Martina Kunze-Busch

High incidence of implantable cardioverter defibrillator malfunctions during radiation therapy: neutrons as a probable cause of soft errors

AIMS To investigate the behaviour of the implantable cardioverter defibrillator (ICD) function during actual radiotherapy sessions. METHODS AND RESULTS Fifteen patients with an ICD underwent 17 radiation treatments for cancer [cumulative dose to the tumour was between 16 Gray (Gy) and 70 Gy; photon beams with maximum energies between 6 megaelectronvolt (MeV) and 18 MeV were employed]. During every session, the ICD was programmed to a monitoring mode to prevent inappropriate therapy delivery. Afterwards, the ICDs were interrogated to ensure proper function. Calculated radiation dose at the ICD site was <1 Gy in all patients. In 5 out of 17 radiation treatments (29%) the ICDs showed 6 malfunctions (35%). We noticed four disturbances in the memory data or device resets during radiation treatment and one case of inappropriate ventricular fibrillation detection due to external noise. In one case a late device data error was observed. All malfunctions occurred at 10 and 18 MeV beam energies. CONCLUSION Despite the fact that all recommended precautions were taken to minimize the damage to the ICDs during radiotherapy and the calculated dose to the ICDs was <1 Gy, in 29% of the treatments a malfunction occurred. We observed a possible correlation between the beam energy and the malfunctions. This correlation may be due to an interaction between neutrons produced in the head of the linear accelerator at beam energies ≥10 MeV, and boron-10 which is present in the integrated circuit.

Anal wall sparing effect of an endorectal balloon in 3D conformal and intensity-modulated prostate radiotherapy.

BACKGROUND AND PURPOSE To investigate the anal wall (Awall) sparing effect of an endorectal balloon (ERB) in 3D conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) for prostate cancer. MATERIALS AND METHODS In 24 patients with localized prostate carcinoma, two planning CT-scans were performed: with and without ERB. A prostate planning target volume (PTV) was defined, and the Awall was delineated, using two different methods. Three-field and 4-field 3D-CRT plans, and IMRT plans were generated with a prescription dose of 78Gy. In 144 treatment plans, the minimum dose (D(min)), maximum dose (D(max)), and mean dose (D(mean)) to the Awall were calculated, as well as the Awall volumes exposed to doses ranging from >or=20Gy to >or=70Gy (V(20)-V(70), respectively). RESULTS In the 3D-CRT plans, an ERB significantly reduced D(mean), D(max), and V(30)-V(70). For IMRT all investigated dose parameters were significantly reduced by the ERB. The absolute reduction of D(mean) was 12Gy in 3D-CRT and was 7.5Gy in IMRT for both methods of Awall delineation. CONCLUSIONS Application of an ERB showed a significant Awall sparing effect in both 3D-CRT and IMRT. This may lead to reduced late anal toxicity in prostate radiotherapy.

Optimal normal tissue sparing in craniospinal axis irradiation using IMRT with daily intrafractionally modulated junction(s).

PURPOSE To develop a treatment technique for craniospinal irradiation using intensity-modulated radiotherapy (IMRT) with improved dose homogeneity at the field junction(s), increased target volume conformity, and minimized dose to the organs at risk (OARs). METHODS AND MATERIALS Five patients with high-risk medulloblastoma underwent CT simulation in supine position. For each patient, an IMRT plan with daily intrafractionally modulated junction(s) was generated, as well as a treatment plan based on conventional three-dimensional planning (3DCRT). A dose of 39.6 Gy in 22 daily fractions of 1.8 Gy was prescribed. Dose-volume parameters for target volumes and OARs were compared for the two techniques. RESULTS The maximum dose with IMRT was <107% in all patients. V<95 and V>107 were <1 cm3 for IMRT compared with 3-9 cm3 for the craniospinal and 26-43 cm3 for the spinal-spinal junction with 3DCRT. These observations corresponded with a lower homogeneity index and a higher conformity index for the spinal planning target volume with IMRT. IMRT provided considerable sparing of acute and late reacting tissues. V75 for the esophagus, gastroesophageal junction, and intestine was 81%, 81%, and 22% with 3DCRT versus 5%, 0%, and 1% with IMRT, respectively. V75 for the heart and thyroid was 42% and 32% vs. 0% with IMRT. CONCLUSION IMRT with daily intrafractionally modulated junction results in a superior target coverage and junction homogeneity compared with 3DCRT. A significant dose reduction can be obtained for acute as well as late-reacting tissues.

Magnetic resonance lymphography-guided selective high-dose lymph node irradiation in prostate cancer.

PURPOSE To demonstrate the feasibility of magnetic resonance lymphography (MRL) -guided delineation of a boost volume and an elective target volume for pelvic lymph node irradiation in patients with prostate cancer. The feasibility of irradiating these volumes with a high-dose boost to the MRL-positive lymph nodes in conjunction with irradiation of the prostate using intensity-modulated radiotherapy (IMRT) was also investigated. METHODS AND MATERIALS In 4 prostate cancer patients with a high risk of lymph node involvement but no enlarged lymph nodes on CT and/or MRI, MRL detected pathological lymph nodes in the pelvis. These lymph nodes were identified and delineated on a radiotherapy planning CT to create a boost volume. Based on the location of the MRL-positive lymph nodes, the standard elective pelvic target volume was individualized. An IMRT plan with a simultaneous integrated boost (SIB) was created with dose prescriptions of 42 Gy to the pelvic target volume, a boost to 60 Gy to the MRL-positive lymph nodes, and 72 Gy to the prostate. RESULTS All MRL-positive lymph nodes could be identified on the planning CT. This information could be used to delineate a boost volume and to individualize the pelvic target volume for elective irradiation. IMRT planning delivered highly acceptable radiotherapy plans with regard to the prescribed dose levels and the dose to the organs at risk (OARs). CONCLUSION MRL can be used to select patients with limited lymph node involvement for pelvic radiotherapy. MRL-guided delineation of a boost volume and an elective pelvic target volume for selective high-dose lymph node irradiation with IMRT is feasible. Whether this approach will result in improved outcome for these patients needs to be investigated in further clinical studies.

Endorectal balloon reduces anorectal doses in post-prostatectomy intensity-modulated radiotherapy

BACKGROUND AND PURPOSE To investigate the effect of an endorectal balloon (ERB) on anal wall (Awall) and rectal wall (Rwall) doses in high-dose post-prostatectomy intensity-modulated radiotherapy (IMRT). MATERIALS AND METHODS For 20 patients, referred for salvage IMRT after prostatectomy for prostate cancer, two planning CT-scans were performed: one with and one without an air-filled ERB. A planning target volume (PTV) was defined, using international guidelines. Furthermore, the Awall and Rwall were delineated. In both the scans, IMRT plans were generated with a prescribed dose of 70 Gy. The mean dose (D(mean)), maximum dose, minimum dose, and volumes exposed to doses ranging from ≥ 20 to ≥ 70 Gy (V(20)-V(70)) to the Awall and Rwall were calculated. Finally, inner Rwall surface areas exposed to doses ranging from ≥ 20 to ≥ 70 Gy (A(20)-A(70)) were calculated. Dose-parameters were compared between plans with and without ERB. RESULTS All Awall parameters, except V(70), were significantly reduced by the ERB with an overall D(mean) reduction of 6 Gy. Absolute reductions in dose-volume parameters varied from 5% to 11%. Significantly reduced Rwall V(30), V(40), and A(40) were observed with ERB, irrespective of the target volume size. CONCLUSION ERB application significantly reduces Awall and to a lesser degree Rwall doses in high-dose post-prostatectomy IMRT.

A practical approach to assess clinical planning tradeoffs in the design of individualized IMRT treatment plans.

BACKGROUND AND PURPOSE To investigate the tradeoffs between organ at risk sparing and tumour coverage for IMRT treatment of lung tumours, and to develop a tool for clinical use to graphically represent these tradeoffs. MATERIAL AND METHODS For 5 patients with inoperable non-small cell lung cancer (NSCLC) different IMRT plans were generated using a standard TPS. The plans were automatically generated for a range of IMRT settings (weights and dose levels of the objective functions) and were systematically evaluated, focusing on the tradeoffs between organ at risk (OAR) dose and target coverage. A method to analyze and visualize planning tradeoffs was developed and evaluated. RESULTS Lung and oesophagus were identified as the critical organs at risk for NSCLC, the sparing of which strongly influences PTV coverage. Systematically analyzing the tradeoffs between these organs revealed that the sparing of these organs was approximately linearly related to PTV coverage parameters. Using this property, a tool was developed to graphically present the tradeoffs between the sparing of these organs at risk and the PTV coverage. The tool is an effective method to visualize the tradeoffs. CONCLUSIONS A tool was developed to assist IMRT plan design and selection. The clear presentation of the tradeoffs between OAR dose and coverage facilitates the optimization process and offers additional information to the clinician for a patient specific choice of the optimal IMRT plan.

SU‐E‐T‐590: Automate IMRT Planning in Pinnacle: A Study in Head‐And‐Neck Cancer

PURPOSE We investigated whether the auto-planning prototype included in a research version of Pinnacle 9.700 (Philips Healthcare) is able to create treatment plans with consistent quality, independent of the experience of the planner using a single template. METHODS The auto-planning module requires the user to define a template with prioritized optimization goals for PTV-coverage and dose constraints for organ at risks (OARs). Prioritized optimization goals are used by the auto-planning engine to formulate optimization objectives. Multiple optimization loops iteratively reformulate and adjust the optimization objectives to meet the goals and further lower dose to OAR with minimal compromise to the target coverage. Dose conformality and uniformity to the target(s) are also controlled automatically. The quality of ten oropharynx IMRT auto-planned plans was evaluated by calculating the target coverage (V95) and conformity index (CI) of the PTVs (prescribed dose to PTV> was 50.3 Gy and 68 Gy to PTV<), the maximum dose to the cord, and mean dose to parotids and oral cavity. Efficiency was evaluated by measuring the total planning time. RESULTS All auto-planned plans fulfilled the clinical dose criteria for OARs and PTV coverage. The average V95 and CI to PTV> were 99.1% + /- 1.6% and 0.8 + /- 0.1, respectively and to PTV< 96.2% + /- 1.5% and 0.6 +- 0.1, respectively. The average maximum dose to the cord was 44.9 + /- 2.0 Gy, average mean dose to the parotids was 28.4 + /- 4.5 Gy and 33.7 + /- 7.0 Gy to the oral cavity. Total planning time could be reduced from about 4 hours to less than 30 minutes. CONCLUSION The auto-planning module generates plans with consistent quality and reduces total planning time significantly. The tool is designed to automatically perform many of the manual operations in the current IMRT process, any further optimization for an individual patient has to be done outside auto-plan.

SU‐E‐T‐580: Does Arc Therapy Have the Potential to Improve Radiation Treatment of Hodgkin's Lymphoma Patients?

PURPOSE To evaluate whether arc therapy (helical Tomotherapy and volumetric arc therapy; VMAT) is superior to step and shoot IMRT regarding sparing of lungs while maintaining adequate planning target volume (PTV) coverage in Hodgkins lymphoma patients . METHODS Radiation treatment plans for eleven Hodgkins lymphoma patients were created employing the following techniques: coplanar and noncoplanar Step & Shoot IMRT, VMAT and Tomotherapy, i.e., for every patient 4 different treatment plans were created. The IMRT and VMAT planning was performed with Pinnacle software (v. 8 and 9, Philips) suitable for delivery with an Elekta linear accelerator, Tomotherapy plans were calculated with Tomotherapy planning software (v. 3.4). Four patients received a single prescription dose of 30 or 36 Gy, and 7 patients received a simultaneous integrated boost (30 Gy/36 Gy). Treatment plans were optimized such that the normal tissue constraints for the lung [volume receiving more than 20 Gy (V20) is less than 30% and mean lung dose (MLD) is less than 14 Gy] were met, even if PTV coverage (V95%=99%) had to be sacrificed. RESULTS All 4 techniques delivered clinically acceptable treatment plans. Tomotherapy achieved the highest dose homogeneity in the PTV and highest dose coverage of the boost volume (on average 98% versus 96% for the other 3 techniques). Since lung sparing was the first planning objective, all techniques scored equally well for V20 en MLD. CONCLUSIONS The strength of arc therapy lies in the large number of beamlets entering the patient from a high number of angles. For Hodgkins lymphoma patients this does not automatically translate into a superior treatment due to the high weight on the lung objectives limiting the number of beamlets allowed to pass through the lung. This means that for Hodgkins lymphoma arc therapy has no added value for sparing of the lungs.