and which techniques to employ.

Second primary cancers after radiation for prostate cancer: a review of data from planning studies

A review of planning studies was undertaken to evaluate estimated risks of radiation induced second primary cancers (RISPC) associated with different prostate radiotherapy techniques for localised prostate cancer. A total of 83 publications were identified which employed a variety of methods to estimate RISPC risk. Of these, the 16 planning studies which specifically addressed absolute or relative second cancer risk using dose-response models were selected for inclusion within this review. There are uncertainties and limitations related to all the different methods for estimating RISPC risk. Whether or not dose models include the effects of the primary radiation beam, as well as out-of-field regions, influences estimated risks. Regarding the impact of IMRT compared to 3D-CRT, at equivalent energies, several studies suggest an increase in risk related to increased leakage contributing to out-of-field RISPC risk, although in absolute terms this increase in risk may be very small. IMRT also results in increased low dose normal tissue irradiation, but the extent to which this has been estimated to contribute to RISPC risk is variable, and may also be very small. IMRT is often delivered using 6MV photons while conventional radiotherapy often requires higher energies to achieve adequate tissue penetration, and so comparisons between IMRT and older techniques should not be restricted to equivalent energies. Proton and brachytherapy planning studies suggest very low RISPC risks associated with these techniques. Until there is sufficient clinical evidence regarding RISPC risks associated with modern irradiation techniques, the data produced from planning studies is relevant when considering which patients to irradiate, and which technique to employ.

A dosimetric analysis of interstitial intensity modulated implants for pelvic recurrences, base of tongue and orbita tumors with specific references to the ICRU-58

BACKGROUND AND PURPOSE

In this article the conversion of the dosimetry of three different kinds of IMBT (intensity modulated brachytherapy) implants into ICRU-58 formalism is presented. The results allow an inter-study comparison of relative reference doses between different sites.

PATIENTS AND METHODS

The evaluation included 76 patient plans: (a) 31 pelvic recurrences, (b) 30 base of tongue tumors, and (c) 15 orbita tumors were analysed retrospectively and the mean central doses (MCD) and relative reference doses were evaluated.

RESULTS

The reference doses D(ref) normalized to the mean central doses of three subgroups resulted in (a) 66%, (b) 68%, and (c) 52%. This is in contrast to the generally proposed standard reference dose of 85% of the Paris system.

CONCLUSIONS

Reduction of the reference dose yields to higher dose inhomogeneities and affects the positive local tumor control. It was found that in IMBT implants the 85% reference dose of the Paris system is suitable for reporting purposes but not necessarily for dose prescription. Consequently, in IMBT implants the prescription dose of 85% should be critically used.