Influence of photon beam energy on IMRT plan quality for radiotherapy of prostate cancer

Comparison of dose distribution in IMRT and RapidArc technique in prostate radiotherapy

AIM

The aim was to provide a dosimetric comparison between IMRT and RapidArc treatment plans with RPI index with simultaneous comparison of the treatment delivery time.

BACKGROUND

IMRT and RapidArc provide highly conformal dose distribution with good sparing of normal tissues. However, a complex spatial dosimetry of IMRT and RapidArc plans hampers the evaluation and comparison between plans calculated for the two modalities. RPI was used in this paper for treatment plan comparisons. The duration of the therapeutic session in RapidArc is reported to be shorter in comparison to therapeutic time of the other dynamic techniques. For this reasons, total treatment delivery time in both techniques was compared and discussed.

MATERIALS AND METHODS

15 patients with prostate carcinoma were randomly selected for the analysis. Two competitive treatment plans using respectively the IMRT and RapidArc techniques were computed for each patient in Eclipse planning system v. 8.6.15. RPIwin(®) application was used for RPI calculations for each treatment plan. Additionally, total treatment time was compared between IMRT and RapidArc plans. Total treatment time was a sum of monitor units (MU) for each treated field.

RESULTS

The mean values of the RPI indices were insignificantly higher for IMRT plans in comparison to rotational therapy. Comparison of the mean numbers of monitor units confirmed that the use of rotational technique instead of conventional static field IMRT can significantly reduce the treatment time.

CONCLUSION

Analysis presented in this paper, demonstrated that RapidArc can compete with the IMRT technique in the field of treatment plan dosimetry reducing the time required for dose delivery.

Comparison of individual and composite field analysis using array detector for Intensity Modulated Radiotherapy dose verification

AIM

To compare the measured and calculated individual and composite field planar dose distribution of Intensity Modulated Radiotherapy plans.

MATERIALS AND METHODS

The measurements were performed in Clinac DHX linear accelerator with 6 MV photons using Matrixx device and a solid water phantom. The 20 brain tumor patients were selected for this study. The IMRT plan was carried out for all the patients using Eclipse treatment planning system. The verification plan was produced for every original plan using CT scan of Matrixx embedded in the phantom. Every verification field was measured by the Matrixx. The TPS calculated and measured dose distributions were compared for individual and composite fields.

RESULTS AND DISCUSSION

The percentage of gamma pixel match for the dose distribution patterns were evaluated using gamma histogram. The gamma pixel match was 95-98% for 41 fields (39%) and 98% for 59 fields (61%) with individual fields. The percentage of gamma pixel match was 95-98% for 5 patients and 98% for other 12 patients with composite fields. Three patients showed a gamma pixel match of less than 95%. The comparison of percentage gamma pixel match for individual and composite fields showed more than 2.5% variation for 6 patients, more than 1% variation for 4 patients, while the remaining 10 patients showed less than 1% variation.

CONCLUSION

The individual and composite field measurements showed good agreement with TPS calculated dose distribution for the studied patients. The measurement and data analysis for individual fields is a time consuming process, the composite field analysis may be sufficient enough for smaller field dose distribution analysis with array detectors.

Evaluation of combining bony anatomy and soft tissue position correction strategies for IMRT prostate cancer patients

BACKGROUND

Radiotherapy treatment requires delivering high homogenous dose to target volume while sparing organs at risk. That is why accurate patient positioning is one of the most important steps during the treatment process. It reduces set-up errors which have a strong influence on the doses given to the target and surrounding tissues.

AIM

The aim of this study was to investigate the efficiency of combining bony anatomy and soft tissue imaging position correction strategies for patients with prostate cancer.

MATERIALS AND METHODS

The study based on pre-treatment position verification results determined for 10 patients using kV images and CBCT match. At the same patients' position, two orthogonal kV images and set of CT scans were acquired. Both verification methods gave the information about patients' position changes in vertical, longitudinal and lateral directions.

RESULTS

For 93 verifications, the mean values of kV shifts in vertical, longitudinal and lateral directions equaled: -0.11 ± 0.54 cm, 0.26 ± 0.38 cm and -0.06 ± 0.47 cm, respectively. The same values achieved for CBCT matching equaled: 0.07 ± 0.62 cm, 0.22 ± 0.36 cm and -0.02 ± 0.45 cm. Statistically significant changes between the values of shifts received during the first week of treatment and the rest time of the irradiation process were found for 2 patients in the lateral direction and 2 patients in vertical direction among kV results and for 3 patients in the longitudinal direction among CBCT results. A significant difference between kV and CBCT match results was found in the vertical direction.

CONCLUSIONS

In clinical practice, CBCT combined with kV or even portal imaging improves precision and effectiveness of prostate cancer treatment accuracy.

Moderate dose escalation with single-fraction high-dose-rate brachytherapy boost for clinically localized intermediate- and high-risk prostate cancer: 5-year outcome of the first 100 consecutively treated patients

PURPOSE

To analyze the clinical outcome and toxicity data of the first 100 consecutive patients treated with a single-fraction high-dose-rate brachytherapy (HDR-BT) and external beam radiotherapy (EBRT).

METHODS AND MATERIALS

Two-hundred eighty patients have been treated with HDR-BT boost for localized intermediate- to high-risk prostate cancer. Among these, the outcome and toxicity of the first 100 patients treated with a single HDR-BT fraction were assessed. A median dose of 60Gy EBRT was given to the prostate and vesicles. Interstitial HDR-BT of 10Gy was performed during the course of EBRT.

RESULTS

Median followup time was 61.5 months. The 5-year actuarial rates of overall survival, cause-specific survival, disease-free survival, and biochemical no evidence of disease (bNED) for the entire cohort were 93.3%, 99.0%, 89.3%, and 85.5%, respectively. The 7-year actuarial rate of bNED was 84.2% for the intermediate-risk group and 81.6% for the high-risk group (p=0.8464). The 7-year actuarial rates of bNED for Grade 1, 2, and 3 tumors were 97.5%, 80.0%, and 67.1%, respectively. The 5-year probability for developing late Grade 3 gastrointestinal and genitourinary (GU) toxicity was 2.1% and 14.4%, respectively. Grade 3 GU complications occurred significantly more frequently in patients with a history of preirradiation transurethral resection (29.1% vs. 8.8%; p=0.0047).

CONCLUSIONS

Five-year outcome after 60Gy EBRT plus a single fraction of 10Gy HDR-BT boost is encouraging. Preradiation transurethral resection significantly increases the risk of late severe GU complications.

A dosimetric analysis of 6 MV versus 15 MV photon energy plans for intensity modulated radiation therapy (IMRT) of carcinoma of cervix

BACKGROUND

Intensity modulated radiotherapy (IMRT) is being used to treat carcinoma of cervix (Ca Cx). Integral dose to normal tissue and increased leakage are the concern about IMRT. 6 MV photon beam is a good choice of energy for Ca Cx IMRT treatment.

AIM

The objective of this study was to compare intensity modulated radiotherapy (IMRT) plans generated by 6 MV and 15 MV photon energies for carcinoma of cervix (Ca Cx) with regards to dosimetric parameters of planning target volume (PTV) and organs at risk (OAR), homogeneity index (HI), conformity index at 98% level (CI 98%), integral dose to normal tissue (NTID) and total number of monitor units (MUs).

MATERIAL AND METHODS

A cohort of 16 patients was selected for this study. All patients were to receive a dose of 50 Gy in 25 fractions. IMRT plans were generated for both energies using same dose-volume constraints.

RESULTS

Our results show a comparable coverage of planning target volume (PTV) for both energies. Volume of PTV receiving a prescription dose is 97.8 ± 0.5% and 98.8 ± 0.4% for the 6 MV and the 15 MV plans. Volume of PTV receiving a dose of 107% is 4.4 ± 7.8% and 16.1 ± 22.2%. Bladder and rectum mean doses for the 6 MV and the 15 MV photon plans were 39.8 ± 3.0 Gy and 40.0 ± 3.2 Gy, and 35.8 ± 3.1 Gy and 36.0 ± 3.1 Gy, respectively. Homogeneity index (HI) for both energies was 1.04. The conformity indices at 98% isodose (CI 98%) were 1.3 ± 0.1 and 1.4 ± 0.1 for 6 MV and 15 MV photon plans, respectively.

CONCLUSIONS

We conclude that a 6 MV photon is a good choice for Ca Cx IMRT as it produces a highly conformal, homogeneous plan with superior target coverage and better OAR sparing.